Modern materials and engineering practices require many sorts of adhesives to create strong bonds between pieces and parts. Bonds may be designed for an attachment during manufacturing processes or for repair purposes after a failure. The first critical step of bonding is finding the proper adhesive to work with the materials that are being bonded. The properties and working time of the adhesive must be considered for the scenario to work and result in a long-lasting and stable bond of the parts involved.
Improper preparation of the bonding surfaces is often the cause of bond failure. It is critical to achieve good contact with the bonding surfaces and materials beneath the outer surface. Some materials such as PVC and ABS plastic can have the surface treated with a liquid primer to create a bonding surface. Other materials require physical material removal and use sanding and grinding to disturb the material substrate to create a good bond. Regardless of material, all surface coatings and contaminants must be removed from the contact area of the adhesive.
Preparing the surface can be accomplished many ways using abrasive tools. Sandpaper is a good starting point, and tools such as grinders and media blasting can be employed, with consideration of chemical strippers for some applications. Critical to this task is the treatment of the entire surface, so that any low spots get prepared as much as the high spots. The entire surface should be uniform and consistent.
There are basically two types of bonding; mechanical and chemical. Chemical bonding creates a bond between the actual material compositions of the pieces. Mechanical bonding creates a bond by attaching the adhesive around the surface irregularities of the part surface, explaining why we desire a rough surface for a good bond. Rough surfaces also give us more surface area for the adhesive to be in contact with. Smooth surfaces, even if chemically bondable, will not provide a bond as well as a rough surface, which has more surface area because of the profile of high and low areas that will contact the adhesive.
Properly prepared parts get the adhesive applied and are pressed together to keep as much contact between them as possible. It is important to minimize the distance between the parts to minimize the stress placed on the adhesive for it to do its job.
Testing of a sample bond is important. If possible, it is always nice to use a couple of small sample pieces to make a trial bond, testing for strength after adhesive selection, surface preparation, and adhesive application. This will help determine if the outcome will be successful. It adds time and minimal expense to the project, but can gather important information about the overall success of the project, and the experience that is gained can be applied to make for a more attractive final bond area.
Adhesives are successfully used in the world we live in. Successfully bonding similar and dissimilar materials can be accomplished by properly preparing the surface, selecting the proper materials, and properly testing the bond on a small scale before the actual pieces are attempted.