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Technology and development of cutter brazing

Coalcutters and roadheaders break rocks by picks, and most of the machine’s power is also consumed by picks. Due to the crushing mechanism, when the pick is cutting, the reaction force of coal rock makes the pick bear a strong impact load. At the same time, during the cutting process, violent friction must occur between the pick and the coal. If the coal contains high-abrasive materials, the friction will cause the pick to generate extremely high temperatures. Picks work under complex and changing working conditions, and are the components with the largest loss on the shearers and roadheaders, which have a great influence on the cost per ton of coal and the cost per meter. The failure modes of picks are mainly alloy head drop, chipping, wear, and bending and breaking of the shank. Among them, the alloy head drop is the most common form of damage. Therefore, the brazing quality of picks is highly valued. In our pick production, brazing mostly uses high and medium frequency induction or gas flame heating. Both of these process methods require the operator to have a high technical level and proficiency in operation. The operator has a high labor intensity and a harsh working environment. The brazing quality of the pick is not easy to ensure and the production efficiency is low. In addition, these two processes are carried out in air, which inevitably exposes the pick to the hazards of oxidation and decarburization. To this end, this article discusses and discusses another method of pick brazing in pick furnace brazing.

1. Characteristics of brazing in furnace

Brazing in the furnace is a production method that uses metallurgical bonding to connect the parts in the small assembly. It uses non-ferrous metal solder as the bonding material, and the furnace as the heat source. Brazing in the furnace can only be carried out by placing the brazing material on the joint before brazing and keeping the brazing material position unchanged during the brazing process. The characteristics of brazing in the furnace are as follows.

1.1 Prevent oxidation and decarburization of picks

In order to prevent the oxidation and decarburization of steel during brazing and cooling, brazing in the furnace can use a suitable atmosphere in the brazing room and cooling room of the furnace. Appropriate brazing atmosphere can also make the molten copper brazing material wet the joint surface properly without flux. The protective atmosphere used for brazing is mainly rich in exothermic atmosphere, endothermic atmosphere and some nitrogen-based atmospheres. These atmospheres have a good ability to prevent oxidation. According to the need, the carbon potential of the atmosphere can be controlled between 011% and 012%. This range of carbon potential is fully adapted to the pick body steel.

1.2 Better economy

Generally speaking, the weight of the pick is less than 116kg, which is very suitable for brazing in the furnace. The brazing in the pick-tooth furnace can use a batch furnace or a continuous furnace, which can perform a large amount of brazing at a low unit cost. Therefore, brazing in the furnace is the most effective and economical in mass production. It also has good adaptability to occasional small batch production, especially when the brazing of the pick is combined with the heat treatment of the pick, the most economical effect can be achieved.

1.3 Brazing quality is stable and reliable

Cut brazing equipment temperature control, atmosphere supply and operation, mostly use computer digital monitoring, its brazing quality and stability is fully guaranteed by the advanced equipment. The brazing quality of traditional brazing methods such as high-frequency induction and gas flame heating depends too much on the technical level and proficiency of operators. In addition, due to the high degree of automation of the brazing furnace, the labor intensity of the operator is greatly reduced, and the working environment is greatly improved.

2 Operation process

2.1 Cleaning: When the pick is machined, the surface is stained with oil, or the surface will be rusted due to storage and other reasons after the machining is completed. In order to ensure the welding is firm, the surface must be cleaned before brazing, especially the brazing surface. General oil stains can be cleaned with aviation gasoline and acetone; when there is rust, mechanical rusting or pickling can only be used to remove rust. If it is cleaned with pickling, the pickled surface must be cleaned with water and dried. The carbide head and brazing material also need to be cleaned. If there is oxidation on the surface of the solder, pickling treatment should also be carried out to avoid affecting the melting point temperature of the solder and the fluidity of the solder.

2.2 Assembly and clamping: The components that are brazed in the furnace are generally designed to be assembled by press-fitting, flaring or other methods without using fixtures. However, since the joint between the pick body and the cemented carbide head must have a weld gap, special fixtures must be designed to keep the pick upright and stable. When assembling, put the cleaned brazing material into the joint hole of the pick body, and then put the cemented carbide into the hole, and the assembled assembly is fixed into the furnace with fixture. The design of the fixture for brazing in the pick furnace should be considered: ¹ strong, stable, and not easy to overturn due to small vibration; º select materials that are heated multiple times without deformation; ; ¼ should consider applying a P force on the cemented carbide, so that when the solder melts, the cemented carbide can smoothly reach the predetermined position.

2.3 Brazing: The pick assembly installed in the fixture is fed into the brazing chamber of the furnace and heated in an appropriate protective atmosphere. When the temperature of the pick assembly exceeds the melting point of the brazing material, the brazing material wets and diffuses in the cutting The bottom of the tooth body and the cemented carbide enter the joint under the action of capillary. In the gap between the pick body and cemented carbide. In forming a bond, the brazing material forms a solid melt with the unmelted steel and cemented carbide surface.

2.4 Cooling: After the pick is brazed, move it into the cooling chamber of the furnace and cool it in a protective atmosphere (usually the same as the atmosphere in the brazing chamber) until the pick is cooled to a sufficiently low temperature (even if it is in air When the surface of the pick is oxidized, the pick is moved out of the cooling chamber. If the pick body needs to be heat treated, the combination of cooling after brazing and heat treatment cooling of the pick body should be considered as much as possible.

3 Brazing material and weld gap

3.1 Selection of brazing material For the selection of brazing material in the pick furnace, the following should be considered:

(1) has good wettability, at the brazing temperature, it is easy to fill the gap of the brazing seam, that is, the brazing material is required to be suitable for both steel and cemented carbide materials to form a good brazed joint;

(2) Meet the mechanical properties of the pick, that is, the shear strength of the formed joint weld should be 180 MPa, and have a certain toughness and meet the requirements of withstanding higher working temperature;

(3) Satisfy the brazing process and brazing performance used, and have a suitable melting point. The brazing temperature is required to be lower than 930e to prevent the pick body from growing its steel structure grains at too high temperature and affecting the pick The toughness of the body, in addition, too high brazing temperature is also easy to cause damage to the cemented carbide, and also has an impact on the life of the brazing furnace;

(4) cost factors. The price of brazing material varies greatly, the cost of copper brazing material is lower, and the cost of silver brazing material is higher, generally 40 ~ 50 times the price of copper solder of the same volume. Comprehensive consideration from the above four aspects, if there are no special requirements, the brazing material in the pick furnace should choose copper brazing material as much as possible. The main advantages of copper solder are: low cost and high welding strength. The disadvantages are: the temperature of the brazing point is relatively high, generally above 900e, and the weld stress is large.

The advantages of silver solder are: good process performance, low melting point, good wettability, ability to fill gaps, good strength and plasticity.

The disadvantages are: high price, low working temperature of brazed joints, etc.

At present, better pick brazing copper-manganese-nickel solder.

3.2 Weld gap gap The size of the weld gap is the key factor affecting the density of the weld seam and the strength of the weld seam. The gap is too small, which prevents the brazing material from flowing in. So that the solder can not fill the gap. The brazing of picks is the brazing of dissimilar materials of steel and cemented carbide.It is considered that the linear expansion coefficient of cemented carbide is smaller than that of steel. In the case of HL106 brazing solder, the gap between the pick brazing joints is generally 0.105 ~ 0.15mm.In addition, in order to ensure that the weld gap around the cemented carbide is uniform, the lower end of the cemented carbide can be designed into a truncated cone shape in order to use the pick body and the carbide The two cone surfaces produce a self-centering effect.

4 Conclusion

To sum up, brazing in the furnace of the pick is due to its high production efficiency and the quality of the brazed joint is stable.It can be protected by the atmosphere during heating, brazing and cooling in the furnace, so that the pick can avoid oxidation and decarbonization . Therefore, the brazing process in the pick-tooth furnace will be more and more commonly used.

Selection of brazing furnace
Brazing is a very important step in the manufacturing process of picks. The quality of brazing directly determines the quality, wear resistance, hardness and other properties of the product.

Brazing in the atmosphere furnace, by filling the protective gas to exhaust the gas inside the brazing furnace, can effectively protect the product from oxidation.

Vacuum brazing in a vacuum brazing furnace. The vacuum furnace evacuates the heating cavity before heating, which can reach a high vacuum of 10-2-10-3pa. At this time, the brazing environment is very guaranteed to ensure the quality of the product brazing. , You can get higher performance quality.

As a professional vacuum furnace manufacturer, SIMUWU has 20 years of production experience. Vacuum brazing furnace is the main research and production field of SIMUWU. It has established good cooperative relations with many countries in the world. SIMUWU vacuum brazing furnace is aimed at Vacuum brazing of various products can be customized to meet every key point in the user’s product manufacturing process.