The liner is an important part of the ball mill equipment, which is related to the normal operation of the equipment. When the bolts of the liner of the ball mill break, it will seriously affect the long-term safe operation of the ball mill. Therefore, it is necessary to detect problems in time and stop grinding and replace them as soon as possible. After investigation, it is found that the downtime of the mill due to the tempering of the liner bolts of the ball mill can reach more than 8-16 hours per month, so it not only endangers production, but also causes damage to a series of equipment such as the ball mill and reducer.

Cause of bolt breakage

Let's first analyze the reasons for the breakage of the bolts on the liner of the ball mill. The reasons for the breakage of the bolts are relatively complicated. According to the information obtained, it is mainly caused by three aspects: force, material, and processing.

1. Stress condition of bolts

Most of the bolt fractures are not so obvious at the beginning, they are tiny cracks, and after a long time, they will expand layer by layer, causing the bolts to break. From the perspective of the section, there are smooth and rough areas, and there is no significant plastic deformation at the fracture, which belongs to fatigue fracture.

2. The material of the bolts

When the ball mill is running, the temperature of the barrel is generally above 100°C, and the bolts of the liner will expand due to heat. When the mill is stopped, the temperature of the barrel will drop, and the bolts will also shrink with the temperature, and the temperature in winter and summer is also different. Yes, so the material of the bolt is affected by the temperature, it is easy to become brittle, its strength will also decrease, and it will cause fracture after a long time.

3. Bolt processing method

Bolts for ball mill liners are usually forged first, and then threaded. Steel is prone to temper brittleness after forging, and there are no strict requirements for thread processing. Generally, the root of the back of the car pin is sharp. The stress concentration at the root of such a tooth type is relatively large, and fatigue cracks are easily formed, resulting in bolt fatigue training.

In summary, we found that the stress of the bolts is the main cause of the fracture, so we must pay attention to prevention. To solve the problem of bolt tempering of the ball mill liner, we must improve the fatigue resistance of the bolts.
Measures to prevent bolt breakage

Without changing the form and material of the bolt hole and lining plate of the ball mill cylinder, the following points can be used to prevent the bolt from breaking:

1. Increase the diameter of the dangerous section of the bolt. In order to avoid the thread of the dangerous section of the bolt, the bolt can be increased by 10mm, 2-3 washers are added under the bolt, and a high-pressure rubber asbestos board pad is added on the surface of the cylinder. High-pressure rubber asbestos board has high strength, high temperature resistance, and water resistance, which can not only prevent material leakage, but also have certain cushioning properties.

2. The material of the bolts must be strictly controlled. Because the internal structure of Q235-A steel is relatively pure, the interior and exterior are relatively light, so the impact toughness is good, and the measured tensile strength and yield strength are relatively high. Therefore, it is recommended to use Q235-A steel when making bolts for ball mill liners.

3. For the stress control of bolts, the fillet radius at the thread root can be increased. The stress concentration at the root of the thread has a great influence on the fatigue strength of the bolt. Increasing the fillet radius of the root can effectively reduce the stress concentration, thereby improving the fatigue strength and prolonging the service life of the bolt. In addition, the pre-tightening force of the bolts should also be controlled. If the tightening is too tight, the pre-tightening force of the bolts will be too large and the bolts will easily break. Therefore, a torque wrench should be used to control the pre-tightening force of the bolts.