How to choose the “medium frequency induction melting furnace

Medium frequency induction melting heating has the advantage of speedy melting , high efficiency, less loss of heat, reducing dust, energy conservation improve productivity, improve working conditions, reduce labor intensity, clean up the workshop environment..etc.Especially for cast iron, the induction melting furnace is conducive to access to low-sulfur molten iron  which  cupola can not be compared,Foundry enterprises should be based on the transformer capacity, production requirements, investment quotas as the selection criteria when choose the  induction melting furnace.

1.Medium frequency induction melting electrical conditions

1.1 medium frequency induction melting transformer capacity

Industry commonly used SCR full-bridge parallel inverter IF power, transformer capacity and power values of the numerical relationship as follows: the value of the transformer capacity = power supply value x 1.2

For the IGBT half-bridge series inverter IF power supply (commonly known as dural track, one furance melting and the other furnace heat preservation, or two at the same time work) Transformer capacity and power power of the numerical relationship: transformer capacity value = power supply value x 1.1

In order to reduce the interference of the harmonics,  suggest one intermediate frequency power source to  equip  one  rectification transformer.

1.2 IF induction melting line voltage

For the intermediate frequency power  supply below 1000KW  generally adopt the  three-phase  380V, 50HZ industrial electricity, configure the 6-pulse  single rectifier IF power.

For the power supply over 1000KW which is  focused on the use of 660V line voltage (some manufacturers use 575V or 750V, 575VZ or 750V is a non-standard voltage level which is not recommended),Configuration of 12-pulse dual rectifier IF power supply, followings are  two reasons: First, by increasing the line voltage to increase the rated voltage; Second, high-power harmonic generation will interfere with the grid, through the double rectifier can be more straight DC current, load Current is a rectangular wave, the load voltage close to the sine wave, in this way can reduce the impact of grid interference on other equipment.

Some users blindly pursuit of high voltage (for example :1000KW adopt 900V input line voltage), low current to achieve the purpose of energy saving, but  this is will do much harm to the lifetime of the furnace.,High voltage easily lead to shortened life expectancy of electrical components, copper, cable fatigue, the electric furnace life greatly reduced.

2.Production capacity requirement

In general, according to the weight of a single work piece and the required production of each working day, you can determine the capacity of medium frequency induction melting furnace.And then determine the power and frequency of the IF power. Induction heating equipment are non-standard products. The general configuration of the industry is shown in Table 1

  1. The choice of structure

with the  reducer for the tilting mode of  aluminum alloy melting furnace commonly known as aluminum frame induction furnace. With the  hydraulic cylinder for the tilting of the steel frame structure commonly known as steel frame induction furnace

The difference between the steel shell furnace and the aluminum shell furnace (take 1 ton cast iron stove as the example)

  Project                      steel shell furnace                      aluminum shell furnace

Shell material                      steel                                      aluminum alloy

Tilting System                   Hydraulic                                reducer

Hydraulic station                 yes                                           no

Magnetic yoke                         yes                                           no

Furnace cover                         yes                                         no

Leakage system                      yes                                       no

Energy consumption          580KW.h/t                          630KW.h/t

Life time                            10 years                                          5 years

Price                              high                                                    low

Relative to the aluminum shell furnace,  steel furnace has five advantages

durable, beautiful, especially for the large-capacity furnace, the need r strong rigid structure, from the perspective of the safety of the furnace,  steel frame induction melting furnace is more recommended.

magnetic yoke made of  Silicon steel sheet played shielding and emission to the magnetic field lines created by the  induction coil  what is more, can also   reduce the leakage flux, improve the thermal efficiency, increased production, energy saving 5% -8%

  • The furnace cover can  reduces the heat loss and also increases the safety of the equipment
  • Long life, the aluminum oxidation  at high temperatures , resulting in metal toughness fatigue. In the foundry site, often see the  aluminum shell furnace shell broken and old, while the  steel furnace because of less magnetic leakage , equipment life much more than aluminum furnace
  • Safety performance Steel shell furnace is much better than aluminum shell furnace, aluminum shell furnace in the melting time due to high temperature and pressure, aluminum shell is easy to deformation, security is poor. Steel furnace furnace using hydraulic furnace, safe and reliable

The same type of  coreless induction furnace why the price difference is very large and how to choose “IF melting furnace”?

Material differences

Shell and yoke: take the aluminum shell for example , the standard 1-ton aluminum shell furnace shell weight is 400Kg of cast aluminum alloy, the thickness of 40mm,  but some manufacturers aluminum shell is not enough in the  the weight and thickness . The most important of the steel frame furnace is the choice of steel yoke furnace, the same model   steel frame furnace ,different steel yoke, price will be big difference.The general should choose a new high-permeability of the Z11 cold-rolled silicon steel sheet manufacturing, silicon steel sheet thickness of 0.3mm, the use of copy structure,The outer arc of the inner arc and the induction coil should  the same, so that the yoke can abut against the outside of the induction coil, and the maximum restraining coil diverges outwardly the magnetic field lines,

(Some manufacturers use waste, no orientation, and even dismantled the waste transformer silicon steel to produce yoke,)

Copper tube and bar : the core of the melting furnace is the induction coil ,the cold extruded brass and  casting  copper has the great difference in the  effect and price difference. Should use the  large cross-section T2 cold extrusion brass,Copper surface insulation treatment using electrostatic spraying, to achieve H-class insulation,In order to protect the insulation strength, in the surface with mica tape and alkali-free glass ribbon bandaged,And then coated with moisture-proof insulating enamel,

(Some manufacturers are using copper or T3 brass, poor conductivity, easy to break and casue the water leakage)

SCR: the manufacturers use SCR, the quality is generally uneven, good quality temperature control thyristor is good, fast response, low failure rate. So choose well-known manufacturers of SCR, reliable, stable.

When choose the furnace should  require the electric furnace manufacturers indicate the manufacturer of SCR, and get the SCR  certification, H good quality SCR are: (Xiangfan Taiwan Semiconductor Co., Ltd., Xi’an Power Electronics Research Institute, etc.)

Capacitor: The most important thing is to be equipped with a sufficient number of capacitors : generally the amount of compensation is the value of the power supply 18 —- 20 times: Capacitance compensation (Kvar) = (20- 18) x power supply power. And use the regular manufacturers of capacitors.

Reactor: the main material in the Reactor is the silicon steel, should use regular manufacturers of new products, can not use recycled silicon steel sheet.

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