Industrial Adhesives in Prosthetic and Orthotic Construction
Gennaro J. Labate, C.O. *
During the past year the VA Prosthetics Center has been investigating various types of adhesives, especially those adhesives useful in prosthetics or orthotics. The following table is designed to be used as a quick reference by the prosthetist or orthotist for joining most materials used in limb and brace shops. The table also gives the sources of supply, cost as of March 1959. and characteristics of the adhesive tested.
In the past, the adhesive most commonly used to join wood were animal flake or ground glues. Today for wood, Timbond, a polyvinyl acetate, and the polyesters and epoxy resins are best. For bonding rubber, leather, fabric, etc., rubber cements are used. Stabond, a hexane toluol, and neoprene based adhesives are excellent substitutes for the rubber cements.
Although the tabulation is not complete and our investigations were not exhaustive, we can recommend that these listed adhesives are generally stronger and, in most cases, easier to apply than adhesives used formerly.
It should be recognized that adhesives are not the panacea for all fastening or bonding problems. On the contrary, adhesive bonding has its limitations just as do other methods of fastening. From a structural standpoint, a sandwich construction using adhesives as a bonding agent offers a number of advantages over riveting. For example, B/K joints can be sandwiched in a plastic B/K prosthesis shank by utilizing polyester or epoxy resins with such fillers as Solka-Floc (wood flour) or any fibrous filler. Local stress concentrations experienced around rivet holes on such joint attachments are eliminated by the relatively uniform distribution of the shear loads over the entire adhesive contact area.
The polyester and/or epoxy resin filled adhesives are being used routinely by the Limb and Brace Section, VAPC, as an adhesive to bond wood to wood, wood to metal, plastic to wood, and also for joining urethene foams to various other structural materials. However, the use of adhesives in metal to metal joining over small contact areas has not shown satisfactory results to date. A few metal to metal adhesives can be used for bonds that are subject to very low loads.
Further studies are continuing in the Testing and Development Laboratory of the VAPC to determine if adhesives can be applied more generally to replace some riveting, soldering, or welding. Interest is centered on developing adhesives that will provide metal to metal joints that will withstand high shear loads, have high peel and impact strength as well as satisfactory fatigue resistance. See tables below.