Certified Composites Technician Study Guide and Test Preparation

Transcription

1 American Composites Manufacturers Association Certified Composites Technician Study Guide and Test Preparation CCT Compression Molding Modules 1-7 American Composites Manufacturers Association 2004

2 When you apply to become a Certified Composites Technician Compression Molder (CCT-CM), you have taken the first step toward achieving excellence in the compression molding industry, advancing your career, and pursuing comprehensive compression molding knowledge. The CCT-CM program is designed to elevate standards in the industry by enhancing individual performance and recognizing those who demonstrate critical knowledge of the compression molding industry. The CCT-CM designation is a noted symbol of education among employers, employees, and industry professionals. As the industry advances, being a CCT-CM will become increasingly important. If you have worked in the compression molding industry for at least one year and are committed to developing your career, attaining the CCT-CM designation will allow others to recognize you as a compression molding industry professional.

3 2004 by American Composites Manufacturers Association Arlington, VA, USA Phone: Fax: All rights reserved. No part of this book may be reproduced, in any form or by any means, without permission from the publisher. Printed in the United States. Disclaimer The sole purpose of this Study Guide is to assist in the preparation for the CCT-CM Examination. It is not a formal code or standard of the American Composites Manufacturers Association nor is the information contained herein based upon such a code or standard. While the Study Guide reflects ACMA s understanding of current industry practices in general, nothing herein should be viewed as a recommendation by ACMA that any application, technique, or process is appropriate in any particular circumstances. Similarly, the fact that a particular application, technique, or process is listed in the Study Guide should not be viewed as an endorsement by ACMA of such application, technique, or process. ACMA makes no claims concerning the accuracy or applicability of the information contained in the Study Guide, and ACMA is not responsible for the results obtained from the use of such information. Determination of the suitability of the information in the Study Guide other than for the preparation for the CCT-CM Examination is the sole responsibility of the user. This Study Guide is sold without warranties, express or implied, including but not limited to any implied warranty of merchantability or fitness for a particular purpose. ACMA expressly disclaims all such warranties. ACMA is not responsible for any damage or loss caused or alleged to be caused by the information contained herein. Accordingly, ACMA shall not be liable for any direct, indirect, incidental, special, or consequential damages, resulting from the use of the Study Guide. ACMA does not accept any liability based on the designation conferred upon an in individual who successfully completes the certification program. Any company recognizing the conference of such a designation is responsible for verifying any and all credentials and skills of anyone with the CCT-CM designation.

4 Certified Composites Technician COMPRESSION MOLDING STUDY GUIDE Table of Contents Module 1 General Composites Knowledge Section 1 Composites Overview Section 2 The Composites Industry Section 3 What are Composites? Section 4 Why Are Composites Different? Section 5 The Advantages of Composites Section 6 History of the Composites Industry Module 2 Composites Manufacturing Processes Section 1 Composites Manufacturing Processes Section 2 Compression Molding Section 3 Pultrusion Section 4 Vacuum Infusion Processing Section 5 Resin Transfer Molding Section 6 Vacuum Bag Molding Section 7 Filament Winding Section 8 Open Molding Module 3 Compression Molding Materials Section 1 Component Materials Section 2 Sheet Molding Compound Section 3 Bulk Molding Compound Section 4 Preformed Reinforcements Addendum: General Overview of Composites Materials Section 1 The Polymer Matrix Section 2 Thermoset Resins Section 3 Overview of Polyester and Vinyl Ester Resins Section 4 Initiators/Promoters/Inhibitors Section 5 Resin Additives Section 6 Gel Coat Section 7 Reinforcement Materials Section 8 Core Materials

5 Module 4 Overview of the Matched Metal Die Molding Process Section 1 Compounding Processes and Equipment Section 2 Molding Processes, Equipment, and Tooling Section 3 The Press-Mold System Section 4 In-Mold Coating Module 5 Hydraulic Press Systems Section 1 Fundamentals of Hydraulics Section 2 Hydraulic Pumps Section 3 Hydraulic Cylinders Section 4 Molding Presses Section 5 Press Design Factors Section 6 Press Operating Speeds Section 7 Mold Temperature Control Module 6 Compression Molding Process Quality Control and Troubleshooting Section 1 Quality Control Section 2 Troubleshooting Methodology Section 3 Troubleshooting for Press Operators Section 4 Defect Terminology and Descriptions Module 7 Compression Molding Plant Safety Section 1 Safety Overview Section 2 Chemical Safety Section 3 Materials Safety Section 4 Fire Safety Section 5 Thermal Burn Protection Section 6 Compression Molding Press Safety Section 7 Electrical Safety Section 8 Power Tool Safety Section 9 Compressed Air Safety Section 10 Lockout/Tagout Procedures Section 11 Lift Truck Safety Section 12 Manual Lifting Section 13 High-Pressure Hazards Section 14 General Personal Safety Section 15 Bloodborne Pathogen Safety Section 16 Housekeeping and Safety GLOSSARY

6 STUDY GUIDE CERTIFIED COMPOSITES TECHNICIAN COMPRESSION MOLDING 3-1 Study Module 3 Compression Molding Materials Section 1 Component Materials Matched Metal Die Applications Resins Unsaturated polyester resins (UPR) are the basis for most MMD moldings. The specific type of resin used may vary, depending on the required finished part performance and cost. The most widely used polyester resins are characterized in four broad categories: Fiber Reinforcement The most common reinforcement used in molding compounds is glass fiber, although carbon/graphite and aramid (Kevlar ) are used in specialized applications. Various forms of glass fiber are used depending on the type of compression molding compound being formulated and molded. Chopped fibers ranging in length from 1/8 inch to 1 inch are used in bulk molding compounds. Glass fiber in the form of continuous strand roving is used as the input product in sheet molding compounds. The roving strands are cut into shor t lengths using specialized equipment that deposits the chopped fiber on a conveyor of compounded resin. Fiber lengths generally range from 0.5 inches to two inches, with one inch being the average length. When used in the Liquid Composite Molding (LCM) process, chopped fiber or continuous strand mat is fabricated into preforms (a pre-formed shape) for insertion into the mold. In this process, the reinforcement fiber and compound paste are combined in the mold rather than during compound manufac- MMD Molding Resins Resin Category Formulation Use Structural Resins Low-Profile Resins General Purpose Resins Specialty Resins Isophthalic and Terephthalic Formulations with low volumetric shrinkage Orthophthalic or Dicyclopentadiene (DCPD) Formulations for specific applications Structural resins are used in applications requiring higher mechanical properties, temperature resistance, or chemical resistance. Low-Profile Resins are used in applications requiring high quality finish appearance or low surface profile, such as automotive body panels. These resins are characterized by high reactivity rather than by polymer type. General Purpose Resins are used in applications that are cost sensitive and have more lenient part performance requirements compared with structural or low profile applications. Specialty resins are designed for specific application requirements, such as weather resistance, f lame resistance, or FDA-approved articles.

7 3-2 CERTIFIED COMPOSITES TECHNICIAN COMPRESSION MOLDING STUDY GUIDE turing as for SMC and BMC. Surface veil is often used in LCM to provide a resin-rich layer. Surfacing veil is a thin non-woven mat, of either glass or synthetic fiber, used to improve the part appearance and/or corrosion resistance. Fillers Most MMD resin pastes are formulated with a high level of inert bulk fillers, except for structural applications that require higher resin content. The use of fillers can lower material cost, enhance finished part appearance, reduce shrinkage, promote glass f low during molding and contribute to increased mechanical properties. However, the inclusion of fillers increases the viscosity of the molding compound paste, thus limiting the amount of glass that can be used. The mechanical properties of the molded part are directly related to the fiber content, sometimes referred to as glass content, glass load, or fiber volume fraction. A high glass content results in higher mechanical properties. In the design process, there is a trade-off between glass load, filler content, materials cost, and the resulting mechanical properties of the finished article. Fillers also provide opacity (lack of transparency) and increased part density. The most common fillers are calcium carbonate, clay, and alumina trihydrate (ATH). Clay fillers are often used in combination with calcium carbonate fillers to control the compound paste viscosity, promote f low, and improve crack resistance in molded parts. Alumina trihydrate is used in applications requiring improved fire performance and enhanced electrical properties. Shrinkage-Control Additives During the polymerization process, thermoset resins shrink as the polymer molecules contract into a higher-density solid. Unsaturated polyester resins generally shrink 4% to 7% by volume during the curing process. This loss of Key Words Study Module 3 Sheet Molding Compound (SMC) A process and a material. Refers to the SMC compression molding process and sheet molding compound as a molding material. Tool Also called a die or a mold. The form placed in the press to create the shape of the molded part. Low-Pressure Molding Compound Sheet molding compound that can be molded at lower pressure than standard compounds. Low-Pressure/Low-Temperature Molding Compound Sheet molding compound that can be molded at lower pressure and lower temperature than standard compounds. Unsaturated Polyester Resin (UPR) The most commonly used thermoset resin employed in SMC and BMC. Liquid Composite Molding (LCM) Combining UPR paste and glass mat or preform at the press. Fillers Usually an inert material, such as calcium carbonate (limestone), added to resin to increase the volume of the mixture and modify the properties and cost. Shrinkage-Control Additives Resin additives designed to counter resin shrinkage during curing. As the resin polymerizes and contracts, the shrink-control additive expands to off-set the loss of volume. Initiator A reactive peroxide that causes the resin to polymerize. Initiator is sometimes referred to as catalyst, although this is a technically incorrect term. Thickeners Additives that increase the viscosity of the molding compound, transforming it from a f lowable liquid to a high-viscosity paste. Mold Release A resin additive that forms a barrier between the molded part and the mold surface allowing the part to separate after being cured. Pigments Colorants added to molding compound for cosmetic purposes. Bulk Molding Compound (BMC) A form of molding compound that is in a mass rather than a sheet, as with SMC. Preforms (Pre-forms) Pre-formed glass fiber used primarily in liquid composite molding (LCM).

8 STUDY GUIDE CERTIFIED COMPOSITES TECHNICIAN COMPRESSION MOLDING 3-3 volume can create a variety of defects in molded parts, such as surface distortion, waviness, fiber print, and warping. The loss of volume of polyester resins can be controlled by the use of shrink-control additives. However, use of these shrink-control additives may reduce the mechanical properties. Shrink-control additives can be divided into two categories: lowshrink additives and low-profile additives.. Low-Shrink Additives Minimize shrinkage but do not eliminate it altogether. Low-shrink additives are used in applications where surface appearance and dimensional stability requirements are needed but are not as demanding as these required by the use of low-profile additives. These additives are especially helpful in applications requiring pigmentation. The common lowshrink additives are thermoplastic polystyrene and rubber-like elastomers.. Low-Profile Additives Eliminate shrinkage and can even result in slight volumetric expansion. Lowprofile additives are used in applications requiring a high level of surface appearance and dimensional stability, such as automotive body panels. Molding compounds formulations using low-profile additives have limited pigment levels and generally are used with white or light pastel colors. Common low-profile additives are thermoplastic polyesters and polyvinyl acetates. Initiators These reactive peroxides are the source of free-radical molecules, that begin the resin polymerization (curing) process. It is commonly referred to as catalyst, although this is a technically an incorrect term. For the elevated temperature curing in the SMC process, the heat from the mold causes the initiator to decompose, beginning the crosslinking reaction. Initiator selection is based on the molding temperature. Common initiators used in SMC are t-butyl Perbenzoate (TBPB) and t-butyl Peroctoate (PDO). Often two or more initiators are combined in the sheet molding compound to create a specific curing profile and ensure complete cure. Thickeners Thickening agents are used in sheet molding compounds to transform the liquid mixture into a high-viscosity material that can be handled in sheet form. Thickening agents chemically react with the resin in the compound, increasing the viscosity to the point where it no longer flows at room temperature. Thickeners are the last component added to the compound paste, and the viscosity increase begins to occur immediately. Commonly used thickeners include alkaline earth oxides or hydroxides, such as magnesium oxide (MgO), magnesium hydroxide (MgO(OH)2), calcium oxide (CaO), and calcium hydroxide (Ca(OH)2). Magnesium oxide (MgO) provides the quickest thickening and is the most widely used thickener. Thickeners can be used in combinations to achieve a particular viscosity profile and can be added as a powder or a pre-dispersed paste. Pre-dispersed pastes are often easier to integrate into the mixture during the SMC compounding process and result in more uniform consistency. A thickening profile is described in terms of the mixed SMC paste viscosity; this includes all ingredients except the fiber reinforcement. During compounding, the paste viscosity must be low enough to allow the thickened liquid resin to be pumped and to wet-out the reinforcement. Compounding (i.e., mixing the formulated resin paste with the chopped fibers) typically takes place within 15 to 60 minutes from the time the thickener is added to the resin mixture. Immediately after the addition of the thickening additive, the paste viscosity becomes similar to a thick pancake batter, measured at about 10,000 to 60,000 centipoise (cps). Within about 60 minutes, the paste viscosity then increases to 300,000 to 1,000,000

9 3-4 CERTIFIED COMPOSITES TECHNICIAN COMPRESSION MOLDING STUDY GUIDE cps to the consistency of pudding. Following compounding, the material is moved to a maturation room, where the viscosity continues to develop to the final specification. In the maturation process, the material is maintained at about 90 degrees Fahrenheit until it reaches its specified viscosity. This point is called the release viscosity of the compound. At the release viscosity, the compound has acquired characteristics that allow it to be molded. These include:. The compound must be manageable, to allow for preparing and handling the charge.. The viscosity must be sufficient to transport the fiber reinforcement as the material f lows in the mold.. The viscosity must be in a range that permits sufficient flow for mold filling at the required molding pressure. At the end of the maturation period, the release viscosity is similar to bread dough or about 10 to 30 million cps this is achieved in one to three days. The viscosity of the material continues to increase even after it has reached its release viscosity. The rate of increase determines the time window when the material may be used. SMC may be moldable up to 100 million cps depending on part complexity and molding pressure. Factors effecting thickening of a SMC formulation include thickener type and level, the acid value of the polyester resin, molecular weight of the resin, and water content of the compound. Mold Release MMD pastes contain a release agent to facilitate removal of the cured part from the mold. The release agent is known as an internal mold release. During the molding process, the release agent melts and forms a barrier between the mold surface and the molded parts to ensure separation of the part and mold. These materials are selected on the basis of melting point and are typically used in a concentration of less than 2% of the weight of the total compound. Excessive amounts of mold release can reduce mechanical strength, cause objectionable cosmetic appearance on the surface, and effect paint and/or bond adhesion characteristics. Pigments Many MMD formulations are pigmented for cosmetic purposes, and a broad range of colors is available. However, some limitations on colors do exist. The fillers used in SMC can impart color to the compound and affect the range of pigmented colors of the molded part. Also, the type of shrink-control additive used can limit the color possibilities; darker and richer colors are more difficult to achieve. Pigments are added during the compounding process in either dry powder or pre-dispersed paste form. Dry powder pigments can be difficult to dispense in the compound due to agglomeration (or clumping) of the pigment particles. Pre-dispersed pigment pastes are pigments that are dispersed in an unsaturated polyester grinding vehicle. This is essentially a resin that is used to create the paste dispersion. Commonly used white pigments are titanium dioxide and zinc sulfide. Carbon black is often used for black pigmentation. Pigments can affect the shelf-life stability and reactivity of molding compounds. Specialty Additives There are a number of additives used in MMD formulations to enhance various performance properties. These include: surfactants, to enhance the wet-out of fillers allowing more filler to be used; fire performance additives, to reduce f lame spread or smoke generation, such as antimony trioxide, tri-phosphate, chlorinated paraffin, and zinc borate; and additives to improve weathering, such as ultraviolet (UV) absorbers.