What is pretreatment and why is it important?
Protective coatings can add significant longevity and durability to machined components. Corrosion, abrasion and chemical resistance are all highly valued properties of protective coatings, as well as reduced friction and resistance to extreme temperatures.
What many do not realise, however, is that protective coatings are only as effective as their pre-treatment. The surface of your metal components must be adequately prepared prior to coating to ensure it provides optimum protection.
What types of pre-treatment are available?
There are two main types of pre-treatment: chemical and mechanical.
Chemical
Chemical pre-treatment typically involves using an etchant to remove impurities from the surface of the metal. Chemical Pre-treatment can come in various different forms, these can include Non-Chrome, Iron phosphate, anodisation and chrome based options, however the most suitable solution will depend on the desired outcome and the base material.
Mechanical
Mechanical pre-treatments typically involve treating the surface of the metal using machinery. Wet and dry abrasive blasting are the most common forms of mechanical pre-treatment, during which abrasive particles are propelled at the surface to strip old coatings, remove surface contaminants and creating a rougher surface profile for better coating adhesion. Polishing and burnishing are also forms of mechanical pre-treatment.
There are several reasons why these pre-treatments are highly beneficial for your parts prior to applying a coating.
Better adhesion
Pre-treating the surface of a metal part can create a slightly rougher surface. This means that coatings such as powder coatings can adhere better to the metal, therefore reducing the likelihood that they will flake or peel off.
Remove surface contaminants
Surface contaminants such as rust particles or external substances such as dust can affect how well your coating adheres and protects your part. If left on, corrosion can start to deteriorate the part from beneath the coating. This can also cause the coating to bubble and detach from the part over time. Pre-treatments such as blasting and etching strip the part of surface contaminants, ensuring a ‘clean’ surface ready to coat.
Remove old coatings
If your part has been coated in the past, the old coating will need to be fully removed before a fresh one is applied. Particles of old coatings can also act as surface contaminants, preventing effective adhesion of the new coating and therefore compromising its integrity.
An extra layer of protection
Some pre-treatments not only prime parts, but add protection of their own against corrosion and deterioration. An example of this are conversion coatings. The thin chemical layer (Non-Chrome, Iron Phosphate or Trivalent Chrome) layer on the surface of the metal offers protection against corrosion, and once the top coating (such as powder coating) is applied, this protective layer is sealed in. This means even if the protective coating were to be damaged, the metal beneath can still be protected by the pre-treatment.
Aesthetics
Sometimes, your specifications may require a specific texture finish (such as a matt anodised finish or a brushed finish). Pre-treatments such as etching and brushing can create different textures prior to processes such as anodising, affecting the appearance of the finished product.
Pre-treatment is an essential part of any coating process. DECO Australia can offer numerous types of pre-treatment, including etching, non-chrome, trivalent chrome and iron phosphate conversion coatings, as well as both wet and dry abrasive blasting. To find out more about which pre-treatment is suitable for your desired coating and project specifications, contact us.
