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Vacuum cycle melting furnace

1. main technical indicators of periodic vacuum melting furnace

1.1 capacity (steel gauge): 0.1t
 1.2 maximum working temperature: 1700 C
 1.3 limit vacuum: 6.6 x 10-2Pa
 1.4 working vacuum: 6.6 x 10-1Pa
 1.5 pressure rise rate (leakage): 0.06Pa/min
 1.6 input power supply voltage: 380V + 10%
 1.7 input phase: 3 phase
 1.8 input power frequency: 50Hz
 1.9 output intermediate frequency voltage: 250V - 375V
 1.10 output if frequency: 2000Hz
 1.11 maximum if power: 200kW
 1.12 cooling water volume: 16m3/h
 1.13 total weight of equipment: 8t (calculated value)

Working principle of 2. cycle vacuum melting furnace

Vacuum induction furnace is a new type of vacuum smelting equipment heated by medium frequency induction. There is a spiral tube coil inside the furnace. When the coil is connected with medium frequency current, alternating magnetic field is produced. Under the action of magnetic field, metal burden induces electric potential and produces annular current. Under the action of magnetic field, this current concentrates on the outer layer of metal burden (the so-called skin effect), so that the outer metal burden has a high current density, thus producing a concentrated and powerful thermal effect, which has caused the metal burden to be heated. Or melts.


Vacuum cycle melting furnace


Structure, performance and advantages of 3. cycle vacuum melting furnace

3.1 advantages
 The vacuum induction furnace has the following advantages:
 3.1.
 3.1.2 No matter how tilted the crucible is, the connection between the electrode and the inductor coil will not be interrupted, so the bridge material can be melted by tilting the crucible without tamping rods, and the casting can be carried out electrically to maintain the required temperature for casting.
 3.1.3 A discharge check valve (air inlet valve) is provided, which can be fed into inert or chemical gases to protect the molten metal from oxidation.
 3.1.4 Due to the Self-Stirring property of induction heating, the melted alloy is homogeneous without segregation, and the degassing rate is accelerated, so that the melted alloy is homogeneous and the gas content is low.
 3.1.5 The melting time of steel is about 20-30 minutes under the conditions of magnesium oxide, alumina and crucible.
 3.1.6 accuracy is high:
 Controlling melting time, temperature and composition is very accurate, making the work highly accurate.
 3.1.7 is widely applicable.
 Iron base, nickel base and non-ferrous metals can meet the requirements of smelting.
 3.1.8 Easy to use, good working conditions, complete sets of power supply, furnace body and accessories, etc., can be smelted at any time. When the toxic metal is melted, the toxic gas can be excluded to the outside through a vacuum unit for non-pollution treatment.
 The vacuum time of 3.1.9 vacuum unit is short:
 From the atmosphere to the range of 6.6 *10-2 Pa, it has a large pumping capacity and can maintain a stable limiting vacuum.
 3.1.10 is safe and reliable:
 For example, if the intermediate frequency power supply overload, induction coil, water-cooled cable, diffusion pump, capacitor, SCR power supply and other water-cut, all have protective devices (through water pressure or water temperature to protect the alarm).
 In view of the above situation, 100 kg vacuum induction furnace can meet the general requirements of vacuum smelting in terms of operation, production efficiency and technology.
 3.2 structural features:
 3.2.1 furnace body (i.e. melting chamber):
 The melting chamber of vacuum induction furnace is a vertical container with double walls. The inner wall of the vacuum melting chamber is carefully polished and the surface is smooth. Therefore, the volatile metal and dirt produced by gasification in the melting chamber can be removed by simple mechanical cleaning method. This will not only shorten the pumping time, but also achieve a good vacuum limit. The rear part of the vacuum melting chamber is an exhaust port, and the electrode can still be energized when the crucible is poured. The exhaust port has shutters. This is generally sufficient to prevent metal from penetrating into a high vacuum pump because the metal vapor diffuses directly in the vacuum and then adheres to the cold wall of the vacuum.
 3.2.2 furnace door:
 A square furnace door is arranged on the furnace body, and a shell insulation heating interface is arranged on the furnace door, and a square furnace door is added to facilitate the clamping and removal of the shell, so as to facilitate maintenance.
 3.2.3 furnace lid:
 The furnace cover is equipped with two inspection holes and double-layer quartz insulated glass, which can observe the effective positions in the furnace. At the same time, it can be used for two people to observe the smelting situation and there is a self-brushing mechanism under the hole glass. To clean up the dirt on the glass, the opening of the furnace cover is lifted by a cylinder, which can be opened and closed easily.
 3.2.4 charging, temperature measurement, sampling, organization:
 The vacuum induction melting furnace is equipped with alloy feeding, on-line temperature measurement and sampling mechanism (user selections).
 3.2.5 induction coil:
 Induction coil is a flat round copper tube, sprayed insulation layer, through their peripheral insulation plate to fix the position, induction coil and the connection between the electrode is connected by two nuts, easy to disassemble, both to ensure good conductivity, but also to ensure reliable vacuum sealing.
 3.2.6 rotary electrode and tilting mechanism:
 The rotating shaft is a coaxial power supply mode. The water-cooled assembly structure saves the user from the hardship that the epoxy resin casting electrode can not maintain by itself and can be disassembled by itself. Hydraulic tilt furnace is developed by our Institute of hydraulic valve control (bi-directional proportional valve).
 3.2.7 vacuum unit:
 In order to have a good working vacuum in the whole smelting process, the unit is configured as one KT-600 diffusion pump, one ZJ-600 Roots pump and one H-150 slide valve pump.
 3.2.8 has two inspection windows on the furnace lid to inspect the melting condition in the melting room.
 3.2.9 vacuum measurement:
 It is suggested to use thermocouple ionization combined vacuum gauge. According to the production process requirements, vacuum pressure gauge is also installed on the vacuum unit. The gauge pressure is used to observe the coarse vacuum degree in the furnace or the pressure of protective gas.
 3.2.10 temperature measuring device:
 There is a temperature measuring device on the top of the furnace cover. When the temperature is needed, the thermocouple and thermocouple protection tube (usually cermet) can be installed. When the temperature is measured, the thermocouple is inserted into the crucible metal liquid only by turning the handle. There is a rack operating mechanism to stop the thermocouple at the liquid level, to read the temperature values from the digital meter, and to measure the temperature through the viewing window using an optical thermometer or a far infrared radiation thermometer.
 3.2.11 power supply system:
 The power supply system adopts coaxial water cooling, with small braid power input, high efficiency and convenient disassembly and assembly.

4 commissioning and operation

4.1 inspection before commissioning
 4.1.1 SCR medium frequency power supply check, see the intermediate frequency power supply manual.
 4.1.2 After the vacuum unit is connected with the power supply of the H-150 rotary vane vacuum pump, check whether the rotation direction of the pump conforms to the direction indicated by the arrow on the pump cover. If the rotation direction is opposite, the phase sequence of the three-phase power supply can be changed. The roots should be checked in the same way.
 4.1.3 water cooling system:
 Open the main water valve and each diversion valve, water flow shows whether the branch flow is smooth, cooling water pipe must be connected according to the water cooling system diagram.
 4.2 operation
 Inspection before 4.2.1 operation:
 4.2.1.
 4.2.1.2 Check the whole water-cooling system, the water pressure should comply with 0.15-0.3 MPa pressure requirements, the total flow rate is not less than 2.5 cubic meters / hour, pay special attention to the induction coil flow;
 4.2.1.3 check whether the distribution part is complete and good, whether there is short circuit or open circuit.
 4.2.1.4 check whether the interturn distance of induction coil is short or not.
 4.2.1.5 Check the power supply voltage is stable, if the grid voltage changes more than + 15%, that should not be opened to avoid damage.
 4.3 order of operation:
 4.3.1 Before charging, the whole furnace must be inspected, such as: coil crucible, ingot mold drying, cleaning, etc., all normal after loading;
 4.3.2 Check the sealing condition of the vacuum vessel, close the container cover, check the oil standard of the slide valve pump, see if the oil quantity meets the requirements, start the slide valve pump to vacuum, open the pre-vacuum valve to pump the Z-400 oil booster pump.
 4.3.3 The pre-vacuum pump is pumped to less than 10Pa, the pre-vacuum valve is closed, the low vacuum valve is opened, and the melting chamber is pumped to less than 10Pa. At the same time, the K-400 oil booster pump cooling water valve is opened, and the power supply is turned on for preheating. Generally, after 60 minutes of heating, the oil booster pump can start to work, and the induction coil can be started to supply electricity.
 4.3.4 turn on the cooling water valves of the equipment.
 4.3.5 check the voltage regulator pointer, whether it refers to zero, according to the intermediate frequency power supply manual to start the inverter system.
 4.3.6 smelting is adjusted according to process to suitable working power (adjusting power according to process requirements).
 When adjusting intermediate frequency voltage and current, 4.3.7 should pay attention to whether the ratio of intermediate frequency voltage to DC voltage is normal.
 4.3.8 When the metal is close to melting, attention must be paid to the situation in the furnace. If it is found that the gasification of liquid metal in the furnace is more intense, the power should be reduced. The power must be adjusted according to the vacuum and furnace temperature to avoid intense gasification and splash.
 4.3.9 casting must be closely monitored when melting is finished.
 4.4 points for attention in operation:
 4.4.1 Before operation, the operator must understand the operation principle of each part through smelting practice so as to avoid personal and equipment damage accidents during operation.
 When 4.4.2 is cast in non vacuum, the operator must take protective equipment, especially the protective cover.
 4.4.3 Cooling water is important for vacuum smelting equipment. When the cooling temperature of induction coil is too high, it is easy to make the coil deform or even melt. Therefore, when the water stoppage is found (furnace temperature is 1500-1600 C), the power to induction coil and vacuum pump should be stopped first, then the vacuum valve should be closed, and the standby water tank switch should be opened. Damage equipment and affect normal work. Therefore, in the smelting process, should be checked regularly, pay attention to adjusting the amount of water, cooling water temperature should not rise more than 20 degrees Celsius;
 4.4.4 If the melting chamber is in a vacuum state, start the slide valve pump first and then open the vacuum valve to avoid pulling the valve.

5 daily maintenance and precautions

5.1 After smelting, when the melting chamber pressure is lower than 10 Pa, cooling water can be given to the furnace body, induction coil and oil booster pump, so as to avoid condensation water droplets on the furnace body and induction coil surface and affect the vacuum degree during the pumping time. After smelting, before destroying the vacuum of the melting chamber, the cooling water of the furnace body should be stopped and the outlet temperature of the induction coil should be maintained in the range of 34-50 C.
 5.2 When the melting chamber pressure is lower than 30 Pa, the oil booster pump can be used for pumping. When the pressure is higher than 30 Pa, the high vacuum valve should be closed, only the low vacuum valve should be opened, and the slide valve pump should be used for direct pumping.
 5.3 it is forbidden to destroy the vacuum of the furnace when pumping in high vacuum so that the oil booster pump is oxidized and can not work. When the oil booster pump stops working, cooling water should continue to flow, about 30 minutes to cut off the pump cooling water.
 5.4 during the melting process, the slide valve pump should be operated frequently and can not be stopped. If the high vacuum pumping, can open the high vacuum valve, close the low vacuum valve, if the low vacuum pumping (only with the slide valve pump), close the high vacuum valve to open the low vacuum valve.
 5.5 The rotating sealing part of the furnace body should be properly protected, and sealing grease should be added frequently to ensure good sealing. The saturated vapor pressure of sealing oil should not exceed 1.3 * 10-5Pa at room temperature.
 5.6 As the smelting proceeds, the inner wall of the melting chamber is wetted by condensed water vapor, which wets the surface of the adsorbed gas will affect the vacuum degree, increase the vacuum time, so at any time wipe and clean wet the inner wall, is important to shorten the extraction time.

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