Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 26 of 707

automatic machines, solenoids allow the flow of air to operate the guns. The sole- noids are connected to an electric timer where an on-time and an off-time can be set depending on the frequency of the compound needed on the buff face. A buffing head is a series of buffing wheels put together producing a buff face. This buff face can vary in length depending on contact time needed to do a certain job function. To adequately apply buffing compound to the wheel face, spray gun movers or multiple gun set-ups are usually employed. This allows the liquid com- pound to be applied across the entire buff wheel face. Spray guns will generally pro- duce a fan of 10 to 12 inches per gun. In manual operations, the main advantage of the spray composition method is to save the operator time. He or she does not have to stop buffing to apply the cake of conventional solid composition. The operator can remain buffing and apply the liquid compound by the use of a foot peddle, hence less motion is used in applying the compound thus increasing productivity. In the case of automatic machines, the spray equipment replaces mechanical application. Shutdown time for regulation of mechanical applicators in most cas- es amounts to more than 25% of the theoretical maximum production time. This is almost entirely eliminated. The advantages of liquid spray buffing for both automatic and manual buffing procedures are as follows: 1. Optimum quantity of composition is readily controlled on the buff surface, the composition being supplied regularly rather than haphazardly. With buff- ing bars, an excess of composition is present when the first piece is buffed and an insufficient amount is present for the last piece of work before another application of the bar. If this were not true, the operator would handle the bar of composition more often than the work. Using the spray method, the desired amount of composition is present for each piece buffed. 2. With a deficiency of composition of buffing compound present, the buff- ing cloth is worn excessively. Spray compositions, eliminating this defi- ciency of coating, also eliminate this cause of unnecessary buff wear. 3. Solid buffing dirt is packed into the crevices of the work when an excess of buffing composition is present. The serious cleaning problem pre- sented by this dirt is well known. As there need be no excess of composi- tion using the spray method with properly formulated compositions, cleaning after buffing is greatly simplified. 4. Significant savings can be realized in compound consumption, because all the liquid composition brought to the lathe can be used. There are no nubbins left over. 5. Where high pressures exist between the work and the buffs, a deficiency of compositions has often resulted in such a high frictional heat that the muslin buff catches fire. The spray method eliminates this hazard by keeping the buff properly coated at all times; however, a spray composi- tion must be selected that does not constitute a fire hazard, which would be present if a liquid composition were composed of volatile, combustible fluids. When using bar compound on an automatic machine, wheel speeds must be maintained in the higher range to generate sufficient friction to exceed the melt- ing point of the bar; however, much lower wheel speeds may be used when liquid compounds are used. The ability to slow down the surface feet enables more intri- cate parts to be buffed. The lower buffing wheel speeds with large buff faces and liq- 25

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