Difference between medium frequency induction furnace and power frequency induction furnace

1、 Medium frequency induction furnace

Medium frequency induction furnace refers to the induction furnace with power supply frequency within the range of 150-10000 Hz, and its main frequency is in the range of 150-2500 Hz. The power frequency of domestic small frequency induction furnace is 150, 1000 and 2500 Hz.

Medium frequency induction furnace is a special smelting equipment suitable for smelting high-quality steel and alloy, which has the following advantages compared with the induction furnace of work amount:

1) The melting speed is fast and the production efficiency is high. The power density of medium frequency induction furnace is large, and the power configuration per ton of molten steel is about 20-30% larger than that of power frequency induction furnace. Therefore, under the same conditions, the intermediate frequency induction furnace has fast melting speed and high production efficiency.

2) Strong adaptability and flexible use. The liquid steel in each furnace of medium frequency induction furnace can be completely discharged, which is convenient to change the steel grade; However, the molten steel in each furnace of the power frequency induction furnace is not allowed to be discharged completely, and a part of the molten steel must be reserved for the next furnace startup. Therefore, it is inconvenient to change the steel grade, and it is only applicable to smelting a single type of steel.

3) The effect of electromagnetic stirring is good. As the electromagnetic force borne by the molten steel is inversely proportional to the square root of the power frequency, the stirring force of the medium frequency power supply is smaller than that of the power frequency power supply. The stirring effect of medium frequency power supply is better for removing impurities, uniform chemical composition and uniform temperature in steel. The excessive stirring force of the power frequency power supply increases the scouring force of the molten steel on the furnace lining, which not only reduces the refining effect but also reduces the life of the crucible.

4) The starting operation is convenient. As the medium frequency current is far greater than the power frequency current, the medium frequency induction furnace has no special requirements for the furnace charge when it is started, and can quickly heat up after charging; The power frequency induction furnace requires a specially made charging block (a cast steel or iron block with a size similar to that of the crucible and about half the height of the crucible) to start heating, and the heating rate is very slow. Therefore, the medium frequency induction furnace is mostly used under the condition of periodic operation. Another advantage of easy starting is that power can be saved during periodic operation. Due to the above advantages, the medium frequency induction furnace has been widely used in the production of steel and alloy in recent years, as well as in the production of cast iron, especially in the foundry workshop with periodic operation. Auxiliary equipment of medium frequency induction furnace

The complete set of equipment for medium frequency induction furnace includes: power supply and electrical control part, furnace body part, transmission device and water cooling system.

Skin effect is also called skin effect, skin effect. When the alternating current passes through the conductor, the current will tend to flow through the conductor surface. This phenomenon is called skin effect. When the current or voltage is conducted in a conductor with electrons of higher frequency, they will gather on the surface of the conductor rather than be evenly distributed in the cross-section of the entire conductor. The higher the frequency, the more significant the skin effect.

principle

Because when the conductor flows through the alternating current, according to Lenz's law, eddy currents will be generated inside the conductor, which is opposite to the direction of the central current of the conductor,. Since the magnetic linkage of the wire center is larger than that of the wire surface, the electromotive force generated at the wire center is larger than that generated near the wire surface. As a result,

The current flows on the surface while there is no current in the center. This magnetic field generated by the current of the wire itself makes the wire current flow on the surface.

Skin effect is the term of electromagnetics and eddy current (eddy current). This phenomenon is caused by the electrified ferromagnetic material, which is close to the non electrified ferromagnetic material, and generates a magnetic field in the opposite direction on the surface of the non electrified ferromagnetic material. With the magnetic field, the current that cuts the magnetic line of force will be generated. This current is the so-called eddy current, and this phenomenon is the skin effect.

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Calculation formula: we can calculate the depth of skin effect of alternating current:

δ= 1/sqrt(1/2*w* σ*μ)

Where w is the alternating current frequency, σ Is conductor conductivity, μ Is the magnetic flux of the conductor. Edit this paragraph

influence

In high-frequency circuit, hollow conductor can be used instead of solid conductor. In addition, in order to weaken the skin effect, in high-frequency circuits, it is also often used to braid multiple strands of mutually insulated thin wires to replace the thick wires with the same cross-sectional area. This multi strand wire harness is called braided wire. In industrial applications, the skin effect can be used for surface quenching of metals.

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effect

Considering the skin effect of alternating current, in order to effectively use conductor materials and facilitate heat dissipation, the large current buses in power plants are often made into channel or diamond buses; In addition, in the high-voltage transmission and distribution lines, the steel cored aluminum strand is used to replace the aluminum strand, which not only saves the aluminum conductor, but also increases the mechanical strength of the conductor, which is based on the principle of skin effect.

Skin effect is one of the most basic distortion processes in the signal line, and it may also be the most easily overlooked and misunderstood. According to the exaggerated propaganda of general signal lines, the skin effect will not change all high-frequency signals, and will not cause any loss of related kinetic energy. On the contrary, the skin effect will be inconsistent when transmitting high-frequency signals due to different components of the transmission conductor. Similarly, on the old wire harness conductor, the skin effect encourages the signal current to interact with each other on multiple wire harnesses, causing harsh marks for the sound.

2、 Power frequency induction furnace

Power frequency induction furnace is an induction furnace that uses industrial frequency current (50 or 60 Hz) as power supply. The power frequency induction furnace has developed into a 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. The complete set of equipment for power frequency induction furnace includes four major parts.

1. Furnace body

The furnace body of the industrial frequency induction furnace for smelting cast iron is composed of induction furnace (two, one for smelting and the other for standby), furnace cover, furnace frame, furnace tilting oil cylinder, furnace cover moving hoist, etc.

2. Electrical part

The electrical part consists of power transformer, main contactor, balance reactor, balance capacitor, compensation capacitor, electrical console, etc.

3. Water cooling system

The cooling water system includes capacitor cooling, inductor cooling and flexible cable cooling. The cooling water system is composed of water pump, circulating water pool or cooling tower, pipe valves, etc.

4. Hydraulic system

The hydraulic system includes oil tank, oil pump, oil pump motor, hydraulic system pipeline and valve, hydraulic console, etc.