Carbide Cutting Pick

1. What is a carbide cutting pick?

 

carbide cutting pick

Carbide cutting pick is one of the important tools for cutting coal and rock. The pick is composed of carbide ball teeth brazed and alloy structural steel. It is generally used for direct cutting and mining of coal by shearers, so it is also called For cemented carbide coal picks.

The alloy head of the pick is the frontmost part of the pick, which is in direct contact with the coal and rock. The pick advances and cuts in the coal seam in the way of impact and rotation, and needs to bear high-pressure stress and shear bending stress at the same time. This is a periodic and alternating impact load. During the construction process, the pick and the coal seam will also undergo intense friction to generate friction heat. Local yield, contact fatigue, corrosion, and fracture may also occur during the entire wear process. and other mechanical behaviours.

Commonly used picks adopt a special heat treatment process, which can reach 40-45 degrees, and the surface is basically free of oxidation. Brazing and heat treatment need one heating to complete, which can avoid problems such as alloy embrittlement and welding strength reduction caused by secondary heating. Avoid the phenomenon of oxidation of the brazing surface in contact with air in the traditional process, and ensure that the molten solder is in direct contact with the brazing surface. The lower end of the pick shank of road header and shearer is designed with an unloading groove, which needs to be equipped with a clip spring (also called a snap ring) to facilitate loading and unloading with the tooth seat, and to avoid partial wear caused by stagnation.

 

2. What aspects does the quality of picks depend on?

 

1) The quality of the alloy is high or low.

 

The higher the alloy quality, the better the pick quality.

 

2) The size of the alloy (usually refers to diameter mm and height mm).

 

The larger the alloy head, the higher the level of rock formation that can be impacted generally, and the lower the damage.

During the working process of the pick, since the alloy will be in constant contact with the rock formation, many parts including the pick head, alloy, and tooth body will be worn out, and in more serious cases, the alloy will also fall off. Therefore, the larger the alloy, the more materials are used in the alloy, and the less likely it is to be worn.

But the alloy is not the bigger the better, the choice of the alloy must follow the manufacturer’s suggestion, with the appropriate alloy, in order to make the pick to play the best role.

 

3) Processing technology includes welding level and quenching level.

 

Maybe you think that the alloy of the pick completely represents the quality of the pick, which is obviously wrong. If there is no advanced heat treatment process, the pick shank will break, and even the best alloy will not help. The heat treatment time, temperature, processing tools and methods, etc. during the pick processing will determine the quality of the pick.

For alloys above 25mm, if no effective welding is carried out, the alloy will also fall off. In addition, there are factors such as the shape of the alloy, which will affect the quality of the pick.

 

3. Wear-resistant layer of carbide picks

 

The wear-resistant carbide pick adopts advanced plasma pick cladding technology, and cladding a kind of wear-resistant, corrosion-resistant, and tough strengthening layer (wear-resistant layer) on the outer surface of the cone of the pick, which enhances the wear resistance of the cone Sex, to prevent the tooth head from falling off prematurely. The picks produced by plasma cladding technology also have the characteristics of no sparks when they collide with rocks and are safer to use in high-gas mines. The industry calls this kind of picks “non-spark wear-resistant picks”

 

4. Carbide pick failure

 

During the coal seam excavation process, due to the impact load, the surface is in a state of high-pressure stress, and the cemented carbide picks collapse. Due to the uncertainty of coal seam geology, the tooth head cannot maintain a complete and good contact state with the coal seam during excavation, and a certain amount of gangue is mixed in the coal seam, which will inevitably increase the number of areas with poor contact or even no contact.

Therefore, such a stress state is prone to impact fatigue and thermal fatigue cracks under the action of alternating loads. In addition, micro-defects on the surface or inside of the tooth head will also cause stress concentration and damage the carbide pick.

 

5. Why are carbide cutting picks resistant to wear and impact?

 

The pick is the main tool used for coal falling and crushing in coal mining machinery such as road headers. During the excavation process, due to the harsh working environment and the impact and friction of the pick when working, it is required The carbide pick has high corrosion resistance, wear resistance and hardness. In order to improve the service life of the pick, the current pick is generally made of hard alloy pick.

At present, the main problem of many cemented carbide tooth heads on the market is insufficient toughness. Under the action of impact load, they are easy to be brittle and cracked. How can we make the cemented carbide picks wear-resistant and impact-resistant?

In this regard, the picks of the LMM Research Center have carried out many in-depth research and development and tests on this problem. The carbide pick heads are made of tungsten carbide and cobalt powder pressed and sintered and are cylindrical, mushroom-shaped or other geometric shapes. Assemblies, brazed to the top of the tooth body. In this way, the quality and long service life of the cemented carbide picks can be guaranteed to a certain extent.

The material of the alloy, the shape and size of the alloy head and the brazing process all have a certain influence on the impact resistance of the carbide pick, so the selection of high-quality carbide picks plays a very important role in the efficiency of pick construction.

6. Optimization of carbide picks

 

According to the failure mode and the cause of the cemented carbide pick, its performance can be improved by adjusting the particle size, composition and ratio of the alloy.

First of all, the content of Co should not be too low, because it can effectively improve the thermal fatigue resistance, enhance the plasticity of the alloy, relax stress, etc. Moreover, the increase of Co content will affect the wear resistance to a certain extent. According to the hardness of the coal seam, it is generally controlled between 8% and 13%. When the texture is hard, the Co content should be increased appropriately.

The second is the selection and proportion of WC particle size. The total surface area of fine-grained WC particles decreases, the specific surface area increases, and the mean free path of Co increases, which is equivalent to increasing the Co content, which is beneficial to the improvement of alloy fracture toughness.

In order to strengthen the Co phase, it is also a relatively effective method to adopt an appropriate heat treatment process. The polymorphic transformation of Co is used to generate other phases to strengthen the face-centred cubic cobalt, so as to achieve the purpose of strengthening and toughening the carbide pick.

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