Process of rolling thread for high strength bolt

Generally speaking, high strength bolts are formed by cold working. Rolling screw thread is a kind of processing method which uses plastic deformation principle to make spiral tooth form high strength bolt. High strength bolt is a kind of high strength bolt which is formed by plastic deformation principle and high strength bolt.
The rolling die with the same pitch and shape as machining high strength bolt thread (i.e. backing plate) is adopted in the process of construction to extrude the cylindrical blank and make the blank continuously rotate. The final goal is to transfer the contour above the rolling die to the billet of high strength bolt, thus forming the thread.
It should be noted that the rolling speed should not be too high, which will reduce the efficiency, and there will be separation or derailment on the surface of high strength bolt thread. If the rolling times are too few, which is not conducive to the formation of high strength bolt thread, the thread diameter is easy to be out of round. The initial rolling pressure is very high, in this state, the die life will be greatly shortened.

1. From the perspective of raw materials, high-strength bolts are made of high-strength materials. The screw, nut and washer of high strength bolt are made of high strength steel. 45 steel, 40 boron steel and 20 manganese titanium boron steel are commonly used. Ordinary bolts are usually made of Q235 steel.
2. In terms of strength grade, high strength bolts are widely used. 8 s and 10.9 s are commonly used, of which 10.9 is the most. The strength grade of ordinary bolts is low, generally 4.4, 4.8, 5.6 and 8.8.
3. From the mechanical characteristics, the common bolt connection transfers the shear force by the bolt bar shear and the hole wall pressure. In addition to its high material strength, the high-strength bolt also exerts a great pre tension on the bolt, which makes the connection members produce extrusion pressure, so that there is a great friction force perpendicular to the screw direction.
The high-strength bolt connection is to clamp the plate of the connecting plate through the large tightening pre tension in the bolt rod, which is enough to produce great friction force, so as to improve the integrity and stiffness of the connection. When the shear force is applied, according to the different design and stress requirements, it can be divided into two types: high-strength bolt friction type connection and high-strength bolt bearing type connection However, it is the same kind of bolt, but there are great differences in calculation method, requirements, scope of application and so on.
In the shear design, the ultimate state of high strength bolt friction type connection is that the external shear force reaches the maximum friction force provided by the bolt tightening force between the contact surfaces of the plate as the limit state, that is to ensure that the internal and external shear force does not exceed the maximum friction force during the whole service life. The relative slip deformation of the plate will not occur (the original gap between the screw and the hole wall is always maintained), and the connected plate is stressed as a whole according to elasticity.
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