Intermediate frequency induction heating equipment has a wide range of applications in areas such as heat penetration, melting, quenching, welding, etc. However, due to the high power of the equipment, electronic components are prone to failure due to overheating. So what are the maintenance skills of intermediate frequency induction heating equipment?
First, the system check
(1) Power supply: Use a multimeter to test whether there is electricity behind the main circuit switch (contactor) and control fuse. This will rule out the possibility of these components being disconnected.
(2) Rectifier: The rectifier uses a three-phase full-control bridge rectifier circuit, which includes six fast fuses, six thyristors, six pulse transformers, and a freewheeling diode. There is a red indicator on the fast-blow fuse. Normally, the indicator is retracted inside the housing. When the fast-blow is blown, it will pop up. Some fast-blow indicators are tighter. When the fast-blow is blown, it will get stuck inside So, for the sake of reliability, you can use a multimeter to switch on and off to test the fast melting to determine whether it is burned out.
(3) Inverter: The inverter includes four fast thyristors and four pulse transformers, which can be inspected as described above.
(4) Transformer: Each winding of each transformer should be open. Generally, the primary resistance is about tens of ohms, and the secondary pole is several ohms. It should be noted that the primary side of the intermediate frequency voltage transformer is in parallel with the load, so its resistance value is zero.
(5) Capacitors: Electric heating capacitors connected in parallel with the load may be broken down. Capacitors are generally installed in groups on capacitor racks. The group where the broken down capacitors are located should be determined before inspection. Disconnect the connection point between the busbar and the main busbar of each group of capacitors, and measure the resistance between the two busbars of each group of capacitors, which should be infinite when normal. After confirming the bad group, disconnect each electric heating capacitor and lead it to the soft copper skin of the busbar, and check the breakdown capacitors one by one. Each electric heating capacitor is composed of four cores, the shell is one pole, and the other pole is led to the end cap through four insulators. Generally, only one core is broken down, and the leads on this insulator are jumped off. The capacitor can continue to be used, and its capacity is 3/4 of the original. Another failure of the capacitor is oil leakage, which generally does not affect the use, but pay attention to fire prevention. The angle steel on which the capacitor is installed is insulated from the capacitor frame. If the insulation is broken, the main circuit will be grounded. You can determine the insulation status of this part by measuring the resistance between the capacitor casing lead and the capacitor frame.
2. Overhaul of abnormal work after startup
Through the inspections listed above, failures that cannot be started at all can be basically eliminated. After starting, it works abnormally, and generally manifests in the following aspects:
(1) Phase loss of the rectifier: The fault is manifested as abnormal sound during operation, the maximum output voltage does not rise to the rated value, and the strange noise of the power cabinet becomes louder. At this time, the output voltage can be reduced to about 200V. The output voltage waveform (the oscilloscope should be placed on the power supply synchronization), the input voltage waveform has six waveforms per cycle under normal conditions, and two in the absence of phase. This fault is usually caused by a thyristor of the rectifier that has no trigger pulse or trigger non-conduction. At this time, you should first look at the gate pulses of the six rectifier thyristors using an oscilloscope. Take a look at each gate resistor and replace the thyristor that is not open or has a particularly large gate resistance.
(2) Induction coil failure: The induction coil is a load of an intermediate frequency power supply. It is made of a square copper tube with a wall thickness of 3 to 5 mm. Its common faults are as follows: a. Water leakage in the induction coil, which may cause ignition between the turns of the coil, and must be repaired in time to run. b. The molten steel sticks to the induction coil. The steel slag is hot and red, which will cause the copper tube to burn through. It must be removed in time. c. Inter-turn short circuit of induction coil, this kind of fault is especially easy to happen on small intermediate frequency induction furnace, because the furnace is small, it will be deformed by the thermal stress during work, resulting in short-circuit between turns. When high.