Engineering Chemistry S Datta

15
Adhesives
Adhesives
Adhesive is defined as a material that is capable of joining bodies together by surface adhesion
and internal strength without the structures of the bodies undergoing any changes. The process
of this adhesion is called bonding and the bodies are called adherends.
Bonding has several advantages
1. The common feature of all adhesive joints is the highly uniform distribution of forces
over the entire joint area and free from any residual stresses which leads to optimal
utilization of material strength compared to rivet and screw joints.
2. Adhesives are capable of joining numerous materials which cannot be joined by other
techniques even those differing widely in type such as glass and metal, metal and
plastic etc.
3. The process of adhesion can be carried out very rationally, quickly and economically.
4. Many adhesives can be applied at room temperature hence the adherends are not
exposed to high temperature as in the welding of plastics with metals.
5. The after-finishing process in case of bonding is not required as in the case of welding,
soldering etc.
6. Some adhesives set even in relatively thick layers, so any unevenness of the adherends
can be smoothed out during bonding.
7. Bonding of dissimilar metals with adhesives prevents galvanic corrosion as the metal
to metal contact is avoided.
8. The adhesive layer of an adhesive joint can have a vibration-dampening effect.
9. Adhesives can introduce electrical and heat insulating layers between the adherends.
10. Better composite materials having improved properties than the adherends can be
designed by the adhesive bonding e.g., metal-faced plywood.
11. Adhesive bonding can be utilised to make the material leak-proof for liquids and
gases.
Limitation and Restrictions of Adhesive Bonding
1. The usability of adhesives can be restricted when stringent requirements are imposed
on the thermal stability on adhesive point.
2. Adhesives based on organic polymers show a dependence on temperature in their
strength, properties and their bond strength decreases with rise in temperature.
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