Mechanism of adhesive bonding defined by the general factors:
Assembling and bonding process of adherends and adhesives is a complex phenomenon. Some common factors can help to practice for perfect bonding of any adhesive application. It may be any type of adhesive or adherends.
Pre-process like sandblasting, chemical treatment is done to make the surface fit for applying adhesive to make a strong bond between adherends. Sandblast is done when a plastic or wood material is to be bonded by using high pressure and temperature, if not just using a sandpaper the surface is smoothed. In certain cases, metal are chemically treated because due to the presence of grease and oil. The metal surface is washed with a solvent or with a detergent. Metal when going to expose to acidic chemical than it is treated with alkali or vapour dressed.
Wood and metal adherends are flatted and smoothed by machining the surface. By doing this, a thin film of adhesive is sufficient for strong attachment of the surfaces. The adhesive should be prepared in following ways like dissolving it in some solvent, thinning of liquid adhesive, melting solid adhesive and adding additives like extenders, plasticisers, fillers, harder’s, catalyst and fortifiers.
One of the following methods can be used for applying the prepared adhesive bonding:
- Roller or knife coats molten adhesive.
- By using pressure sensitive tape
- By laying the film or sheet of adhesive.
One of the most used adhesives is the chemical reactive type. It works in a different manner. Two chemicals 1) thermosetting resin 2) catalyst or reactivating solvent are applied on each surface of adherends separately. One chemical on one component surface. When the two components are attached, the chemicals react and gets harder. High-temperature epoxy resins work based on this procedure.
What happens when adhesively applied on the adherend?
When thermosetting type adhesives are used in the molten state they immediately become hard and strong enough to bond the assembled surfaces. Precaution to be followed is that when this type of adhesive is used adherends should be assembled immediately before they get harder.
Thermoplastic type adhesive has a different mechanism. It is a rubber solution in an organic solvent. Applied to the surface and allowed to expose in the air. So that solvent is vaporized then the surfaces are assembled. It can be handled without any caution of hardening immediately.
Woodworking adhesive practice:
By laying the adhesive on the surface of the woods, the contact is assembled. However, the joint should be allowed for a certain time under pressure to make the joint get harder. Under pressure, the contact surface is attached by the reaction of the glue.