Handbook of Plastics, Elastomers and Composites Part 13 pdf

480 Table 7.33 Properties of Structural Adhesives Used to Bond Metals Service temp. °F Shear strength, lb/in. 2 Peel strength Impact strength Creep resistance Solvent resistance Moisture resistance Type of bond Adhesive Max Min Epoxy-amine 150 –50 3000–5000 Poor Poor Good Good Good Rigid Epoxy-polyamide 150 –60 2000–4000 Medium Good Good Good Medium Tough and moderately flexible Epoxy-anhydride 300 –60 3000–5000 Poor Medium Good Good Good Rigid Epoxy-phenolic 350 –423 3200 Poor Poor Good Good Good Rigid Epoxy-nylon 180 –423 6500 Very good Good Medium Good Poor Tough Epoxy-polysulfide 150 –100 3000 Good Medium Medium Good Good Flexible Nitrile-phenolic 300 –100 3000 Good Good Good Good Good Tough and moderately flexible Vinyl-phenolic 225 –60 2000–5000 Very Good Good Medium Medium Good Tough and moderately flexible Neoprene-phenolic 200 –70 3000 Good Good Good Good Good Tough and moderately flexible Polyimide 600 –423 3000 Poor Poor Good Good Medium Rigid Polybenzimidazole 500 –423 2000–3000 Poor Poor Good Good Good Rigid Polyurethane 150 –423 5000 Good Good Good Medium Poor Flexible Acrylate acid diester 200 –60 2000–4000 Poor Medium Good Poor Poor Rigid Cyanoacrylate 150 –60 2000 Poor Poor Good Poor Poor Rigid Phenoxy 180 –70 2500 Medium Good Good Poor Good Tough and moderately flexible Thermosetting acrylic 250 –60 3000–4000 Poor Poor Good God Good Rigid Plastics and Elastomers in Adhesives 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. Plastics and Elastomers in Adhesives 481 displace the adhesive, and result in bond failure. These weak boundary layers may come from the environment or from within the plastic substrate itself. Moisture, solvent, plasticizers, and various gases and ions can compete with the cured adhesive for bonding sites. The process where a weak boundary layer preferentially dis- places the adhesive at the interface is called desorption. Moisture is the most common de- sorbing substance, being present both in the environment and within many polymeric substrates. Solutions to the desorption problem consist of eliminating the source of the weak boundary layer or selecting an adhesive that is compatible with the desorbing material. Excessive moisture can be eliminated from a plastic part by post curing or drying the part before bonding. Additives that can migrate to the surface can possibly be eliminated by re- formulating the plastic resin. Also, certain adhesives are more compatible with oils and plasticizers than others. For example, the migration of plasticizer from flexible polyvinyl chloride can be counteracted by using a nitrile-based adhesive. Nitrile adhesive resins are capable of absorbing the plasticizer without degrading. 7.5.3.1 Thermoplastics. Many thermoplastics can be joined by solvent or heat weld- ing as well as with adhesives. These alternative joining processes are discussed in detail in another chapter. The plastic manufacturer is generally the leading source of information on the proper methods of joining a particular plastic. 7.5.3.2 Thermosetting plastics. Thermosetting plastics cannot be heat or solvent welded. They are easily bonded with many adhesives, some of which have been listed in Table 7.31. Abrasion is generally recommended as a surface treatment. 7.5.3.3 Reinforced plastics. Adhesives that give satisfactory results on the resin matrix alone may also be used to bond reinforced plastics. Surface preparation of rein- forced thermosetting plastics consists of abrasion and solvent cleaning. A degree of abra- sion is desired so that the reinforcing material is exposed to the adhesive. Reinforced thermoplastic parts are generally abraded and cleaned prior to adhesive bonding. However, special surface treatment such as used on the thermoplastic resin ma- trix may be necessary for optimal strength. Care must be taken so that the treatment chem- icals do not wick into the substrate and cause degradation. Certain reinforced thermoplastics may also be solvent cemented or heat welded. However, the percentage of filler in the substrate must be limited, or the bond will be starved of resin. 7.5.3.4 Plastic foams. Some solvent cements and solvent-containing pressure-sensi- tive adhesives will collapse thermoplastic foams. Water-based adhesives, based on styrene butadiene rubber (SBR) or polyvinyl acetate, and 100 percent solid adhesives are often used. Butyl, nitrile, and polyurethane adhesives are often used for flexible polyurethane foam. Epoxy adhesives offer excellent properties on rigid polyurethane foam. 7.5.4 Adhesives for Elastomers Plastics and Elastomers in Adhesives 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. 482 Chapter Seven 7.5.4.1 Vulcanized elastomers. Bonding of vulcanized elastomers to themselves and other materials is generally accomplished by using a pressure-sensitive adhesive de- rived from an elastomer similar to the one being bonded. Flexible thermosetting adhesives such as epoxy-polyamide or polyurethane also offer excellent bond strength to most elas- tomers. Surface treatment consists of washing with a solvent, abrading, or acid cyclizing as described in Table 7.18. Elastomers vary greatly in formulation from one manufacturer to another. Fillers, plas- ticizers, antioxidants, etc., may affect the adhesive bond. Adhesives should be thoroughly tested on a specific elastomer and then re-evaluated if the elastomer manufacturer or for- mulation is changed. 7.5.4.2 Unvulcanized elastomers. Unvulcanized elastomers may be bonded to metals and other rigid adherends by priming the adherend with a suitable air- or heat-dry- ing adhesive before the elastomer is molded against the adherend. The most common elas- tomers to be bonded in this way include nitrile, neoprene, urethane, natural rubber, SBR, and butyl rubber. Less common unvulcanized elastomers such as the silicones, fluorocar- bons, chlorosulfonated polyethylene, and polyacrylate are more difficult to bond. However, recently developed adhesive primers improve the bond of these elastomers to metal. Surface treatment of the adherend before priming should be according to good stan- dards. 7.5.5 Adhesives for Wood Resorcinol-formaldehyde resins are cold-setting adhesives for wood structures. Urea- formaldehyde adhesives, commonly modified with melamine formaldehyde, are used in the production of plywood and in wood veneering for interior applications. Phenol-form- aldehyde and resorcinol-formaldehyde adhesive systems have the best heat and weather resistance. Polyvinyl acetates are quick-drying, water-based adhesives commonly used for the as- sembly of furniture. This adhesive produces bonds stronger than the wood itself, but it is not resistant to moisture or high temperature. Table 7.34 describes common adhesives used for bonding wood. 7.5.6 Adhesives for Glass Glass adhesives are generally transparent, heat-setting resins that are water-resistant to meet the requirements of outdoor applications. Adhesives generally used to bond glass, and their physical characteristics, are presented in Table 7.35. 7.6 Effect of the Environment For an adhesive bond to be useful, it not only must withstand the mechanical forces acting on it; it must also resist the service environment. Adhesive strength is influenced by many common environments, including temperature, moisture, chemical fluids, and outdoor weathering. Table 7.36 summarizes the relative resistance of various adhesive types to common environments. 7.6.1 High Temperature Plastics and Elastomers in Adhesives 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. Plastics and Elastomers in Adhesives 483 All polymeric materials are degraded to some extent by exposure to elevated temperatures. Not only are physical properties lowered at high temperatures, they also degrade due to thermal aging. Newly developed polymeric adhesives have been found to withstand 500 to 600°F continuously. To use these materials, the designer must pay a premium in adhesive cost and also be capable of providing long, high-temperature cures. For an adhesive to withstand elevated-temperature exposure, it must have a high melt- ing or softening point and resistance to oxidation. Materials with a low melting point, such as many of the thermoplastic adhesives, may prove excellent adhesives at room tempera- ture. However, once the service temperature approaches the glass transition temperature of these adhesives, plastic flow results in deformation of the bond and degradation in cohe- sive strength. Thermosetting materials, exhibiting no melting point, consist of highly cross-linked networks of macromolecules. Many of these materials are suitable for high- temperature applications. When considering thermoset adhesives, the critical factor is the rate of strength reduction due to thermal oxidation and pyrolysis. Thermal oxidation initiates progressive chain scission of molecules resulting in losses of weight, strength, elongation, and toughness within the adhesive. Figure 7.30 illustrates the effect of oxidation by comparing adhesive joints aged in both high-temperature air and inert-gas environments. The rate of strength degradation in air depends on the temperature, the adhesive, the rate of airflow, and even the type of adherend. Certain metal–adhesive in- terfaces are capable of accelerating the rate of oxidation. For example, many structural ad- hesives exhibit better thermal stability when bonded to aluminum than when bonded to stainless steel or titanium (Fig. 7.30). High-temperature adhesives are usually characterized by a rigid polymeric structure, high softening temperature, and stable chemical groups. The same factors also make these TABLE 7.34 Properties of Common Wood Adhesives (from Ref. 36) Resin type used Resin solids in glue mix, % Principal use Method of application Principal property Principal limitation Urea formaldehyde 23–30 Wood-to-wood interior Spreader rolls Bleed-through-free; good adhesion Poor durability Phenol formaldehyde 23–27 Plywood exterior Spreader rolls Durability Comparatively long cure times Melamine formaldehyde 68–72 Wood-to-wood, splicing, patching, scarfing Sprayed, combed Adhesion, color, durability Relative cost; poor washability; needs heat to cure Melamine urea 1/1 55–60 End and edge gluing exterior Applicator Colorless, durability and speed Cost Resorcinol formaldehyde 50–56 Exterior wood-to-wood (laminating) Spreader rolls Cold sets durability Cost, odor Phenol-resorcinol 10/90 50–56 Wood-to-wood exterior (laminating) Spreader rolls Warm-set durability Cost, odor Polyvinyl acetate emulsion 45–55 Wood-to-wood interior Brushed, sprayed, spreader rolls Handy Lack of H 2 O and heat resistance Plastics and Elastomers in Adhesives 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. 484 Chapter Seven adhesives very difficult to process. Only epoxy-phenolic-, polyimide-, and polybenzimida- zole-based adhesives can withstand long-term service temperatures greater than 350°F. 7.6.1.1 Epoxy. Epoxy adhesives are generally limited to continuous applications be- low 300°F. Figure 7.31 illustrates the aging characteristics of a typical epoxy adhesive at elevated temperatures. Certain epoxy adhesives are able to withstand short terms at 500°F and long-term service at 300 to 350°F. These systems were formulated especially for ther- mal environments by incorporation of stable epoxy co-reactants, high-temperature curing agents, and antioxidants into the adhesive. One successful epoxy co-reactant system is an epoxy-phenolic alloy. The excellent thermal stability of the phenolic resins is coupled with the adhesion properties of epoxies to provide an adhesive capable of 700°F short-term operation and continuous use at 350°F. The heat-resistance and thermal-aging properties of an epoxy-phenolic adhesive are com- pared with those of other high-temperature adhesives in Fig. 7.32. TABLE 7.35 Commercial Adhesives Most Desirable for Glass (from Ref. 37) Trade name Chemical type Bond characteristics Strength, lb/in 2 Type of failure Weathering quality Butacite, Butvar Polyvinyl butyral 2000–4000 Adhesive Fair Bostik 7026, FM–45, FM–46 Phenolic butyral 2000–5500 Glass Excellent EC826, EC776 Adhesion and glass N–199, Scotchweld Phenolic nitrile 1000–1200 Excellent Pliobond M–20, EC847 Vinyl nitrile 1200–3000 Adhesion and glass Fair to good EC711, EC882 EC870 Neoprene 800–1200 Adhesion and cohesive Fair EC801, EC612 Polysulfide 200–400 Cohesive Excellent EC526, R660T, EC669 Rubber base 200–800 Adhesive Fair to poor Siliastic Silicone 200–300 Cohesive Excellent Res–N–Glue, du Pont 5459 Cellulose vinyl 1000–1200 Adhesive Fair Vinylite AYAF, 28–18 Vinyl acetate 1500–2000 Adhesive Poor Araldite, Epon L–1372, ERL–2774, R–313, C–14, SH–1, J–1152 Epoxy 600–2000 Adhesive Fair to good Plastics and Elastomers in Adhesives 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. 485 Table 7.36 Relative Resistance of Synthetic Adhesives to Common Service Envir onment (from Ref. 38) Adhesive type Shear Peel Heat Cold Water Hot water Acid Alkali Oil, grease Fuels Alcohols Ketones Esters Aromatics Chlo- rinated solvents Thermosetting adhesives 1. Cyanoacrylate 2 6 5 – 6 6 6 6 3 3 5 5 5 4 4 2. Polyester + isocyanate 2 2 3 2 1 3 3 2 2 2 3 2 2 6 2 3. Polyester + monomer 2 6 5 3 3 6 3 6 2 2 2 6 6 6 6 4. Urea formaldehyde 2 6 3 3 2 6 2 2 2 2 2 2 2 2 2 5. Melamine formaldehyde 2 6 2 2 2 5 2 2 2 2 2 2 2 2 2 6. Urea-melamine formaldehyde 2 6 2 2 2 2 1 1 2 2 2 2 2 2 2 7. Resorcinol formaldehyde 2 6 2 2 2 2 2 2 2 2 2 2 2 2 2 8. Phenol-resorcinol formaldehyde 2 6 2 2 2 2 2 2 2 2 2 2 2 2 2 9. Epoxy (+ polyamine) 2 5 3 5 2 2 2 2 2 3 1 6 6 1 10. Epoxy (+ polyanhydride) 2 5 1 4 3 3 2 2 – 2 2 6 6 2 11. Epoxy (+ polyamide) 2 2 6 2 2 6 3 6 2 2 1 6 6 3 12. Polyimide 2 4 1 1 2 4 2 2 2 2 2 2 2 2 2 13. Polybenzimidazole 2 4 1 1 2 4 2 2 2 2 2 2 2 2 2 14. Acrylic 2 6 5 3 1 3 2 2 2 2 2 2 2 2 2 15. Acrylate acid diester 2 5 3 3 4 4 6 6 3 3 5 5 5 4 4 Thermoplastic adhesives 16. Cellulose acetate 2 6 2 3 1 6 1 2 – 2 4 6 6 6 6 17. Cellulose acetate butyrate 2 3 3 3 2 – 3 2 – – 6 6 6 6 6 18. Cellulose nitrate 2 6 3 3 3 3 3 6 2 2 6 6 6 6 6 19. Polyvinyl acetate 2 6 6 – 3 6 3 3 2 2 6 6 6 6 6 20. Vinyl vinylidene 2 3 3 3 3 3 – – 2 2 2 2 2 – – 21. Polyvinyl acetal 2 6 5 2 2 – 6 3 2 2 3 3 6 3 2 22. Polyvinyl alcohol – 2 3 – 6 6 5 5 2 1 3 1 1 1 1 Plastics and Elastomers in Adhesives 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. 486 23. Polyamide 2 3 5 – 5 6 6 2 2 2 6 2 2 2 6 24. Acrylic 2 2 4 3 3 3 – – 2 – – 4 4 – 4 25. Phenoxy 2 3 4 3 3 4 3 2 3 5 5 – – 6 – Elastomer adhesives 26. Natural rubber 2 3 3 – 3 – 3 3 6 6 2 4 4 6 6 27. Reclaimed rubber 2 3 3 – 2 – 3 3 6 6 2 4 4 6 6 28. Butyl 3 6 6 3 2 6 1 2 6 6 2 2 2 6 6 29. Polyisobutylene 6 6 6 3 2 6 2 2 6 6 2 2 2 6 6 30. Nitrile 2 3 3 3 2 5 5 6 2 2 3 6 6 3 6 31. Styrene butadiene 3 6 3 3 1 – 3 2 – 5 2 6 6 6 6 32. Polyurethane 2 3 3 2 2 3 3 3 2 2 2 5 5 – 5 33. Polysulfide 3 2 6 2 1 6 2 2 2 2 2 6 6 2 6 34. Silicone (RTV) 3 5 1 1 2 2 3 3 2 3 3 3 3 3 3 35. Silicone resin 2 2 1 2 2 2 – 2 2 2 2 4 4 3 6 36. Neoprene 2 3 3 3 2 – 2 2 2 2 3 6 6 6 6 Alloy adhesives 37. Epoxy-phenolic 1 6 1 3 2 2 2 2 3 3 2 6 6 2 38. Epoxy-polysulfide 2 2 6 2 1 6 2 2 2 2 2 6 6 2 6 39. Epoxy-nylon 1 1 6 2 2 6 – – – 2 3 6 6 6 6 40. Phenolic-nitrile 2 2 2 3 2 2 2 2 2 2 2 6 6 6 6 41. Phenolic-neoprene 2 3 3 2 2 – 3 2 2 2 3 6 6 6 6 42. Phenolic-polyvinyl butyral 2 3 3 3 2 3 4 2 2 2 4 6 6 6 6 43. Phenolic-polyvinyl formal 2 3 6 6 2 6 6 4 2 2 2 4 6 6 6 Key: 1. Excellent; 2. Good; 3. Fair; 4. Poor; 5. Very poor; 6. Extremely poor Table 7.36 Relative Resistance of Synthetic Adhesives to Common Service Envir onment (Continued) (from Ref. 38) Adhesive type Shear Peel Heat Cold Water Hot water Acid Alkali Oil, grease Fuels Alcohols Ketones Esters Aromatics Chlo- rinated solvents Plastics and Elastomers in Adhesives 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. Plastics and Elastomers in Adhesives 487 Anhydride curing agents give unmodified epoxy adhesives greater thermal stability than most other epoxy curing agents. Phthalic anhydride, pyromellitic dianhydride, and chlorendic anhydride allow greater cross-linking and result in short-term heat resistance to 450°F. Long-term thermal endurance, however, is limited to 300°F. Typical epoxy formu- lations cured with pyromellitic dianhydride offer 1,200 to 2,600 lb/in 2 shear strength at 300°F and 1,000 lb/in 2 at 450°F. 7.6.1.2 Modified phenolics. Of the common modified phenolic adhesives, the ni- trile-phenolic blend has the best resistance to shear at elevated temperatures. Nitrile phe- nolic adhesives have high shear strength up to 250 to 350°F, and the strength retention on aging at these temperatures is very good. The nitrile phenolic adhesives are also extremely tough and provide high peel strength. 7.6.1.3 Silicone. Silicone adhesives have very good thermal stability but low strength. Their chief application is in nonstructural applications such as high-temperature pressure- sensitive tape. Attempts have been made to incorporate silicones with other resins such as epoxies and phenolics, but long cure times and low strength have limited their use. Figure 7.30 The effect of 500°F aging in air and nitrogen on an epoxy-phenolic adhesive (HT-424). 39 Figure 7.31 Effect of temperature aging on typical epoxy adhesive in air. Strength measured at room temperature. 40 Plastics and Elastomers in Adhesives 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. 488 Chapter Seven 7.6.1.4 Polyaromatics. The most common polyaromatic resins, polyimide and poly- benzimidazole, offer greater thermal resistance then any other commercially available ad- hesive. The rigidity of their molecular chains decreases the possibility of chain scission caused by high temperatures. The aromaticity of these structures provides high bond-dis- sociation energy and acts as an “energy sink” to the thermal environment. Polyimide. The strength retention of polyimide adhesives for short exposures to 1000 o F is slightly better than that of an epoxy-phenolic alloy. However, the thermal endur- ance of polyimides at temperatures greater than 500°F is unmatched by other commer- cially available adhesives. Polyimide adhesives are usually supplied as a glass-fabric-reinforced film having a lim- ited shelf life. A cure of 90 min at 500 to 600°F and 15 to 200 lb/in 2 pressure is usually necessary for optimal properties. High-boiling volatiles can be released during cure, which causes a somewhat porous adhesive layer. Because of the inherent rigidity of this material, peel strength is low. Figure 7.32 Comparison of (a) heat resistance and (b) thermal aging of high-temperature structural adhesives. 41 Plastics and Elastomers in Adhesives 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. Plastics and Elastomers in Adhesives 489 Polybenzimidazole. As illustrated in Fig. 7.32, polybenzimidazole (PBI) adhesives offer the best short-term performance at elevated temperatures. However, PBI resins oxi- dize rapidly and are not recommended for continuous use at temperatures over 450°F. PBI adhesives require a cure at 600°F. Release of volatiles during cure contributes to a porous adhesive bond. Supplied as a very stiff, glass-fabric-reinforced film, this adhesive is expensive, and applications are limited by a long, high-temperature curing cycle. 7.6.2 Low Temperature The factors that determine the strength of an adhesive at very low temperatures are (1) the difference in coefficient of thermal expansion between adhesive and adherend, (2) the elastic modulus, and (3) the thermal conductivity of the adhesive. The difference in ther- mal expansion is very important, especially since the elastic modulus of the adhesive gen- erally decreases with falling temperature. It is necessary that the adhesive retain some resiliency if the thermal expansion coefficients of adhesive and adherend cannot be closely matched. The adhesive’s coefficient of thermal conductivity is important in minimizing transient stresses during cooling. This is why thinner bonds have better cryogenic proper- ties than thicker ones. Low-temperature properties of common structural adhesives used for cryogenic appli- cations are illustrated in Fig. 7.33. Epoxy-polyamide adhesives can be made serviceable at very low temperatures by the addition of appropriate fillers to control thermal expansion. But the epoxy-based systems are not as attractive as some others because of brittleness and corresponding low peel and impact strength at cryogenic temperatures. Epoxy-phenolic adhesives are exceptional in that they have good adhesive properties at both elevated and low temperatures. Vinyl-phenolic adhesives maintain fair shear and peel strength at –423°F, but strength decreases with decreasing temperature. Nitrile-phenolic adhesives do not have high strength at low service temperatures, because of rigidity. Polyurethane and epoxy-nylon systems offer outstanding cryogenic properties. Poly- urethane adhesives are easily processable and bond well to many substrates. Peel strength ranges from 22 lb/in at 75° to 26 lb/in at –423°F, and the increase in shear strength at Figure 7.33 Properties of cryogenic structural adhesive systems. 41 Plastics and Elastomers in Adhesives 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. [...]... Terms of Use as given at the website Plastics and Elastomers in Adhesives Plastics and Elastomers in Adhesives 505 20.Krieger, R B., Advances in Corrosion Resistance of Bonded Structures, Nat SAMPE Tech Conf Proc., vol 2, Aerospace Adhesives and Elastomers, 1970 21.Cagle, C V., Adhesive Bonding Techniques and Applications, McGraw-Hill, New York, 1968 22.Landrock, A H., Adhesives Technology Handbook, ... of Use as given at the website Plastics and Elastomers in Adhesives 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 Source: Handbook of Plastics, Elastomers, and Composites Chapter 8 Plastics Joining Edward M Petrie Materials and. .. introduce foreign materials into the part and, as a result, plastic parts are more easily recycled Success in heated-tool welding depends primarily on having the proper temperature at the heating surface and on the timing of the various steps in the process These periods include time for application of heat, time between removal of heat and joining of parts, and time the parts are under pressure The tool... Adhesives in Modern Manufacturing, p 29, Society of Manufacturing Engineers, 1970 35.Lichman, J., Water-based and Solvent-based Adhesives, in I Skeist, Ed., Handbook of Adhesives, Reinhold, New York, 1977 36.Hemming, C B., Wood Gluing, in I Skiest, Ed., Handbook of Adhesives, 1st ed., Reinhold, New York, 1962 37.Moser, F., Bonding Glass, in I Skiest, Ed., Handbook of Adhesives, 1st ed., Reinhold, New York,... dies, and press Operation can range from hand-fed to semiautomatic with speeds depending on thickness and type of product being handled 3–35 kW units are most common Basic apparatus is a spinning device, but sophisticated feeding and handling devices are generally incorporated to take advantage of high-speed operation Requires a hand gun, special welding tips, an air source and welding rod Regular hand-gun... of Structural Adhesives, in D J Alner, Ed., Aspects of Adhesion, vol 4, University of London Press, Ltd., London 1968 3 Bikerman, J J., Causes of Poor Adhesion, Ind Eng Chem., September 1967 4 Reinhart, F W., Survey of Adhesion and Types of Bonds Involved, in J E Rutzler and R L Savage, Eds., Adhesion and Adhesives Fundamentals and Practices, Society of Chemical Industry, London, 1954 5 Merriam, J C.,... and packaging Speed, simplicity, and reliability are key concerns in most of these high-volume assembly processes Speed and simplicity are usually considered to be of greater value than reliability or durability when bonding commodity plastic substrates Because of the nature of the polymeric substrate and the type of applications for which such materials are best suited, exceedingly high strength and. .. increases and as the batch size becomes larger One -part, and some heatcuring, two -part, adhesives have very long working lives at room temperature, and application and assembly speed or batch size are not critical For a large-scale bonding operation, hand mixing is costly, messy, and slow, and repeatability is entirely dependent on the operator Equipment is available that can meter, mix, and dispense... Application of Adhesives The selection of an application method depends primarily on the form of the adhesive: liquid, paste, powder, or film Table 7.38 describes the advantages and limitations realized in using each of the four basic forms Other factors influencing the application method are the size and shape of parts to be bonded, the total area where the adhesive is to be applied, and production volume and. .. alone may (1) restrict the degrees of freedom in designing the end product, (2) determine the types and number of adhesives that can be considered, (3) affect the quality and reproducibility of the joint, and (4) affect the total assembly cost 7.7.1 Measuring and Mixing When a multiple -part adhesive is used, the concentration ratios have a significant effect on the quality of the joint Strength differences . Because of the inherent rigidity of this material, peel strength is low. Figure 7.32 Comparison of (a) heat resistance and (b) thermal aging of high-temperature structural adhesives. 41 Plastics and. the degrees of freedom in designing the end product, (2) determine the types and number of adhesives that can be considered, (3) affect the quality and reproduc- ibility of the joint, and (4) affect. the most common source of heat for bonded parts, even though it in- volves long curing cycles because of the heat-sink action of large assemblies. Ovens may Plastics and Elastomers in Adhesives Downloaded