Metal Finishing Guide Book


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production parts? 16. Do your currently purchased coatings meet your specifications on test panels? 17. What is your current pretreatment process? Does it provide a quality base for adhesion and salt spray? 18. What are your current process controls for pretreatment and finishing? Do they get done? Are they logged, recorded, and reviewed? 19. What preventative maintenance steps are taken? Is it by poundage, hours, weeks, or need? 20. What space limitations do you have for expanding pretreatment and finishing? 21. What are the local, state, and federal laws and regulations for effluent emissions? Do you currently meet these? 22. What safety program do you have? What products can be replaced? What energy sources do you have? What are the limitations? 23. What manpower resources are available? 24. What type of training do you or your vendors offer? 25. What are your financial resources or limitations? 26. What is your competition doing in the marketplace and where do you fit in the market niche? Where do you want to be? What do you have to accomplish to be there from a finishing perspective? THE MECHANISMS OF AQUEOUS CLEANING Wetting: Cleaners contain surface-active agents (surfactants) that "wet out" the soil. This loosens the soil-surface bond by a reduction of surface tension. Wetting is actually the first requirement for soil removal. Emulsification: This occurs following wetting. Simply stated, emulsification is the dispersion of two mutually immiscible liquids (i.e., oil and water). Primary factors affecting emulsification are type of oil encountered and choice of surfactants used in th cleaner. Secondary factors include pH, temperature, and concentration of the cleaning solution. Neutralization (saponification): A reaction where in fatty acid soils (oils) are neutralized in the presence of alkali. The result is generation of water-soluble soaps that assist in cleaning and rinsing. Examples of fatty oils are vegetable (corn), animal fats (lard), and marine (whole). Solubilization: "Like dissolves like." This simply means that the solubility of waterinsoluble soils (oil) is increased in the presence of surfactants. Displacement: Soil is displaced from the surface as a result of select surfactant activity. This is particularly desirable in spray applications where the soil can be removed using oil-skimming techniques. Mechanical Action: This can greatly increase the speed and efficiency of soil removal in aqueous cleaning systems. It can be accomplished by solution movement or movement of the part itself. Examples include air, impeller, ultrasonic, spray, and gas scrubbing (electrolytic). Sequestration: Water must be properly conditioned or softened in order for effective cleaning and rinsing to occur. Hard water consists of divalent calcium, magnesium, and iron ions that must be complexed to avoid generation of insolubles 92

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