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Design of Heating Chamber of High Temperature Vacuum Brazing Furnace
Brazing is a welding technology that uses a solder with a lower melting temperature than the base metal, adopts an operating temperature lower than the solidus of the busbar and higher than the liquidus of the solder, and connects the base metals together through the molten solder.
The vacuum brazing furnace is a heating equipment that uses resistance heat as a heat source for vacuum brazing. The vacuum brazing furnace heats evenly, the deformation of the weldment is small, no flux is required, and no cleaning is required after welding. The quality of the brazed products is high and can be easily brazed. It has been widely used in aerospace, aviation, automobile, refrigeration, electronics and other fields.
1 Improve the background
We discovered the problem of insufficient temperature during a process. The brazing process is briefly described as follows:
(1) Preparations before welding: remove the surface oxide scale and degreasing and cleaning (sandpaper).
(2) Parts assembly and positioning.
(3) Filling solder: CO50NiCrWB.
(4) Selection of process parameters: the cold vacuum degree is 8×10-3Pa, the working vacuum degree is 1×10-2Pa, and the melting point of the solder is 1087℃~1149℃. The specific temperature requirements are as follows: at a speed of 350℃/h Raised to 350 °C ± 10 °C, hold for 20 min; raised to 1 000 °C + 10 °C at a rate of 600 °C/h, held for 30 min; raised to 1180 °C ± 10 °C at a speed of 600 °C/h, held for 15 min~ 20 min; filled with argon, cooled to 100 °C, opened the furnace and reclaimed the material.
According to this, the process is soldered, and it is found that the solder is not completely melted when the furnace is opened. After repeated research on the brazing process, it is found that in order to obtain a good brazed joint in vacuum brazing, the following issues must be paid attention to: First, the brazing temperature and holding time. The brazing temperature is a very important factor in brazing, which is mainly It is selected according to the melting point composition, shape, joint form, part size and brazing space position of the solder. Generally, increasing the brazing temperature is beneficial to improve the wettability of the solder and the degree of interaction between the solder and the base metal, so it is beneficial to obtain a solder joint with rounded corners that is uniform, smooth and firmly bonded. Second, the holding time is also an important factor affecting the quality of vacuum brazing. The purpose of holding the heat is to make the brazing filler metal flow sufficiently, so that the brazing filler metal and the base metal can have a sufficient degree of mutual diffusion to enhance the bonding strength of the joint. The holding time is mainly determined according to the size, quantity and solder composition of the workpiece. Generally, when the number of large workpieces and workpieces is large, the holding time should be longer, but the holding time should not be too long to avoid the loss of solder. In addition, in the vacuum state, the temperature of the heated workpiece lags behind the furnace temperature, so the determination of the holding time cannot be ignored.
According to the analysis, due to the perennial use of the equipment, the phenomenon of heat leakage occurs, and the constant temperature of the workpiece is not enough, resulting in the failure of brazing. It can be seen that the temperature index has become the focus we need to overcome, and the heating chamber is the core structure to maintain the temperature. Therefore, we have systematically researched and summarized the heating chamber from theoretical calculation to practical experience on how to reach a high temperature of 1300℃.
2 The overall structure of the equipment
3 Heating chamber design
3.1 Working principle
The brazing heating chamber is located in the vacuum chamber, and the workpiece to be processed is placed on the support frame in the heating chamber. The controlled low-voltage and high-current alternating current passes through the electrodes to make the heating element generate resistance heat, and the reflection effect of the radiation screen is used to concentrate the heat and make the heating The room temperature rises, and the temperature is controlled by the automatic temperature control system to make the temperature reach the set value. A uniform temperature environment is formed in the heating room, and the welding components are heated. According to the user’s brazing process requirements, the process can be completed automatically or manually according to the program.
3.2 Main structure
The heating chamber is placed in the furnace and consists of a jacket and an inner liner. The jacket is designed to form a strong cold air duct, and the bottom is equipped with 4 rollers. The entire heating chamber can move along the front and rear guide rails in the furnace shell, so that the heating chamber can be pulled out for maintenance.
3.3 Liner design
The interior of the vehicle shooting screen is composed of a door screen, a side screen and a bottom screen. In order to ensure that the temperature door screen and the side screen and the bottom screen and the side screen are connected by steps. If the outer diameter of each layer of the two screens is flush with the inner diameter of the side screen, a heat leakage area will be formed at the junction; if the outer diameter of each layer of the two screens is flush with the outer diameter of the side screen, the screens will deform at high temperature , squeeze each other, and a serious heat leakage area will be formed at the junction. At the same time, it is necessary to leave an appropriate distance between the two screens and the side screen for the extension space during high temperature deformation. It has been proved by several equipments that this method greatly improves the thermal insulation performance of the body.
During brazing, the workpiece is often heated as a whole or evenly over a large area around the brazing, so the relative deformation of the workpiece and the residual stress of the brazed joint are much smaller than those of welding, which is easy to ensure the precise size of the workpiece. In addition, as long as the brazing conditions are appropriately changed, it is also conducive to the simultaneous or connection welding of multiple welds and large batches of workpieces.
Brazing is a precise connection method in today’s high technology, which is widely used in military and civil industries such as aerospace, aviation, automobile, chemical industry, machinery, and electronics. After repeated study and design of temperature, the equipment not only achieves the high temperature index required by customers, but also does not affect the cooling speed of the workpiece and improves the overall performance. Good temperature conditions can satisfy the brazing and process of workpieces and improve the yield of weldments. In the long run, the excellent quality of equipment can undoubtedly bring great advertising effect to our products, and its potential value is unlimited.
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