TABLE OF CONTENTS. DRYING 14 Effects of Moisture on Finished Parts 15 Drying Equipment. 1 of 66

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2 TABLE OF CONTENTS INTRODUCTION 5 Product Description 6 Product by Grade Type 6 Product by Market 7 Nomenclature 7 Grade Designation 7 Color Designation 8 Color Concentrates 8 Packaging and Labeling MACHINE SELECTION 9 Machine Type and Design 9 Screws: Material, Configuration, and Wear 11 Non-Return Valves 12 Nozzles: Types and Tips 12 Nozzle Materials 12 Nozzle Size 12 Nozzle Temperature Control 13 Process Controls: Time, Temperature, and Pressure 13 Shot Size and Machine Capacity 13 Machine Ventilation DRYING 14 Effects of Moisture on Finished Parts 15 Drying Equipment INJECTION MOLDING PROCESS 19 Typical Processing Temperatures 19 Barrel Heating Zones 20 Nozzle 20 Melt Temperature 21 Machine Conditions 21 Injection Pressure 21 Hold Pressure 21 Injection Speed 21 Injection Cushion 21 Back Pressure 21 Screw Speed 22 Clamp Tonnage 22 Decompression 22 Mold Temperature 23 Mold Temperature Control 23 Shot Weight 23 Cycle Time 23 Mold Release Agents 24 Using Regrind 24 Machine Preparation 24 Purging and Cleaning 25 Startup Procedure 25 Shutdown Procedure 26 Short-Term Shutdown 27 Long-Term Shutdown 27 Process Interactions 28 Moisture vs. Mechanical Properties 29 Minimum Part Thickness 29 Melt Flow Testing As a Quality Control Procedure 30 Post-Mold Conditioning 30 Hot Air Oven Annealing 30 Infrared Annealing 1 of 66

3 TABLE OF CONTENTS, continued TOOLING 31 Mold Shrinkage 31 Mold Design 31 Material Selection 32 Surface Finish 32 Venting 32 Part Draft 33 Texturing 33 Weld Lines 33 Undercuts 33 Tolerances 34 Mold Types 34 Single- and Multi-Cavity Molds 34 Sprue Considerations 34 Sprue Bushings 35 Sprue Pullers 35 Runners and Runner Systems 35 Insulated Runner Molds 36 Hot Runner Molds 36 Gating 37 Edge Gates 37 Sprue Gates 38 Tunnel Gates 38 Ring (or Diaphragm) Gates 38 Insert Molding 38 Molded-In Stress 47 Jetting 48 Silver Streaks/Splay 50 Short Shots/Cold Flow 51 Sinks and Voids 52 Warped Parts 53 Weld Lines SAFETY CONSIDERATIONS 54 General 54 Health and Safety Information GENERAL INFORMATION 55 Developmental Product Information 55 Regulatory Compliance 55 Technical Support APPENDIX A 56 List of Tables APPENDIX B 57 List of Figures TROUBLESHOOTING GUIDE 39 Black Specks 40 Brown Streaks/Burning 42 Brittle Parts 43 Bubbles 44 Charred Area 45 Flash 46 Gate Blush INDEX 59 Index 3 of 66

4 INTRODUCTION Maximizing productivity and profitability in the injection molding of highquality parts depends on achieving and maintaining process consistency. Process consistency is affected by two major factors: resin uniformity and molding conditions. Reducing the variation in these factors can minimize testing, rejected parts, and scrap. In addition, once molding conditions have been established for a part, they should not have to be changed as long as the feedstock remains uniform. As Figures 1 and 2 show, Makrolon polycarbonate resin provides uniformity from lot to lot for superior process consistency. Injection molders have achieved similar results time after time under a variety of conditions. At Bayer Corporation, it is our goal to help injection molders enjoy a high degree of process consistency and the benefits in productivity and profitability this provides. Our resin quality, our technical service staff, and this manual are dedicated to that goal. PRODUCT DESCRIPTION Since its commercial introduction in 1953, Makrolon polycarbonate, with its superior combination of functional characteristics, has become one of the worldõs premier engineering thermoplastics. It has excellent clarity for transparent parts, high impact strength, outstanding electrical properties, high heat resistance, and excellent dimensional stability. In addition, it exhibits toughness over a wide range of temperatures. MELT FLOW RATE (g/10 min) Lot-to-Lot Melt Flow Uniformity of The Effect of Makrolon Resin Makrolon Polycarbonate Resin Figure 1 Melt Flow on Productivity Figure 2 30% REJECTION RATE 25% 20% 15% 10% 5% 0% CompetitorÕs Resin Inconsistent Resin Change to Makrolon Resin Consistent Resin LOT NUMBER TIME (8-HOUR SHIFTS) 5 of 66

5 Product by Grade Type Makrolon polycarbonate resin is available in general-purpose, glass-fiberreinforced, flame-retardant, and specialty grades that are used in applications such as structural foam and medical devices. Makrolon resin grades are supplied in six standard viscosity ranges (see Table 1). Each grade is controlled to the tightest viscosity limits using the most modern production technology in the industry. The outstanding lot-to-lot consistency and superior cleanliness of Makrolon resin promote easier molding and lower rejection rates. General properties are presented more fully in the Bayer publication, Makrolon Polycarbonate: A General Reference Manual. Product Information Bulletins are available on individual resin grades. Consult the Makrolon Polycarbonate Design Manualfor engineering data and design assistance for parts and tooling. For detailed assistance on specific design and molding problems, contact any Bayer Corporation district sales office listed on the back of this brochure or a Bayer Corporation Technical Group representative for Makrolon resin at Product by Market Makrolon polycarbonate is successfully used in a broad range of markets and applications. They include electrical/ electronics components; optical memory disks; solid and hollow-core glazing; office equipment; household and consumer appliances; bottles; medical and laboratory equipment; ophthalmic lenses; automotive parts; and sports and leisure equipment. As with any product, the use of Makrolon polycarbonate resin in a given application must be tested (including field testing, etc.) in advance by the user to determine suitability. Table 1 Viscosity Ranges of Makrolon Polycarbonate Resin Table 2 Performance Additives and Designations for Makrolon Polycarbonate Makrolon Reference Resin Melt Flow Grade Description Application Rate* 3200 High viscosity; recom- Thick-walled parts and 4.5g/10 min. mended for its superior maximum impact strength. physical properties Medium-high viscosity; Relatively thick-walled parts. 6.5g/10 min. excellent physical properties Medium-low viscosity; Large, complex parts. 10g/10 min. general-purpose resin with good melt flow characteristics Low viscosity. Small, complex parts. 12g/10 min Very low viscosity. Parts with thin sections. 15g/10 min. FCR-2400 Lowest viscosity. Parts with thin sections or 20g/10 min. long flow lengths. Performance Additive Designations General-purpose with no special additive 00 UV-stabilized 03 Mold release 05 Mold release and UV-stabilized 07 Compliance with FDA regulations 08 Mold release and compliance with FDA regulations 58 *Typical property data are presented as general information only. They are approximate values and are not part of the product specification. See page 31 for other information. 6 of 66

6 INTRODUCTION, continued NOMENCLATURE Grade Designation For general-purpose grades, the first two digits of the grade designation indicate the viscosity and flowability of the product. For example, grades starting with 24 have the lowest viscosity (highest melt flow), while grades starting with 32 have the highest viscosity (lowest melt flow). General-purpose grades of Makrolon resin are available with performance additives designated by the third and fourth digits of the grade designation (see Table 2 and Figure 4). Non-reinforced flame-retardant Makrolon resin grades are identified by the number Ò6Ó as the first digit of the grade designation (e.g., 6455). Impact-modified Makrolon resin grades are identified by the number Ò7Ó as the first digit of the grade designation (e.g., T-7435). Glass-fiber-reinforced Makrolon resin grades are identified by either the number Ò8Ó as the first digit for general-purpose grades (e.g., 8325) or Ò9Ó for flame-retardant grades (e.g., 9415). Color Designation Transparent, translucent, and opaque colors, as well as natural and clear tints, are available in pellet form. The color coding system for Makrolon polycarbonate is listed in Table 3. It is also possible to color Makrolon resin with concentrates on reciprocating-screw injection molding machines. Table 3 Color Coding System for Makrolon Polycarbonate Figure 3 Makrolon Polycarbonate Resin Pellets Color Codes Natural and Clear Tints 1000 Ð1499 Blacks 1500 Ð1999 Grays Whites Browns Yellows Oranges Reds Blues Greens 2000 Ð Ð Ð Ð Ð Ð Ð Ð9999 Injection molding grades of Makrolon resin are supplied as pellets and are available in natural, clear tints, and various transparent, translucent, and opaque colors. 7 of 66

7 COLOR CONCENTRATES Makrolon polycarbonate can be colored by blending either Bayer or other commercially available color concentrates into the resin. Thoroughly blend the color concentrate with the virgin resin and properly dry the mixture before introducing it to the molding machine. When using commercial color concentrates, take care to ensure that the color carrier is polycarbonate. If the color carrier is another type of polymer, make sure that it is compatible with Makrolon polycarbonate. PACKAGING AND LABELING All injection molding grades of Makrolon resin are supplied in pellet form at a bulk density of approximately 45 lb/ft 3 (721 kg/m 3 ). Makrolon resin is available in 50-1b (23-kg) plastic bags, 1,000-1b (454-kg) plastic-lined cartons, and 1,500-1b (680-kg) tote bags. It is also available in bulk in trucks and rail cars. The bags and cartons are sealed to help prevent contamination from dust or dirt. Take care in opening and resealing them that dust or dirt do not get in among the clean resin. Any particulate contamination in the feedstock may show up in the finished molding. Makrolon resin is hygroscopic and will begin absorbing moisture as soon as it is exposed to the air. Resin exposed to the air for as little as 15 minutes can absorb enough moisture to cause injection molding problems. Resin exposed to a moist atmosphere for a few days and processed without having been properly dried will suffer permanent reduction in physical properties. Therefore, keep each bag or carton of Makrolon resin sealed until it is to be used and avoid storing it in areas that are subject to high humidity. (See also ÒDrying,Ó page 14, for more information.) An example of a label for Makrolon resin is shown in Figure 4. Figure 4 Label Information for Makrolon Polycarbonate Resin DRYING INSTRUCTIONS KEY ELEMENTS FOR PROPER DRYING OF MAKROLON POLYCARBONATE IN A DESICCANT DRYER Air Temperature at Hopper Inlet. 2. Dew point of 0 F or Lower. 3. Four Hours Drying Time. 4. Minimum Blower Capacity Should Be 1.00 cfm/lb/hr. Material Used, i.e., Running 100#/hr. x 1.00 = 100 cfm Blower. 5. A Properly Designed Hopper. PRIOR TO PROCESSING The above five (5) key elements must be present at the same time to obtain a 0.02% or less moisture content. This will insure consistent processing along with optimum property performance. Viscosity Grade Mold Release and Compliance with FDA Regulations NOTE: If your desiccant dryer has not been in use for 24 hours, allow the dehumidifying unit to dry cycle with no material in the drying hopper (see manufacturer s recommendations). Clear Tint Drying Conditions 8 of 66

8 MACHINE SELECTION MACHINE TYPE AND DESIGN Makrolon resin can be processed on most of the common types and sizes of injection molding machines, including plunger machines with various cylinder designs. An in-line reciprocating screw machine like the one shown in Figure 5 is preferred because it provides the most uniform plasticizing and good filling efficiency. Use a machine that can provide temperature control up to 650 F (345 C) and injection pressures of up to 20,000 psi (138 MPa) for filling difficult geometries. The mold clamp force needed for Makrolon polycarbonate resin is 3Ð5 t/in. 2 (0.5 Ð 0.8 mt/cm 2 ) of a partõs projected area. SCREWS: MATERIAL, CONFIGURATION, AND WEAR Following are important considerations in choosing a screw for injection molding Makrolon polycarbonate resin: A three-zone, general-purpose screw of traditional geometry is recommended. The preferred metering and feed zone depths are given in Figure 6. Figure 5 Typical Injection Molding Machine Preferred Screw Flight Depths Figure DEPTH ZONE (in.) Feed Zone Depth Metering Zone Depth SCREW DIAMETER (in.) Makrolon resin can be molded on most conventional injection molding machines, though reciprocating screw machines are preferred because they provide the most uniform plasticizing and good filling efficiency. 9 of 66

9 Screws with a length-to-diameter ratio (L/D) in the range of 18:1Ð22:1 are recommended. If a shorter screw is used, reduce the pitch to obtain 20 flights as shown in Figure 7. Screws with an L/D ratio greater than 22:1 can lead to material degradation. A 2.0:1Ð3.0:1 compression ratio is normally used. Rapid-transition (nylon type) screws are not recommended because of the high power requirements and localized shear heating that can occur with them. Screws should be chrome-plated and highly polished. The flight lands should not be plated, however, because the plating may chip off and contaminate the resin melt. Use screws made of surface-hardened steel when injection molding glassfiber-reinforced Makrolon polycarbonate resin. The glass fibers can chip and abrade chrome plating, contaminating the resin melt. Figure 7 Screw Profile Metering Zone Depth 20 D D D Metering Zone 20% Transition Zone 20% Compression Ratio = Feed Zone 60% Feed Zone Depth Metering Zone Depth Feed Zone Depth The injection molding screw feeds the resin from the throat of the resin hopper through the barrel of the injection molding machine to the nozzle. The screw should be chrome-plated and highly polished. 10 of 66

10 MACHINE SELECTION, continued An abrasion-resistant, bimetallic barrel liner, such as Xaloy*, is preferred. Avoid using worn barrels since they tend to cause inconsistent shot size and black specks. *Xaloy is the registered trademark of Xaloy, Inc. NON-RETURN VALVES Non-return valves prevent the molten polymer in the holding space in front of the screw from flowing back into the screw during the injection cycle. When processing Makrolon polycarbonate, use a free-flowing, sliding check-ring style non-return valve made of fully hardened H-13 steel, preferably nitrided, to retard wear (see Figure 8). Good flow characteristics, as shown in Figure 9, are essential. A fully channeled tip will minimize flow restrictions. Good flow characteristics are an important feature of the non-return valve because Makrolon polycarbonate, like most thermoplastics, will degrade when subjected to excess shear at flow restrictions. Free-Flowing, Sliding Check-Ring Style Figure 8 Non-Return Valve Figure 9 Flow Characteristics of the Non-Return Valve Resin Flow Note: Cross-sectional area in valve should equal cross-sectional area of the screw metering section. This type of valve checks the return of material during the injection cycle. Ball-check valves are not recommended. 11 of 66

11 NOZZLES: TYPES AND TIPS Most standard nozzle types can be used to mold Makrolon resin. Generalpurpose, uniformly open channel designs are recommended. Nozzles are available with and without removable tips. (See Figure 10.) A reverse taper at the nozzle exit is preferred. It causes the melt to tear off inside the nozzle, allowing the portion of the material forming a cold slug for the succeeding shot to be removed with the sprue. (See Figures 11 and 12.) Restrictive nozzles, such as static mixer, filtering, and shutoff types, are not recommended because they can cause material to hang up and degrade. Also, they reduce the maximum attainable cavity pressure. Nozzle Size The nozzle should be as short as possible with its internal diameter determinedby the length and required throughput. Nozzles up to 6 in. (150 mm) long generally require an internal diameter of in. (9 mm). Nozzles longer than 6 in. (150 mm) usually require an internal diameter of 0.375Ð in. (9Ð13 mm). The inner diameter should taper only near the end to diminish pressure losses. The major inside diameter at the threaded end should be exactlyequal to the diameter of the end cap. It is essential that the nozzle and sprue bushing mate properly and be firmly seated. The nozzle discharge opening must not exceed the diameter of the sprue bushing inlet to avoid forming an undercut that could cause the sprue to stick. To promote material flow, the nozzle opening should be at least 80% of the diameter of the sprue bushing inlet. Nozzle Temperature Control Nozzles should have separate temperature controls to prevent cooling or solidification of the melt. If the sprue freezes off or the nozzle cools down too much, the sprue may stick in the stationary side of the tool and may become difficult to remove because polycarbonate is very rigid material. A temperature that is about 20 Ð30 F (10 Ð15 C) lower in the nozzle than in the barrelõs front zone will prevent drooling. Nozzle Materials Standard steel nozzles can be used. Nozzles of Type 420 stainless steel offer better protection, however, against black specks in long production runs. Figure 10 Removable and Non-Removable Nozzle Tips 12 of 66

12 MACHINE SELECTION, continued Long nozzles require complete coverage with heater bands to maintain good temperature control. Heater bands connected to the same power source must be of the same watt density. If different watt densities are used, separate controllers must be used. It is important that all heater bands work properly. Burned-out bands can result in material hang-ups or cause other bands to overwork, both of which can overheat or burn the material. PROCESS CONTROLS: TIME, TEMPERATURE, AND PRESSURE Uniform cycles are necessary to maintain optimum processing conditions and produce the highest-quality part. State-of-the-art closed loop control systems ensure both the precise injection stroke and switchover point that are critical for molding quality parts. They can adjust hold pressure in increments to minimize sinks and voids. In addition, they can maintain melt pressure in the mold cavity uniformly from shot to shot despite variations in the operating conditions of the machine. Some advanced controls adjust the holding pressure and cooling time to ensure that each part is ejected from the mold at the same temperature and weight. Precise process control ensures dimensional uniformity and part-to-part consistency. Shot Size and Machine Capacity Utilization of 50%Ð80% of the barrel capacity is preferred. However, a shot weight smaller than 50% can be molded successfully if it is done carefully. Machine Ventilation A ventilating hood should be located at the front or nozzle end of the molding machine to remove any fumes generated by the injection molding process or purging. Figure 11 Internal Flow Channel of a Standard Nozzle Tip Figure 12 Internal Flow Channel of a Reverse-Taper Nozzle Tip Either standard straight-through or reverse-taper nozzles are recommended for molding Makrolon resin. The reverse-taper type is preferred, however, because it causes the melt to tear off inside the nozzle. This allows the portion of the material forming a cold slug to be removed with the sprue. 13 of 66

13 DRYING The most important requirement for molding high-quality parts from any grade of Makrolon polycarbonate resin is to remove any moisture from the resin prior to processing. Makrolon resin is hygroscopic and under normal storage conditions it will absorb enough ambient moisture to cause severe problems. Even in the original sealed containers, the resin can contain more than the 0.02% maximum moisture level recommended for trouble-free processing. At normal processing temperatures, any moisture present in the pellets will react with the polycarbonate, resulting in the degradation of the polymer. Degradation due to inadequate pellet drying may not be visible, but it will reduce the inherent impact strength and toughness of the finished part. Sometimes, the presence of moisture in the resin is visible as silver streaking and bubbles in the finished part. It cannot be overemphasized: drying polycarbonate resin is essential. Dried pellets left exposed to the open air in an improperly sealed container can and will pick up enough moisture in about 15 minutes to create processing problems, as illustrated in Figure 13. EFFECTS OF MOISTURE ON FINISHED PARTS Very wet resin can yield splay and bubbles in the processed part, as shown in Figures 14 and 15. Marginally dry Moisture Gain of Dried Resin Exposed to the Air Figure 13 Figure 14 Splay MOISTURE LEVEL (%) EXPOSURE (min.) 14 of 66

14 DRYING, continued material, however, will not show these visual signs of moisture because the water is being held in solution by injection molding pressures. The residual water will degrade the polymer by decreasing the average molecular weight and can reduce a finished partõs ability to withstand impact. Many processing problems Ñblack specks, sticking, and flash, to name a few Ñ can be traced directly to the presence of residual moisture. Experience has shown that improper drying is the main cause of rejected parts. DRYING EQUIPMENT Use a desiccant dehumidifying hopper dryer to remove moisture from Makrolon resin and to maintain proper resin moisture content of less than 0.02% during processing. The dryer must meet the following requirements to properly remove moisture from Makrolon resin: Hopper capacity 4 times the output per hour of the injection molding machine. This will ensure that the resin remains in the drying hopper at least 4 hours. Hopper inlet air temperature of 250 F (120 C). Airflow to the hopper of 1.0 cubic foot per minute (CFM) for every pound of resin per hour of throughput. Dew point of the inlet air to the hopper at 0 F (18 C) or less. Figure 15 Moisture Bubbles Figure 16 Typical Desiccant Dehumidifying Hopper Dryer System 15 of 66

15 Some recent dryer designs perform to less demanding requirements. However, use caution when deviating from these guidelines since the quality of molded polycarbonate parts critically depends on low moisture content. A typical desiccant dehumidifying hopper dryer system and airflow are shown in Figures 16 and 17. Note that the hopper is tall and cylindrical and has a diverter cone to diffuse the air uniformly and reduce channeling of the pellets. ensure the desiccant is dry prior to processing (refer to the manufacturerõs recommendations for the procedure). Then load the resin and dry it for at least 4 hours prior to beginning injection molding. If the hopper dryer has not been used for 24 hours, dry-cycle it before introducing the Makrolon resin. This will Figure 17 Desiccant Dehumidifying Hopper Dryer System Airflow Air Outlet Resin Inlet 175 F After Cooler 110 F Heater Off 275 F Air Path for Resin Drying Heater Heater Desiccant 550 F Heater Off Desiccant Diverter Cone Inlet Air 250 F and Dew Point of < 0 F Heater Filter Air Path for Dessicant Drying Air Intake Heater 16 of 66

16 DRYING, continued There are many ways of detecting excessive moisture content in the resin. One simple way for transparent Makrolon polycarbonate is to look for bubbles in the melt during purging (see Figure 18) or by visually inspecting an air shot after it has been made (see Figure 19). If regrind is used, dry it to the same moisture content level as required for virgin pellets. In fact, it may be necessary to dry regrind longer than virgin pellets due to the irregular shape and size of the regrind pellets. Beware of excessive ÒfinesÓ (very small particles caused by grinding). Fines melt more rapidly and may cause black specks to form. Moisture can also be removed with vented-barrel molding machines. However, the advantages of vented-barrel molding machines may be offset somewhat by the loss of processing latitude. Contact a Bayer Corporation Technical Group representative for Makrolon resin at for more information. Figure 18 Bubble Formation During Purging Figure 19 Material Dried in a Desiccant Hopper Dryer at 250 F (120 C) 17 of 66

17 Table 4 Dehumidifying Hopper Dryer Troubleshooting Guide Improper Drying Condition Drying Equipment Defect Possible Corrective Action Poor Dew Point Dirty filter(s). Clean or replace filter(s). Saturated desiccant. Excessive return air temperature. Burned-out heater(s). Contaminated or worn-out desiccant. Bad heater thermostat or thermocouple. Malfunctioning regeneration cycle timer. Air control butterfly valves not seating. Moist room air leaking into the dry process air. Desiccant beds not switching. Dry-cycle machine for several complete cycles. Saturated desiccant is a common problem with machines that are not in continuous use. Add after-cooler on return air line. Repair or replace heater(s). Replace desiccant. Repair or replace thermostat or thermocouple. Adjust or replace timer. Adjust valve seating. Check all hose connections and tighten as required. Check all hoses for leaks and replace as needed. Check filter covers for secure fit and tighten as required. Check electrical connections. Check switching mechanism. Material Residence Time in Dryer hopper too small for the amount of Use a larger dryer hopper. Hopper Too Short material being processed per hour. Not keeping hopper at least 2/3 filled. Keep drying hopper full. Incorrect Process Air Temperature Incorrect drying air temperature. Dial in correct temperature of 250 F (120 C). Dryer temperature controller malfunction. Repair or replace controller. Thermocouple malfunction. Repair or replace thermocouple. Faulty process air heating elements. Repair or replace heating elements. Supply voltage different than required Check supply voltage against nameheater voltage. plate voltage. Non-insulated inlet-air hose. Repair or replace inlet-air hose. Excessive changeover temperature. Increase reactivation airflow. Insufficient Inlet Airflow Dirty or clogged filter. Clean or replace filters. (Good dew point but resin still wet.) Incorrect blower rotation. Change blower rotation. (Consult equipment manufacturerõs electrical instructions.) Obstruction in air ducts. Remove air duct obstruction. 18 of 66

18 INJECTION MOLDING PROCESS TYPICAL PROCESSING TEMPERATURES Makrolon polycarbonate is an amorphous polymer that has a melting range rather than the distinctive sharp melting point of semi-crystalline resins like Durethan polyamide 6. Pay attention to processing temperatures when injection molding Makrolon resin. Suggested starting points are provided in Table 5. While the material is relatively insensitive to overheating, avoid exceeding the recommended maximum melt temperature of 630 F (330 C). Barrel Heating Zones The temperature profile in the barrel should increase incrementally from the rear of the barrel to the front. Considering the high barrel temperatures that can be reached when processing Makrolon resin, you may want to Table 5 Suggested Starting Conditions for Processing Makrolon Polycarbonate Resins Makrolon Resin Makrolon Resin Makrolon Resin Makrolon Resin FCR Conditions FCR Processing Temperatures Zones Rear 445 Ð495 F (230 Ð255 C) 480 Ð520 F (250 Ð270 C) 500 Ð540 F (260 Ð280 C) 520 Ð560 F (270 Ð290 C) Middle 510 Ð550 F (265 Ð290 C) 520 Ð560 F (270 Ð295 C) 530 Ð570 F (275 Ð300 C) 540 Ð580 F (280 Ð305 C) Front 530 Ð570 F (275 Ð300 C) 545 Ð585 F (285 Ð305 C) 555 Ð595 F (290 Ð315 C) 565 Ð605 F (295 Ð320 C) Nozzle 510 Ð530 F (265 Ð275 C) 515 Ð585 F (270 Ð305 C) 535 Ð595 F (280 Ð315 C) 540 Ð605 F (280 Ð320 C) Melt* 535 Ð 565 F (280 Ð 300 C) 550 Ð 580 F (290 Ð 305 C) 560 Ð 590 F (290 Ð 310 C) 570 Ð 600 F (300 Ð 315 C) Mold** 150 Ð220 F ( 65 Ð105 C) 150 Ð220 F ( 65 Ð105 C) 150 Ð220 F ( 65 Ð105 C) 150 Ð220 F ( 65 Ð105 C) Machine Conditions Injection 10,000 Ð 20,000 psi 10,000 Ð 20,000 psi 10,000 Ð 20,000 psi 10,000 Ð20,000 psi Pressure (70 Ð 140 MPa) (70 Ð 140 MPa) (70 Ð 140 MPa) (70 Ð 140 MPa) Hold 50% Ð 70% Injection 50% Ð 75% Injection 50% Ð 75% Injection 50% Ð 70% Injection Pressure Pressure Pressure Pressure Pressure Back 50 Ð 100 psi 50 Ð 100 psi 50 Ð 100 psi 50 Ð 100 psi Pressure (350 Ð 700 kpa) (350 Ð 700 kpa) (350 Ð 700 kpa) (350 Ð 700 kpa) Injection Speed Moderate to Fast Moderate to Fast Moderate to Fast Moderate to Fast Injection Ð in Ð in Ð in Ð in. Cushion (3 Ð 6 mm) (3 Ð 6 mm) (3 Ð 6 mm) (3 Ð 6 mm) Screw Speed 50 Ð 75 rpm 50 Ð 75 rpm 50 Ð 75 rpm 50 Ð 75 rpm Clamp 3 Ð 5 t/in. 2 3 Ð 5 t/in. 2 3 Ð 5 t/in. 2 3 Ð 5 t/in. 2 Tonnage (0.5 Ð 0.8 mt/cm 2 ) (0.5 Ð 0.8 mt/cm 2 ) (0.5 Ð 0.8 mt/cm 2 ) (0.5 Ð 0.8 mt/cm 2 ) * To obtain proper melt temperature, take an air shot and measure the melt with a heated pyrometer probe. ** Check mold temperature on the part cavity and core surface. 19 of 66

19 thermally isolate the hopper from the feed section of the molding machine to prevent bridging. Nozzle In most cases, the optimum nozzle temperature is slightly lower than the front barrel section. If the nozzle is too much cooler, however, the sprue may stick. A temperature that is about 20 Ð 30 F (10 Ð15 C) lower in the nozzle than in the barrelõs front zone will prevent drooling. Melt Temperature Makrolon resin exhibits excellent melt stability over a wide temperature range. The normal processing temperature range varies by grade. Makrolon resin will usually process well within ±20 F (±10 C) of the suggested temperatures. When exposed to temperatures above this range for a long time, polycarbonate can darken and lose its toughness. Figure 20 shows how barrel temperature affects spiral flow length. Check the actual temperature of the melt at the nozzle from an air shot and correct the nozzle temperature control settings accordingly. To obtain an accurate melt temperature measurement, make an air shot from a normal processing cycle and immediately insert a preheated thermocouple probe into the center of the melt. Keep it in the melt until the maximum temperature is reached (see Figure 21). Effect of Barrel Temperature on Spiral Flow Length* Figure 20 Figure 21 Making an Accurate Melt Temperature Reading FCR FLOW LENGTH (in.) To obtain an accurate melt temperature for adjusting the controller settings, make an air shot from a normal processing cycle. Immediately insert the temperature probe into the center of the melt until the maximum temperature is reached. BARREL TEMPERATURE ( F) *Measured at: in. (2.5 mm) Thickness 18,000 psi (124 MPa) Injection Pressure 175 F (80 C) Mold Temperature 20 of 66

20 INJECTION MOLDING PROCESS, continued MACHINE CONDITIONS Injection Pressure Generally, injection pressures of 10,000Ð20,000 psi (70Ð140 MPa) are required to fill most molds with a melt of Makrolon resin. Too little injection pressure may not fill the mold completely. Too much pressure may cause the material to either flash the part or overpack the part and/or the sprue. Hold Pressure Hold pressure should be 50%Ð75% of the injection pressure. Too little hold pressure may lead to warping, dimensional problems, sinks, or voids. Too much hold pressure may overpack the part, make it hard to release, and affect its dimensions. Injection Speed Overall injection time depends on the machine and part geometry. In general, fill the mold rapidly to minimize the appearance of weld lines, cold flow lines, and molded-in stresses. If the injection speed is too slow, the flow front can cool down and solidify as it contacts the cold mold surfaces. Fast injection is necessary for thinwalled parts in order to fill the mold cavity before the material cools. Excessive speed, however, can cause jetting, silver streaking, and gate blush. Very slow injection may be necessary for thick sections (0.375 in./9.5 mm, or more) to prevent formation of internal bubbles and voids. Slow injection results in lower temperatures and higher pressure in the melt during filling, which serves to reduce the formation of internal bubbles and voids. Injection Cushion A slight cushion of 0.125Ð0.250 in. (3Ð6 mm) is suggested. Too little cushion may cause the screw to bottom out and prevent packing. Too much cushion may lead to longer time in the barrel and degradation. Any fluctuation in the amount of cushion can indicate problems such as screw slippage or the non-return valve is allowing resin to backflow. Back Pressure The function of back pressure is to improve the uniformity and shearheating of the melt. It also removes any air drawn in with the pellets. Set nominal back pressure at 50Ð100 psi (350Ð700 kpa). Low back pressure may cause inconsistent feeding and trapped air. During injection, this air is compressed and heated, which can cause black or brown degradation and bubbles in the part. High back pressure may cause thermal damage to the material through overshearing. In filled resin grades, high back pressure can cause excessive fiberglass breakage. Screw Speed The recommended screw speed for injection molding Makrolon resin is 50Ð75 revolutions per minute (rpm). A higher speed of 75Ð150 rpm may be used with screw diameters less than 1.50 in. (38 mm). A screw speed that is too low can lead to longer cycles and poor shear heating. Higher screw speeds with large screw diameters can overheat and degrade the material. 21 of 66

21 Clamp Tonnage Properly matching the size of the injection molding machine to the part to be molded is very important. A clamp tonnage of 3Ð5 t/in. 2 (0.5 Ð 0.8 mt/cm 2 ) of projected part surface area is required to successfully mold Makrolon polycarbonate resin. Decompression Drooling can occur when injection molding polycarbonate resin. If it does, lower the nozzle temperature 10 Ð20 F (5 Ð10 C) to correct the problem. Melt decompression or Òsuck-backÓ must be applied carefully Figure 22 Measuring Mold Temperature to correct the problem because excessive decompression can cause splay. If drooling persists, moisture is probably still present in the resin, and further drying is necessary. Mold Temperature Check mold temperatures on the steel cavity and core surfaces rather than relying on mold temperature control settings (see Figure 22). The normal mold temperature range for Makrolon resin is 150 Ð220 F (65 Ð105 C). While mold temperature does not strongly affect flow length, in some cases temperatures up to 250 F (120 C) may be necessary to fill the mold. Lower temperatures create higher molded-in stress and poor surface appearance. Higher mold temperatures can lengthen cycle times. It may be necessary at times to operate the core half of the mold 10 Ð20 F (5 Ð10 C) lower than the cavity half to hold the part on the core so that it can be ejected. Cores and pins often require special cooling control. Small-diameter core pins are difficult to cool adequately, so a lower overall coolant temperature may be necessary. Inadequate core cooling causes the resin to stick to the knock-out pins and can create a rough part surface. When processing glass-fiber-reinforced materials, it may be necessary to heat the molds above 250 F (120 C) to achieve good surface appearance. 22 of 66

22 INJECTION MOLDING PROCESS, continued Mold Temperature Control Cycle Time MOLD RELEASE AGENTS Generally, water-circulating mold heating units are used to achieve mold temperatures of 170 Ð220 F (75 Ð 105 C) when processing unfilled general-purpose and flame-retardant grades of Makrolon resin. A separate control for each half of the mold is desirable in order to operate the mold halves at slightly different temperatures. Some complicated molds with large lifters and cams may require additional temperature control zones. To achieve mold temperatures higher than 220 F (105 C) may require the use of oil-circulating mold-heating units. It is recommended that mold heaters running at this temperature be equipped with shielded high-temperature hoses for operator safety. The optimum cycle to produce quality parts includes a fast fill, a hold time just long enough for the gates to freeze, and a cooling time long enough so that the part ejectors do not penetrate the part. Cooling time is the major portion of the total molding cycle. The cooling requirements of a part are strongly dependent on its wall thickness (see Figure 23). Most grades of Makrolon resin are available with an internal mold release. Therefore, keep the use of additional external mold lubrication to a minimum. If parts are sticking to the mold, the best remedy is to adjust the mold and/ or melt temperature, injection pressure, or cycle time. In some cases, additional mold polishing and increasing the knock-out pin area will help. Many external mold release agents and lubricants can be detrimental to the properties of Makrolon polycarbonate. They can cause loss of impact strength, Effect of Part Wall Thickness on Total Mold Cycle Time Figure 23 Shot Weight Utilization of 50%Ð80% of the barrel capacity is preferred, although shot weights smaller than 50% can be molded successfully. Makrolon resin can degrade when the residence time in the barrel is too long THICKNESS TOTAL CYCLE TIME (s) 23 of 66

23 part delamination, or surface blemishes on the molded parts. If a mold release agent is necessary, consult a Bayer Corporation Makrolon Technical Group representative at USING REGRIND Up to 20% regrind may be used with all grades of virgin Makrolon polycarbonate resin, depending upon the end-use requirements of the molded part and provided that the material is kept free of contamination and is properly dried (250 F/120 C for 4 hours). (See ÒDrying,Ó page 14, for details.) Any regrind Figure 24 Regrind Pellets used must be generated from properly molded parts, sprues, and/or runners. All regrind used must be clean, uncontaminated, and thoroughly blended with the virgin resin prior to drying and processing. Under no circumstances should degraded, discolored, or contaminated material be used for regrind. Discard such material. Improperly mixed and/or dried resin may diminish the desired properties of Makrolon resin. You must conduct testing on finished parts produced with any amount of regrind to ensure that your end-use performance requirements are fully met. Regulatory organizations, e.g., Underwriters Laboratories (UL), may have specific requirements limiting the allowable amounts of regrind. Miles does not recommend the use of third-party regrind because it usually does not have a traceable heat history, nor does it offer any assurance that proper temperatures, conditions, and/ or materials were used in processing. Exercise extreme caution when buying and using third-party regrind. Avoid using regrind material entirely when resin properties equivalent to virgin material are required, including but not limited to color quality, impact strength, resin purity, and/or load-bearing performance. MACHINE PREPARATION Purging and Cleaning An essential requirement for molding the highest-quality parts with Makrolon resin is a cylinder that is thoroughly clean of any residual polymer from a previous run. The high viscosity of polycarbonate tends to loosen deposits of residual material from the machine. In addition, the high processing temperature of polycarbonate is usually higher than the degradation temperature of many other thermoplastics. So nylon or ABS, for example, can degrade at temperatures used for polycarbonate processing and contaminate the polycarbonate. One method of removing residual polymer from the molding machine cylinder is to purge it with generalpurpose polystyrene. After purging, introduce Makrolon resin and make air shots of the melt until it is free of any contamination. Another method is mechanical cleaning as shown in Figure 25. It is more thorough than purging and is preferred by many molders. The same procedure can be used either prior to running Makrolon resin or upon the completion of a run. Follow these steps: 1.Flush the cylinder with polystyrene. Recommended grinder screen size is 0.31 in. (8mm). 2.Remove the nozzle while keeping the heat on in the main cylinder. 24 of 66

24 INJECTION MOLDING PROCESS, continued 3.Clean the nozzle either by heating it in a muffle furnace or by soaking it in an appropriate solvent (following the manufacturerõs MSDS recommendations) after it has cooled. 4.Once the nozzle has been removed, turn off the heat in the main cylinder and push the screw forward until a few flights are exposed. 5. Remove the hot melt from the screw with a brass brush and a brass knife. Push the screw forward and clean it in this manner until all of the flights are clean. 6.Remove the screw and clean the barrel with a rotary-type brush on an extension rod attached to an electric drill. Figure 25 Mechanical Cleaning of the Screw Startup Procedure Suggested starting conditions for injection molding Makrolon resins are provided in Table 6. Process changes generally affect parts molded of Makrolon polycarbonate as they would other engineering thermoplastic resins. For example, injection speed and melt temperature strongly affect flow length. The injection molding machine and the mold are just two of the many variables that make each set of process conditions unique. Changes from the suggested starting conditions usually will be made until the mold is filled. However, once the process variables are set, the exceptional consistency of Makrolon resin will make further adjustments unlikely. Make initial shots with less than maximum injection pressure. A spray-on mold lubricant may be a good idea for these initial shots. Overpacking on the initial shots can create part removal problems, due to the natural toughness and rigidity of Makrolon polycarbonate. Start with a short shot that contacts the ejector pins, then increase the shot size and injection pressure until the mold is filled. The minimum cycle to produce quality parts is usually characterized by a fast mold fill, a hold time just long enough for the gate to freeze, and a minimum cooling time. Makrolon FCR-2405 resin is unique among all of the grades of Makrolon resin. It can be processed either at much lower temperatures to reduce cycle time or at higher temperatures to fill very thin-walled parts. Shutdown Procedure Shut down the molding machine at the end of a production run according to the procedure for either a short- or longterm shutdown. Observing proper shutdown procedure is important to prepare the machine to restart production and to avoid problems that may be caused by 25 of 66

25 the material or machine during future startups. For example, if a full barrel of polycarbonate is allowed to cool and shrink inside the molding machine, it may pull particles of poorly adhered chrome from the surface of the screw. These particles would contaminate future moldings. Short-Term Shutdown For shutdowns limited to a period of 4Ð6 hours: Shut off the hopper feed. Purge the machine empty, or make shots until no material remains in the machine. Move the screw forward. Lower all heat zones on the cylinder and nozzle to 300 F (150 C). Table 6 Suggested Starting Conditions for Processing Makrolon Polycarbonate Resins Makrolon Resin Makrolon Resin Makrolon Resin Makrolon Resin FCR Conditions FCR Processing Temperatures Zones Rear 445 Ð495 F (230 Ð255 C) 480 Ð520 F (250 Ð270 C) 500 Ð540 F (260 Ð280 C) 520 Ð560 F (270 Ð290 C) Middle 510 Ð550 F (265 Ð290 C) 520 Ð560 F (270 Ð295 C) 530 Ð570 F (275 Ð300 C) 540 Ð580 F (280 Ð305 C) Front 530 Ð570 F (275 Ð300 C) 545 Ð585 F (285 Ð305 C) 555 Ð595 F (290 Ð315 C) 565 Ð605 F (295 Ð320 C) Nozzle 510 Ð530 F (265 Ð275 C) 515 Ð585 F (270 Ð305 C) 535 Ð595 F (280 Ð315 C) 540 Ð605 F (280 Ð320 C) Melt* 535 Ð 565 F (280 Ð 300 C) 550 Ð 580 F (290 Ð 305 C) 560 Ð 590 F (290 Ð 310 C) 570 Ð 600 F (300 Ð 315 C) Mold** 150 Ð220 F ( 65 Ð105 C) 150 Ð220 F ( 65 Ð105 C) 150 Ð220 F ( 65 Ð105 C) 150 Ð220 F ( 65 Ð105 C) Machine Conditions Injection 10,000 Ð 20,000 psi 10,000 Ð 20,000 psi 10,000 Ð 20,000 psi 10,000 Ð20,000 psi Pressure (70 Ð 140 MPa) (70 Ð 140 MPa) (70 Ð 140 MPa) (70 Ð 140 MPa) Hold 50% Ð 70% Injection 50% Ð 75% Injection 50% Ð 75% Injection 50% Ð 70% Injection Pressure Pressure Pressure Pressure Pressure Back 50 Ð 100 psi 50 Ð 100 psi 50 Ð 100 psi 50 Ð 100 psi Pressure (350 Ð 700 kpa) (350 Ð 700 kpa) (350 Ð 700 kpa) (350 Ð 700 kpa) Injection Speed Moderate to Fast Moderate to Fast Moderate to Fast Moderate to Fast Injection Ð in Ð in Ð in Ð in. Cushion (3 Ð 6 mm) (3 Ð 6 mm) (3 Ð 6 mm) (3 Ð 6 mm) Screw Speed 50 Ð 75 rpm 50 Ð 75 rpm 50 Ð 75 rpm 50 Ð 75 rpm Clamp 3 Ð 5 t/in. 2 3 Ð 5 t/in. 2 3 Ð 5 t/in. 2 3 Ð 5 t/in. 2 Tonnage (0.5 Ð 0.8 mt/cm 2 ) (0.5 Ð 0.8 mt/cm 2 ) (0.5 Ð 0.8 mt/cm 2 ) (0.5 Ð 0.8 mt/cm 2 ) * To obtain proper melt temperature, take an air shot and measure the melt with a heated pyrometer probe. ** Check mold temperature on the part cavity and core surface. 26 of 66

26 INJECTION MOLDING PROCESS, continued Long-Term Shutdown For a shutdown exceeding 6 hours or extending to several days: Shut off the hopper feed. Flush the machine with generalpurpose polystyrene, and purge it empty. Leave the screw forward in the cylinder. Turn off all heat zones. PROCESS INTERACTIONS During processing, the injected melt fills the mold and then is compressed. As the melt cools and shrinks, additional melt is forced into the mold. The pressure decreases as the part continues to cool and solidify until the part is removed from the mold. The part continues to cool (and shrink) until it reaches room temperature. The quality of a molded part greatly depends on the pressure in the mold cavity during molding. A mold pressure profile is shown in Figure 26. The filling portion of the molding cycle mainly affects the surface appearance and molecular orientation of the part. The mold filling phase is influenced by the mold and melt temperature and the injection speed. The compression phase of the cycle increases pressure in the mold cavity to completely fill out surface detail and counteract shrinkage. This phase, often referred to as packing, affects flash formation. Mold Pressure Profile Figure 26 Surface Details, Flash Voids, Sinks, Warpage, Weight Surface Layer Orientation, Appearance Mold Opens CAVITY PRESSURE Mold Com- Holding and Cooling Filling pression TIME 27 of 66

27 The holding phase of the injection portion of the molding cycle often occurs at a lower, secondary pressure. It serves to force additional melt into the mold cavity as the part cools. The holding phase of injection molding greatly affects the formation of voids, sinks, warpage, and total part weight. Part cooling includes the mold holding phase and the remaining time until the mold opens. Many machine adjustments affect the main process variables; most affect more than one (see Table 7). Moisture vs. Mechanical Properties Inadequate resin drying is the most common cause of problems when injection molding Makrolon resin. Moisture levels exceeding 0.02% in the resin during injection molding will cause significant hydrolytic degradation of the polymer. This results in a reduction in molecular weight. Parts Table 7 The Effect of Machine Adjustments on Process Variables Melt Temperature Mold Temperature Injection Speed Cylinder Temperature Heat Exchanger Injection Pressure Nozzle Temperature Fluid Temperature Melt Temperature Feedstock Temperature Flow Rate Displacement of Air in Mold Screw Back Pressure Melt Temperature Additional Vents Screw Rotational Speed Injection Speed Clamp Pressure Injection Speed Cycle Time To increase the melt temperature, increase the cylinder, nozzle, or feedstock temperature. Increasing the screw back pressure, rotational speed, or injection speed will also increase the melt temperature. Mold temperature is a major factor in surface quality and the total length of the cycle. Internal stresses and shrinkage are also affected. Low temperatures can increase production rates at the cost of more orientation and internal stress. Temperatures vary from point to point in the mold and vary with time during the cycle. Mold temperature is an average of these values. The mold temperature is affected directly by the temperature and inversely by the flow rate of the heat exchange fluid in the mold temperature controller. Secondary effects on the mold temperature are caused by changes in the melt temperature and the injection speed. The injection speed is set directly on the machine but can be limited by the available injection pressure. Reducing the resistance to plastic flow can increase the usable injection pressure. Increasing the melt temperature and increasing nozzle and runner temperatures all increase usable injection pressure. Effective injection pressure is increased by decreasing resistance to airflow from the mold. Reducing clamp pressure is one method to increase venting. A leaking screw check valve can severely affect injection rate as well as many other critical molding parameters. 28 of 66

28 INJECTION MOLDING PROCESS, continued molded from poorly dried resin will suffer greater part-to-part variation and reduced mechanical property performance. They also often exhibit splay, bubbles, or discoloration. The best indicator of how well the resin has been dried is the change in melt flow rate between the dried pellets and the molded part. An increase in the part melt flow rate greater than about 15% above the melt flow rate of the pellet usually indicates that the resin was inadequately dried and/or processed. Minimum Part Thickness Determining the proper wall thickness for any part is a function of end-use requirements, the geometry of the part, and the grade of Makrolon resin used. Figure 27 shows the relationship between wall thickness and flow length for various grades of Makrolon resin. Makrolon polycarbonate exhibits the characteristic of critical thickness, which is that thickness beyond which notched Izod impact strength undergoes a significant reduction. Accordingly, the part should be designed with a wall thickness that will provide the required end-use performance without (a) sacrificing the inherent toughness of the grade of Makrolon resin being molded or (b) impairing the efficient molding of quality parts by creating long cycle times. MELT FLOW TESTING AS A QUALITY CONTROL PROCEDURE Bayer plastics technical product literature identifies the typical properties of natural resin. Melt flow rate according to ASTM D1238 condition O (300 C and 1.2 kg load) is provided in the General grouping of properties in our product information data sheets for Makrolon FLOW LENGTH (in.) Injection Pressure 18,000 psi Mold Temperature 175 F Melt Temperature 580 F polycarbonate to assist in material selection. Improper processing, such as failing to dry resin properly (page 14) before processing or excessive processing temperatures (Table 5, page 19), can decrease the property performance of Makrolon polycarbonate resin. Melt flow rate is an indicator of molecular Flow Length vs. Wall Thickness for Various Grades of Makrolon Resin FCR-2405 Figure WALL THICKNESS (in.) 29 of 66

29 weight, which, in turn, is a significant determinant of the impact strength potential and other properties of Makrolon polycarbonate resin. In general, as melt flow rate increases, molecular weight and impact strength decrease. Melt flow testing of molded or extruded parts can be performed to determine whether the polycarbonate resin has been degraded during processing. This is done by comparing values for incoming virgin material to those of the processed parts (both dried as noted on page 14) from the same lot of resin using devices known as a melt flow indexer or melt viscometer. Bayer Plastics Technical Service Representatives can arrange for melt flow testing of a customerõs parts produced in Makrolon polycarbonate if in-house testing capability is unavailable. If you would like further information on melt flow testing, the equipment, and/or procedures, contact the Plastic Technology Group in the Plastics Department of Bayer, Polymers Division, Pittsburgh, Pennsylvania, or one of our regional sales offices. POST-MOLD CONDITIONING The need for post-mold conditioning or annealing is dictated by the end-use performance requirements of the part. Annealing can also help improve certain secondary operations, such as plating or coating, by reducing part stress as a variable. Two methods can be used to anneal Makrolon polycarbonate: hot air oven annealing and infrared (IR) annealing. Hot air oven annealing has been used with some success for many years. IR annealing is new, patented technology. It can be used only after receiving a license. Use of this technology can be licensed through Bayer in the U.S. Regardless of the method you choose, never use annealing as a substitute for proper material selection, good part and mold design, or appropriate molding technique. Hot Air Oven Annealing Annealing is a time- and temperaturedependent operation. Do not permit the oven air temperature to exceed 250 F (120 C). Keep the exposure time to about 4 hours. Take care to guard against dimensional changes caused by additional shrinkage and part warpage. Extended annealing times can result in the reduction of part performance. Infrared Annealing New technology has emerged using infrared (IR) heating to produce the desired level of post-mold conditioning. Unlike conventional oven annealing where part heating occurs through conduction, part heating in IR annealing is caused by the absorption of IR energy by the plastic itself. Annealing with IR energy takes only a few seconds compared to the several hours required in a hot air oven. Contact a Bayer Corporation Makrolon Technical Group representative at for assistance and information on the proper application of this patented technology. 30 of 66

30 TOOLING Molds used for processing Makrolon polycarbonate resin have requirements similar to molds for most other thermoplastics. However, molds specifically designed for polycarbonate give the best results. Existing molds may be used for Makrolon resin provided the following requirements are observed: Flow length relative to the wall thickness of the part is acceptable for the grade being molded. Overall part design follows good thermoplastic design guidelines. Mold shrinkage designed into the cavity is equivalent to the grade selected. The only modification required may be to alter the gate. MOLD SHRINKAGE As an amorphous plastic material, unfilled Makrolon polycarbonate exhibits isotropic shrinkage. In other words, it shrinks basically the same amount in both the flow and crossflow directions. For unreinforced grades of Makrolon polycarbonate resin, typical mold shrinkage is 0.005Ð0.008 in./in. (0.005Ð0.008 mm/mm), depending upon the particular grade. For glassfiber-reinforced grades of Makrolon resin, typical mold shrinkage is 0.002Ð0.005 in./in. (0.002Ð0.005 mm/mm). These grades shrink more in the cross-flow direction than in the direction of flow. The actual mold shrinkage observed fora given mold is as much related to the size and geometry of the part as it is to the resin being molded. For more information, refer to the Bayer Corporation publication, Engineering Resins Design Guide, orconsult a Bayer Corporation Makrolon Technical Group representative. MOLD DESIGN Material Selection Use only production molds made from a high-quality tool steel. Tools having a Rockwell Hardness of about 52C are well-suited for long production runs. SAE H-13 or 420 stainless steel is suggested for molding parts requiring a high-polish finish, such as for optical applications. High-alloy steel is not recommended because its lower heat conductivity increases the cooling time required to solidify the melt. Molds made of aluminum alloys or Kirksite* may be suitable for short runs or prototyping. These materials are less expensive to use because they can be easily cast and require little or no machining. *Kirksite is available from N.L. Industries, Inc. 31 of 66

31 Surface Finish A variety of tool surfaces such as chrome, electroless nickel, or nitrided steel have been used successfully with Makrolon resins, depending upon the end-use requirements of the molded part and the grade selected. The standard surface finish for most molds is an SPI #A-3. Makrolon resins accurately reproduce mold surfaces. Therefore, if a part requires a glossy surface, the mold surface must be highly polished. Chrome plating does not improve the smoothness of the mold surface, but it can increase surface hardness and reduce wear. Chrome plating also will help protect tooling against corrosion caused by broken cooling lines, storage condensation, or humidity. The surface finish can have a significant effect on part ejection from the mold. Highly polished surfaces can cause a vacuum to occur during part ejection. Such vacuum problems are most common at closed ends of the mold near the start of a flow path. Polish lines can act as small undercuts, causing difficult part ejection. To reduce this effect when molding parts having long pulls with minimal draft, use molds that have been drawpolished, that is, polished in the direction of the ejection. Venting As a mold cavity fills, the air being displaced by the molten resin must have a way out of the tool. Venting enables this displaced air to easily escape from the mold. This permits faster filling, prevents material burns and deterioration of the cavity surfaces, and results in stronger weld lines. Recommended vent dimensions are Ð in. (0.013Ð mm) deep by 0.25Ð0.75 in. (6Ð19 mm) wide. At a distance of 0.15Ð0.30 in. (4Ð8 mm) from the cavity, vent channels should be deepened to 0.04 in. (1.0 mm) or more (see Figure 28). Part Draft The walls of parts molded of Makrolon polycarbonate resin require 1 of draft per side where possible (see Figure 29). Some parts have been successfully molded with as little as 1/2 of draft Figure 28 Mold Vent Design Figure 29 Draft Angle, Length, and Taper Relationship Vent 0.15 in in. Vent Channel > 0.04 in. Cavity Gate/Runner Perimeter Vent Cavity in. Vent in. Edge of Mold Length 1 in. 1 Draft Angle Taper in. 32 of 66

32 TOOLING, continued per side. Glass-fiber-reinforced polycarbonate shrinks less than standard resin grades and requires draft angles of 1 Ð2. Texturing Typically, the surface texture of the mold depends upon the end-use requirements of the finished part. Textured surfaces require an additional 1 of draft for every in. (0.025 mm) depth of texturing. Weld Lines Weld lines are created wherever two flow fronts come together in the cavity during injection of the melt. Try to locate any weld line away from an impact and/or load-bearing area of the part. Undercuts Undercuts can make it difficult to remove parts molded of Makrolon resin due to the rigid nature of the material. Raised letters and texturing may create undercuts. Even small undercuts can cause problems and may require side cores or special mold features to facilitate part ejection. Avoid any undercut that creates a strain greater than 1.5% during ejection. Tolerances Many factors influence the final size of a molded part, including the mold, the material, and the process. Unreinforced Makrolon polycarbonate shrinks uniformly in all directions and permits tighter tolerances than many other thermoplastics. Typical mold shrinkage for Makrolon polycarbonate ranges from Ð in./in. (0.005 Ð mm/mm). The higher end of this range represents shrinkage in heavier sections. The lower end of the range represents restricted shrinkage around cores and thin sections. Uniform shrinkage in all directions allows more freedom to gate the part in a variety of areas. Glass-fiber-reinforced Makrolon polycarbonate shrinks less than unreinforced polycarbonate Ñ 0.002Ð0.005 in./in. (0.002 Ð0.005 mm/mm). It shrinks less in the flow direction than in the crossflow direction. Typical post-mold shrinkage is in./in. (0.13 mm/mm) and, therefore, negligible in most cases. Tolerances for Makrolon polycarbonate are usually set at ±0.002 in./in. (±0.002 mm/mm). Tighter tolerances are possible but add to part cost. Additional information on tolerances for Makrolon polycarbonate is available in the Bayer Corporation publication, Engineering Resins Design Guide. It can be obtained from your Bayer Corporation representative or by contacting a Bayer Corporation Makrolon Technical Group representative at of 66

33 MOLD TYPES Single- and Multi-Cavity Molds A single-cavity mold is best for producing precision parts with close tolerances. A multi-cavity mold may be used to produce small parts. However, the greater the number of cavities, the more difficult it is to fill them simultaneously. This can cause variations in part dimensions, leading to sticking and overpacking. The minimum requirement for a multi-cavity mold is equal runner length and diameter for each cavity, unless the runner system has been balanced by computer flow analysis. Figure 30 Sprue Design If a family mold (dissimilar parts in the same mold) is attempted, use computer flow balancing to reduce surface flaws, molded-in stresses, and dimensional variations. Since a computer-balanced runner system is usually employed for a specific material and set of processing conditions, any change in either the material or the process conditions can unbalance the runner system and create problems. SPRUE CONSIDERATIONS Sprue Bushings Use sprue bushings having a taper of 0.5 in./ft. (0.4 mm/cm) and an orifice (small end) diameter of Ð in. (3.2 Ð9.5 mm), depending on the size of the molding. The spherical radius of the bushing should be equal to or, preferably, slightly larger than that of the nozzle. The nozzle discharge opening must not exceed the diameter of the sprue bushing inlet to avoid forming an undercut that could cause the sprue to stick. To promote material flow, the nozzle opening should be at least 80% of the diameter of the sprue bushing inlet. A generous radius of 0.02 Ð0.08 in. (0.5 Ð 2.0 mm) is recommended at the transition from the sprue into the runner system or the mold cavity (see Figure 30). 0.5 in./ft. Taper Orifice Diameter Ð in. 0.02Ð0.08 in. Radius Nozzle Tip Sprue Bushing 34 of 66

34 TOOLING, continued Sprue Pullers Use sprue pullers of any common design, but avoid any that restrict the flow of the material. A 5 reverse-taper sprue puller, as shown in Figure 31, works well. Cold-slug wells are recommended and should be built into the base of the sprue and at every branch or sharp turn in the runner system. This provides a trap for cold, solidified material, keeping it out of the cavity. RUNNERS AND RUNNER SYSTEMS Keep runners as short as possible to reduce unnecessary pressure drops between the sprue and gate. Full-round cross sections are best. If the runner must be placed only on one-half of the mold, then use a trapezoidal shape with a round bottom. Half-round and flat runners are not very efficient in conveying the proper volume of resin and are not recommended (see Figure 32). Insulated Runner Molds Insulated runner molds with hot-tip drops have performed satisfactorily in some polycarbonate applications. A runner diameter larger than in. (9.5 mm) will permit formation of an insulation layer of solid material. The temperature of each hot-tip nozzle must be controlled separately. It is advisable not to gate directly. Rather, use a short sprue between the nozzle and the part to separate the hot nozzle surface from the part wall. Insulated runners are prone to black specks and streaking problems and should be avoided in critical appearance applications. Figure 31 Sprue Pullers Undercut Ring Reverse Taper* Sprue Runner Knock-Out Pin Bushing Knock-0ut Pin ÒZÓ Puller Attached to Knock-Out Plate Front View 5 End View *Exaggerated to show concept. 35

35 Hot Runner Molds Hot runner molds have been successfully employed in molding Makrolon resin. However, problems typically involving proper temperature control can occur during startups. Results are generally better with complete hot runner systems compared to systems built from components. Following are recommendations for using hot runner molds to produce parts molded of Makrolon polycarbonate: In most cases, use hot runner molds only for continuous, 24-hour production or for large parts where multiple gating requirements make two-plate molds impractical. Keep the hot runner system as simple as possible, with the fewest number of hot drops and the least complicated flow path. Avoid positive valve gate shut-offs. Positive shut-offs often work well when new but tend to cause streaking from the gates when they wear. Use externally heated hot runner systems for a smooth, unrestricted flow path. While internally heated runners respond much more rapidly to temperature controllers than externally heated runners, they may have hot spots and high pressure drops. Avoid low vestige gate tips with annular flow around a probe. Improper probe positioning often causes excessive gate shear. GATING Gates must provide wide processing latitude while not leaving conspicuous marks on the molded part. During cooling, the resin in the gate should solidify at the same time as the molded part. Gates that are too small may cause filling and packing difficulties, burning, jetting, and splay. Gates that are too large can require excessive hold time. In addition, improperly sized gates may contribute to excessive sinks and voids. To fill the part uniformly, locate the gate to obtain the shortest flow lengths to minimize pressure loss during filling. Gate into the thickest section of Figure 32 Runner Design Figure 33 Gate Designs Which Prevent Jetting Impinging Edge Gate Overlap Gate Section Side View Good Better Best Poor Poor Bottom View Bottom View 36

36 TOOLING, continued the part to reduce the formation of sinks and voids and to reduce warpage. Avoid sharp corners where possible. The gate land length should be as short as possible and never longer than in. (1.5 mm). To reduce jetting, position the gate so that the melt flow impinges on an opposite wall or a core pin at a distance of within three times the gate width (see Figure 33). Gates for glassfiber-reinforced grades of Makrolon resin should be about 25% larger than for standard grades. Edge Gates Examples of edge gate dimensions are shown in Figure 34. The gate thickness (depth) can vary from 50% to 65% of the nominal part thickness. The gate width is usually 2 or 3 times the gate thickness. Even wider gates are used to reduce shear in large-volume parts. A rounded edge where the gate meets the cavity will reduce gate blush. A wide flare will help the material to enter smoothly and reduce chances for surface blemishes at the gates. Variations of edge gating are shown in Figure 35. Sprue Gates Sprue gates are simple but tend to promote splay in parts having heavy walls. The diameter of the sprue base increases with sprue length, so keep the sprue as short as possible. A minimum radius of in. (0.4 mm) at the sprue/ cavity edge is recommended. Sprues which are too large can cause excessive cycle times. Figure 34 Rectangular Edge Gate Side View Bottom View Max in Ð 0.65 T Runner Typically 2Ð3 Times Gate Thickness T T- Part Thickness 37

37 Tunnel Gates INSERT MOLDING MOLDED-IN STRESS Tunnel gates are variations of the pinpoint gate. Maintain a sharp edge on the gate steel in order to properly shear off the gate without tearing it out of the part. Typical tunnel gate configurations are shown in Figure 36. Ring (or Diaphragm) Gates Ring gates work well with cylindrical parts because weld lines can be avoided in most cases. Molded-in metal inserts can cause high residual stresses in plastic bosses. Avoid inserts in parts made of polycarbonate resins because the residual stress may result in crazing, cracking, and eventual part failure. Plastic, having a much higher coefficient of thermal expansion than metal, shrinks around the insert and becomes stressed at the interface due to the restriction imposed by the insert. Because glass-reinforced resins have thermal coefficients closer to those of metal, they are less likely to cause problems. Consult the Bayer Corporation brochure, Plastics Joining Techniques for more information on molded-in inserts. Take all reasonable care to minimize stress within the part during the molding operation. This is critical to help ensure that the molded part meets its required level of end-use performance and that the material can provide its expected level of property performance. Pay attention to the use of recommended processing temperatures and machine conditions, adequate gating, and part and tool design. (See ÒPost- Mold Conditioning,Ó page 30.) Figure 35 Variations of Edge Gating Figure 36 Typical Tunnel Gate Configurations Width= Typically 2 Ð 3 D Radius >3D D Parting Line in. Ð in. Land D= 50% Ð 65% C Part Wall 40 Ð50 Parting Line C Parting Line 30 C = Part Thickness D = Gate Depth 50% Ð 65% Part Thickness 38

38 TROUBLESHOOTING GUIDE BLACK SPECKS Description of Problem Possible Causes Possible Corrective Action Black specks may develop from any of several sources. Other resins not cleaned from the machine may degrade at the high temperatures reached when processing polycarbonate. Residual ABS, PVS, and nylon are particularly troublesome since these resins can initiate degradation in polycarbonate. Thermal degradation may form in any area in the melt flow path where resin flow can stagnate. During processing, an extremely thin layer of stationary melt adheres to the cylinder wall. The extended exposure time to this heat degrades a very thin film of resin. This creates no problem during normal processing. However, if the melt in the cylinder cools and becomes more viscous, it tends to separate this film of degraded resin from the wall. Upon startup, the film breaks into small flakes and creates a black speck problem. Degraded material on barrel or screw. Degraded material in hot runner or manifold. Figure 37 Black Specks Purge 5 Ð 10 shots with existing material. Remove and clean nozzle tip and extension. Dismantle, inspect, and mechanically clean screw, non-return valve, and barrel. Check all parts for damage, excessive wear, or proper fit. Check heater bands for overheating. Purge hot manifold; dismantle, inspect, and clean. If only a small amount of degraded material appears on startup or shutdown, purging the machine may be adequate. Continued appearance of black specks usually means that a pocket of carbonized material has formed. 39

39 BROWN STREAKS / BURNING Description of Problem Possible Causes Possible Corrective Action Localized overheating or extreme residence times can cause degradation in the resin melt that results in streaks of discoloration in the molded part. Splay may accompany the burning. Streaks that appear mainly at weld lines or at the end of flow paths are probably due to air trapped in the mold. Degradation localized in the same position each time indicates a source at the nozzle end. A more dispersed discoloration source is usually at the hopper end. Moisture in the resin will cause degradation of polycarbonate during processing. Follow the procedures described in ÒDrying,Ó page 14, for details. Shear heating and burning can be caused by the gate, runner, or cavity restrictions, usually at sharp corners. It appears at specific points in the part consistently. Material left in the barrel for a long time at processing temperatures will degrade and need complete purging. Moisture in polycarbonate. Barrel overheating. Nozzle overheating. Shear heating in nozzles. Figure 38 Brown Streaks/ Burning Follow proper drying procedure. Keep melt temperature below 630 F (330 C). Check barrel heater bands and controllers. Reduce temperature setpoint. Check nozzle heater and controllers. Spread heater bands on long nozzles. Remove possible blockage in nozzle. Increase nozzle tip diameter. Increase nozzle tip diameter to 80% of sprue bushing, maximum. 40

40 TROUBLESHOOTING GUIDE, continued BROWN STREAKS / BURNING, CONTINUED Description of Problem Possible Causes Possible Corrective Action Loose nozzle. Remove, clean, tighten, then later retighten when heated. Shut-off nozzle. Replace with general-purpose nozzles. Dead spots in dead manifold. Clean hot mold systems. Lower temperatures. Revise hot manifold systems. Change mold to cold runner system. Gate/runner too small. Enlarge flow areas. Radius sharp corners. Reduce speeds. Contamination. Purge barrel and screw. Clean hopper dryer and auxiliary equipment. Check resin for foreign objects. Restricted flow. Add or enlarge vents to a maximum depth of Ð in. (0.013 Ð mm). Check vent channels for blockage. Improperly designed or defective nonreturn valve. Inspect for cracks in the slip ring and scoring on the valve tip. Check valve seats. Replace with free-flow valve. Poor shutdown procedures. Follow shutdown procedures as described on page

41 BRITTLE PARTS Description of Problem Possible Causes Possible Corrective Action Low part strength can be caused by wet resin, high molded-in stress, and poor part design. Wet resin. Molded-in stress. Check drying conditions. Increase melt temperature. Reduce injection pressure. Review part design. Poor part design. Review design for notches and other stress concentrators. Figure 39 Brittle Part 42

42 TROUBLESHOOTING GUIDE, continued BUBBLES Description of Problem Possible Causes Possible Corrective Action Bubbles can form from moisture in the resin or trapped air in the mold. The air is severely compressed and heated during injection. The result is brownblack cloudy streaks and/or bubbles in the part. Bubbles usually form in areas where sinks and voids are common. High moisture level in resin. Trapped air. Check each step of the drying process. Check dried resinõs exposure to air. Force air out the feed vent. Increase screw speed. Reverse cylinder temperature profile. Figure 40 Bubbles 43

43 CHARRED AREA Description of Problem Possible Causes Possible Corrective Action Charring can occur when air trapped in a mold is rapidly compressed by the injection melt. The compression heats the air to a high temperature that can locally degrade and burn the adjacent melt (dieseling). Improved mold venting, slower injection, and lower surrounding temperatures reduce this effect. Trapped air. Reduce injection rate. Reduce melt temperature. Reduce mold temperature. Vent at burned area. Add more vents. Decrease clamp pressure. Relocate gates. Figure 41 Charring 44

44 TROUBLESHOOTING GUIDE, continued FLASH Description of Problem Possible Causes Possible Corrective Action Flash formation depends on the fit of the parting line, the applied force, and the viscosity of the melt. It is usually due to a mold or clamp deficiency that allows material to flow to unwanted areas. Check the mold design, the clamp rating (tonnage) for the projected area, and the injection pressure. Flash at the end of flow paths is a sign of an excessive shot size. Flash in the runner system may indicate continued holding pressure after the gates freeze off. Insufficient clamp tonnage. Excessive vent depth. High injection pressure. Damaged mold. Misaligned platen. Wet material. Use larger molding machine. Change mold design. Lower injection pressure. Repair mold. Align platen. Check drying procedures. Figure 42 Flash 45

45 GATE BLUSH Description of Problem Possible Causes Possible Corrective Action Gate blush is melt fracture at the gate that is usually caused by sharp corners, excessive injection speed, or gate design. It appears as a dull spot on the part. Melt temperature too low. Injection speed too rapid. Gate too small. Increase temperature. Reduce injection speed. Enlarge gate. Sharp edge in gate area. Radius edges, fan gate. No cold slug well. Add cold slug well. Figure 43 Gate Blush 46

46 TROUBLESHOOTING GUIDE, continued JETTING Description of Problem Possible Causes Possible Corrective Action The melt may jet when entering a mold and create dull spots and disturbances in the appearance of the part. Jetting occurs with high-velocity flow into an open area. Its snake-like appearance is due to the melt not spreading evenly in the cavity during fast injection. To eliminate jetting, check the gate size and ram speed, making sure that the gate is large enough and the ram speed is not too high. Possibly relocate the gate to make the flow run against a mold wall upon entering the cavity. High injection speed. Gating into open area. Gate too small. Reduce injection speed. Redesign or relocate gate. Enlarge gate. Figure 44 Jetting 47

47 SILVER STREAKS/ SPLAY Description of Problem Possible Causes Possible Corrective Action This problem appears as silver-white marks generally following the flow paths of the melt. They are usually moisture, air, or degradation products of thermally abused resin. Wet material. Use desiccant dryer. Follow drying recommendations as described on page 14. Follow dryer manufacturerõs operating and maintenance instructions. Material overheating. Reduce heat, back pressure, or screw speed. Check the heater bands and controller for malfunction. Air trapped in melt. Eliminate screw decompression. Increase back pressure. Shear heating. Slow injection speed. Reduce injection pressure. Nozzle restricted. Enlarge gates. Remove nozzle and mechanically clean. Replace with free-flow valve. Figure 45 Silver Streaks/ Splay 48

48 TROUBLESHOOTING GUIDE, continued SILVER STREAKS/ SPLAY, CONTINUED Description of Problem Possible Causes Possible Corrective Action Improperly designed or defective nonreturn valve. Use a check-ring non-return valve that has deep, large radius flutes and a flow area equal to the screws. Replace the check ring if it has any chips, cracks, or damage. Do not use a ball-check-type valve. Inadequate mold venting. Add or enlarge vents (vent depth Ð in./ 0.013Ð mm). Cold slugs at nozzle. Increase nozzle temperature. Add heater bands or move heater bands closer to nozzle tip. Move/adjust hot tip heat source nearer to orifice. Radius sharp corners adjacent to gate. Contamination. Purge barrel and screw. Clean dryer hopper and auxiliary equipment. Improve material handling. Poor tool design. Radius all sharp edges (0.015 Ð in. /0.40 Ð7.75 mm). 49

49 SHORT SHOTS/COLD FLOW Description of Problem Possible Causes Possible Corrective Action A rippled surface in the last-filled area of the mold may indicate the onset of short shots. This cold flow appears as fine ridges (record grooves) running perpendicular to the flow front. Short shots and cold flow may be caused by low mold and/or melt temper-atures, insufficient machine pressure, or inadequate shot capacity. The part flow path may be excessive, or air in the mold may be restricting flow. Insufficient feed. Insufficient injection pressure. Insufficient injection speed. Low temperature on barrel, nozzle, or mold. Cycling from wet to dry resin. Undersized machine for shot size. Increase shot size. Increase injection pressure. Increase injection speed. Increase temperatures. Follow proper drying procedures. Increase machine size. Nozzle obstruction. Remove and clean nozzle. Gate and/or sprue restriction. Enlarge runner. Inadequate mold venting. Increase venting. Excessive flow length. Revise mold or part design. Figure 46 Short Shot/ Cold Flow 50

50 TROUBLESHOOTING GUIDE, continued SINKS AND VOIDS Description of Problem Possible Causes Possible Corrective Action As the material cools and shrinks in the mold, the melt must continue to flow to keep the mold cavity full. Thick sections take longer to cool than thin ones and may continue to shrink after the melt path has frozen. This can create sink marks and voids. Sinks and/or voids can result from insufficient material in the cavity and are often formed in thick sections next to thin sections. Voids are created when the partõs external surfaces solidify and shrinkage continues internally. Sinks are associated with high mold temperatures; voids are associated with colder mold temperatures. Check for insufficient packing pressure, high stock temperature, and excessive restriction in flow due to undersized gates, sprues, runners, or part design; improper gate location; too long a gate land; and thick sections due to improper part design. Injection rate can have an effect on sinks. It affects the temperature profile in the melt at the start of the hold pressure phase. Decreasing melt temperature can reduce sink marks. However, lower melt and mold temperatures may freeze the surface so that instead of sinks, voids are formed in the interior of the part. Backflow from the mold, suck-back, or a faulty screw non-return valve affect packing pressures and can create sink problems. As a last resort, use a small amount of blowing agent to control sinks. Insufficient feed. Low holding pressure. Hold time too short. Thick section. Premature gate freeze-off. Gating into thin section. Inadequate mold cooling. Figure 47 Sinks and Voids Increase shot size. Increase holding pressure. Lengthen holding time. Reduce thickness. Increase gate thickness. Relocate gate. Add or relocate cooling lines, increase coolant flow. 51

51 WARPED PARTS Description of Problem Possible Causes Possible Corrective Action As a molded part cools from ejection temperature to room temperature, sections of the part shrink in different amounts because of non-uniform temperatures. The part tends to become concave on the side that cooled last. Glass or other fibers tend to orient in the direction of flow and create less shrinkage in the flow direction than the crossflow direction. Uneven part temperatures. Poor processing conditions. Glass fiber orientation. Check cooling system. Adjust temperature of mold halves separately. Adjust packing time and pressures. Change gate location or switch to unreinforced material. Figure 48 Warpage 52

52 TROUBLESHOOTING GUIDE, continued WELD LINES Description of Problem Possible Causes Possible Corrective Action Weld lines occur where two melt streams join. The surface of the contacting melt streams is colder than the body of the melt. The melt streams do not fuse well and result in weak areas in the part. Weld line strength depends primarily on the material temperature at the weld junction and secondarily on injection and holding pressure. Sometimes, a cold slug may create a flow disturbance that looks like a weld line. This can be caused by the melt solidifying in the nozzle. Increase the nozzle temperature or add a cold slug well in the mold to correct this problem. Weld lines. Altered weld line locations. Increase melt temperature. Increase injection rate. Increase mold temperature. Increase injection pressure. Increase holding pressure. Check for vent restrictions. Change gate location. Increase gate size. Increase runner size. Change part design. Add overflow area. Vary mold section temperatures. Figure 49 Weld Line 53

53 SAFETY CONSIDERATIONS GENERAL Good molding practice calls for operators to wear safety glasses and/or face shields, especially during purging, and use proper gloves and other appropriate garments when handling hot tools and auxiliary equipment. Material Safety Data Sheets (MSDS) are available and should be consulted prior to processing Makrolon polycarbonate resins. HEALTH AND SAFETY INFORMATION Appropriate literature has been assembled which provides information concerning health and safety precautions that must be observed when handling Bayer Corporation products mentioned in this publication. Before working with any of these products, you must read and become familiar with the available information on their hazards, proper use, and handling. This cannot be overemphasized. Information is available in several forms, e.g., material safety data sheets and product labels. Consult your Bayer Corporation representative or contact the Product Safety and Regulatory Affairs Department in Pittsburgh, Pennsylvania at For materials mentioned that are not Bayer Corporation products, appropriate industrial hygiene and other safety precautions recommended by their manufacturer(s) should be followed. 54

54 GENERAL INFORMATION DEVELOPMENTAL PRODUCT INFORMATION Any product in this publication with a grade designation containing the letters DP, KU, or KL is classified as a developmental product and is not considered part of the Bayer Corporation line of standard commercial products. Testing of properties and application suitability is not final. Further information, including data which could change or add hazards associated with use, may be developed. Such information might be needed to properly evaluate and/or use this product. Use is undertaken at the sole risk of the purchaser. Such material is sold Òas isó without warranty or guarantee. Bayer Corporation shall not be liable for any damages, of whatever nature, arising out of the purchaserõs/ userõs receipt and/or use of the material. Commercialization and continued supply are not assured. Bayer Corporation reserves the right to discontinue at any time. REGULATORY COMPLIANCE Some of the end uses of the products described in this publication must comply with applicable regulations, such as those of the FDA, USDA, NSF, and CPSC. If you have questions on the regulatory status of Makrolon resins, contact your Bayer Corporation representative or the Bayer Corporation Regulatory Affairs Manager in Pittsburgh, Pennsylvania. TECHNICAL SUPPORT To get material selection and/or design assistance, just write or call and let us know who you are and what your needs are. So that we can respond efficiently to your inquiry, here are some of the points of information we would like to know: physical description of your part(s) and engineering drawings, if possible; current material being used; service requirements, such as mechanical stress and/or strain, peak and continual service temperature, types of chemicals to which the part(s) may be exposed, stiffness required to support the part itself or another item, impact resistance, and assembly techniques; applicable government or regulatory agency test standards; tolerances that must be held in the functioning environment of the part(s); and any other restrictive factors or pertinent information of which we should be aware. In addition, we can provide processing assistance nationwide through a network of regional Field Technical Service Representatives. We can help customers optimize the quality and performance of their parts by offering the following types of assistance: on-site processing, equipment and productivity audits, startup and troubleshooting support, and tool design. Upon request, Bayer Corporation will furnish such technical advice or assistance it deems to be appropriate in reference to your use of our product, Makrolon resin. It is expressly understood and agreed that, since all such technical advice or assistance is rendered without compensation and is based upon information believed to be reliable, the customer assumes and hereby expressly releases Bayer Corporation from all liability and obligation for any advice or assistance given or results obtained. Moreover, it is your responsibility to conduct enduse testing and to otherwise determine to your own satisfaction whether or not Bayer Corporation products and information are suitable for your intended uses and applications. For assistance, contact any of our regional sales offices listed on the back cover, or call or write us at the following address: Bayer Corporation Polymers Division, Plastics Makrolon Product Management 100 Bayer Road, Building 8 Pittsburgh, PA Phone:

55 APPENDIX A: LIST OF TABLES Page No. Description Table No. Page No. Description Table No. 6 Viscosity Ranges of Makrolon Table 1 Polycarbonate Resin 18 Dehumidifying Hopper Dryer Table 4 Troubleshooting Guide 6 Performance Additives and Designations Table 2 for Makrolon Polycarbonate 7 Color Coding System for Makrolon Table 3 Polycarbonate 19 Suggested Starting Conditions for Table 5 Processing Makrolon Polycarbonate Resins 26 Suggested Starting Conditions for Table 6 Processing Makrolon Polycarbonate Resins 28 The Effect of Machine Adjustments Table 7 on Process Variables 56

56 APPENDIX B: LIST OF FIGURES Page No. Description Figure No. Page No. Description Figure No. 5 Lot-to-Lot Melt Flow Uniformity of Figure 1 Makrolon Polycarbonate Resin 13 Internal Flow Channel of a Figure 11 Standard Nozzle Tip 5 The Effect of Makrolon Resin Figure 2 Melt Flow on Productivity 13 Internal Flow Channel of a Figure 12 Reverse-Taper Nozzle Tip 7 Makrolon Polycarbonate Resin Pellets Figure 3 8 Label Information for Makrolon Figure 4 Polycarbonate Resin 14 Moisture Gain of Dried Resin Figure 13 Exposed to the Air 14 Splay Figure 14 9 Typical Injection Molding Machine Figure 5 15 Moisture Bubbles Figure 15 9 Preferred Screw Flight Depths Figure 6 10 Screw Profile Figure 7 11 Free-Flowing Sliding Check-Ring Style Figure 8 Non-Return Valve 11 Flow Characteristics of the Figure 9 Non-Return Valve 12 Removable and Non-Removable Figure 10 Nozzle Tips 15 Typical Desiccant Dehumidifying Figure 16 Hopper Dryer System 16 Desiccant Dehumidifying Hopper Figure 17 Dryer System Airflow 17 Bubble Formation During Purging Figure Material Dried in a Desiccant Hopper Figure 19 Dryer at 250 F (120 C) 20 Effect of Barrel Temperature on Figure 20 Spiral Flow Length 20 Making an Accurate Melt Figure 21 Temperature Reading 22 Measuring Mold Temperature Figure Effect of Part Wall Thickness on Figure 23 Total Mold Cycle Time 57

57 APPENDIX B: LIST OF FIGURES, (continued) Page No. Description Figure No. Page No. Description Figure No. 24 Regrind Pellets Figure Typical Tunnel Gate Configurations Figure Mechanical Cleaning of the Screw Figure Black Specks Figure Mold Pressure Profile Figure Brown Streaks/ Burning Figure Flow Length vs. Wall Thickness for Figure 27 Various Grades of Makrolon Resin 32 Mold Vent Design Figure Draft, Angle, Length, and Taper Figure Sprue Design Figure Sprue Pullers Figure Runner Design Figure Gate Designs Which Prevent Jetting Figure Rectangular Edge Gate Figure Variations of Edge Gating Figure Brittle Part Figure Bubbles Figure Charring Figure Flash Figure Gate Blush Figure Jetting Figure Silver Streaks/ Splay Figure Short Shot/ Cold Flow Figure Sinks and Voids Figure Warpage Figure Weld Line Figure 49 58

58 INDEX A air displacement, 28 ambient moisture, 14 annealing, 30 annealing, 30 extended annealing times, 30 hot air oven, 30 infrared (IR) annealing, 30 part performance, 30 applications, 6, 55 suitability testing, 6, 55 B back pressure, 21 air removal from melt, 21 black or brown degradation, 21 bubbles, 21 fiberglass breakage, 21 inconsistent feeding, 21 melt uniformity, 21 shear-heating, 21 thermal damage, 21 trapped air, 21 barrel capacity, 13 barrel heating zones, 19 barrel liner material, 11 barrel temperature, 20 Effect of Barrel Temperature on Spiral Flow Length (Figure 20), 20 black or brown degradation, 21 black specks, 15, 17, 35, 39 black specks Black Specks (Figure 37), 39 degraded material, 39 bridging, 20 brittle parts, 42 Brittle Part (Figure 39), 42 molded-in stress, 42 part design, 42 wet resin, 42 brown streaks/burning, 40 barrel overheating, 40 Brown Streaks/Burning (Figure 38), 40 localized overheating, 40 moisture, 40 nozzle overheating, 40 shear heating, 40 trapped air, 40 bubbles, 14, 17, 21, 29, 43 Bubbles (Figure 40), 43 Bubble Formation During Purging (Figure 18), 17 moisture, 43 Moisture Bubbles (Figure 15), 15 sinks and voids, 43 trapped air in mold, 43 burning, 32, 36, 40 C charring, 44 Charring (Figure 41), 44 injection speed, 44 mold temperature, 44 trapped air, 44 venting, 44 clamp pressure, 28 clamp tonnage, 22 clamping force, 45 clear tints, 7 closed loop control systems, 13 cold flow lines, 21 cold slug(s), 12, 49, 53 weld lines, 53 Color Coding System for Makrolon Polycarbonate (Table 3), 7 color concentrates, 7, 8 color designation, 7 clear tints, 7 natural, 7 opaque, 7 translucent, 7 transparent, 7 compression ratio, 10 computer-balanced runner system, 34 contamination, 8, 41, 49 cores, 22 critical thickness, 29 cycle, 28 cycle time, 22, 23, 28, 37 cylinder temperature, 28 cylindrical parts, 38 D dead spots in dead manifold, 41 decompression, 22 drooling, 22 splay, 22 degradation, 14 dehumidifying hopper dryer, 15, 18 air control butterfly valves, 18 air duct obstruction, 18 air leak, 18 bad heater thermostat/thermocouple, 18 blower rotation, 18 burned-out heaters, 18 contaminated/worn-out desiccant, 18 desiccant beds not switching, 18 dirty filter(s), 18 dryer temperature controller malfunction, 18 59

59 excessive return air temperature, 18 inlet air hose, 18 malfunctioning regeneration cycle timer, 18 saturated desiccant, 18 supply voltage, 18 design assistance, 55 developmental product, 55 diaphragm gates, 38 dimensional problems, 21 dimensional uniformity, 13 dimensional variations, 34 discoloration, 29, 40 draft, 32 draw polishing, 32 drool/drooling, 20, 22 drying, 14-18, 22 Bubble Formation During Purging (Figure 18), 17 Dehumidifying Hopper Dryer Troubleshooting Guide (Table 4), 18 desiccant dehumidifying hopper dryer, 15 Material Dried in a Desiccant Hopper Dryer (Figure 19), 17 regrind, 17 drying equipment, airflow, 15 Desiccant Dehumidifying Hopper Drying System Airflow (Figure 17), 16 dew point of inlet air, 15 hopper capacity, 15 hopper inlet air temperature, 15 operation, 16 requirements, 15 Typical Desiccant Dehumidifying Hopper Dryer System (Figure 16), 15 dull spot(s), 46, 47 E edge gates, 37 gate blush, 37 land, 37 Rectangular Edge Gate (Figure 34), 37 surface blemishes, 37 Variations of Edge Gating (Figure 35), 38 ejector pins, 25 engineering data and design assistance, 6, 55 Engineering Resins Design Manual, 31, 33 Makrolon Polycarbonate Design Manual, 6 excessive moisture content, 17 external mold lubrication, 23 F family mold, 34 feedstock temperature, 28 fiberglass breakage, 21 filled resin grades, 21 flame-retardant resin, 6, 23 flash, 15, 21, 27, 45 Flash (Figure 42), 45 in runner system, 45 melt viscosity, 45 mold clamping force, 45 mold design, 45 parting line, 45 shot size, 45 flow length, 20, 22, 29, 36 Effect of Barrel Temperature on Spiral Flow Length (Figure 20), 20 Flow Length vs. Wall Thickness for Various Grades of Makrolon Resin (Figure 27), 29 flow rate, 28 flowability, 7 fluid temperature, 28 fumes, 13 G gate/gating, 21, 35-37, 46 blush, 21, 37, 46 burning, 36 cooling cycles, 36 cylindrical parts, 38 design, 46 edge gate, 37 flow lengths, 36 Gate Blush (Figure 43), 46 Gate Designs Which Prevent Jetting (Figure 33), 36 glass-fiber-reinforced resin, 37 jetting, 36 land length, 37 part surface, 36 poor filling, 36 pressure loss, 36 Rectangular Edge Gate (Figure 34), 37 ring (or diaphragm) gates, 38 sharp corners, 36 shear, 36, 38 sinks, 36 splay, 36 sprue gates, 37 tunnel gates, 38 Typical Tunnel Gate Configurations (Figure 36), 38 uniform part filling, 36 Variations of Edge Gating (Figure 35), 38 voids, 36 warpage, 36 60

60 INDEX, continued general properties of Makrolon polycarbonate, 6 general-purpose resin grade, 6, 7 grade designation, 7 performance additives, 7 glass-fiber-reinforced resin grades, 6, 7, 22, 31, 33, 37 shrinkage, 33 grade designations, 7 flame-retardant, 7 general-purpose, 7 glass-reinforced, 7 impact-modified, 7 nonreinforced with flame-retardant properties, 7 special grades, 7 structural foam, 7 H health and safety information, 54 heat exchanger, 28 heater bands, 13 burned-out, 13 hold pressure, 21, 53 dimensional problems, 21 overpacking, 21 part release, 21 sinks, 21 voids, 21 warping, 21 weld lines, 53 hold time, 36 hot air oven annealing, 30 hot runner molds, 36 recommendations for use, 36 temperature control, 36 hydrolytic degradation, 28 I impact-modified resin, 7 impact strength, 23, 30 inadequate resin drying, 28 inconsistent feeding, 21 infrared (IR) annealing, 30 initial shots, 25 injection cushion, 21 fluctuation, 21 resin backflow through nonreturn valve, 21 screw slippage, 21 injection molding machine, 9, 11, 12, 13 barrel liner, 11 in-line reciprocating screw machine, 9 injection pressures, 9 mold clamp force, 9 non-return valve, 11 nozzles, types and tips, 12 process controls, 13 screw, 9 selection, 9 temperature control, 9 type and design, 9 Typical Injection Molding Machine (Figure 5), 9 ventilation, 13 injection pressure, 9, 21, 25, 28, 45, 50, 53 flash, 21 overpacking, 21 weld lines, 53 injection speed, 21, 28, 44, 46, 51 bubbles, 21 cold flow lines, 21 gate blush, 21 jetting, 21 machine, 21 molded-in stress, 21 part geometry, 21 silver streaking, 21 sinks and voids, 51 thin-walled parts, 21 voids, 21 weld lines, 21 inserts/insert molding, 38 insulated runner molds, 35 gates, 35 hot-tip nozzles, 35 processing problems, 35 temperature control, 35 internal mold release, 23 internal stresses, 28 isotropic shrinkage, 31 J jetting, 21, 36, 47 Jetting (Figure 44), 47 K knock-out pins, 22 L Label Information for Makrolon Polycarbonate Resin (Figure 4), 8 land length, 37 leaking screw check valve, 28 length-to-diameter ratio (L/D), 10 lifters and cams, 23 long cooling cycles, 36 long cycles, 21 61

61 M machine adjustments, 28 effect on process variables, 28 The Effect of Machine Adjustments on Process Variables (Table 7), 28 machine conditions, 19, 21, 22, 23, 26 back pressure, 21 clamp tonnage, 22 cycle time, 23 decompression, 22 Effect of Part Wall Thickness on Total Mold Cycle Time (Figure 23), 23 hold pressure, 21 injection cushion, 21 injection pressure, 21 injection speed, 21 Measuring Mold Temperature (Figure 22), 22 mold temperature, 22 mold temperature control, 23 screw speed, 21 shot weight, 23 Suggested Starting Conditions for Processing Makrolon Polycarbonate Resins (Table 5), 19, 26 machine preparation, 24 purging and cleaning, 24 Makrolon 9415 resin, 22 Makrolon FCR-2405 resin, 25 Makrolon polycarbonate functional characteristics, 5 grade type, 6 markets and applications, 6 Makrolon Polycarbonate Design Manual, 6 Makrolon Polycarbonate Resin Pellets (Figure 3), 7 Makrolon Polycarbonate: A General Reference Manual, 6 material selection and/or design assistance, 55 material temperature, 53 weld lines, 53 measuring mold temperature, 22 mechanical cleaning, 24 Mechanical Cleaning of the Screw (Figure 25), 25 mechanical property performance, 29 melt backflow or Òsuck-backÓ sinks and voids, 51 melt decompression, 22 melt flow, 5, 19, 20, 28, 29, 46, 50 fracture at gate (gate blush), 46 Lot-to-Lot Melt Flow Uniformity of Makrolon Polycarbonate Resin (Figure 1), 5 rate, 29, 30 stability, 20 temperature, 19, 28, 50 testing, 30 The Effect of Resin Melt Flow on Productivity (Figure 2), 5 melt temperature, 19, 28, 50 checking, 20 Making an Accurate Melt Temperature Reading (Figure 21), 20 measurement, 20 sinks and voids, 51 melt uniformity, 21 melt viscosity, 45 minimum cycle, 25 moisture, 8, 14, 15, 17, 28, 40, 42, 43, 48 bubbles, 14 content levels, 14 degradation, 14 detecting excessive content, 17 effects on finished parts, 14, 15 excessive moisture content, 17 maximum, 14 Moisture Bubbles (Figure 15), 15 Moisture Gain of Dried Resin Exposed to the Air (Figure 13), 14 processing, 14 removal, 14 silver streaking, 14 Splay (Figure 14), 14 storage, 14 visual signs in finished parts, 14, 15 mold clamp force, 9 mold cycle time Effect of Part Wall Thickness on Total Mold Cycle Time (Figure 23), 23 mold design, 31-33, 45 Draft Angle, Length, and Taper (Figure 29), 32 Engineering Resins Design Guide, 33 material selection, 31 Mold Vent Design (Figure 28), 32 part draft, 32 surface finish, 32 texturing, 33 tolerances, 33 undercuts, 33 venting, 32 weld lines, 33 mold heaters, 23 oil-circulating units, 23 water-circulating units, 23 mold lubricant, 25 mold pressure, 27 Mold Pressure Profile (Figure 26), 27 mold release agents, 23 effect on Makrolon polycarbonate properties, 23 62

62 INDEX, continued mold shrinkage, 31, 33 part size and geometry, 31 unreinforced vs. glass-fiber-reinforced grades, 31 mold surface finish, 32, 33 draw-polishing, 32 polish lines, 32 mold surface texture, 33 mold temperature, 22, 28, 44, 50 cores and pins, 22 flow length, 22 glass-fiber-reinforced resin, 22 good surface appearance, 22 inadequate mold cooling, 22 lengthened cycle times, 22 Measuring Mold Temperature (Figure 22), 22 molded-in stress, 22 part ejection, 22 poor surface appearance, 22 rough part surface, 22 sinks and voids, 51 sticking resin, 22 mold temperature check, 22 mold temperature control, 22, 23 control settings, 22 flame-retardant resin, 23 lifters and cams, 23 oil-circulating mold-heating units, 23 part removal, 23 unfilled general-purpose resin, 23 water-circulating mold heating units, 23 mold types, 34 family mold, 34 multi-cavity, 34 single-cavity, 34 molded-in inserts, 38 part failure, 38 Plastics Joining Techniques, 38 residual stress, 38 molded-in stress, 22, 38, 42 gating, 38 machine conditions, 38 part and tool design, 38 processing temperatures, 38 molded-in stress, see also post-mold conditioning, 21, 34, 38 molding filling, 32 muffle furnace, 25 multi-cavity molds, 34 runner system, 34 N natural resin, 7 nomenclature, 7 color designation,, 7 grade designation, 7 non-return valve, 11, 41, 49 flow characteristics, 11 notched Izod impact strength, 29 nozzle(s), 12, 13, 20, 28, 48 drool, 12, 20 filtering, 12 heater bands, 12 heater control system, 20 hot-tip, 35 Internal Flow Channel of a Standard Nozzle Tip (Figure 11), 13 materials, 12 proper fit, 12 restrictive, 12 shutoff, 12 sizes, 12 static mixer, 12 temperature/temperature control, 12, 28 tips, 12 standard/general-purpose, 12 nozzle tip Internal Flow Channel of a Reverse- Taper Nozzle Tip (Figure 12), 13 Removable and Non-Removable Nozzle Tips (Figure 10), 12 O oil-circulating mold-heating units, 23 opaque resin, 7 overheating, 21 overpacking, see also packing, 21, 25, 34 P packaging, 8 bulk, truck/rail car, 8 plastic bags, 8 plastic-line cartons, 8 tote bags, 8 packing sinks and voids, 51 part, 21-25, 28, 30, 32, 35, 36 appearance, 35 delamination, 24 design, 42 draft, 32 Draft Angle, Length, and Taper (Figure 29), 32 ejection, 22, 32 failure, 38 geometry, 21, 29 release, 21 removal, 23, 25 stress, 30 surface, 22, 36 wall thickness, 23 weight, 28 63

63 part failure, 38 molded-in inserts, 38 part removal problems, 25 part wall thickness, 23 Effect of Part Wall Thickness on Total Mold Cycle Time (Figure 23), 23 part-to-part consistency, 13 parting line, 45 pellet drying, 14 performance additives/designations, 6 Performance Additives and Designations for Makrolon Polycarbonate (Table 2), 6 pins, 22 polish lines, 32 poor mold filling, 36 poor shear heating, 21 poor surface appearance, 22 positive valve gate shut-offs, 36 post-mold conditioning, 30 post-mold shrinkage, 33 pressure drops, 35 process changes, 25 process consistency, 5 process controls, 13 cooling time, 13 holding pressure, 13 process interactions, 27 compression phase or packing, 27 holding phase, 28 mold filling phase, 27 process variables, 28 The Effect of Machine Adjustments on Process Variables (Table 7), 28 processing assistance, 55 processing temperatures, 19, 20, 26 barrel, 19 melt temperature, 20 nozzle, 20 Suggested Starting Conditions for Processing Makrolon Polycarbonate Resins (Table 5 and Table 6), 19, 26 Product Information Bulletins, 6 property performance, 29 purging and cleaning, 24 Bubble Formation During Purging (Figure 18), 17 procedure, 24 purging compound, 24 R rapid-transition (nylon- type) screws, 10 regrind, 17, 24 drying, 17 Regrind Pellets (Figure 24), 24 third-party, 24 traceable heat history, 24 regulatory compliance, 55 residual polymer removal, 24 residual stress, 38 molded-in inserts, 38 Resin Pellets (Figure 3), 7 restricted flow, 41 ring gates, 38 rough part surface, 22 runners and runner systems, 34-36, 45 balanced, 34 cold-slug wells, 35 flat, 35 half-round, 35 multi-cavity molds, 34 Runner Design (Figure 32), 36 unbalanced, 34 S safety, 54 Material Safety Data Sheets (MSDS), 54 screw, 9-10, 28 back pressure, 28 compression ratio, 10 length-to-diameter (L/D) ratio, 10 material, 10 metering and feed zone depth, 9 preferred screw flight depths, Figure 6, 9 rapid-transition (nylon-type), 10 slippage, 21 Screw Profile (Figure 7), 10 speed, 21, 28 screw speed, 21, 28 long cycles, 21 overheating and material degradation, 21 poor shear heating, 21 sharp corners, 37 shear heating, 21, 40 short shot, 25 short shots/cold flow, 50 injection pressure, 50 melt temperature, 50 mold temperature, 50 Short Shot/Cold Flow (Figure 46), 50 shot capacity, 50 shot capacity, 50 shot size, 45 shot weight, 13, 23 excessive heat, 23 excessive barrel residence time, 23 too small, 23 64

64 INDEX, continued shrinkage, 28, 32, 33 post-mold, 33 shutdown, 25 shutdown procedure, long-term, 27 short-term, 26 side cores, 33 silver streaks/splay, 14, 21, 48 moisture, 48 Silver Streaks/Splay (Figure 45), 48 thermal degradation, 48 trapped air, 48 single-cavity molds, 34 sinks and voids, 13, 21, 28, 36, 43, 51 injection speed, 51 melt backflow or Òsuck-backÓ, 51 melt temperature, 51 mold temperatures, 51 packing, 51 Sinks and Voids (Figure 47), 51 specialty resin grades, 6 spiral flow length, 20 Effect of Barrel Temperature on Spiral Flow Length (Figure 20), 20 splay, 14, 22, 29, 36, 37, 40 Silver Streaks/Splay (Figure 45), 48 Splay (Figure 14), 14 sprue, 34-35, 37 bushings, 34 gates, 37 pullers, 35 Sprue Design (Figure 30), 34 Sprue Pullers (Figure 31), 35 standard resin grades, 33 starting conditions, process conditions, 25 start-up procedure, 25 Suggested Starting Conditions for Processing Makrolon Polycarbonate Resins (Table 5 and Table 6), 19, 26 sticking, 15, 34 sticking parts, 23 additional polishing, 23 cycle time, 23 increasing knock-out pin area, 23 injection pressure, 23 mold and/or melt temperature, 23 streaking, 35 streaks, 43 stress, 38 surface blemishes, 24 surface flaws, 34 surface quality, 28 T temperature control, 9, 12, 35 temperature control settings, 20 texture, 33 thermal damage/degradation, 21, 39, 48 thin-walled parts, 21, 25 tolerances, 33 mold shrinkage, 33 tool design, 49 translucent resin, 7 transparent resin, 7 trapped air, 21, 40, 43, 44, 48 tunnel gates, 38 Typical Tunnel Gate Configurations (Figure 36), 38 U undercuts, 33 part ejection, 33 raised letters and texturing, 33 Underwriters Laboratories (UL), 24 unfilled general-purpose resin, 23 unreinforced resin grades, 31 V valve, 11 Flow Characteristics of the Non-Return Valve (Figure 9), 11 Free-Flowing, Sliding Check-Ring Style Non-Return Valve (Figure 8), 11 resin backflow, 21 vented-barrel molding machines, 17 ventilating hood, 13 venting/vents, 28, 32, 44, 49 material burning, 32 mold filling, 32 Mold Vent Design (Figure 28), 32 weld lines, 32 viscosity/viscosity ranges, 6, 7 Viscosity Ranges of Makrolon Polycarbonate Resin (Table 1), 6 viscosity ranges, 6 voids, 21, 28, 36, 43, 51 Sinks and Voids (Figure 47), 51 65

65 W wall thickness, 29 Flow Length vs. Wall Thickness for Various Grades of Makrolon Resin (Figure 27), 29 warpage/warped parts, 21, 28, 37, 52 Warpage (Figure 48), 52 water-circulating mold heating units, 23 weld lines, 21, 32, 33, 53 cold slug, 53 holding pressure, 53 injection pressure, 53 material temperature, 53 Weld Line (Figure 49), 53 wet resin, see also moisture, 14, 42 Moisture Gain of Dried Resin Exposed to the Air (Figure 13), 14 66

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