Professional Polymer Technology
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There are manifold advantages of using Hot Melt Adhesiv […]
There are manifold advantages of using Hot Melt Adhesive over other adhering processes. Using adhesives instead of traditional binding ensures a reduced cost of production. It neither needs equipments for drilling, welding, soldering or other fastening agents, nor manual force to operate them. Welding is a rigid method which brings physical changes in the materials adhered. If you need to undo the process after using adhesive, there are agents available to serve your purpose. Using them, the fastening or adherence can be undone without distorting the item retaining their original look. Due to this flexibility, undoing becomes easier. It saves production time and it does not take very long. This not only saves time, but also reduces production costs in the long run. Items needed to fasten are not disfigured or discoloured.
One of the greatest advantages of adhesive use is that it distributes the stress load uniformly. It does not let the stress be concentrated in one place. Locally accumulated stress further increases the possibility of rupture. Apart from that, since mating surfaces are always in contact, it protects the items against many environmental odds. The continuous bonding makes this possible.
Another remarkable feature of adhesives is it does not affect the weight of the item noticeably. Usually brazing and soldering, along with physical changes, bring change in weight as well. But with adhesive this change is almost negligible. This versatility of adhesives is known to everyone and the same is reflected in its varied usage all around.
In general there are six main types of adhesive
l contact adhesive, of which the most familiar are Evo-stik and Thixofix
l woodworking adhesives - Unibond, for example
l cyanoacrylale adhesives or 'super glues'
l two-part epoxy adhesives Araldite is the most well known
l two-part acrylics, similar in usage to acrylics
l 'universal' or general-purpose adhesives, such as U H U or Durofix.
As well as these main types, there are several specialist repair adhesives - for joining glass, for mending PVC and for joining polystyrene as well as adhesives for jobs such as fixing wall tiles, putting up wallcoverings and hobby work with paper and card.
When choosing an adhesive for a particular job, there are several points you need to think about.
First, what materials are you joining together? Obviously, the adhesive has to be suitable for both materials if they are different, but the main problem here is with plastics and recognising the plastic is the first task.
Second, how important is strength? With wood glues, the bond can be as strong as the wood itself, while with metal and plastics it will usually be weaker. If strength is all-important, you might need to think about reinforcing the joint in some way.
Third, how big a gap is there to fill? Often, joining two materials will also involve a degree of gap-filling, and adhesives vary in their ability to cope with this. Contact adhesives, for example, need a slight gap in which to work, while eyanoacrylates won't work unless the gap is very small indeed. Epoxy glues, on the other hand, will work with cither small or large gaps.
Fourth, what kind of temperature is the adhesive going to be subjected to? Some adhesives (known as thermoplastic), such as contact adhesives and many of the 'universal' glues, will not withstand heal, while many others (known as thermosetting) will retain their strength up to moderately high temperatures. This could matter when you are repairing crockery.
Finally, how important is the appearance? Most adhesives dry to a clear finish, but some end up a pale creamy yellow. Whether or not this will show obviously depends on the thickness of the glue line and, equally importantly, how well you clear away the excess; with many glues, it is difficult to avoid some glue remaining.