Explain in detail the causes of ignition in induction melting furnaces, common ignition phenomena and treatment methods

It is a common phenomenon that the induction melting furnace fires or arcs in the inductor during the production process, which seriously affects the equipment safety and production efficiency. The consequence is that the equipment production efficiency is reduced, the equipment is damaged, and the production accident and life and property safety are severely affected. And must therefore be given sufficient attention

First, the phenomenon of ignition in the induction melting furnace

1, both ends of the coil are lit

The copper pipe and the brace are connected at the stud side, and are distributed at both ends. The vibration at both ends of the coil causes the friction between the stud, the copper pipe and the fixed brace. The friction causes the copper shavings to fall off, causing sparks and sparks.

2, the contact surface between the iron core and the coil ignites

 At the contact surface between the iron core and the coil, the coil vibration causes wear of the gasket, which causes the coil to contact the iron core, causing a discharge phenomenon.

3, coil and water-cooled ring light

The water-cooled ring is not closed, and no net current flows, but there will be currents in the opposite direction to the upper and lower parts of the water-cooled ring. The current close to the coil and the current in the coil are in the opposite direction, creating a repulsive force, and the vibration will be greater. Strengthen fixing and insulation.

4.The lead wires and connectors are on fire

This is caused by the pulling of the water-cooled cable, and it can be fixed.

5. Water and dust cause sparks

During the operation of the induction melting furnace, moisture and dust are inevitable. How to determine the thickness of the insulation material layer and whether it is reliable? Due to the poor actual operating conditions, the method of winding mica tape is not recommended. One is not waterproof, and the other is that when the vibration problem is solved, the tape has a gap with the copper pipe and the combination with the return layer is not good. A more reliable method is to use high-temperature insulation paints with excellent abrasion resistance and temperature resistance.

Second, the cause of ignition of induction melting furnace

1, the coil insulation ability is reduced

①Insulation paint is damaged

 The insulation paint used on the surface of the intermediate frequency coil is usually a conventional insulation paint. Due to the poor working conditions of the electric furnace, it was found that the insulation paint fell off and carbonized on the site. In the later part of the furnace service, the refractory material in the furnace becomes thinner, the heat radiated to the coil increases, and the ambient temperature of the coil operation becomes high. Ordinary insulating paint has no high temperature resistance and is easily carbonized. When the electric furnace is tapped, steel slag splashes onto the coil of the induction furnace, and the insulation paint on the surface of the coil is directly damaged.

② The coil is damaged

If the molten steel leaks from the refractory due to the furnace penetration, it directly contacts the coil surface and immediately destroys the insulation layer on the coil surface. You need to repair after understanding the reason of the intermediate frequency furnace furnace penetration. And because the current insulation paint does not have high temperature resistance, it can not protect the coil. The exuded high temperature molten steel can easily burn the coil directly, and the common deep scars on the coil also prove this. The ambient atmosphere where the coils are located is highly corrosive. Ordinary insulating varnishes cannot effectively resist corrosion, easily deteriorate and fall off, and lose insulation capacity.

2, metal dust on the coil surface

The metal dust in the factory is usually serious. Because the coil surface loses the insulation ability, the dust adheres to the coil surface to form a conductor, which causes the coil short circuit and the ignition of the coil.

3, coil leakage

When the new furnace lining is baked, the water volatilizes to the coil surface, or there is a leakage of cooling water in the coil part. When the coil surface has no insulation ability, the line is turned on, causing the IF furnace coil to ignite.

III. Detection method of IF furnace ignition

1, observe the voltage and ammeter value

It is mainly to observe whether the indication values of the four small meters in the intermediate frequency furnace cabinet are normal. Among them, the rectification control voltmeter is 30V, the rectification pulse ammeter is 130 ～ 150mA, the inverter control voltmeter is 12V, and the inverter pulse ammeter is 100 ～ 120mA. The previous article also introduced the reason why the intermediate frequency voltage of the intermediate frequency furnace cannot rise. If the value is within the normal range, it proves that there is no problem in the power supply part.

2, Use a multimeter to detect the resistance value

 Use a digital multimeter to check the rectifier, inverter thyristor anode, cathode resistance, and control electrode and cathode resistance values (you don't need to remove them from the cabinet to measure, the tube radiator is still supplied with cooling water). The positive and negative resistance values of the anode and the cathode are both ∞, and the resistance values of the control electrode and the cathode are 10 to 508. In addition, check whether the fuse is blown.

3.Detect waveform with oscilloscope

Set the transfer switch SA in the check position, use an oscilloscope to check the waveforms of the rectifier and inverter trigger pulses, and check whether the IF furnace amplitude and time interval are normal. Among them, the rectification trigger pulse is double pulse, the time interval is 3.33ms; the inverter trigger pulse is a continuous pulse train, and its amplitude is generally 4-6V. Requires neat pulses and no burrs. The inspection sequence is from the thyristor control pole to the pulse transformer, and then to the rectifier board and inverter board.

4, test whether the rectifier board is normal

The inverter board can be removed, and the transfer switch is placed in the check position. Press the start button and turn the power adjustment potentiometer to see if the DC voltage can be adjusted to about 500V. If the voltage can be adjusted to 500V, the rectifier board is normal.

5. Check the capacitor charging circuit

This refers to checking the capacitor charging circuit in the IF furnace circuit during startup. The method still unplugs the inverter board and connects to the check gear. After pressing the start button, use a multimeter to measure the voltage across the capacitor cf. If it can reach about 500V, it will prove the startup. The capacitor charging circuit is normal.

The above is the introduction of the reason for the ignition of the intermediate frequency furnace. The direct reason for the ignition of the intermediate frequency furnace is the damage of the insulation layer on the coil surface, which is caused by a short circuit under the condition of high voltage and high current. method