Questions about polishing

Polishing is a process of modifying the surface of a workpiece using flexible polishing tools, abrasive particles, or other polishing media. Polishing does not improve the dimensional accuracy or geometric precision of a workpiece; rather, its purpose is to achieve a smooth surface or a mirror-like finish, and sometimes it is also used to remove luster (matting). A polishing wheel is usually used as the polishing tool. A polishing wheel is generally made by stacking multiple layers of canvas, felt, or leather, which are held together at both sides by metal discs; its edge is coated with a polishing agent composed of finely ground abrasives and oils mixed evenly. During polishing, the high-speed rotating polishing wheel (with a circumferential speed of over 20 meters per second) presses against the workpiece, causing the abrasives to roll and slightly cut the surface of the workpiece, thereby producing a smooth finished surface. The surface roughness can generally reach Ra0.63 to 0.01 microns; when non-greasy matting polishing agents are used, the smooth surface can be matted to improve its appearance. When producing bearing balls in large quantities, the drum polishing method is often used. During rough polishing, a large number of steel balls, lime, and abrasives are placed in an inclined drum-shaped container. As the drum rotates, the steel balls and abrasives roll and collide randomly inside the drum, thereby removing surface protrusions and reducing surface roughness; this process can remove about 0.01 millimeters of material. During fine polishing, steel balls and pieces of fur are placed in a wooden barrel; continuous rotation for several hours yields a brilliantly shiny surface. The polishing of precision linear scales is carried out by immersing the machined surface in a polishing solution, which is composed of chromium oxide micro-particles with a particle size of W5 to W0.5 mixed with an emulsion. The polishing wheel is made of wood with a uniform texture and degreased, or of specially designed fine felt; its movement follows a uniform and dense mesh pattern. The surface roughness after polishing is no greater than Ra0.01 microns, and no surface defects can be detected under a microscope magnified 40 times. There are also methods such as electropolishing.

Polishing is required, and the requirements for surface finish should be determined based on the product specifications.

A new dryer? Didn’t you request a polishing treatment? Actually, it’s fine not to polish; the first few batches can just be used as wash dryers. If polishing is truly desired, there are two methods. The first is to use oxy-acetylene spraying of nickel-based alloys or electroplating, which takes 2 days. The second is mechanical polishing, which takes 5–7 days; for the first level of polishing, the cost is 300–500 per square meter ； Moreover, the inside of the dryer (rake type) is very difficult to clean.

This post was last edited by bingyu252 on 2009-5-17 at 10:53. The requirements for polishing the inner surface of equipment are mainly related to its surface roughness. The parameters commonly used to evaluate surface roughness are generally selected from the following three: 1. Ra – Arithmetic average deviation of the profile; 2. Rz – Height of ten micro-irregularities; 3. Ry – Maximum height of the profile. Within the typical range of values for these parameters, Ra ranges from 0.025 to 6.3 μm, while Rz ranges from 0.100 to 25 μm； The national standards recommend giving priority to Ra 5, and relevant standards are provided (a new version should exist): GB1031-83 \"Parameters of surface roughness and their values\", GB3505-83 \"Terms related to surface roughness, surfaces and their parameters\"