Adjustment
In addition, since January, some models of complete machines for newly approved domestic and foreign investment projects, such as front shovel mining excavators, electric traction shearer scraper conveyors, scraper loaders, hydraulic supports, and large crushing stations , fixed belt conveyors, etc., shall stop implementing the import duty-free policy. The adjustment of the import tax policy reflects the government’s support for the revitalization of the domestic equipment manufacturing industry. The tax rebates for imported key parts and raw materials are transferred to the capital of enterprises, which can provide a source of capital for enterprises to carry out technological transformation and technological innovation. At the same time, under the premise that the domestic equipment can meet the basic needs of the country, stopping the tax exemption for imported complete equipment can provide an opportunity for domestic equipment to compete fairly with imported equipment, and can reduce the production of newly developed domestic equipment within a certain period of time. cost pressure.
Choice of Surface Roughness
Surface roughness is an important technical index that reflects the microscopic geometric shape error of the part surface, and is the main basis for testing the surface quality of the part; whether it is reasonable or not is directly related to the quality, service life and production cost of the product. There are three methods for selecting the surface roughness of mechanical parts, namely calculation method, test method and analogy method. In the design of mechanical parts, the most commonly used method is the analogy method, which is simple, rapid and effective. The application of the analogy method requires sufficient reference materials, and various existing mechanical design manuals provide more comprehensive materials and documents. The most commonly used is the surface roughness appropriate to the tolerance class. In general, the smaller the dimensional tolerance requirement of mechanical parts, the smaller the surface roughness value of mechanical parts, but there is no fixed functional relationship between them. For example, handles, handwheels on some machines, instruments, sanitary equipment, and the modified surface of some mechanical parts on food machinery, their surfaces are required to be processed very smoothly, that is, the surface roughness requirements are high, but their dimensional tolerance requirements are very high. Low. In general, for parts with dimensional tolerance requirements, there is still a certain correspondence between the tolerance level and the surface roughness value.