Gluing metals with adhesives: the correct preparation of surfaces

Gluing metals with adhesives, as we have noted before in this blog, is absolutely possible, and often extremely beneficial. By using high-performance double-sided adhesive and special metal adhesives, it is possible to avoid side effects and extended processing times involved in other methods, such as welding, drilling, and so on. Of course, to effectively glue metals with adhesives it is necessary to choose the right product, considering the type of metal surface, the required strength, the usage context, and so on. But that’s not all: once the perfect metal adhesive has been found, before using it, it is paramount that you properly prepare the metal surface. Let’s see have a look at the necessary steps.

Why it is essential to clean the surface before gluing metals with adhesives

Why is it necessary to remove all contaminants from the object’s surface before fastening? We are referring to anything which may be present on the metal surface that you wish to glue using high-performance double-sided adhesive tape for metals or special metal glues: for instance, powders, oils, fats, various types of debris, and even simple fingerprints.

Though, even at first glance, it is obvious why a metal surface should be cleaned before using any adhesives on it, it is worth explaining concretely why it is essential to eliminate any type of contaminant. The presence of contaminants on the surface can, in fact, significantly reduce the area of contact between the adhesive and the metal, thus compromising its strength from the beginning. On a technical level, when examining the possibility of gluing metals with adhesives, the ability of an adhesive to “wet” a surface, in this case metal, is also taken into consideration: distributing or placing the adhesive on a not perfectly clean or degreased metal surface will only give the impression, or rather, the illusion of having “wetted” the entire surface when, instead, the area actually in direct contact with the adhesive is reduced. An adhesive placed on a layer of dust or grease is therefore irremediably little or not at all effective.

Degreasing to clean metals

It is, therefore, essential to properly clean the metal surface to be glued using, if possible, isopropyl alcohol surface cleaner (for instance, 3M VHB Surface Cleaner, which is available in our online store in both the one litre (0.2 gal) liquid format and the wet towel format). When oils or fats are heavily present, the specific use of ketones should be considered.

Abrasion of the surface before using metal adhesives

Sometimes classic or standard cleaning of the metal surface is not enough to ensure the full effectiveness of metal adhesives. For example, when industrial greases that are resistant to solvents are present, and therefore could remain on the surface even after using specific cleaners. Or, sometimes, the issue isn’t oils, but rather of surface oxides, a consequence of oxidation processes already in progress. In these scenarios, , before proceeding with the use of adhesives and double-sided adhesives for metals, it is necessary to proceed with some abrasion, using the most suitable professional abrasive tools, depending on the surface to be treated. It should always be stressed that, as a result of abrasion activity, the real adhesion surface available increases, often by large percentage.

Treatments for chemical etching

There is another method to treat metal surfaces before their gluing. It is chemical etching, used in the case of self-priming metals specifically, such as aluminium and stainless steel, which are characterized by the spontaneous formation of oxide, allowing a great resistance to corrosion. When can a chemical etching be useful? In certain situations, degreasing simply is not enough to ensure full adhesion. For example, the stripping of a stainless-steel surface previously subject to welding – a process which compromises the surface due to the high temperatures (which could obviously be avoided when using adhesives, which do not require any heat treatment) – is needed.

Stripping is just one of several possible chemical treatments which may be needed in specific situations to prepare a metal for fastening by means of high-performance adhesives.