Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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SPRAY WASHER OPERATION In a spray washer, parts to be cleaned come in contact with washing solution un- der pressure. The basic components of a spray washer are discussed separately. Shroud The shroud that encloses the spray system should be designed to maintain the individuality of each stage of the operation. There should be access doors to permit inspection of the system along the whole length of the washer. There should be baffles between stages to prevent splash-out. A drain area between stages is essential to minimize cross contamination. If there are no baffles or drain-off sections, or if, for one reason or another, the washer is running parts through too fast, cross contamination of solutions or loss of solution is almost certain to occur. Tank The size of the tank should be 2.5 to 3.5 times the volume of solution pumped per minute, so that every three minutes the full tank capacity will be used up. (This is generally referred to as "turning the tank over".) The solution would be very difficult to heat in a smaller tank, and solids would not have time to settle out to the bottom because the pump would move the solution too fast. Each tank should have an automatic water makeup device to replace water lost by evapo- ration or carry-out. Pump Pump sizes are measured in gallons per minute and are related to the nozzle sizing and pressure required. Generally, a pump pressure of 25 psi, at a flow rate of about 2.5–3.0 gpm per nozzle, is required. Most pump problems result from either poor packing and the resultant leaks or a worn impeller, which causes a loss of pressure and volume. Pressure gauges should be incorporated into the pump- ing system. A loss of pressure could indicate, among other things, a bad pump or missing end caps. An increase in pressure could indicate clogged nozzles. Pumps should be protected by a series of screens to keep large pieces of sludge or scale away from them. These screens must be kept clean so that the solution can pass through them readily. If they get too clogged and the flow of solution is reduced, the pumps could be starved and wear excessively, reducing their ef- ficiency. Screens Screens are used in pairs; when you clean one, the other is still in the tank. It is a good idea to keep a spare set of screens to use as replacements while cleaning a set of screens in the tank. Screen cleaning should be done daily. Nozzles A nozzle is a device that directs, meters, and distributes the solution. Worn or miss- ing nozzles result in lower pressure and reduced efficiency. Nozzles that are plugged or not directed at the part do absolutely nothing. Areas of the soiled part that are not directly hit by the washing solution will not be effectively cleaned. Exhaust System The exhaust system should be sufficient to keep all vapor out of the atmosphere around the machine. The exhaust manifold should be put on a separate section 58

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