The correct selection method of medium frequency induction melting furnace
Medium frequency induction melting furnace has fast heating speed, high efficiency, low burning loss and small heat loss. The workshop temperature is relatively low, reducing smoke and dust, saving energy, increasing productivity, improving working conditions, reducing labor intensity, and purifying the workshop environment. The effect is significant. Especially for cast iron, the induction melting furnace is conducive to obtaining low-sulfur molten iron, which is incomparable to the cupola. When choosing an intermediate frequency smelting furnace, a foundry company should select transformer capacity, output requirements, investment quota, etc. as the selection criteria, and pay attention to the following matters when purchasing equipment.
1. Medium frequency induction melting power conditions
1.1 Capacity of medium frequency induction melting transformer
At present, for the SCR full-bridge parallel inverter intermediate frequency power supply commonly used in the industry, the numerical relationship between the transformer capacity and the value of the power supply is: the value of the transformer capacity = the value of the power supply x 1.2
For the IGBT half-bridge series inverter intermediate frequency power supply (commonly known as one for two, one for smelting, one for heat preservation, and two at the same time), the numerical relationship between transformer capacity and power supply power is: the value of the transformer capacity = the value of the power supply x 1.1
The transformer is a rectifier transformer. In order to reduce the interference of harmonics, try to use a dedicated machine as much as possible, that is, an intermediate frequency power supply is equipped with a rectifier transformer.
1.2 Intermediate frequency induction melting incoming line voltage
For the intermediate frequency power supply below 1000KW, generally use three-phase five-wire 380V, 50HZ industrial power, equipped with 6-pulse single rectifier intermediate frequency power supply; for the intermediate frequency power supply above 1000KWY, focus on the use of 660V incoming line voltage (some manufacturers use 575V or 750V) ,Because 575VZ or 750V is a non-standard voltage level, it is not easy to purchase accessories, it is recommended not to choose to use) Configure 12-pulse dual rectifier intermediate frequency power supply, there are two reasons: one is to increase the rated working voltage by increasing the incoming line voltage; The harmonics generated by the power will interfere with the power grid, and a relatively straight DC current can be obtained through double rectification. The load current is rectangular wave and the load voltage is close to a sine wave, reducing the impact of grid interference on other equipment.
Some users blindly pursue high voltage (some 1000KW use 900V incoming line voltage) and achieve the goal of energy saving since low current. Don’t you know that this is at the expense of the life of the electric furnace, and the high voltage will easily cause the life of electrical components to be shortened. , Copper bars and cables are exhausted, which greatly reduces the life of the electric furnace. In addition, for electric furnace manufacturers, high voltage reduces raw materials in terms of materials and saves costs. Electric furnace manufacturers are definitely willing to do this (high price and low cost.) It is the manufacturers who use electric furnaces that ultimately suffer.
2. Capacity requirements
Generally speaking, according to the weight of a single piece and the weight of molten iron required for each working day, the capacity of the intermediate frequency induction melting furnace can be determined. Then determine the power and frequency of the intermediate frequency power supply. Induction heating equipment is a non-standard product.
The power density of domestic intermediate frequency induction smelting furnace is basically about 500KW/ton, which is lower than the theoretical best value of 600-800KW, mainly considering the life of the furnace lining and production management. Under high power density, electromagnetic stirring will produce strong scouring of the furnace lining, which requires higher requirements for furnace lining materials, furnace building methods, smelting processes, materials, and auxiliary materials. According to the above configuration, the melting time of each furnace is 75 minutes (including feeding, salvaging impurities, and quenching and tempering time). If it is necessary to shorten the melting time per furnace, the power density of the power supply can be increased by 100KW/ton while the capacity of the furnace body remains unchanged.