Customized high-strength pan head self-tapping screw pan head cross screw self-tapping screw 3/8

The flat key is simple in manufacture, reliable in operation, convenient in assembly and disassembly, and widely used. The flat key transmits torque by contacting the two sides of the keyway with the two sides, that is, the side is the working surface, so the main technical requirements for assembly are: to ensure the matching requirements between the flat key and the keyway of the parts on the shaft, and to transmit the movement smoothly and torque. The matching nature of the key and the keyway generally depends on the working requirements of the mechanism. The key can be fixed on the shaft or the hub, and can slide relative to another matching part (guide flat key); it can also be fixed on the shaft and the hub at the same time (ordinary flat key), and based on the size of the key, by changing the shaft The size of keyway and hub keyway can meet different matching requirements.

The pull-out type positioning pin and the tie-suspended type positioning pin are in the form of a straight cylindrical shape. The pull-out locating pin is temporarily pulled out from the connected piece of the tooling, and it is in a loose state; the tail of the tie-suspended locating pin is connected with a tie such as iron wire or string to the connecting piece of the tooling. After the locating pin is pulled out, the tie Suspended on tooling. The main disadvantages of the two types of positioning pins are as follows: First, the suspension straps are easy to fall off after long-term wear, and the pull-out positioning pins of the same parts are not convenient for on-site storage and placement, and are usually placed on the nearby ground at will; All kinds of positioning pins are prone to position transfer, forgetting and losing, which affects the reset of the tooling and the subsequent manufacture and assembly of aircraft products.

2. Low cycle fatigue Low cycle fatigue means that the fatigue stress is close to or exceeds the yield limit of the material. The material has a certain amount of plastic deformation in each strain cycle. The life is generally in the range of 102 to several times 104, and the fatigue curve is generally used. ε-N curve representation. The finite element calculation results show that after the bolt is screwed into the lock nut, the stress at the root of the threaded piece is large, and part of the surface area is in a yield state, while the strain in the central area of the root of the threaded piece is small, and the strain situation is more complicated. The area with high strain at the root of the thread piece experiences reciprocating loading, which is prone to low cycle fatigue, which reduces the pressure of the thread piece and reduces the screw-out torque.

At present, the main four kinds of anti-shedding nuts are still prone to falling off. Friction and anti-shedding are in the case of shock, vibration and variable load. At the beginning, the nut will decrease in preload due to relaxation. As the number of vibrations increases, the loss of preload will increase. The force increases slowly, eventually causing the nut to loosen and the threaded connection to fail. The mechanical nut is prevented from falling off by adding a stopper, which makes it inconvenient to disassemble. The riveting and punching prevention is to prevent the separation by welding, bonding, etc. This method can only be disassembled by destroying the bolt pair.

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