ADHESIVES, GLUES AND SEALANTS
The main objective in the preparation of metal surfaces is to improve the wetting properties and adhesion of the metal surface before to apply the adhesive.
On the surface of a metal we find the following layers:
Layer of contaminants.
The contaminant layer is a thin layer of dust or chemicals agents adsorbed onto the surface of the metal, to the elimination of that kind of contaminants cleaning agents are used.
All metals react with oxygen in the atmosphere, resulting in an oxide layer. Depending on the material of the metal, this oxide layer it can provide an active or passive surface and it may need one treatment or another to ensure a good adhesion of the adhesive on the surface of the metal.
For example, the steel forms different oxide layers depending on its level of alloy with other metals:
The carbon steel or low alloy reacts so fast with oxygen to form a porous oxide layer that is not bond to the metal base, which is why it is necessary to completely remove that oxide layer before to apply the adhesive.
The steel alloyed with chromium or nickel reacts with oxygen to form a thin and firmly attached oxide layer to the base material, the layer acts as a passivity agent avoiding the phenomenon of corrosion. But on the contrary, it reduces the surface energy of the metal surface, producing worst wetting properties on the surface.
If you need to remove the metal oxide layer before to apply the adhesive, you can use the following techniques or processes such as surfaces pretreatment:
Saco - Sand blasting Coating
Pretreatment by laser
The choice of surface pretreatment to use is determined by:
The type of metal and adhesive.
The requirements of the adhesive joint.
The cost of preparation.
After making the correct pre-treatment on the metal surface, this surface produces active sites that react with the environment becoming an inactive surface, to avoid such effects activators and primers are used before adhesive application.
Generally the adhesive manufacturer indicated in the technical data sheet recommended surface preparation products or methods for every type of metal that can bond the adhesive.
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