What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
The lifting ring screw should be made of 20 or 25 steel (GB699). The lifting ring screw must be forged as a whole. The forgings should be normalized and the oxide scale should be removed. The grain size of the finished product should not be lower than grade 5 (YB27-77). There must be over-burning, crack defects.
Most electrical appliance manufacturers only require the size and riveting gap to be tested for riveted contact components. There is no clear requirement for riveting strength. Only a few manufacturers perform torsion testing on riveting strength. The torque detection method is as follows: use a saw blade to open a one-shaped groove on the rivet head of the riveted contact element, and then insert a torque wrench into the one-shaped open groove to rotate, and measure the torque value. Because most of the electrical contacts are made of copper-silver alloy, the strength is low, and it is easy to slip during the test, and when a saw blade is used to open the one-shaped groove, the width and depth cannot be accurately positioned, so the measured value fluctuates greatly. , has always been an unsolvable technical problem in the industry.
At present, many manufacturers do not want the product to be disassembled by the user, so they set the anti-disassembly mark on the product. The common method is to apply red or blue anti-disassembly paint on the fastener, such as the nut, once the user disassembles it by himself. , the paint at the connection will fall off, and it can no longer be aligned, so that the manufacturer can judge and identify it and provide a basis for warranty. However, it is inconvenient to paint some joints, and the use of tamper-evident paint is not healthy and environmentally friendly.
Many standoffs are used in sheet metal and aluminum profile processing. However, the existing pressure riveting nut column generally adopts a clearance fit between the pressure riveting and the pressed plate, which has no effect on the general pressure riveting, but it has high surface quality requirements for aluminum profiles, especially Painting aluminum profiles will have a certain impact. First, because the bottom holes of pressure riveting on aluminum profiles are generally processed on ordinary punching machines, a tapered hole with a horn will be generated, which will further increase the gap between the pressure riveting nut columns. Make the mutual tightening force smaller, causing some aluminum profile components to loosen the riveting nut when installing screws, resulting in unqualified surface quality. Therefore, we urgently need a way to reduce the matching gap with the bottom hole of the aluminum profile pressure riveting. The pressure riveting standoff is used to increase the wrapping force between the pressure riveting standoff and the aluminum profile hole.
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