Polishing refers to a machining method that uses mechanical, chemical or electrochemical effects to reduce the surface roughness of workpieces so as to obtain a bright and flat surface. Polishing tools and abrasive particles or other polishing media are used to modify the surface of the workpiece.
Polishing cannot improve the dimensional precision or geometric shape precision of the workpiece, but aims at obtaining smooth surface or mirror gloss, and sometimes it is also used to eliminate gloss (extinction). Polishing wheels are usually used as polishing tools. Polishing wheels are usually made of multi-layer canvas, felt or leather, with both sides clamped by metal circular plates, and their rims coated with polishing agent made of fine powder abrasive, grease and other evenly mixed materials.
During polishing, a high-speed rotating polishing wheel (with a circumferential speed of more than 20m/s) presses against the workpiece, causing the abrasive to roll and slightly cut the surface of the workpiece, thus obtaining a bright machined surface with a surface roughness generally reaching Ra0.63～0.01 micron; When non-greasy matte polishing agent is used, it can matte bright surface to improve appearance. Roller polishing is often used in mass production of bearing steel balls.
During rough polishing, a large number of steel balls, lime and abrasives are placed in an inclined can-shaped drum. When the drum rotates, the steel balls and abrasives are randomly rolled and collided in the drum to achieve the purpose of removing the surface convex front and reducing the surface roughness, and the balance of about 0.01mm can be removed.
During fine polishing, steel balls and pelt fragments are loaded into wooden barrels, and a dazzling and bright surface can be obtained by continuously rotating for several hours. The polishing of the precision thread rule is carried out by immersing the processed surface in polishing solution, which is formed by mixing chromium oxide micro powder with particle size of W5-W0.5 and emulsion. The polishing wheel is made of wood with uniform and fine materials and degreased or special fine felt. Its motion track is uniform and dense net. The surface roughness after polishing is not more than Ra0.01 micron. No surface defects can be observed under a microscope with magnification of 40 times. In addition, there are electrolytic polishing and other methods.