As previously mentioned, diluent water quality is highly scrutinized in metal cleaning and pretreatment processes. Rinsing in particular is closely monitored and can often be the difference between proper part finish or excessive scrap and rework. For these reasons, reverse osmosis (RO) or deionized (DI) water rinsing is regularly employed.
We’ve discussed how poor quality or excessively hard water can impact corrosion, stability and dry-down residues of stamping lubricants—so the next logical step is to highlight the removal of these residues in modern pretreatment processes. If the resultant residues left on stamped parts are complexes with hard water ions or there are localized areas of irregular staining or oxidation due to corrosive water ions—surface pretreatment can be compromised.
In traditional iron and zinc phosphate systems—cleaning processes have traditionally been higher in temperature and more aggressive in solution pH. With the advent of transition metal coatings (TMC), lower temperature and neutral pH cleaning chemistries, surface soils/contaminants need to be more carefully considered. Neutralization of lubricant residues with more aggressive pH and higher temperatures to fluidize and soften residues is significantly lower. Cleaners with more neutral pH will be comparatively less aggressive regarding surface etching/pickling which may lead to coating issues that may go undiagnosed or undetected until after finishing through paint.
Porcelain enameling is another process that can benefit from improved diluent water quality for stamping lubricants. As the porcelain enameling process is very sensitive to surface cleanliness—any steps that can be taken to make stamping lubricants more easily removed is highly advised. With the increased cost of scrap due to the energy demands of finishing porcelain enameled components—optimizing part cleanliness can have a massive impact on scrap and rework costs.
One should consider if the quality of their process water is critical to their most sensitive and costly operations—why wouldn’t you want to take the necessary steps to improve the quality of your parts prior to finishing? Shouldn’t your water quality be as much a concern in producing your parts as it is in finishing them? IRMCO thinks it should be.