Industrial large fans, as a type of special equipment with high requirements, have certain high requirements for the roughness of the inner and outer surfaces of some structural components. Therefore, polishing processes are required. With a reasonable polishing process, the expected results can be achieved. If the polishing process is not reasonable, even if the best raw materials are used, qualified fan parts cannot be produced.
Currently, commonly used polishing methods for industrial large fan parts include mechanical polishing, chemical polishing, electrolytic polishing, ultrasonic polishing, fluid polishing, and magnetic grinding polishing. However, compared with other mirror polishing, the polishing of industrial large fan parts has extremely high requirements, not only considering the polishing itself but also the geometric accuracy of the component surface. There can't be any deviation, otherwise, it will affect the performance of the fan. Since it is difficult to precisely control the geometric accuracy of the parts using methods such as electrolytic polishing and fluid polishing, and the surface roughness values of methods such as chemical polishing, ultrasonic polishing, and magnetic grinding polishing cannot meet the requirements, machine polishing using consumables such as oil stone, sandpaper, and diamond paste is generally used, with manual operation as the main method.
Various components of industrial large fans go through machining, electrical discharge machining, grinding, and other processes before entering the polishing process, which is divided into rough polishing, semi-precision polishing, and precision polishing according to different component functional process requirements.
(1) Rough polishing: After the parts are machined with a milling machine, electrical discharge machining, and grinding, rough polishing is performed using a rotating surface polishing machine with a speed of 35000~40000r/min or an ultrasonic grinding machine. Usually, a WA400 grinding wheel with a diameter of 3mm is selected to remove the white layer from electrical discharge machining. Then, a strip-shaped oil stone is held, and kerosene is added to lubricate and cool while grinding.
(2) Semi-precision polishing: The key points of semi-precision polishing process operations are as follows:
a. When using sandpaper for polishing, softwood or bamboo sticks can be used. When polishing a circular or spherical surface, using a softwood stick can make it easier to shape the circular surface. When polishing a plane, using a harder stick like cherry wood is more appropriate. When polishing, the end of the hard stick should be trimmed to maintain as much flat contact as possible with the surface of the material, and avoid deep scratches caused by the sharp corners of the hard stick coming into contact with the surface.
b. When changing the granularity of the sandpaper, the polishing direction must change by 45°-90% to remove the polishing scratches left by the previous particle process, and carefully check with the naked eye or magnifying glass.
c. During the process of replacing sandpapers with different particle sizes, the mold surface must be carefully cleaned with natural cotton wool soaked in benzene to ensure that all grinding particles have been removed. Otherwise, even if one particle of sand remains on the surface, it will destroy the subsequent polishing results.
d. When using sandpaper for polishing, it should be avoided that the sand grains stick to the mold surface and cause overheating. Special attention should be paid to precision polishing when using 1200# and 1500# sandpapers.
(3) Precision polishing: The key points of precision polishing process operations are as follows:
a. When the polishing process changes from sandpaper to diamond paste, the cleanliness of the industrial fan component surface is equally important. Before proceeding to the next process, all particles and kerosene must be removed. When polishing with diamond paste, not only the mold surface must be cleaned, but also the polisher's hands must be cleaned, and the diamond paste must be applied to the tool.
b. The polishing must be carried out with the lightest possible pressure, especially when polishing pre-hardened steel or using finer diamond paste for polishing. The polishing pressure must be stable and even, although this is difficult to achieve. A simple method is to use a slender, handled wooden stick made of phosphor bronze or bamboo, which has better flexibility and flexibility in the polishing area.
c. When polishing, start from the corners, convex parts, edges, or difficult-to-polish parts of the component, and the final polishing direction should be consistent with the demolding direction. For sharp edges and corners, a harder polisher should be used.
d. Each polishing process cannot be too long, and the shorter the time, the better the polishing effect. Excessive polishing due to long polishing time can cause "orange peel" and "pinholes." Softer materials are prone to produce "orange peel" during over-polishing. This can be solved by nitriding or other heat treatment methods to increase the surface hardness of the material and use soft polishing tools.
e. In order to obtain high-quality polishing, it is necessary to avoid using polishing tools and methods that produce heat easily. For example, avoid using polishing tools such as "Aluminum Oxide", "Chromium Oxide", and "Red Iron Powder" that do not have the polishing ability but only generate heat. Using a polishing wheel for polishing usually generates heat, which is easy to cause "orange peel."
f. When it is necessary to interrupt polishing, it is very important to clean the surface of the part. All grinding agents and lubricants on the mold surface must be carefully cleaned, and finally, a layer of rust inhibitor is sprayed on the mold surface.
Adopting the above experience, the polishing requirements of most components of industrial large fans can be achieved. Of course, in actual production, there are many factors that affect manual polishing. In order to truly meet the requirements of the manufacturer's product production, operators need to operate carefully and practice repeatedly to continuously improve their polishing level.