2. The causes of stainless steel bolts and nuts biting
1) Rough tooth lines or foreign objects adhering. If there are solder joints and other metal shavings sandwiched between the teeth, it often leads to biting.
2) Excessive tightening force or tightening speed. Excessive tightening force can easily cause significant pressure between the teeth and lead to bite; Tightening too fast can easily cause the temperature between the teeth to rise rapidly and cause biting.
3) The angle of the force application direction is incorrect. When tightening, the tightening direction is not perpendicular to the axial direction of the bolt, which can easily lead to jamming.
3. Dismantling method for stainless steel bolts and nuts after biting
1) Use thread loosening agents (such as kerosene, lubricant, etc.) for lubrication. Spray loosening agent onto the threaded connection during homework, allowing as much loosening agent as possible to penetrate into the threaded connection, and use tools such as rubber hammers to lightly tap the circumference of the nut to create vibration at the threaded connection. After about 30 minutes of spraying loosening agent, try to remove the nut. Through practical application, it can be found that this method has a significant effect on dismantling corroded fasteners, but its effect on tightening and dismantling threads is relatively limited.
2) For nuts that have been sprayed with loosening agent but still cannot be disassembled, the thermal expansion method can be tried, which uses tools such as welding guns to heat the nuts, causing them to expand, and then remove the nuts. The use of this method is subject to certain limitations, and it is necessary to consider whether there is a space for hot work around the fasteners, and whether the fasteners and the connected parts can withstand high temperatures and heat.
3) For bitten bolts and nuts, special tools such as nut splitters can be directly used for disassembly. When using a nut splitter for operation, place the nut splitter on the nut and use mechanical or hydraulic pressure to push the blade to split the nut, thereby separating the nut from the bolt. This method is convenient and fast, especially when using a hydraulic system to advance the cutting head, saving time and effort. However, it should be noted that in order to retain the bolt from being damaged and only remove the nut, some improvements should be made in the operating method. Because at the moment when the cutting head splits the nut, due to inertia, the cutting head also leaves indentations on the bolt and stud. Even if the feed speed of the cutting head is controlled as much as possible during application, a certain mark is still left on the . Through on-site testing, it was found that only the nut was squeezed, and after slight deformation, it immediately stopped. The nut produced visible deformation and could be removed, with almost no damage to the bolt threads.
4. Preventive measures for stainless steel bolts and nuts biting
From the previous analysis, it can be seen that it is extremely inconvenient to disassemble stainless steel fasteners after being bitten. Even some methods or special tools are time-consuming and laborious. Therefore, it is particularly important to do a good job in preventing stainless steel fasteners from being bitten. The following are several methods to prevent stainless steel fasteners from biting.
1) Choose bolts and nuts of different materials for matching.
2) Improving the performance of fasteners themselves, such as adding film on the threads of fasteners to prevent jamming, is a costly method and is currently rarely used.
3) Clean the threads, check that the tooth patterns are complete and continuous, and that there are no impurities between the tooth patterns.
4) Apply lubricant to the threads, such as molybdenum disulfide, butter, etc., evenly and fully fill the thread base, covering the length of the bolt head by approximately (10-15) mm.
5) When tightening the homework, the nut or bolt should be first screwed into the (2-3) thread by hand, and then tightened with a torque wrench or a wrench. The tightening should be evenly applied, and the tightening direction should be perpendicular to the axial direction of the bolt. Try not to use a wrench or an electric or pneumatic wrench.
6) When using an electric or pneumatic wrench for pre tightening, excessive torque or speed should be avoided. It should be ensured that the nut comes into contact with the gasket and is immediately stopped from use. Then, use a torque wrench to tighten, and the tightening torque should not exceed the specified torque value.
