Metal Gluing
The most important adhesives use bisphenol A epoxy resins if the gluing of metals. All the common metals (and probably all the uncommon ones) can be glued, some better than others. The structurally important metals such as aluminum and steel are, fortunately, easy to bond; copper and lead are not so easy. In most cases, however, it is not the metal itself, but some oxide or other substance to which the bond is actually made.
By far the greatest amount of information that has been published deals with the adhesive strength on aluminum alloys.
Copper was the chief subject of study in one paper dealing with the effect of heat on epoxy adhesives, and it was shown that with the type of test used, the strength on copper was only about half that on aluminum.
The bond strength on aluminum including example of relationship to temperature, has been shown in earlier section dealing with hardeners.
The bonding of metal to metal in the manufacture of aircraft is the most spectacular use over made of an adhesive and still a source of some wonder. In the operation of aircraft sharp extremes of temperature may be met, extremes that can nowadays vary between -50 oC and more than 100 oC in few minutes. And whilst a constant strength within these extremes may not be demanded, something approaching it is expected.
In some operations associated with missiles, resistance to extreme cold is more important than resistance to heat. The behavior of an epoxy adhesive has been studied at – 253 oC; at this temperature three systems, one a nylon filled epoxy polyamide, and another a fluorocarbonepoxy polyamine composition have been stated to give food adhesive strength and toughness, (the third adhesive was a polyurethane).