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Fastening methods and principles of standard parts screws and bolts

2021-03-16

Fastening methods and principles of standard parts screws and bolts

1. Before connecting the bolts, confirm that the pitch, tooth type, and direction of rotation of the bolt and the nut are consistent;
2. Thoroughly clean up debris and liquids such as sludge, carbon deposits, coolant or oil in the bolt holes before tightening, and check whether the threads are intact and whether the bolts are elongated;
3. When tightening the bolts, the tightening torque should be tightened according to the torque specified in the instruction manual. If there is no regulation, the tightening torque should be reasonably determined according to the diameter of the bolt;
4. When disassembling the cylinder head bolts, you must wait for the engine to cool down completely. When disassembling, follow the principle of "uniformly loosen from both sides to the middle diagonally" to prevent the cylinder head from warping and deforming;
5. When the same part is fastened with multiple bolts, it should be tightened gradually in a certain order according to the shape of the connected parts and the distribution of the bolts (generally 2 to 3 times). If there is a positioning pin, it should be close to the positioning pin. Start of bolts;
6. When tightening a group of square or round nuts, it must be done symmetrically;
7. When tightening a group of nuts arranged in a rectangular shape, start from the middle and gradually expand symmetrically to both sides.
Type of thread
The thread's detour direction is divided into left-handed thread and right-handed thread, and most of the thread's detour direction is right-handed thread, and a few special parts use left-handed thread.
The number of threads can be divided into single thread, double thread, and three thread. Among them, single thread is mostly used for connection, and the others are mostly used for transmission.
The shape of the thread is divided into triangular thread, rectangular thread, trapezoidal thread and sawtooth thread. Among them, the triangular thread has good self-locking performance and high thread strength. It is generally used for connection and is the most widely used thread. According to the pitch, it is divided into two categories: coarse thread and fine thread. Coarse thread is the basic thread. Fine thread screw has high strength, but the strength of thread thread is lower than that of coarse thread. It is generally used for thin-walled pipe fittings, shaft parts and precision On the adjustment piece of the mechanism. When the screw diameter is greater than 70mm, only fine thread can be used.
Thread self-locking and anti-loosening device
In theory, all standard connecting bolts are self-locking and will not loosen under static load. However, under the action of alternating load, continuous shock and vibration load, the connection may lose its self-locking effect and become loose. Therefore, in order to make the connection reliable, an anti-loosening device must be used. Generally, two types of anti-loosening by friction and mechanical methods are used.
The anti-loosening methods for threaded connections include counter nuts, spring washers, self-locking nuts, high-strength self-locking bolts, application of fastening glue on the threads, split pins, stop washers, tandem steel wires, slotted nuts, stop washers And other forms.

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