Reasons For Bolt Damage

During the production of bolts, in order to ensure that they can be matched with the nuts of all standard parts manufacturers, it is necessary to set a tolerance zone for the bolts. Therefore, relevant standards clearly specify the limit dimensions of bolts, including the minimum and maximum values, and the range between them is the tolerance range. As long as the size of a bolt is within this tolerance range, its versatility in the circulation process can be guaranteed, and there is no need to worry that the bolts cannot be used due to differences in manufacturers.

After the production of bolts is completed, they usually need to be subjected to electroplating or hot-dip plating treatment. This process may change the original tolerance range. Therefore, to determine whether the quality of bolts meets the standard, inspection and judgment should be carried out before electroplating. There are also corresponding implementation standards for electro-galvanizing and hot-dip galvanizing treatments, namely the GB/T 3934 document. This standard stipulates that the size of bolts after electro-galvanizing shall not exceed their limit dimensions. Although it is not possible to absolutely ensure that the thread can be accurately measured with a go/no-go gauge, the actual value must be below the limit dimension. In this way, it can be ensured that the bolts can be smoothly rotated and installed during practical applications.

In daily production, we often find that bolts are damaged, mainly manifested as thread failure or bolt fracture. So, why do seemingly sturdy iron bolts have these problems? What are the real reasons for their damage?

Thread Loosening is the Primary Factor for Bolt Damage

When the thread of a bolt loosens, the vibration generated by the equipment during operation will cause the bolt to bear an external force several times that when it is tightened. The kinetic energy generated at this time can be expressed by . This huge shaking force caused by loosening will lead to continuous collisions between the bolt and the equipment, thereby damaging the thread of the bolt. In severe cases, the head of the bolt will break directly. If there are adjustable rotating parts such as wheels on the equipment, the broken bolt may get stuck in the wheel. In such a situation, the equipment is very likely to be damaged.

This damage process is usually caused by a huge change in the axial force of the bolt, which directly breaks the bolt, and this is a relatively common situation. To prevent such accidents, in a vibrating environment, anti-loosening thread products are usually preferred, and nylon lock nuts can also be used in combination. A customer of Jinrui manufactures submersible pumps. Since the submersible pumps are always in a vibrating state and operate underwater, when the bolts loosen, the staff cannot discover the problem in a timely manner and stop the pump to replace the bolts. Therefore, in this industry, all-metal lock nuts are widely used in combination with bolts. When installing large-scale pumps, double-lap self-locking washers are also equipped to enhance their firmness and reliability.

Types of Bolts That Cannot Be Used

Overall, when the following problems occur with bolts, they cannot be used any longer:

Appearance Rust: If there are abnormal yellow or black spots on the surface of the bolt, do not underestimate them. Once a corrosion point appears, comprehensive corrosion may follow soon. After installing a bolt with rust spots, the entire bolt will rust completely in a short time. A rusted bolt is likely to cause the thread to lock, and subsequent disassembly and replacement will become extremely troublesome.

Thread Damage: During the transportation of bolts, the threads are prone to be damaged by bumps. If thread damage is found, the bolt cannot be used.

Thread Eccentricity: The situation where the thread is not centered is a serious quality problem and must be paid great attention to.

Inconsistent Material Grade: This is the most important point to pay attention to. Many bolts break during use, but no cause can be found. The appearance of the bolts and the installation meet the specification requirements. Eventually, it is found that the material performance of the used bolts is inconsistent with that required in the design.