Stainless steel bolt tooth burning

Quote: Locking of fasteners generally occurs in products made of stainless steel or alloy materials, as these metals possess natural resistance to corrosion. Once the metal surface of the fastener is damaged, an oxide layer forms to provide protection and prevent further corrosion. However, when the fastener is tightened, the pressure and heat generated can destroy this oxide layer, leading to blockage or shearing between the metal threads, which in turn results in sticking – that is, locking. Locking of fasteners cannot be completely prevented, but we can reduce the likelihood of this occurring by paying attention to various factors, such as ensuring the load-bearing capacity of the fasteners and choosing screws and nuts with higher tensile strength. The cleanliness of the threads on fasteners also has an impact on whether they will lock up; locking tends to occur more often when the threads are rough or dirty. Therefore, it is necessary to ensure that the fasteners are clean before use, by removing any iron shavings or dirt. After proper and appropriate lubrication of the fasteners, the heat generated in their metal parts due to stress is effectively reduced, which in turn lowers the likelihood of the fasteners locking up. Stuck fasteners are also less likely to occur when washers are used and they are installed properly.

a. Whether the surface finish of the material is good. If it’s not good, it’s very easy for them to stick together due to pressure from one another during tightening, so they can no longer be unscrewed. b. Make reasonable optimizations in the use of materials. The same material, such as 304, can be processed through various cold working methods to produce billets with different nominal tensile strengths (σb, N/mm*mm), which can then be used to manufacture screws and nuts for use together. Due to the significant difference in their strengths, they can effectively prevent from engaging with each other. c. Apply molybdenum disulfide, copper-based high-temperature anti-galling agents, etc., to the contact surface. If used for a long time, especially in high-temperature environments, the stainless steel material is prone to high-temperature creep, which can cause the components to stick together; therefore, it is essential to apply a coating.

The second point on the third floor seems a bit impractical, and the third point doesn’t have much effect; I’ve tried it before, but thanks so much anyway!

Reply: 2# Wen Bing’s answer is really excellent! ! But it seems like it’s all at the theoretical level! Could you tell me what to do in real life when such a situation actually occurs? Should we consider it in advance? Do all compressed bolts and nuts experience locking? What should be done if this has already happened? ? Is it to replace the bolts directly? ?

Currently, our approach is to use A2-70 for the studs and A2-50 for the nuts; it seems that this gives better results. There’s not much that can be done either.

If bolt and nut locking has occurred, these components should be replaced directly, as the threads are usually damaged once locking takes place and can no longer be used. For the replacement bolts and nuts, if a high tightening force is required, the A193/A194 B8M CL.2 series can be used; the material will perform better after being hardened. However, it is necessary to pay attention to the maximum torque that can be handled according to the relevant specifications when using it; it is best to use a torque wrench with display functions for tightening. Using flat washers between the plane where the bolt and nut make contact with the workpiece can be very effective in preventing locking.

I’ve encountered this situation before; lubricant is often used when tightening things, I can’t remember what it’s called exactly! We removed the bolt and nut lock, re-tapped the thread, applied sealant and wrapped it with PTFE tape before tightening them back in. There were no issues during pressure testing, but I’m not sure if it meets the specifications! Hehe

This happens more easily with stainless steel than with carbon steel; when the threads are tightened too much, they become deformed. If the tooth spacing is deformed, you won’t be able to get out

It only shows that the overall quality in China is declining; this wouldn’t have been the case 20 years ago – there’s been a significant drop!

Once stainless steel bolt connections are tightened, there’s a roughly 50% chance that they will become stuck and cannot be loosened; in such cases, the bolts have to be cut off. This is related to the strength of the studs and nuts, and the approach used on the 6th floor is viable! It really works in practical use!