Induction heating and rolling of copper-clad steel plates using vertical medium frequency induction annealing furnace

Copper-clad steel plates are two different metals. After heating and rolling, the copper plate adheres to the surface of the steel plate. Since the melting points of copper and steel are different, the temperature on the cross section of the workpiece is required to be uniform and the fluctuation range is small during heating. High plasticity can be obtained at the same time. , Metals with low melting points should not be melted, so that the rolled copper-clad steel plate has a small size difference in thickness and the bonding between copper and steel is good.

1. Vertical medium frequency induction annealing furnace

Since the size of the copper-clad steel plate is 455mm x 130mm, the thickness of the steel plate is 25mm, and the thickness of the copper plates on both sides is 1mm, the total thickness is 27mrn. In order to use power frequency current for longitudinal magnetic field induction heating, a special form of heating is adopted, that is, stacking copper-clad steel plates so that the heated cross-sectional area is 455mm x 130mm, and no supporting rails are needed during the heating process. The problem of scratches on the surface of copper-clad steel plates.

The copper-clad steel plate continuously enters the lower part of the inductor from the feeding roller. The ejector hydraulic cylinder lifts the copper-clad steel plate, enters the inductor, and rises to the top of the inductor. The copper-clad steel plate is heated to the required temperature and manually A piece of copper-clad steel plate is clamped in the inductor and sent to the rolling mill for rolling. At the same time, the ejector hydraulic cylinder returns, and the copper-clad steel plate in the entire sensor is again supported by the flipping support mechanism, completing a loading and unloading operation. During the heating process, CO is passed through the sensor as a protective gas to ensure that the rolled copper-clad steel sheets are well bonded.

The inductor is a key part of the vertical medium frequency induction heating furnace, which is mainly composed of coils, magnets, guide rails and thermal layers. The coil is wound with round hole eccentric pure copper tube, arranged in a single layer, and is cooled by water during operation. Considering the balance of the three-phase power load, the inductor is powered by three phases and the coils are connected in a "T" shape. The magnetic conductor is made of silicon steel sheets, divided into 4 groups, and arranged around the coil. There are 4 guide rails, which are respectively arranged at the four corners of the copper-clad steel plate to guide the copper-clad steel plate to move up and down. Between the coil and the copper-clad steel plate is a thermal insulation layer made of thermal insulation material. There is a 4mm thick stainless steel plate on the side close to the copper-clad steel plate. There are slots on the plate to reduce eddy current heating. This steel plate is resistant to high temperatures and is used to protect the insulation in the furnace from damage during the heating process.

2.Power supply system

Since the inductor is three-phase, the unbalance of the three-phase power grid caused by the single-phase load is eliminated, and the three-phase balancer for a single inductor is omitted, making the power supply system simpler. Since the power factor cos of induction heating is relatively low, capacitors are connected in parallel on the power supply line to make the power factor cos of the power supply system above 0.9. Various test instruments are also installed on the power supply system, such as voltmeter, ammeter, power meter and power factor meter.

Since copper-clad steel plates are continuously produced in three shifts a day, the power supply voltage fluctuates greatly 24 hours a day, generally ranging from 10% to 15%, sometimes reaching 20%. Under certain production conditions, voltage fluctuations directly affect the heating of the workpiece. Temperature consistency. In order to ensure the quality of induction heating of copper-clad steel plates, an autotransformer is used in the power supply system to keep the electrical parameters of the inductor relatively stable.

3. Heating temperature and heating time

Since the resistivity, magnetic permeability and thermal conductivity of copper and steel are different, their heating rates are also different during the induction heating process.

Under the same magnetic field strength, copper heats up faster than steel. After 12 minutes of heating, the temperatures of copper and steel coincide. When the copper-clad steel plate leaves the sensor, because the copper plate is wrapped around the steel plate and dissipates heat quickly, the temperature of the steel plate is higher than the temperature of the copper plate during rolling, which is allowed by the rolling process. When the copper-clad steel plate is continuously fed, the temperature difference of the steel plate is larger when it is below the Curie point. After exceeding the Curie point, the current penetration depth increases and the temperature difference gradually decreases. The temperature difference to the sensor outlet is about is 20℃. The above heating curve was measured by a thermocouple fixed on the steel plate. No CO gas was passed into the sensor during the test. When CO gas is introduced for combustion, it is more conducive to uniform heating temperature.

4. Technical parameters of medium frequency induction heating

The process requirements for heating the copper-clad steel plate before rolling are: heating temperature t=900℃, temperature difference ≤20℃, productivity Q=4 pieces/min. The heating time of the copper-clad steel plate in the inductor is 12 minutes, the power is 700kw, and the power consumption per unit product is 235kw.h/t.

5. Rolling of copper-clad steel plates

The copper-clad steel plate is rolled immediately after medium-frequency induction heating. Since the heating temperature is relatively uniform, the thickness tolerance of the rolled copper-clad steel plate is small. On the other hand, due to the fast heating speed and short time at high temperature, the copper of the copper-copper steel sheet rolled with CO gas in the sensor is well bonded to the steel. Since the heating time is very short, the grains of the steel plate have not yet grown up. The grain size of the copper-clad steel sheet after rolling is generally grade 8, sometimes finer than grade 8, which improves the mechanical properties of the copper-clad steel sheet.