WHAT CAN BE BONDED?

Nearly every material natural or synthetic may be bonded with adhesives. What adhesive to use for the best bond is directly related to the material. Some materials bond easily and others require special preparation to achieve a good bond.

POINTS TO CONSIDER WHEN SELECTING AN ADHESIVE

Substrate Materials - are they the same or different, porous or nonporous, rigid or flexible, plastic or metal?
Joint Design - is based on the type of stress the joint must be resistant. Types of joints are covered later in this section.
Gap Filling - is required when mating poorly fitting parts.
Environment - the temperature and moisture, chemical and shock resistance must be evaluated.
Handling Bond - the time for the adhesive to "set" or hold the assembly together must be considered.
Cure Time - the importance of the period of time required for the adhesive to reach its full strength.
Appearance - the color or clarity of the adhesive may affect the appearance of the product.
Cost - the quantity of adhesive, its packaging, shelf life and method of dispensing affect cost.
Preparation - is it a one or two part adhesive. If it is a two part adhesive, how difficult and critical is the mix ratio?
Dispense Method - is relative to the adhesive used and the area to be covered. It may be manual, semi or fully automatic. The selection of an adhesive for your application can be a complex matter of meeting many needs. Therefore, it is advisable to consult the manufacturer or adhesive distributor for technical guidance.

POINTS TO CONSIDER WHEN USING ADHESIVES

Storage Life - Adhesives do not last forever, therefore, do not buy in quantities greater than needed. The storage life of some adhesives may be extended by refrigeration at 40ºF. Do not freeze. Storage life ranges from 6 months to a year - unopened.
Preparation - Other than selecting the the proper adhesive, preparing the resources substrate for bonding is of great importance. Surface contamination is the frequent cause of bond failure. When possible, clean the surfaces with a solvent or cleaner that will not leave a residue of any kind. Be sure the surface is dry. Roughen the surface to help the adhesive grab the material and wipe away any loose particles. Some materials require the application of a primer to improve bondability. The Temperature Limits of most adhesives falls between - 40ºF and 400ºF. However, it is important to check each adhesive for its specific temperature range. There are special ceramic adhesives available for ultra high temperature applications to 4000ºF. The ideal temperature for using an adhesive is 70ºF. The lowest recommended temperature for using an adhesive is 55ºF. In general, raising the temperature of many adhesives will shortened their working life. Keep in mind that the working time given by the manufacturer is normally 70ºF and a summertime temperature of 95ºF may reduce the open, set, and cure times of the adhesive.

Electrical Conductability - most adhesives are good insulators, however, there are some available that are made into conductors for special applications by the use of silver fillers. The Chemical and Environmental Resistance of most adhesives is very good. One of the most common elements that an adhesive must resist is moisture, humidity and water. Check with the manufacturer for this kind of resistance. The adhesive industry does not usually give a chelnical resistance chart for its adhesives, but each user must do his own testing to arrive at the suitability of an adhesive for each application. How Adhesives Cure should be understood by the user. In two part adhesives a chemical cure is created by mixing the resin with the hardner or accelerator. Single part, moisture cure adhesives react to surface moisture or the humidity of the surrounding air. Other solvent or water based adhesives cure with evaporation. Anaerobic adhesives cure in the absence of air. Actural full cure or reaching full strength is a chemical process that varies with each type of adhesive. Setting, or the initial grabbing of the adhesive is only the beginning of the curing process and the assembly should not be subjected to stress or test until the time of full cure has passed.