During the use of fasteners, sometimes the tempe […]
During the use of fasteners, sometimes the temperature is very high. Under the operation of high-temperature fasteners, it is easy to damage the performance of the fasteners, and even some faults. For example, bolts are important connecting parts widely used in high-power boilers, steam turbines and steam pipeline valves. For the recommendations of high temperature fasteners in these areas, the following measures should be taken when using:
1. Temperature stress: When the unit is started and running, due to the temperature difference between the flange and the bolt (the temperature of the flange is higher than the bolt), and the coefficient of linear expansion of the two materials, the free thermal expansion of the flange is larger than that of the bolt. The bolt is subjected to an additional tensile force, and the stress caused by the additional tensile force in the bolt is called temperature stress.
2. Sealing stress: ensuring the sealing of the connecting parts is a basic requirement for bolting. In the case of the geometry of the flange, the processing quality of the joint surface, the pressure of the steam and the temperature, the sealing stress is determined by the tightening force of the bolt.
3. Hot tightening of bolts: Bolts that are subjected to pre-tightening force during installation. When the pilot is running, under the action of steam pressure, the bolts are forced to increase more than the initial pre-tightening force. For general horizontal flanges. The bolt tension is increased by 5%-15%, so that the initial stress of the bolt can be lower than when it is cold. In order to meet this initial stress requirement, it is sometimes impossible to manually tighten the bolt to the required degree in the cold state, and therefore, a heat tight method is usually required.
Changzhou Huyue Standard Parts Factory recommends that the bolts be tightened to a certain extent (cold tight) by hand, and then the bolts are heated by the special electric heater through the center hole of the bolts. After the bolts are heated and extended, the nuts are tightened. This method is called heat tight. Controlling the heat tightness makes it easier to control the preload.