Produce background
Powder plasma arc surfacing technology is a welding method that can adapt to the requirements of surfacing welding of various high-alloy high-performance materials in modern industrial production, and the dilution rate can be controlled between 5% and 15%. However, if conventional powder plasma clump welding technology is used, it is desirable to obtain a deposition rate of less than 5% and a deposition rate of less than 6 kg/h. With the development of modern industry, especially for the large-area high-performance wear-resistant surfacing, advanced high-efficiency, low-dilution powder plasma arc surfacing technology research has been carried out at home and abroad. In the 1970s, the United States studied the "high-energy plasma lump-stacking technology" with a power of 80 kW. Later, the Czech Republic developed a liquid-stable plasma lump welding equipment with a deposition rate of 56 kg/h. However, the dilution rate is still above 20%. In the 1990s, Germany successfully developed a powder plasma plasma welding technology with a deposition rate of up to 70kg/h and a dilution rate of 10% or less. The technology was also studied in the 1990s. A good result has been achieved in which the deposition rate is 15 kg/h and the dilution rate can be controlled below 1%.
2. Technical content and technical key
The traditional powder plasma clump welding technology fails to solve the contradiction between the deposition rate and the dilution rate, mainly because: First, the energy source of the molten powder and the base material in the welding process only pays attention to the heat energy from the arc, Other forms of energy, such as the kinetic energy of powder flying, are not adequately noticed. Secondly, in the past, research focused on the source of energy and neglected the study of energy consumption.
Recently, through the study of the compression characteristics of the plasma arc, the characteristics of the flame flow, and the movement and heating laws of the powder in the plasma solitary beam, the nozzle diameter, the distance at which the powder will cross the workpiece, and other factors affect the flight speed of the powder and the heat absorbed by the powder. The influence law (see Figure 1 and Figure 2), on the basis of this, the difference between the high-efficiency low-dilution powder plasma arc surfacing technology and the conventional powder plasma clercher welding technology is obtained. The key technical parameters are: welding gun nozzle The compression aperture D and the powder will intersect the workpiece to the distance L.
In order to obtain a small dilution rate, the conventional powder plasma arc surfacing technique often uses a nozzle having a larger inner diameter, even a diameter close to a free arc (4.0 to 8.0 mm), and a relatively small compression (0.8 to 0.14) weakly compressed plasma arc. However, if the influence of the flying speed of the powder on the bonding effect is considered, when the powder has a high speed and kinetic energy, the base material only needs to be in a molten state (ie, "sweating" state), and the powder is sprayed to the mother at a high speed. On the material, a good bond is produced, and the dilution ratio of the base material is extremely low. As can be seen from Figure 1, in order to achieve a high powder flight speed, it is desirable to use a small nozzle diameter and a large powder to intersect the workpiece.
In addition, as can be seen from Fig. 2, in order to reduce the amount of heat consumed by melting the unit weight of powder, in order to achieve the same amount of powder under the same current conditions, the purpose of increasing the rate of deposition can be achieved by two approaches: The nozzle pressure is like the pore size, the low powder will intersect; or the large compression pore size, the high powder will intersect. However, after the nozzle aperture is too large, the temperature of the plasma arc will decrease, the heat will be diverged, the energy will not concentrate, and the need to melt a large amount of powder cannot be satisfied. Therefore, when the current is the fixed heat input, it is advisable to take a small compression aperture and a moderate powder.
Of course, the compression aperture should not be too small, otherwise it is easy to cause double arc. At present, it is recommended that D be between 2.0 and 4.0 mm. The distance between the powder and the workpiece should not be too large. Otherwise, the stable burning of the arc is unfavorable. When it is more serious, it will be unfused or some of the powder in the weld bead will not melt. It is recommended to take 10 to 20 mm.
Secondly, in the design of the welding torch, it is necessary to pay attention to the good concentricity of the cathode and the nozzle, the phenomenon that the gun body has no water leakage, the long service life of the wearing parts, and the stable operation for a long time. At the same time, it is necessary to have a powder feeding system with a large enough powder feeding amount. Combined with reasonable surfacing specifications, it can achieve high quality, high efficiency and low dilution rate.
3. Advantages and disadvantages and application range
The high-efficiency and low-dilution powder plasma arc surfacing technology has a lower dilution rate and a deposition rate 2 to 5 times higher than the conventional method at the same welding current compared with the conventional powder plasma arc surfacing technology. (See Table 1), and the maximum surfacing height can reach 6~8mm, which is easy to achieve one surfacing success, reduce the number of surfacing layers and reduce the possibility of defects.
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