What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
Further, the pressure riveting portion and the pressure-bearing portion are both columnar structures, the outer diameter of the pressure-bearing portion is larger than the outer diameter of the pressure riveting portion, the pressure riveting portion is a stepped structure, and the diameter of the lower end of the pressure riveting portion is smaller than that of the pressure riveting portion. The diameter of the upper end of the rivet part.
Standard screw is one of the fasteners commonly used for fastening and assembly. Standard screws and flat washers, grade A, and standard spring washers, are used in combination, and are widely used in the assembly of various products. For manufacturers who use combination screws in small and medium batches, the process of combining screws, spring washers and flat washers generally adopts the method of assembling screws by workers' bare hands. This method is tedious and repetitive, wastes human resources, is time-consuming and labor-intensive, and it is difficult to ensure the normal operation of the workshop. assembly progress. The screw assembly machines currently on the market can replace manual assembly screws, but this type of equipment has disadvantages such as bulky size, high cost, complex structure, inconvenient non-standard manufacturing and maintenance, high noise, and power consumption.
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.
In the riveting operation, the rivet used is composed of a mandrel and a deformed collar. When in use, a through hole is drilled on the two components to be connected, and then the head of the rivet is passed through the through hole and clamped by a rivet. The tail of the rivet will break the rivet, the head of the rivet and the deformed collar remain in the through hole, and the whole riveting process is completed. The existing pull rivets have the following shortcomings: first, the parts where the pull rivet and the two components are connected cannot be completely and tightly fitted, which meets the requirements of non-sealing for parts that have waterproof and leak-proof requirements; second, the existing pull rivets The separation groove of the rivet mandrel is close to its head. When the mandrel is broken by the rivet during the riveting process, basically only the head of the mandrel remains in the deformation collar, and the connection of the two components depends on the deformation of the collar. Under the action of compressive stress, the inside of the deformed collar becomes hollow due to the breaking of the mandrel, and cannot bear large shear stress.
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