Adhesive joining

Adhesives are now used for a huge range of applications, from very low strength uses ( paper glue ) to high strength uses ( epoxy resins ). They can be used to hold party hats together and they can be used to hold the wings on the aeroplane. This is a huge range. For success they have to be selected correctly and the joint has to be designed correctly. They rarely work well when used as a direct replacement for mechanical fasteners.

Joint design Where ever possible ‘peel’ should be avoided in the joint design. The overlap or adhesive area should be as large as possible. The materials/assembly must be able to withstand any processes ( eg heat ) that is required to cure/harden the adhesive. Sketch 3 or 4 xamples.

Advantages of adhesive Reduce the number or parts required. Suited to factory/production type assemble. Can provide air/liquid tight joints ( no extra seals required ) Can join huge range of materials, including elastomers, glass and ceramics. Spread the load, preventing point failure or corrosion. Prevent unwanted dis-assembly. Prevent customer repair- have to buy a new one!

Disadvantages of Adhesive Parts can’t be dis-assembled easily. Chemicals used can be hazardous. Preparation, mixing and temperature can be critical.( field repairs are difficult ) Join design and adhesive selection are critical. Difficult to identify and source the correct adhesive for a repair. Most have expiry dates, after which they don’t work well. Time or a curing process ( eg UV , or heat) is required before use.

Examples of adhesive Wood glue General purpose adhesive Solvent cement Tensol Cyano-acrylates ( super glue ) Epoxy resins