Issue link: http://metalfinishing.epubxp.com/i/218436
SOIL AND SUBSTRATE AUDIT Soils There are many different types of soils used in a manufacturing facility. It is often assumed that all soils will be easily cleaned.The cleaning operation would be less difficult if all the individual soils were understood more completely. Soils are generally shop dirt, smut, oils, metal chips, and drawing, stamping, and buffing compounds.Upon completion of a soil audit, and the determination of a suitable cleaner, every effort should be made not to introduce new soils without pretesting. Soils can be classified as organic or inorganic. Organic soils are oily, waxy films such as mill oils, rust inhibitors, coolants, lubricants, and drawing compounds. Alkaline cleaners should be used to clean organics. Inorganic soils include rust, smut, heat scale, and inorganic particulate, abrasives, flux, and shop dust. These inorganic soils are most easily removed by acidic cleaners. Soils can also be classified by the degree of difficulty present in cleaning. Soils that are very difficult soils to remove include chlorinated lubricants, sulfurized lubricants, heavy-duty rust-inhibiting compounds, honey oils, buffing compounds, stearates, diecast release agents, and oxidized soils. Those that present a moderate degree of difficulty include fatty oils, waxy oils, heavy-duty hydraulic oils, mill oils, lapping compounds, and water-displacing rust inhibitors. Lastly, those soils that are relatively easy to clean are soluble oil-cutting fluids, synthetic cutting fluids, spindle oil, lightweight machine oils, mill oils, water-soluble and rust inhibitors, and vanishing oils. The very difficult soils tend to be heat sensitive. Soils falling into the napthenic, paraffinic, chlorinated paraffin blends, or those containing waxes are generally heat sensitive to some degree. When you encounter this type of soil, it limits the variable of temperature. A heat sensitive soil of say 160¡F requires you to adjust upward accordingly. Specially formulated low-temperature cleaners rely on both soil displacement and slight emulsification. The blend of detergent systems built into the low-temperature cleaners is designed to reduce surface tension at the soil–metal interface. This unique factor enables removal of soils sensitive to heat at a low temperature; lower than the melting point of the waxes of that soil. This fact also produces less contamination if properly skimmed, resulting in longer tank life. SUBSTRATES The composition or chemistry of the base metal is one of the key limiting factors in cleaner choice. The cleaner must be chosen so as to be compatible with the metal being processed. In multimetal cleaning lines, nonferrous metals are typically the limiting factor. With these metals it is important to choose a cleaner that either does not attack or overetch the metal and where the attack is controllable or desirable. A common mistake by both chemical vendors and manufacturers is when a base metal audit is made for cleaner selection, but not done completely. Most aluminum and zinc alloys with slightly different alloy content can vary widely in their ability to withstand either alkaline or acidic cleaner attack. In some cases, where minute etch is desirable, slightly more or less is unacceptable. Substrates should be classified to make cleaner choice easier. 1. Ferrous or Iron Bearing: Cold-rolled steel, hot-rolled steel, stainless steel, 95