Design considerations adhesives

Design considerations. Adhesives in Modern Manufacturing (E J. Bruno, ed.). Society of Manufacturing Engineers (SME), St. Louis, MO, 1970. 

Definitions Substrate Design Guidelines Thermal Design Considerations Adhesives Solder Paste and Joint Formation... 

Poly(phenylene sulfide) (PPS) is another semicrystalline polymer used in the composites industry. PPS-based composites are generally processed at 330°C and subsequently cooled rapidly in order to avoid excessive crystallisation and reduced toughness. The superior fire-retardant characteristics of PPS-based composites result in appHcations where fire resistance is an important design consideration. Laminated composites based on this material have shown poor resistance to transverse impact as a result of the poor adhesion of the fibers to the semicrystalline matrix. A PPS material more recently developed by Phillips Petroleum, AVTEL, has improved fiber—matrix interfacial properties, and promises, therefore, an enhanced resistance to transverse impact (see PoLYAffiRS containing sulfur). 

If both substrates to be bonded are nonconducting, then the adhesive formulation must contain a susceptor material. Susceptors can have a small percentage of magnetic iron oxide, iron filings, or carbon additives. A susceptor can also be a steel screen or perforated steel foil that is embedded in the adhesive bond line. It has been found that graphite fiber composites used in the automotive and aerospace industries are sufficiently conductive that they can be successfully heated with induction. Design considerations must be taken into account in placement of the graphite reinforcement, so that the material heats uniformly. 

Many fectors must be taken into consideration in designing an adhesive. The requirements include low level of ionic impurities, no voids under the chip caused by evaporation of solvent or other volatiles, no resin bleed during cure, and thermal expansion properties that match those of the substrate and chip. A significant mismatch in the thermal expansion coeflScient can lead to development of thermal stresses that can result in cracking or distortion of the chip. This problem is becoming more and more important as die sizes continue to increase. 

Adhesives exposed outdoors are affected primarily by heat and humidity. Thermal cycling, ultraviolet radiation, and cold are relatively minor factors. Structural adhesives, when exposed to weather, rapidly lose strength during the first six months to a year. After two or three years, the rate of decline usually levels off, depending upon the climate zone, polymer, adhesive, and stress level. The following are important considerations when designing an adhesive joint for outdoor service ... 

The strength of a cast-in joint has to be determined only when adhesive/resin failure leads to a total failure of the structure or when the serviceability limits are exceeded due to adhesive/resin failure. This is because in many applications the adhesive/resin is primarily used for purposes other than load transfer and in these cases the bond strength is not a design consideration. 

A further discussion of the topic can be found in Engineering design with adhesives and other relevant considerations in Durability creep rupture and Durability fatigue. 

Painting with zinc dust paints entails the same design considerations applicable to all painting projects (BS 4479 Part 4). With zinc-rich paints, adhesion is best achieved by blasting to at least Sa 2 A, and limitations on thin steel apply as with the metal spraying. 

Acrylics, s poly methyl methacrylate Acitainer, 255 description, 256 design considerations, 258 development, 257 material selection, 263 production details, 267 testing, 269 Adhesives... 

Initial design considerations require a knowledge of the chemical and physical properties of both adhesive and adherends. Furthermore, an adhesive joint is expected to perform satisfactorily under the expected service conditions, for the planned lifetime of the structure. Thus the change in the properties of the materials involved as a function of the effects of environment, fatigue, temperature, loading rate, and age must also be known, or be predicted. ... 

Thompson, R., Five Design Considerations for Adhesive Bonded Plastic Joints, SME Paper AD85-776, Atlanta, Georgia, 1985. 

Two other design considerations are pertinent to generalized width versus depth guidelines for reliable simple sealant butt joints. At very low depths, there is usually insufficient bond area of the sealant to the substrates to have reliable adhesion. On the other hand, at very large width-to-depth ratios, buckling of the sealant can occur when the joint contracts. This can cause the sealant to be extruded from the joint where abrasion of the sealant can occur, drastically reducing the sealant life. Extruded sealant can also be a safety hazard in some instances. 

The overriding consideration with respect to the adhesion of sealants is that the sealant and surface preparation should be selected to ensure that the adhesion strength exceeds the cohesive strength of the sealant. This can necessitate that extra care be used in the substrate bond surface preparation or that a primer be used. Ensuring that any failure that occurs will be cohesive in the sealant rather than adhesively to the substrate is a primary design consideration. 

Thompson JE (1990) Design considerations unique to sealants. In Postal CA (ed) Engineering materials handbook adhesive and sealants, vol 3, 3rd edn. ASM International, Materials Park Wolf AT (2009) Sealant durability and service life of sealant joints. In Mittal KL, Pizzi A (eds) Handbook of sealant technology. CRC Press, Boca Raton, pp 143-190... 

One key consideration in developing radiation curable adhesive systems is the thermal stability and volatility of any photoinitiators used. These chemicals are designed for liquid systems where these issues do not arise. Few of the commercial photoinitiators have adequate thermal stability at the highest hot melt temperatures (180-200°C) and many are too volatile. Reduced application temperatures and special antioxidant packages are often required. 

It will be seen that the design of articles to be electroplated can have a considerable effect on the corrosion resistance of the electrodeposited coating. The chief effects are the result of variations in deposit thickness, but also important are features which can influence the adhesion, porosity and physical properties of the deposit. Good design will also avoid features of the plated article capable of trapping liquids or solid contaminants which might cause more rapid corrosion. 

---