What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
Flat washers are usually thin pieces of various shapes used to reduce friction, prevent leakage, isolate, prevent loosening, or distribute pressure. Such components are found in many materials and structures to perform a variety of similar functions. Restricted by the material and process of threaded fasteners, the bearing surface of fasteners such as bolts is not large, so in order to reduce the compressive stress of the bearing surface and protect the surface of the connected parts, washers are used. In order to prevent the loosening of the connection pair, anti-loose spring washers, multi-tooth lock washers, round nut stop washers and saddle, wave and conical elastic washers are used.
The shaft and gear of financial self-service equipment are often connected by elastic straight groove cylindrical pins. When repairing, the traditional disassembly method is to use the shaft and gear as components. After disassembling together, align the punch with the elastic pin by hand, and use a hammer to remove the elastic pin. Pin out. With this disassembly method, the human hand is easily injured, and the disassembly efficiency is low.
The hexagonal nut is used in conjunction with screws, bolts and screws to connect and fasten parts. Among them, the Type 1 six-purpose nut is the most widely used. The C-level nut is used for machines, equipment or structures with rough surface and low precision requirements; A-level and B-level nuts are used for relatively smooth surfaces and high precision requirements. machine, equipment or structure. The thickness M of the type 2 hexagon nut is thicker, and it is mostly used in occasions where assembly and disassembly are often required. The thickness M of the hexagonal thin nut is relatively thin, and it is mostly used in situations where the surface space of the connected parts is limited.
Usually, the forming of the bolt head adopts cold heading plastic processing. Compared with the cutting process, the metal fiber (metal wire) is continuous along the shape of the product, and there is no cut in the middle, thus improving the strength of the product, especially the mechanical properties. The cold heading forming process includes cutting and forming, single-station single-click, double-click cold heading and multi-station automatic cold heading. An automatic cold heading machine performs multi-station processes such as stamping, heading forging, extrusion and diameter reduction in several forming dies. The processing characteristics of the original blank used by the single-station or multi-station automatic cold heading machine are determined by the size of the bar with a length of 5-6 meters or the wire rod with a weight of 1900-2000KG, that is, the characteristics of the processing technology. The point is that cold heading does not use pre-cut single blanks, but uses the automatic cold heading machine itself to cut and upset (if necessary) blanks from bars and wire rods. Before extruding the cavity, the blank must be shaped. A blank that meets the technological requirements can be obtained by shaping. Before upsetting, reducing and positive extrusion, the blank does not need to be shaped. After the blank is cut, it is sent to the upsetting and shaping station. This station can improve the quality of the blank, reduce the forming force of the next station by 15-17%, and prolong the life of the die, and the bolts can be made with multiple diameter reductions. The precision that can be achieved by cold heading is also related to the selection of the forming method and the procedure used. In addition, it also depends on the structural characteristics of the equipment used, the process characteristics and its state, the precision of the tool and die, the life and the degree of wear. For high-alloy steel used in cold heading forming and extrusion, the roughness of the working surface of the cemented carbide mold should not be greater than Ra=0.2um. When the roughness of the working surface of this type of mold reaches Ra=0.025-0.050um, it has the highest life.
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