What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
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.
Nuts and bolts are one of the most widely used fasteners in modern mechanical structures. At present, the common metric bolts and nuts are generally trapezoidal in cross-section. The connection between the bolt and the nut is prone to loosening under severe vibration, or even falls off by itself, and the tightening force of the bolt and nut thread is mainly concentrated in the bolt thread and Between the teeth of the first few threads where the threads of the nut are in contact, resulting in loosening of the fastener and sliding pressure of the threads
spring washer is installed under the nut to prevent the nut from loosening. It is stated in the national standard. Hexagonal slotted nuts are specially designed for use with bolts with holes at the end of the screw, so that the cotter pin can be inserted into the hole of the screw from the groove of the nut to prevent the nut from automatically loosening. It is mainly used for vibration loads or alternating loads. . The methods to prevent the nut (or bolt) from automatically loosening in the mechanical design and production are as follows: 1. Add a spring washer; (simple and easy to do) 2. Use a hexagonal slotted nut + a split pin; (increase the processing process) 3 . Pad the stop washer; (increase the processing process compared with the same period of last year) 4. Insert the steel wire into the hexagon head opening of the hexagon bolt. (Increased processing steps compared to the same period of last year) Spring washers are used to prevent loosening. For example, the bolts connecting the motor and the machine base generally need to add spring washers, because the motor vibrates without the spring washers, and the nuts will loosen. Generally, the fasteners on the equipment with vibration There is a spring gasket on it, and there is generally no need to add a gasket on the flange! Whether the spring gasket is added to the flange is related to the medium circulating in the pipeline. If it is easy to generate pulses, it is best to add spring gaskets, as well as high-speed fluid, and the caliber changes frequently. Do not generalize. On some valves, the stuffing box gland All flanges need to be added with spring gaskets. The automatic selection of spring gaskets is included.
Fasteners play a very important role in the installation of the main engine. Complex products such as airplanes, automobiles, trains, elevators, air conditioners, and computers all have the problem of installing components on thin plates. There are two traditional installation processes. One is The first is to tap the internal thread on the thin plate, but when the internal thread is tapped on the thin plate below 6 mm, the installation is often not firm because the number of threads is too small, and even the connection fails due to the broken thread when the force is applied; the second way It is a process of welding nuts on a thin plate, which easily leads to deformation of the thin plate and uneven welding surface. Sometimes the welding is not strong and the nut falls off when the force is applied, resulting in damage to the installation. The development of rivet nuts has solved the problem of installing components on thin plates, because rivet nuts combine the characteristics of nuts and rivets, and play an increasingly important role in fastener products. However, with the extensive use of rivet nuts in the electromechanical and mechanical industries such as automobiles, aviation, railways, refrigeration, elevators, etc., ordinary rivet nuts can no longer meet the special assembly requirements of many mechanical and electromechanical products, such as good sealing during assembly. Rivet nut with leak-proof function. Cantonese snail
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