Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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seconds. The chemical choice for cleaning should be made only when the process contact time is known. History and configuration of the part play a key factor in not only cleaner choice, but also the application. Multiconfigured parts, for example, may be best suited for immersion cleaning rather than spray. Usually, machined castings, or parts with ports, threads, extensions, blind holes, etc., are very difficult to clean because the part positioning is typically fixed. In these cases, immersion, or immersion spray combinations, or rotating fixtures may be required. In addition to the configuration of the part, what is the history of the part? Is it a component, finished product, or subassembly? Will it be cleaned once, twice, or more before leaving the factory as a finished product? Finally, how long may the part be staged, or stored? Will the surface corrode or tarnish, and will the in-process soil or rust inhibitor adequately protect with- out becoming more difficult to remove if the part is not in a just-in-time, or on a first-in, first-out inventory schedule? SOIL AND SUBSTRATE AUDIT Soils There are many different types of soils used in a manufacturing facility. It is of- ten 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 buff- ing compounds.Upon completion of a soil audit, and the determination of a suitable cleaner, every effort should be made not to introduce new soils with- out 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 in- organic 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 com- pounds, 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, syn- thetic cutting fluids, spindle oil, lightweight machine oils, mill oils, water-solu- ble 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 in- terface. 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 11

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