How to solve the problem of the lock and nut of stainless steel bolts and nuts?
The cause and solution of the locking of stainless steel fasteners:
1. The reasons for the locking of stainless steel fasteners
1 the thread deflection angle and the softer characteristics of the stainless steel are easy to cause death.
The combination of 1.1 screws and nuts belongs to the gap coordination, and has the international standard tolerance range, so the center axis of the internal and external thread is basically not on the same line when it fits, and the contact surface of the internal and external threads is reduced because of the tilt.
The force of the 1.2 locking process is uneven or incline, causing the center axis of the screw and nut to be maximized, making the screw and the screw thread of the screw not fully exposed, turning from the surface to the point force or increasing the force on each unit.
1.3 from (Fig. 2), the larger the deflection angle, the smaller the force area of the thread fit, the easier the tooth pattern will be damaged.
1.4 stainless steel relative to carbon steel should be soft, if the lock in the process of friction drop iron, adhesion but not falling, thus interfering with the smooth flow of thread, leading to the death of the teeth and the top of the teeth.
2 too high locking force and low thermal conductivity of stainless steel lead to thread locking.
2.1 When the nut is tightened, the torque (locking force) must be greater than that of the screw and nut itself, so that the nut can be rotated. When the nut rotates down the thread, because the action of the counterforce will extend the screw, when the torque (locking force) exceeds the drop point of the screw (that is, the safety torque), the screw will have residual strain and maintain the elongated state. When the screw extends beyond its elastic range, it will cause permanent deformation and lead to thread locking.
2.2 during the rotation of the screw nut, friction generates heat. The thermal conductivity of stainless steel is relatively low (basically in the range of 10-30w/mc degree, about 1/3 of carbon steel). When the produced pressure and heat destroy the chromium oxide layer (the stainless steel is not easily rusty oxidation layer), the metal tooth pattern is blocked / cut directly, and the characteristics of stainless steel are softer, and then the adhesive phenomenon occurs. The greater the locking force, the greater the heat generated. The easier the adhesion of screws to the stainless steel parts of Asan is.
The above principle is the same in loosening (screw nut and exit).
Two. How to reduce the ratio of lock death
In view of the above causes of locking, the use of stainless steel screws should pay attention to:
1, keep the central axis of the screw and nut perpendicular to the locked surface to reduce the deflection angle.
2, use torque wrench or socket wrench as far as possible to avoid excessive force and control torque in safety stock torque range.
3, try to use manual wrench to slow down the locking speed, keep the thread clean, reduce the friction coefficient, reduce heat energy and reduce adhesion by using lubricating oil.
4, choose relatively high hardness products to reduce thread shear.
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