Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 73 of 707

cleaning chambers. Sources of spark or flame that can ignite accumulated hydrogen should be identified and removed from the area in which acid clean- ing is conducted. The use of acidic cleaners for cleaning sulfurized steel or parts that have sulfur- ized oil present can result in the generation of poisonous and flammable hydrogen sulfide gas. The same precautions employed for dealing with hydrogen evolution should also be employed for the potential evolution of hydrogen sulfide. Acid cleaner tanks and equipment should be properly vented to keep work- er exposure to mists and vapors below OSHA limits. The reactivity of substrate material should be evaluated prior to acid cleaning to prevent violent reaction due to incompatibility and/or part damage. Alkaline Cleaners The use of alkaline cleaners containing strong alkaline compounds, such as sodium hydroxide and potassium hydroxide, can result in strong exothermic reac- tions when working solutions are made or replenished. Additions should be made to water or working solutions in a cautious, controlled fashion to prevent splash- ing and localized boiling. Additions should only be made to cool solutions (<100oF). Water should not be added to alkaline powders. The use of alkaline cleaners for etching or cleaning reactive metals, such as alu- minum, zinc, or magnesium, will result in the evolution of flammable hydrogen gas that can accumulate in foam blankets or in enclosed cleaning equipment. Equipment should be ventilated and ignition sources should be removed from areas in which reactive metals are cleaned. The use of alkaline electrocleaners will result in the evolution of hydrogen and oxygen. Tanks should be well vented to remove these gases. Foam blankets on electrocleaners should be sufficient to prevent misting without excessive accumulation of hydrogen and oxygen. Disconnect current prior to removing work from electrocleaning tanks to prevent hydrogen explosions. Personnel using, handling, or working in areas where exposure to alkaline cleaners is pos- sible must wear alkaline-resistant personal protection consisting of safety goggles, face shield, gloves, apron, and boots. Respiratory protection should be worn when dust or mist is a problem. Neutral Cleaners Although the destructive effect of neutral cleaners on body tissues may be min- imal, in many cases these cleaners are used hot and the possibility of thermal burns from splashing may exist. Additions to working solutions should be made slow- ly and cautiously in a controlled manner to prevent splashing. Additions should only be made to cool solutions (<100oF). Equipment A preventive maintenance schedule should be implemented for the inspection and repair of defective cleaning equipment. Hoist systems, exhaust systems, heating systems, and tank systems should be inspected on a routine basis for proper func- tion and equipment integrity. Worn, corroded, or damaged equipment should be repaired or replaced upon discovery. General 1.Never work alone when working with chemicals. 72

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