What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
At present, for roller or needle roller bearings without cages, ribs, and low-speed operation, the structure mainly includes inner and outer rings and rollers or needle rollers in the raceway between the inner and outer rings, and additional The retaining rings on both sides of the roller or needle roller, among which the retaining rings added on both sides of the roller or needle roller are annular steel sheets punched from metal sheet, and their function in the bearing is only Correctly guide the rollers or needle rollers to run normally in the raceway between the inner and outer rings to prevent the rollers or needle rollers from deviating and slipping out of the raceway. The defect of the retaining ring of this structure is that first, because the rigid retaining ring and the inner ring are completely separated, there is a gap between the retaining ring and the installation shaft during installation. When the bearing is working, The retaining ring is driven by the outer ring and the rollers or needle rollers to rotate around the installation shaft. Due to the inconsistency of the structure, the retaining ring is easy to fall off during the rotation process, the safety of use is poor, and the rollers or needle rollers will appear toward the raceway. The situation of one side offset, which causes the bearing load center to offset, affects the reliability of the bearing operation, and ultimately affects the service life of the bearing; There is a gap between the raceways of the needle, so the tidbits, dust, etc. generated during the working process will continue to enter the raceway between the inner and outer rings. It is stuck; in addition, due to the gap between the steel retaining ring and the raceway, the grease stored in the raceway will be continuously lost, which will cause the bearing to heat up due to frequent lack of grease, or even burn out, which also affects the to the service life of the bearing.
In many national standards, there will be a division of intensity levels. Combination screws are no exception. The strength grade of the combined screw is divided according to the material of the screw wire and the hardness index of the screw wire. General combination screw materials are divided into stainless steel and iron, stainless steel is divided into stainless steel 201, stainless steel 304 and stainless steel 316 and so on. Iron is divided into three types: low carbon steel, medium carbon steel, and high carbon steel. Carbon steel combination screws refer to iron combination screws. Generally, iron combination screws are classified into grades 4.8, 8.8, 10.9, and 12.9. However, the combination screws of grade 10.9 and grade 12.9 are rarely used in the market, so we will not talk about them here. And the combination screws on the market are more commonly used combination screws of grade 4.8 and 8.8. 4.8 grade combination screws are generally made of 1010A screw wire rods. After the screw wire rods are beaten into screws, they are combined with spring flat washers. After production, this 4.8 grade combination screw does not need to be hardened. Its hardness can reach 4.8. 8.8 grade combination screws are generally made of screw wire 10B21 piers. After the screw and wire piers are made into screws, they are equipped with spring washers and flat washers. They can pass through the automatic elastic flat washer machine to rub the three pieces together. Fasten the spring-flat washer combination on the screw, and the spring-flat washer will not fall off. After the combination screw is produced, it needs to be hardened to make the hardness reach 8.8. After the hardness reaches 8.8, we need to take it for electroplating. In order to prevent hydrogen embrittlement of the spring washer in the 8.8-level combination screw with added hardness, it is easy to break. In this way, we have to perform hydrogen removal treatment on the hardened combined screws, and only after the hydrogen removal can be plated. In short, there are many kinds of standard grades of combined screw strength, but generally only two types are used in the market, one is the 4.8-level combined screw strength, and the other is the 8.8-level combined screw strength. 4.8-level combination screws are the most used in the market and customer needs, and have a wide range of applications. As for the standard strength of 8.8-level combination screws, we generally refer to 8.8-level hexagon socket head combination screws, 8.8-level pan head combination screws, and 8.8-level external hexagon combination screws. These three are more commonly used.
Guangdong Yueluo Hardware Industry Co., Ltd. discloses a through-hole mounting nut, which includes a hexagonal portion and a cylindrical portion, a threaded hole is arranged between the hexagonal portion and the cylindrical portion, and the cylindrical portion is provided with a threaded hole. Two grooves, each of the two sides of the groove has a convex side, and the upper surface of the side is provided with a convex point; the advantage is that the two sides are squeezed by the bolt, Or after the hammer is struck, it will bend to both sides, and it can be fastened to both sides of the screw hole of the sheet metal without welding.
If the above-mentioned nuts and screws are used as a kind of fasteners that can prevent others from being disassembled, such as when installing iron doors-steel windows, people usually tighten the nuts first, and then use a welding machine to weld the nuts and screws. To prevent the nut from loosening, it may be necessary to use a tool to mill the threads on the screw. It can be seen that this approach is very inconvenient.
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