Although the alternative of opting for an adhesive joint might be appealing in some circumstances, the economics involved can be quite complex. In general, adhesives are less expensive than a welding or fastening procedure. However, the implementation of adhesives in a mass production might prove to be quite expensive when taking for account the surface preparation requirements, the curing times and temperatures and the expertise needed to evaluate and control these processes. However, many companies have established major savings by using adhesives instead of other methods. The Northrop Aircraft Company stated that their conventional riveting operation of fabricating trailing wing sections cost them closely to1312$ where as obtaining similar strengths by using adhesives cost them 149$ per wing (3, 171).

The diffusion principle states that at polymerization, some of the molecules diffuse in the adherent and consequently, some molecules of the adherent diffuse into the adhesive in order to form a solid joint. The mechanical principal states that, the imperfections on the wetted surface of the adherent serve as to grip the adhesive when it turns into it's solid polymer state and takes advantage of these imperfections to establish a solid bond. However, this might not help in explaining why perfectly strong bonds are also possible on highly polished surfaces. The third and most generally accepted theory attributes the bonding forces to the fact of the sharing of valence electrons between the newly formed polymer and the adhered material. Some may like to contribute all three factors working togheter as the proper definition of the bonding process( 3, 170) .

Although many new applications have arisen, they do not contribute an important saving to the automobile producer. Welds are still very present and so are mechanical fasteners due to the requirements of mass production, which can not permit itself of stopping the production line in order to let the structural adhesives cure. However, most of the final assemblies such as the trimmings, the side panel guards, the window rims and other sealed surfaces are joined by adhesion just prior to painting such that when the automobile must be put in an oven for the paint to cure, the adhesives cure also. Some manufacturers do use adhesives to fix the top gears of the transmission due to their low torque capabilities, namely Renault, and the arrival of vehicles made of composite material panels have created the need for an increase in adhesive joints (5, 63-65)

Although the basic application are quite commonly simple, where most adhesives today are still spatula applied, automation is quite common and not such a daunting task to perform. The challenge lies in the preparation of the surfaces to be bonded as well as the study of the optimal curing times and temperatures required to obtain the required bonding strengths.

As for space travel, no mission in space would have ever been possible without the use of high strength and temperature ranging adhesives which are required to mount the heat shields on the shuttles under side which protect it from flaming up on re-entry into the atmosphere ( 9, 7).

Some common words found in the essay are:
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Approximate Word count = 2483
Approximate Pages = 10 (250 words per page double spaced)