Curing structural adhesives

Ultrasonic welding is a frictional process that has been well established for heat welding thermoplastic parts. Like induction welding, it also has been adapted for curing structural adhesives such as epoxy. 

Uses Urethane-acrylic for radiation and peroxide cured structural adhesives, coatings (paper, PVC floor, wood), elastomers, electronics, screen inks... 

Uses Free radical initiator tor UV-cured structural adhesives, coalings (glass, metal, paper, plastic, PVC floor, wood), electronics (conformal, encapsulants, photoresists, solder masks), inks (flexo and gravure, litho, otiset, saeen)... 

Adhesive systems based on free-radical curing epoxymethacrylates are cited (16). And Dudgeon (17) has covered cationic, heat-curable rubber-modified epoxy resin systems which very likely have latent-cure, structural adhesive capability. 

There are, essentially, only three methods of curing structural adhesive joints press, autoclave and oven. 

Shields, J. (1977) Evaluation of an ultra-violet-curing structural adhesive. Adhesion 1, Allen, K. W., Ed., Appl. Sci. Publ., London, Chapter 11. 

Manufacturing economies frequently accompany the use of adhesives because assembly times and labor requirements may be reduced and new designs or materials may be used. Hot melt, pressure sensitive and rapid curing structural adhesive formulations frequently reduce the time required for assembly by a significant amount... 

NBR adhesives can be used at temperatures between 170°C and —40°C. Bond strength can run above 7 MPa and can provide structural bond to many substrates. Even without curing, NBR adhesives show excellent resistance to organic compounds, acids and alkalis. 

In most cases, the allophanate reaction is an undesirable side reaction that can cause problems, such as high-viscosity urethane prepolymers, lower pot lives of curing hot-melt adhesives, or poor shelf lives of certain urethane adhesives. The allophanate reaction may, however, produce some benefits in urethane structural adhesives, e.g., additional crosslinking, additional modulus, and resistance to creep. The same may be said about the biuret reaction, i.e., the reaction product of a substituted urea linkage with isocyanate. The allophanate and biuret linkages are not usually as thermally stable as urethane linkages [8]. 

The soft segments made from asymmetrical (amorphous) polyols are important for two-component structural adhesives and one-component moisture-curing adhesives. These materials are applied and usually cured at room temperature. 

The two-component urethane structural adhesives are among the most difficult to characterize, simply because of the widely varying properties that are possible. These adhesives may be rigid plastics similar in modulus to standard epoxy adhesives, with glass transition temperatures of the cured adhesive being approximately 60°C. 

Table 3 lists the selected properties [16] that we have measured for several commercially available acrylate resins manufactured by the Sartomer Company and the Rohm and Haas Company. The resins were cured in an AECL Gammacell Model 240. The temperature rise was measured for an 8-g sample using Acsion s (formerly AECL Radiation Applications Branch) Gamma Calorimetry method [17]. All of this information is being used to evaluate the applicability of EB-cured acrylate adhesives for repairing composite structures. Combinations of these adhesives can be used to create electron-curable adhesives suitable for composite repair. 

The technology to routinely cure applied adhesives for repairing damaged composite structures at remote repair stations is currently available. There are already systems that use portable accelerators for X-ray radiographic inspection of aircraft components [43]. Fig. 6 shows a conceptual picture of a portable accelerator unit that would contain the power unit, vacuum systems, and computer... 

Campbell, F.J. and Brenner, W., Curing high performance structural adhesives by electron-beam radiation. Nav. Eng. J., June, p. 160 (1982). 

Honeycomb core. Honeycomb core used for aluminum bonded sandwich structure is exclusively aluminum. The core is fabricated by printing offset stripes of adhesive (the node adhesive) on aluminum foil, stacking a large number of these foils and then curing the adhesive in a heated press. The resulting block is called a hobe. Slices are machined from the edge of the hobe and then expanded to... 

Epoxy resins find a large number of uses because of their remarkable chemical resistance and good adhesion. Epoxy resins are excellent structural adhesives. When properly cured, epoxy resins can yield very tough materials. They are used in industrial floorings, foams, potting materials for electrical insulations, etc. One of the principal constituents in many of the Fibre-reinforced plastics (FRP) is an epoxy polymer. 

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