1 Introduction Vacuum brazing is an advanced process that connects parts without the use of flux in a vacuum atmosphere. It can braze materials and structures that are difficult to connect together, resulting in brazed joints with dense, excellent mechanical and corrosion resistance. Due to brazing under vacuum conditions, oxidation, carbonization, decarburization, and contamination deterioration do not occur; and in brazing, the overall heat distribution of the part is uniform and the thermal stress is small, and the deformation amount can be controlled to a minimum, which is particularly suitable. In the brazing of precision products, vacuum brazing has become an indispensable means of production in cutting-edge industries such as aviation, aerospace, atomic energy, and electrical instruments.
The traditional manual control system severely restricts the quality and work efficiency of vacuum brazing. Therefore, it is imperative to introduce an automatic control system. Taking into account the actual needs of vacuum brazing equipment and processes, PLC is used as a vacuum furnace control system. core. In order to further enhance the applicable object and economy of the vacuum furnace, the designed vacuum furnace system has a high-temperature and medium-temperature dual-chamber system, which can work independently and can fully utilize the performance of the shared equipment.
2 control system vacuum furnace is the necessary equipment to achieve the vacuum brazing process, the merits of its work performance, directly affect the quality of brazing products, the vacuum furnace consists of high and medium greenhouses consisting of two chamber furnace should have the following control Conditions: automatic and manual control of the vacuum unit, charge and bleed system, and heating system.
2.1 Vacuum furnace system The simple vacuum furnace system W is mainly composed of a vacuum system, a heating system and related control equipment.
The vacuum system consists of a mechanical pump, a diffusion pump, a main line valve, a bypass valve, and a high vacuum flapper valve. The mechanical pump is a rough vacuum device, its power source is a three-phase AC motor, and the high vacuum oil diffusion pump is a high vacuum device. High-vacuum required suction is accomplished by the role of pre-stage mechanical pump, oil diffusion pump and electric furnace heating. Work, all controlled by contactors.
The heating system consists of a heating power supply and a heating element. The heating power supply uses a magnetic voltage regulator and uses a DC excitation power supply to realize a smooth stepless voltage regulation without contact load. The DC excitation power is controlled by a power regulator, and the power regulator is used. The temperature controller detects the difference between the current value of the furnace temperature and the set value through the thermocouple. After the PID operation, the 420 mA DC signal is output to control the magnetic saturation voltage in the magnetic voltage regulator, and then set by the temperature controller. The temperature control curve automatically controls the heating current and temperature.
2.2 Overview of Vacuum Brazing Furnace Vacuum brazing furnace is an electromechanical integration device for brazing in a vacuum atmosphere. It consists of a vacuum system and a heating system. The vacuum system is used to meet the vacuum degree required by the vacuum brazing process. When the specified value is reached, a vacuum brazing heating process may be performed; the heating system heats the part and melts the brazing material to complete the brazing of the part; the process is automatically controlled by a temperature controller; after the heating process is completed, cooling is performed; When the temperature drops to the furnace temperature, it is released and the brazing of the part is completed.
2.3 Process requirements The furnace type of the furnace is horizontal and cold walls. The vacuum system adopts mechanical pump-oil diffusion pump two-stage pumping. The pre-stage of the diffusion pump is equipped with an oil dust separator. The vacuum system can realize the automatic/manual pumping function. The meter displays the vacuum degree and performs manual or automatic according to the vacuum degree requirement. Control the working procedure of the brazing process; use the temperature controller, thermocouple and trigger to realize automatic microcomputer program control and manual control, digital display, automatic recording, automatic alarm for over-temperature, water cut, and burnout, high-temperature and medium-temperature greenhouses For vacuum cooling.
2.4 Overall design of the electronic control system The vacuum furnace system's requirements for the safety, quality, efficiency, and reliability of the vacuum brazing work are fully demonstrated and the equipment is debugged. The principle of the electronic control system is as shown. The electronic control system consists of four parts: the control cabinet, the operation display, the detection element and the actuator. The control cabinet is equipped with programmable logic controllers, contactors, fuses, relays, controlled rectifiers and other components. The operation display panel is equipped with various operation buttons, indicator lights, temperature controllers, triggers, recorders, vacuum gauges, voltmeters and ammeters. Vacuum furnace system detection components are mainly thermocouples, vacuum gauges and ionization gauges and pressure gauges.
2.5 Main equipment selection resistance and ionization combined vacuum gauge; Temperature controller adopts FP21 of Japan Island Power; PLC selects ORPM CPM1A-40CDR-A type CPU and CPM1A-20EDR external expansion I/O; CPU unit has 24 inputs and The output of the 16-point relay, the expansion unit has 12 inputs and 8 outputs.
3 Control System Procedure To ensure the performance and quality of the vacuum brazed parts, the core is to provide the temperature and vacuum according to the brazing process. Not only do you need to do a full job from the hardware, PLC software design work also has a very important role. For this reason, the PLC program design focuses on the control of the brazing process around the temperature and vacuum, in order to improve the work efficiency. The automatic working mode is the main method. In order to facilitate the timely processing of debugging and special situations, a manual work mode is provided. The two working modes can realize non-disruptive switching according to the current process state.
3.1 Preparation work before brazing Before brazing the parts, the requirements of the process parameters of the part are firstly defined, which lays a necessary foundation for the preparation of the required temperature control curve and related parameters for the temperature controller; secondly, the equipment for the vacuum furnace Perform necessary inspections to ensure safety and reliability, good equipment, and meet the brazing conditions; Thirdly, after the temperature controller in the control cabinet is powered on (power indicator light is on), the process parameters and temperature control curve required for the brazing of parts are carried out. Make necessary programming work for the temperature controller; Fourth, according to the technical requirements of the parts brazing, choose the required working furnace room, that is, the high temperature room or the middle temperature room. When the PLC is started, the corresponding work room lamp is bright, and The related equipments of the two furnace chambers can be switched; Fifthly, they can be selected automatically or manually according to the operation requirements. When the PLC is started, the corresponding working mode indicator lights up.
3.2 Control program flow According to the requirements of the brazing process and the abnormal condition processing, the control program is designed based on the reliability and stability of the system work and the superiority of the brazing quality. The automatic control program flow is as shown.
Table 1 Two kinds of quenching furnace electric energy consumption record comparison table time electric energy consumption / kW * h original imported furnace domestic furnace electricity This test record total hourly average power consumption Note: two quenching furnace processing the same model, specifications with Material, and the strip can be seen from Table 1: The original imported quenching furnace consumes electricity per hour cryogenic quencher is a key component in the entire assembly line, because the strip after high temperature quenching heating 1250 * C, immediately after entering The cryogenic quencher is quenched and cooled and is extremely easy to deform. The straightness and smoothness of the inner plane of the cryogenic quencher are required to be very high. A slight deviation will cause bending deformation of the strip. Therefore, we have improved the internal structure of the cryogenic quencher so that the strip material is not easily hindered during the quenching process, thus ensuring that the strip does not deform due to quenching. The qualification rate for quenching deformation of products has increased from 70% to 95%.
Improve the structure of the cooling system, using a new rail guide support P1, the overall structure of the equipment is more reasonable, reducing the difficulty of installation and adjustment, changing the connection method of the original imported equipment components, so that the cryogenic quencher, cooling water jacket can accurately The furnace tubes are connected on the same horizontal line to ensure that the strip runs from the inlet of the quenching furnace to the outlet of the jacket cooling device on the same horizontal straight line.
The improved cooling block device adopts new materials and new technology to manufacture cooling blocks and sprays new wear-resistant materials. This not only reduces the cost, but also improves the wear resistance of the cooling block. The average service life of the cooling block increases by a factor of two.
The cooling effect of the strip after cooling by the water cooling pipe is further improved, and the technical problem that the strip cannot be cooled to room temperature before entering the tempering furnace after quenching is solved. This ensures that the metallurgical structure of the product meets technical requirements and improves quality.
Through the above improvements, the manufactured traction continuous furnace has been better applied in production. Compared with the original imported equipment, the new-type traction furnace made in China has low cost and better performance, especially the bending of the strip. Deformation problems have been well suppressed, improving production efficiency and at the same time improving product quality.
3 Conclusions The new type of domestic energy-saving traction continuous furnace is more advanced and has important significance for the heat treatment of strips.
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