BOLT BROKEN?! WHY?

Buenos dias, everyone! This is Yamazato from Hanshin Neji. Until recently, I used to say "Sawadee kap!", Because I lived in Thailand a couple years ago.  My family says "You're really a chameleon, Dad" because I can change my attitude so quickly. Finally, the company's formalities are almost complete, and Hanshin Neji Mexico is now able to carry out full-scale sales activities. So, we are actively visiting customers, and when we ask them if they have any problems with screws, they often say "Bolts break a lot." Today, I would like to write about "bolts break." I hope that reading this will help you improve your manufacturing improving.

Find out why the bolt broke

First of all, the causes of broken bolts can be roughly divided into two categories: 1) poor quality of the screw itself, and 2) the screw itself is not bad but it breaks, in other words, some problem other than the quality of the screw. For 1, the problem is obvious, so let's change to a good bolt! In other words, the solution is to change to a Hanshin Neji bolt (lol).

Case1) Load was applied to the loose screw

Loose screws can cause them to break. When a screw is loose, the object being fastened is not in perfect contact with the bolt, creating a gap. The load on the bolt itself is significantly different when it is in that state compared to when it is in perfect contact. If the bolt is subjected to repeated or unexpected force in that state, it will break.

So, next we need to investigate the reason why the bolts become loose. There are many reasons for this, such as overtightening the screws, being subjected to impact, or extreme temperature differences in the usage environment.

Case2) The force is applied from an unexpected direction to the bolt.

Bolts are basically made on the assumption that they will be pulled in the axial direction, and the standards guarantee axial forces such as tensile strength. In design, it is common to try to avoid strong forces in the shear direction as much as possible, but it is also true that there are times when it is necessary to use a bolt in a way that causes forces to be applied in the shear direction. If the force applied is greater than the thread is expected to withstand, it will break.

Case3) The problem of hydrogen embrittlement

This is a problem that occurs when plating high-strength bolts. Before plating, the bolt surface is pickled to clean it, but hydrogen gets into the structure of the bolt during this process, causing a significant drop in the strength of the bolt. This can lead to a very scary phenomenon called delayed fracture, where the head will fly off later, even if there is nothing there when the bolt is tightened.

This issue seems to be overlooked all over the world, as you will often see plated 12.9 cap bolts being sold at screw shops.

How do you keep the bolt from breaking?

When thinking about how to prevent a bolt from breaking, many people think, "What if we use a stronger bolt?", and there are certainly cases where that will solve the problem. However, I think it's best to first investigate the cause of why the bolt breaks and then take appropriate measures.

- Loose screws
- In the first place, the current screws may not be designed to withstand the force.
- Repeated force may be applied to the screw for a long time.
- Maybe it's loosening due to temperature differences...
Etc.

The causes of these problems can be identified to some extent by looking at the fracture surface of the bolt. Therefore, instead of just thinking, "The bolt is broken, I'll throw it away," we would appreciate it if you could keep the broken bolt and contact Hanshin Neji.

 
At Hanshin Neji, we believe that our mission is to contribute to the improvement of customers manufacturing, so we would be happy to work with you to solve these types of problems. If you are having trouble with broken bolts, please feel free to contact us!
 

Thank you for reading this long post!