Speaking of induction furnace manufacturers, let's start with an induction furnace, which is divided into power-frequency induction furnaces and medium-frequency induction furnaces.
The power frequency induction furnace is an induction furnace that uses industrial frequency current (50 or 60 Hz) as the power supply. The power frequency induction furnace has developed into smelting equipment with a wide range of uses. It is mainly used as a melting furnace to smelt grey cast iron, malleable cast iron, nodular cast iron, and alloy cast iron. In addition, it is also used as a holding furnace. As before, the power frequency induction furnace has replaced the quenching furnace as the main equipment in casting production. Compared with the cupola, the power frequency induction furnace has many advantages, such as easy control of molten iron composition and temperature, low gas and inclusion content in castings, no environmental pollution, energy saving, and improved working conditions. Therefore, the power frequency induction furnace has been developed rapidly in recent years.
Heating Principle
The working principle of the power frequency induction furnace is the specific application of the electromagnetic induction law, that is, when an alternating power supply is connected to the induction coil, an alternating magnetic flux is generated, which is linked to the metal furnace charge in the crucible, thus causing an induced electromotive force in the furnace charge.
Because the conductor of the charging system is a closed circuit, the strong induced current is generated under the action of the electromotive force; Due to the surface effect of current, strong current only flows along the surface of the furnace charge, generating a lot of Joule heat, which makes the furnace charge heated and even melted.
Structure of Power Frequency Induction Furnace
The power frequency induction furnace generally consists of a set of power supply and electrical control equipment and two furnaces, one for smelting and the other for standby. Each furnace is mainly composed of a furnace body, fixed frame, furnace cover mechanism, water and electricity introduction system, hydraulic system, etc.
1. Furnace Body
An assembly unit is composed of main parts such as frame type (less than 5 tons) or simple shell type (more than 10 tons) furnace shell, inductor, magnet conductor, and crucible. It is the "heart" of the furnace. How the smelting works are carried out mainly depends on the work of this part. The furnace shell is welded by steel plate or section steel, which has sufficient strength and rigidity. The inductor is made of high-quality special-shaped steel pipe, with water cooling in the middle and power supply connector and water supply connector at the end; The inductor is located on the furnace bottom coil, centered by the surrounding magnetic yokes and compressed in a radial direction, and its upper part is equipped with an elastic axial fastening device to reduce the vibration of the inductor during power transmission and prevent the movement of the induction coil during furnace tilting. There is one group, two groups, and three groups of sensors according to design requirements; According to smelting process requirements, it can be incorporated into the network separately or jointly.
The magnetic yoke is composed of high-quality silicon steel sheets, distributed around the periphery of the inductor, which plays the role of supporting the inductor as a skeleton, and at the same time, it can restrict the leakage of magnetic flux outside the inductor to prevent metal components from heating. As a container for containing molten metal solution, the crucible is usually made of quartz sand during the melting process, high carbon steel, cast iron, copper, aluminum, and other non-ferrous metals and their alloys. The furnace body composed of the above parts is connected to the fixed frame through the bearings on both sides, and two plunger cylinders realize the furnace body tilting and pouring out the metal solution.
2. Fixed Frame
The fixed frame is welded with section steel and firmly fixed on the concrete foundation with anchor bolts. It bears all loads of the whole furnace body and plays a supporting role in furnace body tilting.
3. Furnace Cover Mechanism
Including furnace cover, lifting handle, or lifting cylinder. Through the manual or hydraulic drive, the furnace cover can be lifted and rotated to realize charging and prevent a large amount of radiant heat loss. Refractory materials are filled in the furnace cover ring to reduce heat loss. The stove cover is provided with an observation hole, which can be used to monitor the smelting process at any time. It is also used for temperature measurement and sampling. The maximum opening angle of the furnace cover is 90°.
4. Water and Electricity Introduction System
The system is composed of inlet and return water mains, water-cooled cables, branch waterways, and monitoring instruments. It is mainly used for water-cooling inductors and water-cooling cables.
The inlet temperature of cooling water is generally controlled at 5~35 ℃, and it is better to control it below the ambient temperature. Otherwise, the temperature difference is too large, which will often cause condensation on the surface of the inductor, cable, and pipeline, resulting in insulation damage and electric leakage. The outlet water temperature shall be controlled below 55 ℃ to reduce CaO and MgO in the water from depositing on the inner wall of the inductor and scaling.
The cooling water enters the main pipe from the water source and is distributed to each branch. Some are used to cool the inductor and some are used to cool the cable. Usually, two cables form a cooling water path; Each branch is equipped with a stop valve, whose flow can be adjusted according to the size of the water outlet. The water monitoring system adopts an electric contact pressure gauge installed on the header at the water inlet side. When the water inlet pressure is less than the minimum pressure, it will send out a signal and sound; The outlet water temperature of each branch at the outlet side is controlled by a bimetal signal thermometer. When the water temperature of any branch exceeds the maximum adjusted water temperature of 55 ℃, a quick signal can be sent out. Then, the overtemperature branch can be found according to the indication or measurement, and the cooling water volume of the branch can be adjusted manually.
The cooling water must be clean. The water quality is required to be: pH 6~9, the hardness not more than 10 degrees (10 mg calcium oxide per liter of water), and total solids not more than 250mg/liter. A filter should be placed at the connection between the system and the water source to connect with it, so as to avoid large impurities blocking the water path. The length of the hose used in this system shall not be less than the design value to avoid electric shock accidents caused by electric leakage.
5. Hydraulic System
Two furnace bodies are provided with pressure oil by one or two oil pressure devices. The furnace body is tilted or the furnace cover is opened and closed through the manual valve and button on the console. The oil pressure device is composed of two sets of the same oil pumps, motors, valves, etc. The two sets are on standby for each other. The working oil is the No. 3 stator oil. The maximum tilting angle of the furnace body is 95 °.
The furnace tilting oil cylinder is installed between the furnace body and the fixed frame. As the tilting actuator, its lower oil inlet is equipped with a "pipe break safety valve". Once the oil pipe breaks or the hose is disconnected due to some accident, the safety valve acts immediately to close the oil circuit to prevent the furnace body from dropping automatically.
Daily Operation
1. Furnace Body Inspection:
1.1 Check the furnace body for cold cracks, and do not repair if the cracks are less than 2mm. Cracks exceeding 2mm must be repaired.
1.2 Pay special attention to the horizontal cracks, because it is difficult to bridge the horizontal cracks when starting the furnace. 1.3 Regularly check the melting loss of the furnace body, and the inspection method must be accurate.
2. Cold Furnace Startup:
Temperature rise curve; At the beginning, the temperature rises by 200-300 ℃ per hour; When the temperature rises to 900-1000 ℃; Work according to the normal operation process.
3. Shutdown of the Hot Furnace:
After pouring the molten iron, clean up the slag, put in the starter, heat until the starter turns red, cover the furnace cover, and let the furnace body slowly cool. Remember not to use compressed air to quench the furnace.
4. Operation Matters:
4.1 Pay attention to prevent mechanical damage to the furnace mouth when adding furnace charge.
4.2 The slag in the furnace shall be cleaned as much as possible, because the slag is particularly corrosive to the furnace body, and there are many harmful chemical components in the slag, which is easy to cause abnormal melting loss locally.
4.3 When adding molten iron after desulfurization, the slag must be removed. Prevent the alkaline chemicals in molten iron from entering the medium-frequency furnace through the hot metal transfer package. Once it enters the furnace, it will react with the refractory in the furnace, and the refractory in the furnace will have abnormal melting and erosion.
4.4 When the service temperature cannot reach the service temperature of the selected refractory, the furnace molten iron temperature shall be increased to the service temperature of the refractory once or twice a week.
4.5 When the alloy is added, its solid size shall not be greater than 30mm to prevent the alloy from sinking to the bottom. After reacting with molten iron, the refractory at the bottom of the furnace body will be dissolved.
4.6 Pay attention to iron oxide in molten iron daily. If necessary, add metallurgical-grade carbonized ferrosilicon to reduce Fe2O3 in molten iron. However, the temperature of adding ferrosilicon should be controlled at 1350-1400 ℃ for 15-25 minutes, which is conducive to ferrosilicon melting. 4.7 Each time molten iron is poured out, the power supply of the furnace body must be turned off; Prevent the molten iron at the furnace bottom from overheating.
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