Why Are Cleaning and Pretreatment Needed?
Nearly all metal parts – and many plastic parts, too – have some sort of finish coating applied to improve appearance and to increase resistance to corrosion and wear.
It has been estimated that 7 of 10 coating failures are caused by poor surface preparation; these failures cost millions of dollars in wasted time and resources. Coatings applied over properly prepared surfaces cost less per square foot per year than the same coatings applied over a poorly-prepared surface.
What is the importance of the cleaning and pretreatment process?
During manufacturing, machining, and handling, metal parts can accumulate a variety of contaminants, including shop dirt, lubricants, polishing and burnishing pastes, stamping and buffing compounds, brazing and welding fluxes, stenciling inks, fibers, dust, grit, grease and grime, scale, smut, and metal wastes such as filings, chips, and dust. Machining processes such as cutting, drawing, milling, bending, grinding, drilling, rolling, and burning leave behind contaminants such as machining fluids and fragments of metal. Rusts or tarnishes may also be present on metal stock, particularly on materials that have been in storage or exposed to moisture. In many cases, more than one contaminant may be present. Even fingerprints and glove prints are considered to be contaminants. All must be removed completely before finish paints and coatings can be applied.
The process to remove all these contaminants is known as critical cleaning, precision cleaning, or (less often) industrial cleaning.
In most cases, cleaning alone isn’t enough, especially for parts that will be painted or powder-coated. Most of these items will need surface pretreatment, a process known as conversion coating. This pretreatment process incorporates chemical applications that help to form a chemical bond between the metal surface and the paint or other coating that is to be applied, ensuring that the coatings will adhere properly and provide a high quality, long-lasting finish.
When paints or finishes on metal surfaces flake, peel, delaminate, blister, bubble, or wrinkle, the problem can often be traced back to the pretreatment process, such as failure to remove all contaminants, failure to rinse thoroughly, the uneven or inadequate application of necessary chemical treatments, or operational problems in the chemical systems in which the parts are cleaned and treated.
Overall, the cleaning and pretreatment process improves the durability and longevity of the coating in two ways: first, by producing a clean surface to which the paint or coating can readily adhere, and second, by reducing contamination, a known cause of coating failure. Even the best-quality paints and coatings cannot adhere properly to a poorly-prepared surface.
Cleaning also makes part-handling easier and safer, and makes inspection easier.