120 Chapter Two 2.5 Liquid Resin Processes 10 2.5.1 Potting Process The processing of liquid potting compounds commences with dispersing curing agents and other ingredients with a simple propeller mixer, producing potting compounds capable of a variety of properties achieved by changes in formulations to gain stiffness, color, strength, and electrical properties meeting specific needs and applications. The liquid pot- ting compound is poured into a receptacle or jacket where the compound cures in place, either with added heat or at ambient temperature. The receptacle or jacket remains as the permanent outer skin of the final product. Proper compounding can produce articles with negligible shrinkage and optical clarity along with a minimum of internal stress. Part and mold design, coupled with the proper placement of the reinforcement, are calculated with sophisticated computer software. 2.5.2 Potting Resin Selection Tables 2.2 through 2.5 provide helpful information for guidance in the selection process for potting resins. 2.5.3 Casting Process The process for casting fluid monomeric resin compounds involves pouring the premixed compound into a stationary mold (metal or glass) and then allowing the compound to cure at ambient or elevated temperatures. The mold may contain objects that will have been prepositioned in the mold and they become embedded by the resin as it cures. This tech- nique can be done with minimal equipment and delicate inserts can he embedded, or they can he introduced into the compound prior to the curing stage. The chief disadvantages are that high-viscosity resins are difficult to handle and the occurrence of voids or bubbles can present problems. 2.5.3.1 Cast epoxies. Cast epoxy resins have proven to be very popular in a wide va- riety of applications because of their versatility, excellent adhesion, low cure shrinkage, good electrical properties, compatibility with many other materials, resistance to weather- ing and chemicals, dependability, and ability to cure under adverse conditions. Some of their application fields are adhesives, coatings, castings, pottings, building construction, chemical resistant equipment, and marine applications. The most widely used epoxy res- ins in the casting field are the epi-bis and cycloaliphatic epoxies. Table 2.6 lists the proper- ties of typical cured epi-bis resins with a variety of curing agents, and Table 2.7 provides information on the properties of blends of cycloaliphatic epoxy resins. Novolac epoxy resins, phenolic or cresol novolacs, are reacted with epichiorohydrin to produce these novolac epoxy resins which cure more rapidly than the epi-bis epoxies and have higher exotherms. These cured novolacs have higher heat-deflection temperatures than the epi-bis resins as shown in Table 2.8. The novolacs also have excellent resistance to solvents and chemicals when compared with that of an epi-bis resin as seen in Table 2.9. 2.5.3.2 Cast polyesters. General purpose polyester, when blended with a monomer such as polystyrene and then cured, will produce rigid, rapidly curing transparent castings exhibiting the properties shown in Table 2.10. Other monomers, in conjunction with poly- styrene, such as alpha methyl styrene, methyl methacrylate, vinyl toluene, diallyl phtha- Thermosets, Reinforced Plastics, and Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 121 Thermosets, Reinforced Plastics, and Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 122 Thermosets, Reinforced Plastics, and Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 123 Thermosets, Reinforced Plastics, and Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 124 Chapter Two Thermosets, Reinforced Plastics, and Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 125 Thermosets, Reinforced Plastics, and Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 126 Thermosets, Reinforced Plastics, and Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 127 Thermosets, Reinforced Plastics, and Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 128 Chapter Two late, triallyl cyanurate, divinyl benzene, and chlorostyrene, can be blended to achieve specific property enhancements. The reactivity of the polyester used, as well as the config- uration of the product, affect the choice of systems. Flexible polyester resins are available that are tougher and slower curing and produce lower exotherms and less cure shrinkage. They absorb more water and are more easily scratched but show more abrasion resistance than the rigid type. Their property profile is shown in Table 2.11. The two types, rigid and flexible, can be blended to produce interme- diate properties, as shown in Table 2.12. 2.5.3.3 Cast polyurethanes. Polyurethanes are reaction products of an isocyanate, a polyol, and a curing agent. Because of the hazards involved in handling free isocyanate, prepolymers of the isocyanate and the polyol are generally used. Thermosets, Reinforced Plastics, and Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Thermosets, Reinforced Plastics, and Composites 129 The choice of curing agent influences the curing characteristics and final properties. Di- amines are the best general-purpose curing agent, as shown by Table 2.13. The highest physical properties are produced using MOCA 4,4-methyl-bis (2chloroaniline). The other major class of curing agents, the polyols, are more convenient to use, but the final products have lower physical properties. By providing good abrasion resistance and a low coeffi- cient of friction, polyurethanes find application in roller coatings and press pads as well as gaskets, casting molds, timing belts, wear strips, liners, and heels and soles. 2.5.3.4 Cast phenolics. Phenolic casting resins are available as syrupy liquids pro- duced in huge kettles by the condensation of formaldehyde and phenol at high temperature in the presence of a catalyst and the removal of excess moisture by vacuum distillation. These resins, when blended with a chemically active hardener, can be cast and cured solid Thermosets, Reinforced Plastics, and Composites Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. [...]... 20 04 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Thermosets, Reinforced Plastics, and Composites 136 Chapter Two Figure 2.12 (a) Horizontal treater and (b) decorative laminate treater (Source: Charles A Harper, Handbook of Plastics, Elastomers, and Composites, 3d ed., McGraw-Hill, New York, 1996, p 2.2) and stored in temperature- and. .. Reinforced Plastics, and Composites 144 Chapter Two glass, and synthetic fibers to the high-strength, high-bulk factor types employing long fibers of cotton flock, glass, acrylic, and polyethylene terephthalate 2.7.2 .4 Specifications DAP and DAIP molding compounds meet the requirements of several commercial and military specifications as well as those of certain industrial and electronic firms who will often... Plastics, and Composites Thermosets, Reinforced Plastics, and Composites 137 Figure 2.13 Stress-strain curves for various materials (a) Rein- forced plastics, (b) wood and most metals, and (c) steel (Source: Charles A Harper, Handbook of Plastics, Elastomers, and Composites, 3d ed., McGraw-Hill, New York, 1996, p 2.3) flexural strengths due to the polymerization of the resin with its property enhancement... as given at the website Thermosets, Reinforced Plastics, and Composites Thermosets, Reinforced Plastics, and Composites 141 The following sections will take each of the family members, in alphabetical order, and outline their history; specifications; and reinforcements, fillers, and data sheet value applications 2.7.2 AIlyls: Diallyl-ortho-phthalate (DAP) and Diallyl-iso-phthalate (DAIP) 2.7.2.1 History.13... (www.digitalengineeringlibrary.com) Copyright © 20 04 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Thermosets, Reinforced Plastics, and Composites Thermosets, Reinforced Plastics, and Composites 135 common with the filaments combined into strands, and the strands plied into yarns These yarns can be woven into fabrics on looms 2.6 .4 Processes The liquid resins... to the Terms of Use as given at the website Thermosets, Reinforced Plastics, and Composites Thermosets, Reinforced Plastics, and Composites 145 Underwriters Laboratory (UL) UL rates DAP and DAIP thermally at 266°F (130°C), with a flame resistance rating of 94 VO in a 1/16-in section Neither the DAP nor DAIP compounds have been submitted to UL’s long-term thermal testing However, MIL-M 14 H does recognize... Copyright © 20 04 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Thermosets, Reinforced Plastics, and Composites Thermosets, Reinforced Plastics, and Composites 149 CMI-5: Cellulose filler, impact value of 0.5 ft-lb CMI- 10: Cellulose filler, impact value of 1.0 ft-lb MMD: Mineral filler, general purpose MMI-5: Glass filler, impact value of 0.5 ft-lb... website Thermosets, Reinforced Plastics, and Composites Thermosets, Reinforced Plastics, and Composites 153 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 20 04 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Thermosets, Reinforced Plastics, and Composites 1 54 Chapter Two 2.7.5 Phenolics... value of 4. 0 ft-lb Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 20 04 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Thermosets, Reinforced Plastics, and Composites Thermosets, Reinforced Plastics, and Composites ASTM 155 The ASTM specifications can be found in D-700-65 and D -46 17... Thermosets, Reinforced Plastics, and Composites 148 Chapter Two Melamines Melamine was isolated in 18 34, and it wasn’t until 1933 that Palmer Griffith produced dicyanamide and found that it contained melamine The addition of formaldehyde produced a resin that could be compounded into a desirable molding compound This new compound had a number of desirable qualities superior to phenolics and ureas of that time . (Source: Charles A. H arper, Handbook of Plastics, Elastomers, and Composites, 3d ed., McGraw-Hill, New York, 1996, p. 2.2) Thermosets, Reinforced Plastics, and Composites Downloaded from Digital. for various materials. (a) Rein- forced plastics, (b) wood and most metals, and (c) steel. (Source: Charles A. Harper, Handbook of Plastics, Elastomers, and Compos- ites, 3d ed., McGraw-Hill,. optimum wetting or saturation of the resin into the reinforcement. The sheets come out of the treater and are sheared to size and stacked Thermosets, Reinforced Plastics, and Composites Downloaded from