Technical analysis and explanation of 0.75 ton medium frequency melting steel furnace

1. Name of intermediate frequency furnace :

0.75 tons of molten steel furnace, 0.75 tons of one to one medium frequency melting furnace equipment.

2. Use and composition :

0.75 t of a molten steel furnace system, for the production of cast steel, cast iron, and a variable frequency power supply 0.75 t coreless induction melting steel from the electric furnace set not less than 400 KW required for normal operation and an auxiliary system Equipment composition.

3. Medium frequency furnace working mode: 
A set of furnace smelting production, single furnace melting power 400kw

Main process parameters of 0.75 ton molten steel furnace intermediate frequency furnace

4. Intermediate frequency furnace project

4.3 , the main components supporting manufacturers (for famous manufacturers)

5, the main equipment function, configuration and technical description of the intermediate frequency furnace

0.75 ton molten steel furnace power cabinet: (one rectifier cabinet and one inverter cabinet)

All devices of the series resonant intermediate frequency power supply are installed in a closed cabinet. The incoming power supply is 380 V, 3 phases ( 6 pulses), 50 Hz.

The cabinet is made of cold-rolled steel sheets of not less than 1.5 mm thick and high strength. Opening the door makes it easy to access parts such as rectification and inverter. There are hooks on the top of the power cabinet for easy transportation and installation.

The components of the power cabinet are reasonably arranged, easy to maintain, and the wiring and wiring are in compliance with the specifications. It is convenient for maintenance personnel to easily access all maintenance points. The copper bars are all set to reasonable water cooling as needed.

The isolation control room is provided with a closed isolation control room at the upper part of the front door, and is equipped with control components such as a main control board, a feedback board, and a control power supply, so that the signal of the main control board can be conveniently observed.

The isolation control room does not require additional cooling.

Power receiving part

Rectifier transformer secondary side of the circuit breaker by receiving or copper busbar power circuit breaker West Germany DW 15. They are equipped with a manual switch and an undervoltage coil for interlock protection. It consists of a circuit breaker, a voltage transformer, a current transformer, and the like.

Rectifying section

The voltage feedback is in series; the circuit adopts 6- pulse circuit rectification mode, the incoming voltage is 380 V, and the rectifier part of the thyristor adopts the latest stacked heat sink assembly.

The RC absorption branch at both ends of the thyristor can act as a buffer current sudden change when the thyristor switch is used.

Filter network

Reactor , leveling DC current, removing current ripple and preventing high frequency signals from entering the factory power supply line.

Filter capacitor . Filter capacitor is water cooled

The filter capacitor has an external discharge resistor that can be discharged within 5 minutes after the power is turned off.

The reactor is air-core, water-cooled, vacuum-cast with epoxy resin, and sealed.

Inverter part

The RC absorption circuit is connected in parallel across the thyristor to buffer the thyristor switch.

Constant power output, power output is controlled by constant. During the melting process, when the load and temperature change, the load is always full power output, thus shortening the melting time.

Increase the power factor to ensure that the power factor is not less than 95% at any power.

The starting characteristics are good, and it can be started freely under full load and heavy load conditions, and the starting success rate is 100%.

Inverter capacitor bank

A set of series resonant capacitor compensation device, in order to meet the output, the power transmission can be performed furnace. Capacitance installed in a fully enclosed inverter cabinet,

Control System

It is equipped with output voltage meter, output power meter, working frequency meter, input current meter, input voltmeter, DC voltmeter, DC current meter, phase display on the control panel, and inverter working display.

The circuit board contains all the necessary control and electronic logic components to respond instantaneously to the voltage, current and power of each induction coil and to generate thyristor trigger pulses.

The circuit board sets limits on the inverter to avoid damaging the thyristors and capacitors in the event of current or overvoltage.

The circuit board ensures system reliability; and the system is fully monitored for each half cycle of the furnace current.

Press the button to control the “Run” and “Disconnect” of the inverter.

Main power indicator, this indicator lights when the circuit breaker is closed to power the variable frequency power supply.

0.75 ton molten steel furnace body:

The furnace body is composed of a furnace shell, a fixed frame, a tilting furnace mechanism, an induction coil, a yoke, etc., and is additionally provided with a furnace lining material and a leaking furnace alarm device.

Furnace shell:

The medium frequency melting furnace shell is a squirrel-cage frame structure welded by steel plate, and the lower part of the furnace shell has a fixing bracket of the furnace lining mechanism. A contour yoke is provided in the furnace shell. The yoke shielding can reduce the leakage magnetic flux to prevent the furnace body from heating, improve the electric energy efficiency, support the induction coil at the same time, improve the strength, and can conveniently disassemble the coil and repair, observe and dissipate the coil when the yoke is not taken away.

Fixing frame:

The fixed hob adopts high-strength integral steel structural parts to ensure long-term work without deformation. The furnace platform is made of 10mm pattern steel plate, which can be kept flat and not deformed during long-term use, and the noise on the working platform of the furnace is <85dB.

The tilting mechanism (hydraulic plunger cylinder) tilting furnace adopts two inverted mounted plunger hydraulic cylinders, and the hydraulic cylinder inlet port is directly connected to the speed limiting shut-off valve (flow control valve) to prevent the furnace from being broken due to pipeline breakage and the like. The body drops sharply and causes an accident. The tilting furnace is controlled by a manual speed-regulating valve.

The two oil cylinders are connected in parallel, and there is no jamming at the same time. The furnace body rises and falls smoothly when the furnace is tilted. A high temperature resistant protective sleeve is required on the outside of the cylinder.

Induction coil (ie sensor)

The induction coil is made of TU1 type (purity of 99.97% electrolytic copper), wall thickness / 6mm extruded rectangular copper tube on a special mold, the pitch error is not more than 2mm, and the coil group needs to be relieved after welding. deal with.

The induction coil is made of high temperature resistant, high pressure insulation paint, which is dip coated and vacuum dried. The insulation grade is H grade. The induction coil passed the 12kg/cm3 water pressure withstand test before leaving the factory.

A stainless steel water-cooling ring is arranged on the upper and lower parts of the induction coil to ensure uniform heating of the furnace lining. A Faraday short-circuit ring is required at the upper and lower ends of the coil to fully absorb the leakage flux at the upper and lower ends to prevent the furnace body from heating up. The furnace body is connected to a large-section water-cooled cable, and the lead-out line is in the form of a side lead-out line.The coil pressing device is pulled down on the stainless steel rod.

Yoke

The yoke is laminated with Z11 high-quality crystal oriented cold-rolled silicon steel sheet, and its thickness is ≤0.3mm, which is clamped on both sides with stainless steel. The yoke has a contoured arc-shaped structure that is consistent with the outer diameter of the coil. After assembly, the bending degree is ≤ 4mm, and the deviation between the theoretical center line and the actual center line is ≤ 3mm. The yoke covers the area of the induction coil ≥60%. The yoke fixing method: the yoke is closely attached to the induction coil, and a high-voltage insulating layer is used in the middle, and the outer surface is screwed on the stainless steel plate on the back of the yoke.

The inside of the yoke stainless steel clamping plate needs a water-cooled radiator. When the electric furnace is in operation, the yoke temperature is kept at normal temperature to prevent the yoke temperature from rising and deformation, thereby strengthening the support of the induction coil and improving the strength of the furnace body.

0.75 ton molten steel furnace leak alarm device

It is necessary to set the lining thickness detecting device: when the lining thickness detecting device is working normally, the work indicator lights up and the warning light goes out. When the furnace lining has a low resistance phenomenon or the induction coil has a short circuit to the ground, the alarm lamp lights up and the buzzer sounds an alarm.

The detection device has a self-test button and a reset button. When the device is normal, the self-test button is pressed, the alarm lamp is lit, and the buzzer alarms. Press the reset button to cancel the alarm and resume the detection device to work again. The button below the reset button and the self-test button is used to break the bottom electrode. When the detecting device is in normal operation, the button can be used to initially determine the cause of the alarm. The detecting device can judge the change of the lining.

Output copper row and water cooled cable

The output copper row is made of high quality T2 copper bars with a purity of 99.9%. The copper busbar is connected to the variable frequency power supply and the furnace water-cooled cable.

The water-cooled cable is made of high-quality T2 material multi-strand copper stranded wire. The jacket is made of American Gates carbon-free hose or high-strength flame-retardant rubber tube. The joint needs to be cold-formed to ensure good contact and strong tensile strength.

The water-cooled cable and the induction coil must be connected to ensure better electrical conductivity, no deformation under high temperature working environment, good contact, long service life, impermeability > 10kg/cm 2 , convenient and quick to replace, easy to repair.

Model

The boring die is made of ≥8mm steel plate and can be pulled out at any time as the furnace melts or the slab is finished.

Hydraulic device

The hydraulic device is mainly composed of two parts: a hydraulic pump station and a hydraulic console.

Hydraulic power station

The hydraulic pumping station is used to provide power to the cylinder of the tilting cylinder lining out of the mechanism cylinder. It needs to adopt a dual-machine dual-pump unit (one set of work, one set of spare), and has a pressure regulating device, oil returning and oil suction filtering device. The hydraulic cylinder requires a protective cover to ensure that the cylinder rod is not contaminated by dust and splash metal.

Hydraulic console

The hydraulic console is mounted on the table to control the tilting of the furnace (in the range of 0 to 95 degrees) and the lining. The operation console is operated by manual hydraulic valve. The work should be reliable, stable, without impact and creeping. The speed can be adjusted and can stay at any position.

Seven , the main raw material manufacturers