Polishing(redirected from coronal polishing)
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(1) In machine building and instrumentation, the finishing of articles to raise the class of surface roughness (up to classes 12 to 14), reduce the articles to desired dimensions, achieve specific qualities in the surface layer, and give the surface a cosmetic shine. Polishing is a combination of the processes of plastic microdeformation and fine dispersion of the surface layer of the article being finished; these processes take place as the polishing and lapping materials act on the surface layer (seeABRASIVE MATERIALS). The most widely employed polishing method uses rotating lap disks whose surfaces are coated with an abrasive powder or paste. In true polishing the finishing effect is achieved as a result of the plastic flow in the layer of the worked surface. Polishing is usually carried out at low rotation rates of the polishing disk (60–200 rpm) and under substantial pressure of the disk on the worked surface (more than 200 kilo-newtons per m2[kN/m2]). Cosmetic polishing, on the other hand, is done at higher lap rotation rates (600–800 rpm) and lower pressure (50–200 kN/m2).
Workpieces of complex shape are polished by means of flexible elastic lap disks and by wet-blasting and centrifugal polishing machines. These methods are primarily used in the final finishing and cleaning of casting molds and cutting tools, such as drills, and in cosmetic polishing; a surface roughness of classes 10 to 11 is achieved as a result.
(2) In furniture manufacture and carpentry, the process of obtaining paint and varnish coatings with a mirrorlike shine on the surface of wooden articles. There are two types: polishing of wood and polishing of paint and varnish coatings.
The first type of polishing consists of the gradual filling of pores in a wooden surface with an organic film-forming solution, primarily French polish, which is applied with a pad, usually made from knitting wool wrapped with linen cloth, using circular gliding motions. The coating that results is 20 to 30 microns (μ) thick and requires the application of 400 to 600 layers of French polish. The entire polishing process, whether by hand or by machine, is completed in three to four operations with an interval of several days between operations. Coatings obtained by this method are completely smooth and bring out the texture of the wood; however, polishing by hand is a very laborious and inefficient process. This method is used in finishing valuable woods, such as English walnut, Karelian birch, and rosewood, mainly in restoration work.
The polishing of paint and varnish coatings is the most common type. Coatings 100 to 400 μ thick are applied to the surface of the article; the coatings are chiefly composed of polyester varnishes and enamels. Any resulting roughness is eliminated by sanding and finishing with polishing and lapping materials.
R. F. KOKHAN and E. V. ZHUKOV