Generally speaking, the safety protection of medium frequency induction furnaces can be divided into the safety protection of furnace equipment and the safety protection of operators. This section describes only the safety measures for the device structure.
1. Cooling water system
If power supplies, induction coils, water cables, etc., all need water for cooling, so water is critical to the furnace equipment. There is a high probability of furnace equipment damage due to cooling water failure. Because the cooling devices are mostly charged bodies, such as thyristors, induction coils, water cables, etc., the conductivity of the cooling water used to directly cool these devices must be lower than the specified value, and the connecting hose must be a carbon-free hose. In addition, the inlet temperature, outlet temperature, water pressure, and flow rate of cooling water must meet the design requirements. The cooling water system of the electric furnace is equipped with various sensors to monitor the relevant parameters of cooling water. When the cooling water parameters appear abnormal, beyond the set value will alarm, or stop the operation of the equipment.
The cooling water pump station of a medium frequency electric furnace should be equipped with two main water pumps of the same specifications (one for use and one for backup) and must be equipped with an emergency cooling water system. When the main water pump cannot work due to power supply interruption, the emergency cooling water system can provide cooling for the furnace body to avoid damage to the furnace body.
2. Hydraulic system
The hydraulic system of the medium frequency coreless induction furnace is used to pour molten metal out of the furnace and to open and close the furnace cover. In order to ensure reliable operation, the electric furnace hydraulic station should be equipped with two main pumps of the same specifications (one for use and one for standby).
The inlet end of the hydraulic cylinder of the tilting furnace should be equipped with a throttle valve to prevent the furnace body from falling down suddenly due to the loss of pressure of the hydraulic system.
When the power supply is interrupted for a long time, the molten metal in the electric furnace may cool and solidify, which may damage the furnace lining. It is very dangerous to melt the metal solidified in the furnace by running the electric furnace, so the hydraulic system of the electric furnace should be equipped with an emergency system. When the power supply is interrupted, if necessary, the emergency system can be used to pour out the metal liquid in the furnace, so as not to solidify in the furnace.
3. Connect the floor drain furnace monitoring and alarm
In the operation of a coreless medium frequency induction furnace, if its lining is damaged, it will lead to furnace leakage accident. If molten metal leaks out of the lining, it can damage the insulation of the induction coil, the coil stanchions, and the yoke, and can cause serious leakage if not detected in time. If the molten metal will coil copper tube burn leakage, then the water in the tube and the molten metal contact may cause an explosion, resulting in a serious accident. Therefore, it is necessary to set up an alarm system for leakage furnace lining. At present, the best alarm system is the dc injection leakage furnace.
The center point of the secondary side of the transformer is not grounded, so the AC power supply circuit of the induction coil can be connected to a DC circuit. The molten metal in the furnace is grounded through the electrode at the bottom of the furnace, and the induction coil is connected in series with the DC power supply and the milliammeter and grounded, so that the metal liquid, the furnace lining, the coil, and the milliammeter form a DC loop. When the furnace lining is in good condition because the resistance of the furnace lining is very large, the milliammeter display value is very small; If the furnace lining condition is poor, there is molten metal infiltration into the furnace lining close to the induction coil, the resistance of the furnace lining will be reduced, the indicator value of the milliammeter becomes larger. When the current value exceeds the set value, the alarm will be issued and the main power supply will be cut off, so as to prevent the occurrence of leakage furnace accidents.
4. Automatic fault diagnosis
Modern induction furnaces are equipped with computer management systems. This system has an automatic fault diagnosis function. The system scans each setting point of the equipment, and when it finds that the parameters of the setpoint are abnormal, it will send out an alarm and display and record the fault information. Because of the speed of scanning, up to hundreds of times per minute, faults are detected in their initial state so that they do not cause serious equipment damage. Information about the failure is stored in the computer for future reference.
In addition to the above listed, there are some other safety measures, such as when the cabinet door of the intermediate frequency power supply is opened, through the mechanical chain will automatically cut off the power supply into the line; If each capacitor is equipped with a pressure switch, when the internal pressure of the capacitor exceeds the set value will alarm, and cut off the power supply, in order to prevent the capacitor due to high internal pressure and explosion.
Although all kinds of safety measures have been taken on electric furnace equipment, in order to ensure safety, there must be coordination of management system to improve the safety awareness of personnel.