Design requirements of vacuum furnace

    The vacuum furnace is mainly composed of furnace body, vacuum system, heating system, power supply, explosion-proof system, control system, etc.

    The end of the furnace body of the horizontal vacuum furnace is open, and the material is fed and discharged in the horizontal direction. The bottom of the heating chamber has a bottom frame for supporting the charge. The furnace body of the vertical vacuum furnace is open at the upper end or the lower end, and the material is charged and discharged in the horizontal direction, and the material is fed in the vertical direction. The bottom of the heating chamber has a bottom frame supporting the charge.

    Before the vacuum furnace is heated, the vacuum system should be able to pump the furnace chamber to a predetermined pressure. During the heating phase, the input power should be adjustable. In the cooling stage, the charge in the heating chamber should be able to cool under different pressures and neutral gas (including inert gas, the same below).

    All materials in the heating chamber should be adapted to the atmosphere, pressure and temperature specified by the design. Various materials will not cause damage to the vacuum furnace itself under working temperature.

    The furnace shell shall adopt a double-layer water-cooled wall structure. The inner surface of the furnace shell should be smooth and clean. The inner wall can be made of anti-oxidation material, or ordinary carbon steel, but it should be polished.

    Unless otherwise required, the furnace door of the horizontal furnace can be supported on the left side of the furnace shell and open from right to left, and other structures can also be adopted. The door of the vertical furnace should be able to slide or unscrew in the horizontal direction. There should be a glass observation window on the furnace door.

    The heating area of the vacuum furnace should be surrounded by a thermal insulation screen, which should be made of various insulation materials or metal screens. The materials used should be heat-resistant and will not sag, crack or peel during work.

    The hearth should be made of materials whose performance is compatible with the working conditions of the vacuum furnace. Within the entire working temperature range of the vacuum furnace, the hearth should be able to withstand the maximum load without damage or significant deformation. The furnace shell shall be equipped with a thermocouple lead-out device for measuring the uniformity of furnace temperature.

    The water cooling system should be able to make the surface temperature rise of the furnace shell cylinder, head and furnace door not more than 35°C. The parts that are locally exceeded and accessible to the operator should be protected and warned.

    The vacuum furnace should be able to be filled with protective gas, and be equipped with necessary fans or gas nozzles, control valves and heat exchangers, etc., to circulate the gas through the charge and the furnace chamber, and evenly cool the charge.

    The vacuum system of the vacuum furnace consists of vacuum pumps, pipes, valves, cold traps, bellows, control systems, vacuum gauges, etc. An automatic valve should be installed in the system to automatically shut down when the pump suddenly stops running or a power outage occurs, and put the atmosphere into the front-stage mechanical pump cavity to prevent the vacuum pump oil from contaminating the vacuum system from backflow.

    The furnace temperature control system can be a magnetic voltage regulator or a thyristor type, with a steep drop in external characteristics. The control system should be able to limit the input power not to exceed the required maximum value.

    The vacuum furnace should be equipped with a microprocessor digital display temperature control instrument with a temperature setting accuracy of not less than 0.1% and a resolution of not less than 1℃. The meter should be equipped with an external analog sending port to connect the recorder.

    The vacuum furnace should be equipped with a digital display vacuum instrument, and its range should be from 100000 Pa to the ultimate pressure.

    Pressure and temperature recording instruments should be equipped with printed or paperless recorders.

    The vacuum furnace should be equipped with a program controller for programming, and automatically control the entire process of vacuum, heating and cooling according to the programmed program. Each vacuum furnace should be able to increase the pressure in the furnace to the required value by filling protective gas at any set temperature during heating. The heating rate and time should be adjustable. The control system should be equipped with a microprocessor or programmable controller to have the greatest control flexibility within the specified range of the vacuum furnace design. The microprocessor or programmable controller should have no less than 60 read-write random access memory program segments, and the program can be entered with the keyboard.

    In addition to the automatic control system, the vacuum furnace should also be equipped with a manual control system for use in tests or emergency situations.

    The vacuum furnace should be equipped with a floor-standing control device that is wired in the manufacturing plant (except for instruments) to install instruments and control components. There should be at least two sets of fuses or circuit breakers in the control system: one set is used for the power supply of the heating element, and the other set is used for the power supply of the pump, the motor and the control system. There should be a simulation screen to indicate the operation of the vacuum furnace. All control cables should be encapsulated in cable tray boxes or galvanized metal threaded hoses. Cables that cannot be encapsulated should be insulated with insulating materials and equipped with prominent warning signs.

    The charging and discharging system of the vacuum furnace is composed of pipelines, valves, barometers, etc. The charging and discharging system of the vacuum furnace should have two channels, one is automatic and the other is manual. In the event of a sudden power failure, protective gas can be manually filled into the furnace.

    The vacuum furnace should be equipped with an explosion-proof system to prevent excessive pressure in the furnace from damaging the furnace during charging.

(Huiputech)