Three Major Factors That Affect Screw Life

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1 Three Major Factors That Affect Screw Life Greg Quinn VP Sales - Plastics & Rubber Industries Extreme Coatings GregQ@ExtremeCoatings.net

2 Your Presenter Today Greg Quinn Started with Extreme Coatings in Assisted in development of the Extreme Coatings Technology.

3 Discussion Topics The challenge of processing a wide range of polymers using a general purpose screw. Tips for processing high crystalline polymers and the cost of wear. Wear and corrosion resistance options for feedscrews.

4 Factor #1 Screw Design and Polymers

5 Polymers are typically categorized as Amorphous or Crystalline. The higher the crystallinity, the more energy required to melt the polymer. Amorphous polymers require a more gradual melt with minimal sheer to avoid degradation. Nylon (high crystallinity) and polycarbonate (amorphous) are two good examples of polymers that are on opposite ends of the crystallinity spectrum. Both have very different melt cycles. Range of Polymers Most molders do not have the luxury of multiple screws with varying designs to accommodate the range of polymers they must process. Therefore, processing parameters areakeyfactorforscrew&barrellongevityandconsistentqualityofparts.

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7 GP Feedscrew Design Injection Molders typically mold multiple polymers using a standard General Purpose (GP) feedscrew. 20:1 General Purpose Screw 45/35/15

8 Screw Design Factors to Consider Compression ratio: Must account for non-compressable fillers such as fiberglass. A high compression ratio may lead to severe side loading of the screw to the barrel resulting in premature adhesive wear. Shot size: Barrel capacity must be large enough to allow the proper residence time for melting. These two factors play a large role in determining feedscrew & barrel life when processing abrasive fillers.

9 Result of Severe Side Load 80 mm D-2 Tool Steel 60Rc Worn.018 in 3 months due to severe side loading. Mushroomed Flites

10 Factor #2 Tips for processing high crystalline polymers and the cost of wear.

11 Heat Profiles For Crystalline Polymers Setting the appropriate HEAT PROFILE for a particular polymer is a key factor in prolonging feedscrew and barrel life. Polymer manufacturers have suggested zone temperature settings which do not account for screw design, shot size or compression ratio. It is often necessary to adjust zone temperatures settings to achieve proper melt and avoid severe side load. No hard and fast rules apply. Each project requires a custom solution!

12 Application Requiring Customization Sumitomo 280 ton injection press 63 mm 20:1 feedscrew Nylon with 33% glass filler Machine has a shortened stroke resulting in reduced barrel capacity Screw life +/-18 months

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14 Total Shot Weight (in g) Total Shot Weight (in oz) Machine Rated barrel capacity (oz) GPPS: Specific Gravity of Plastic: 1.17 Shot % of Corrected Barrel Capacity: 97.30% Molding Cycle Time (sec): 40 Residence Time (sec): 41.11

15 Observations Customer set parameters on this 280 ton machine so that it would produce at the same rate as a 350 ton machine running the same mold and injection unit. Results: o In order to meet production requirements the screw speed increased from 145 RPM s to 175 RPM s. o Due to the shortened stroke, residence time was reduced from sec. to sec. o Increasing percentage of barrel capacity from 76.69% to 97.30% o Higher side loading of the screw and reduced service life.

16 Key Processing Parameter Considerations Recommended residence time for nylon is generally around 120 seconds. Recommended percentage of shot used ranges between 25%-65%.

17 Options for Corrective Actions Best solution is to move the mold to a larger machine. If there are no other machine options, a reverse heat profile may increase production life. Increase recovery time to maximum time available. Barrel Temperature has small effect melt temperature. Steel conducts heat 100X greater than plastic. Increasing barrel zone temperatures prevents loss of heat from the plastic to the barrel.

18 What is a Wear Problem? A wear problem occurs when: Scrap rate increases. Productivity decreases. The operator must make adjustments to the machine get consistent output.

19 #1 Cause of Abrasive Wear: Glass Filled Nylon

20 Compensating for wear Compensating for screw/barrel wear through machine parameter modifications can cause excessive shear, burning, and polymer degradation which effects the quality of the resin. Modifications are typically made to maintain out-put rates or decrease scrap rates.

21 Quality Resin Resin of quality may be defined as resin that is free of unmelt, was exposed to minimal shear, has seen standard residence time, and is therefore free of degradation. Degradation is a loss of polymeric physical properties such as compression strength, tensile strength, impact strength, torsion strength, or other tangible or intangible engineered properties.

22 Intangible Cost of Wear As the screw/barrel gap increases, machine efficiency decreases. Polymer and additive degradation & Increased shear - May not be apparent until it s too late. Quality issues unseen in production may become obvious when inspected by the customer. Company Reputation!

23 Tangible Cost of Wear Process stability effected - Stable processes produce less scrap. Increase scrap - Every scrap part produced is a new part that has to be produced for FREE! Lower overall productivity - more scrap equals lower productivity. Disposal of scrap parts Labor, grinding blades, etc. Screw replacement Premature feedscrew wear equals premature feedscrew replacement. Increased Barrel Wear As the screw wears, the gap opens between the screw and barrel. Abrasive polymer back flows over flites and may cause barrel wear. Increased power consumption Increase RPMs, heater band temp adjustments and scrap all lead to increase power consumption. Down Time Non productive employees and machines down for repair cost money.

24 True Cost of Your Feedscrew Calculate over the entire life of the screw the total cost of scrap, regrind and/or disposal of scrap, the cost of parts made FOR FREE to replace scrap parts, power consumption, labor, etc. Add that cost to the original price of the screw to get the REAL cost of the screw.

25 Factor #3 Wear and corrosion resistance options for feedscrews.

26 Commonly Used Feedscrews Nitride typically supplied with new machines 4140 steel with hardfacing (C-56) inlay on the flites and Chrome Plating Most common Powdered Metal Tool Steel Commercial name CPM9V Tungsten Carbide Encapsulation Most wear resistant

27 The Key To Increased Productivity and Barrel & Screw longevity Maintain the OEM tolerances between the Screw O.D. and Barrel I.D.

28 Adhesive Wear high points interact and adhere or weld to each other

29 ASTM G77 Block on Ring Adhesive Wear Test A load (135kg) is applied to the block against the spinning ring (300 RPM) for a fixed number of revolutions (30,000). Each sample coupon is weighted before and after testing and the volume loss in mm 3 calculated.

30 G-77 Adhesive Wear Test Data Bimetallic / Col 56 Volume Loss mm 3 Bimetallic / WC Cermet Blue -Fixed Block Red- Rotating Ring Carbide / CPM-9V Carbide / WC Cermet

31 G-77 Adhesive Wear Test Data Carbide / Nitride Blue -Fixed Block Red- Rotating Ring Nitride /Nitride Volume Loss 1.19 mm

32 Wear Resistance Testing ASTM G65 (Dry Sand) 6000 revolutions 12 Kg Load 23 cm rubber wheel Graduated dry sand abradent Volume loss in mm³

33 7.0 G-65 Wear Resistance Test Data Comparagraph Relative Abrasion Resistance ASTM G65 A 6000 revolution Wear Factor Tungsten Carbide Cermet Powder Metal (9V) D2 Tool Steel Nitrided steel (EN41B) Chrome Plating

34 Why is Carbide Most Wear Resistant Hardness DOES NOT always equate to wear resistance! The volume of carbides in the alloy or composite determines the resistance to wear. Treatment Description Hard. RC Vol. % Carb. Type Carb. Rel. Wear Resist Nitrided Steel Aluminum Alloyed steel heat treated 68 0% AIN 1.0 Chrome Plate Chromium electro deposit surface treatment 70 0% Pure Cr 2.3 Bi-metallic Weld deposit of Ni or Co alloy on flight OD 48 25% CrC/ WC 2.3 Tool Steel Specialty steels heat treated to through-harden 55 20% VC / CrC 3.5 Tungsten Carbide Thermal spray surface coating high carbide content 68 80% WC 11.7

35 TAFA JP-8000 Thermal Spray Gun Temperature 6000 F (3300 C) melt powder particles. (Cobalt or Nickel) Particle velocities > 3300 feet/sec (1000 m/sec) Kinetic energy contributes additional heat and promotes bonding, high density, and high hardness Substrate temperature is maintained below 300 F (150 C)

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37 Empirical Evidence Application Details 26 mm CPM9V screw with a compression ratio of 3.2:1 Processor running 30% GF LCP on 25 machines. Has process issues at.006 OD wear. Approximately 750k shots or 6-8 months. wear was isolated to the O.D. on the last 50% of screw. Inconsistent processing forces removal of the screw from service.

38 Empirical Evidence Solution Compression ratio was reduced to 2.8:1 Last 50% of screw (worn section) was coated on the flite lands with Tungsten Carbide via the HVOF process. After 5 months and 650k shots this screw has a maximum of.001 of O.D. wear. Design change and increased wear resistant O.D. changed the dynamic M shots are now possible.

39 O.D. Surface Treatment Tungsten Carbide Overlay

40 50 mm CPM9V Screw 60% GF Nylon Empirical Evidence Application Details 3-5 months life due to almost 90% of the barrel volume used with each cycle Flight side erosion was observed on all screws. Due to the high barrel usage, residence time was reduced which resulted in accelerated wear.

41 Empirical Evidence Solution The system was upsized to a 57 mm diameter feedscrew which was encapsulated with Tungsten Carbide. Reduced barrel usage to 70% of the total, still high but manageable. Reverse heat profiles implemented.

42 Empirical Evidence A combination of reverse temperature profile, extended recovery (plasticizing) time plus surface treatment of Tungsten Carbide improved overall screw life to 30+ months. (previously 3-5 months) The surface treatment completely eliminated flight side erosion. Tungsten Carbide Overlay

43 Conclusions When planning a project it is important to consider the three major factors that effect feedscrew life and performance. Feedscrew design Processing parameters Wear and corrosion protection

44 Thank you!