What causes a broken pick?

Hello, Shandong Ed is very happy with your question. Does a pick fracture mean a broken tooth? If the tooth body of the pick is broken, there are two main reasons, on the one hand, the material is unqualified, and on the other hand, the heat treatment process is not up to standard.

If the material is unqualified, please choose a more reliable material supplier, and the requirements for pick forgings should be more stringent. If the heat treatment process is not up to standard, it is necessary to improve the production process level of picks.

At present, the automatic brazing and quenching integrated production line used by Ed is mainly used by the computer to accurately control the transmission speed and welding temperature of the picks, which can not only ensure that the welding of each pick alloy head is full without defects such as copper and bubbles, but also make each pick tooth fully heated inside and outside to achieve the required quenching temperature. After that, the picks are then put into the quenching bath by a fully automatic robot. It is important to know that the raw material, concentration ratio and quenching time of the quenching liquid in the quenching pool are the best solutions obtained by Eddid technicians after long-term trial and error.

This is the gap in the heat treatment process, which requires continuous accumulation of experience and research and development attempts.

There are many reasons, this should be combined with the machine you use and the soil quality and the ** of the broken picks, under analysis, it is not difficult to find the reason.

There are many factors for picking and breaking the shank, 1. The material is unqualified 2. The working conditions do not match, and the appropriate pick is not selected 3. The construction operation problem 4. The heat treatment process is unqualified.

Tooth fracture refers to the fracture of one or more teeth of a gear in whole or part thereof. It is usually caused by the alternating stress of the teeth exceeding the fatigue limit of the material. Sometimes, it can also be caused by a short-term overload.

Tooth fracture can be roughly divided into three situations: fatigue fracture, overload fracture and random fracture.

1. Fatigue breakage.

Fatigue fracture is a tooth fracture caused by the continuous expansion of fatigue cracks that originate at the root of the tooth. This fatigue crack often occurs in the direction of the fillet radius of the tooth root and is in the form of a thin line. The fracture of fatigue fracture is generally divided into fatigue expansion area and instantaneous fracture area.

The surface of the fatigue expansion zone is usually smooth, and a "shell" pattern of fatigue expansion traces starting from the fatigue source can often be observed. The fatigue source and its nearby areas are often "eye" in appearance, but some "eyes" are not obvious macroscopically. The surface of the instantaneous fracture area is rough and uneven.

The reason for the fatigue fracture is that the fatigue crack starting from the root fatigue source of the tooth continues to expand under the action of excessive alternating stress for many times, so that the stress on the remaining section of the tooth exceeds its limit stress. Dynamic loads in the transmission system, poor tooth contact, too small radius of tooth root fillet and tooth root surface roughness.

Excessive height, strain during hobbing, inclusions in the material, microcracks caused by heat treatment, grinding burns.

and other harmful residual stresses.

and other factors, will contribute to the fatigue fracture of gear teeth.

Countermeasures for fatigue fracture: modify the geometric parameters of the gear, reduce the surface roughness of the tooth root, carry out the correct shot peening treatment on the tooth root, increase the radius of the tooth root fillet, adjust the tooth root fillet area to reduce the bending fatigue stress of the dangerous section of the tooth root, and carry out appropriate heat treatment of the material to obtain a better metallographic structure.

Measures such as minimizing harmful residual stresses help prevent fatigue breakage.

2. Random fracture.

Random fracture refers to a fatigue fracture that is not related to the fillet section of the tooth root and can be induced by a defect or an excessively high harmful residual stress. The fracture location depends on the location of the defect or excessively high hazardous residual stress. The fracture is similar to that of a general fatigue fracture.

Random fractures are usually caused by tooth defects, pitting, or other sources of stress concentrations where too high a local stress concentration is formed. Tooth defects such as inclusions and micro-grinding cracks are propagated under alternating stress, resulting in tooth fracture. Excessive harmful residual stresses caused by improper heat treatment can cause local fractures of teeth.

Larger foreign bodies entering the meshing site can also cause low-cycle fatigue fracture of local gear teeth.

Countermeasures for random fracture: in the design, select reasonable parameters and structures; Eliminate conditions that produce excessively high local stress concentrations or excessively high harmful residual stresses; Ensure the quality of the material; Strictly control the processing process to prevent various defects and prevent hard foreign matter from entering the mesh.

1.Tungsten carbide head quality problems, domestic cemented carbide head contains graphite impurities, uneven grain distribution, cracks exist in some cemented carbide, under the action of impact load, pick cutter head is in a high stress state, when encountering hard coal and rock, high pressure stress exceeds the strength limit of cemented carbide, brittle cracking occurs. If the content of CO in the carbide is insufficient, resulting in insufficient toughness, the carbide bits are also prone to brittleness under the action of impact load.

2.The residual stress of brazing is large, the domestic picks are mostly copper-zinc brazing filler, the welding temperature reaches more than 920 degrees Celsius, the expansion coefficient between cemented carbide, brazing metal and base metal is very different, and the shrinkage degree of three materials is different when cooling, among which copper shrinkage is the largest, followed by the base metal, and the cemented carbide is the smallest, so that there must be a great tensile stress between the cemented carbide and the brazing metal, the brazing metal and the base metal, resulting in the decrease of weld strength, and the strong impact load during cutting, resulting in the embrittlement of the cemented carbide head.

1.Abrasive wear . The content of alloying elements in domestic alloys does not meet the requirements, contains graphite impurities, uneven grain distribution, pores and uneven structure, which is the main reason for the wear of cemented carbide heads; The unstable quality performance of the tooth material and the improper control of the heat treatment process are the causes of tooth wear.

2.Wear caused by low red hardness. Red hardness refers to the ability of prop materials to maintain high hardness at high temperatures.

Theoretically, cemented carbide can maintain high hardness at high temperatures of 800-1000, but due to some practical problems in the production of domestic cemented carbide, the red hardness of the picks is low. When the pick is cutting coal and rock, the surface temperature of the cutter head can reach 600-800, and its hardness is reduced by about 50%, and the softening of the material accelerates the wear of the pick.

Due to welding and shape design, the alloy head falls off.

Hello, the main reasons for pick failure are the following:

Design Reasons:In the design process, the design parameters and technical requirements of the picks need to be closely combined with the actual working conditions and use conditions of different coal mining machinery, and the picks should be designed according to the characteristics of different coal and rock, so that the design of the picks is more targeted. Special and practical scientific research and experiments are also effective methods for designing picks.

Manufacturing processing reasons:The defects in the manufacturing and processing of shearer drum picks cause the manufacturing quality of picks to fail to meet the technical requirements. Includes:

There are deviations in the chemical composition analysis, non-metallic inclusions, porosity and sand holes in the picks, etc. Due to the neglect of the requirements of the forging ratio in the forging pick, the performance of the material decreases. In the later stage of heat treatment, the quality is not up to standard, and the hardness of the pick during quenching and tempering treatment cannot meet the technical requirements specified in the design; During the quenching treatment, the hardness of the tooth surface of the pick is uneven, the hardening layer is shallow, and the quenching cracks are generated, resulting in the accumulation of large internal stress in the shelf gear.

Combined, these factors can have a direct impact on the age of the pick.

3. The selection of pick type and model is unreasonableDue to the different physical and mechanical properties of coal seams in different regions, the kinematic parameters of various different types of shearers during operation will be different, and the adaptability of the same type of pick is also very limited. If the type of pick is not selected properly in underground production, it is easy to cause the failure of the pick of the shearer drum.

5. Reasons for workers' operation:Relevant statistics show that many coal mine shearer drum pick failures are caused by improper operation by workers. For example, due to improper operation in the process of coal cutting, the pick is cut to the hard rock of the top and bottom plate, resulting in the breaking of the pick.