October 1, 2017

Pre-polishing of Metal Coating

Pre Polishing Process to Metal Coating

To prepare metal before polishing process, called as pre-polishing. Where a final smooth or polished metallic surface is intended, most of the smoothing must be applied to un-coated article, since the metallic coating would be unduly and irregularly thinned by the smoothing process. All these processes are loosely described as 'polishing', but as applied at this stage, they consist in fact only of careful grinding with progressively finer abrasives. The articles are pressed against the abrasive loaded rim of rapidly rotating flexible wheels made of leather or coarse cloth discs. Two or three successive processes are usually used with progressively finer abrasives; grease or oil lubricant is applied during the final cuts, and the surface is brought to a satin smooth but entirely lusterless condition. The grease not only lubricates the operation, but supports and to some extent masks the abrasive particles; it also removes the frictional heat and prevents burning or scorching of the surface.

These processes are known in the trade by various names such as bobbing, scuffing and buffing a finer and milder abrasive is applied to a sisal or cloth wheel from a grease bound cake. In sand is fed between the article and a rotating leather rimmed wheel. The abrasive used in the final stages is often Tripoli, or diatomaceous earth. Of recent years the coarser grinding has often been performed on long endless belt of emery cloth, supported between a soft faced pulley, against which the work is pressed, and another pulley some distance behind. This process is called back-stand emerying.

Because of the irregular shape and contour of most article sent for decorative plating, they mostly have to be presented to the revolving wheels by the hands of operatives, who turn and twist them to ensure that the whole area is smoothed, and who also visually check that all blemishes and roughness are ground out. This is heavy, dirty and tedious work, which nevertheless requires considerable skill and experience. Its is moreover a serious bottleneck in production because the work is unattractive to labor.

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