Why is the price difference between the same type of medium frequency induction melting furnace?

Medium frequency induction melting has a high heating rate, high efficiency, low burning loss, low heat loss, relatively low workshop temperature, reduced smoke generation, energy saving, improved productivity, improved labor conditions, reduced labor intensity, and clean room environment. Especially for cast iron, the induction melting furnace is beneficial to obtain low-sulfur iron liquid which is unmatched by the cupola. When selecting the medium frequency melting furnace, the foundry company should select the following according to the transformer capacity, production requirements, investment quota, etc., when purchasing equipment.

1.   Medium frequency induction melting condition

1.1   Medium frequency induction melting transformer capacity

At present, for the SCR full-bridge parallel inverter IF power supply, the numerical relationship between transformer capacity and power supply is: the value of transformer capacity = the value of power supply x 1.2

For the IGBT half-bridge series inverter IF power supply (commonly known as one for two, one for melting one insulation, two for simultaneous operation), the numerical relationship between transformer capacity and power supply is: value of transformer capacity = value of power supply x 1.1

The transformer is a rectifier transformer. In order to reduce the interference of harmonics, it is as far as possible for the special plane, that is, one intermediate frequency power supply is equipped with a rectifier transformer.

1.2   IF induction fuse line voltage

For medium frequency power supply below 1000KW, three-phase five-wire 380V, 50HZ industrial power is used, and 6-pulse single-rectifier intermediate frequency power supply is configured. For medium-frequency power supply above 1000KWY, the focus is on using 660V incoming voltage (some manufacturers use 575V or 750V). Because 575VZ or 750V is a non-standard voltage level, the accessories are not good to buy, it is recommended not to use). Configure 12-pulse double-rectifier IF power supply for two reasons: one is to increase the rated working voltage by increasing the incoming line voltage; the second is large The harmonics generated by the power will interfere with the grid. The double rectification can obtain a relatively straight DC current. The load current is a rectangular wave, and the load voltage is close to a sine wave, which reduces the impact of grid interference on other equipment.

Some users blindly pursue high voltage (some 1000KW use 900V line voltage), and achieve energy saving since low current. I don’t know if this is at the expense of the life of the electric furnace. It is not worth the loss, high voltage is easy to shorten the life of electrical components. , copper platoon, cable fatigue, so that the life of the electric furnace is greatly reduced. In addition, high voltage for the electric furnace manufacturers, the raw materials are reduced in terms of materials, saving costs. Electric furnace manufacturers are certainly willing to do so (high-priced low-cost.) The ultimate loss is still the use of electric furnace manufacturers.

2. Capacity requirements

In general, the capacity of the medium frequency induction melting furnace can be determined by the weight of the individual pieces and the weight of the molten iron required for each working day. Then determine the power and frequency of the IF power supply. Induction heating equipment is a non-standard product. At present, there is no standard in the country, and the general configuration of the industry is shown in Table 1.

Table 1   Medium frequency induction melting furnace selection parameters

It can be seen from Table 1 that the power density of the domestic medium frequency induction melting furnace is about 500 KW/ton, which is lower than the theoretical optimal value of 600-800 KW, mainly considering the lining life and production management. Under high power density, electromagnetic stirring will produce strong scouring of the lining, and the requirements for lining materials, furnace building methods, melting processes, materials, and auxiliary materials are high. According to the above configuration, the melting time per furnace is 75 minutes (including feeding, salvaging impurities, quenching and tempering time). If it is necessary to shorten the melting time per furnace, the power density of the power source can be increased by 100 KW/ton while the capacity of the furnace body is constant.

3. Structural choice

According to industry habits, the supply melting furnace of aluminum alloy structure with the reducer as the tilting method is commonly known as the aluminum shell furnace. The induction melting furnace of the steel structure with the hydraulic cylinder as the tilting furnace is commonly called the steel shell furnace. The difference between the two is shown in Table 2 and Figure 1.

Table 2 The steel shell furnace and the aluminum shell furnace are different (take 1 ton cast iron furnace as an example)

Compared with the aluminum shell furnace, the advantages of the steel shell furnace are five points:

1) Rugged and elegant, especially for large-capacity furnaces, which require a strong rigid structure. From the safety point of the tilting furnace, try to use steel shell furnace.

2) The yoke made of silicon steel sheet shields and emits magnetic lines generated by the induction coil, reduces magnetic leakage, improves thermal efficiency, increases production, and saves energy by 5%-8%.

3) The presence of the furnace cover reduces heat loss and increases the safety of the equipment.

4) Long service life, aluminum is more oxidized at high temperature, resulting in metal toughness fatigue. In the foundry enterprise site, it is often seen that the aluminum shell furnace shell used for one year or so is broken, and the steel shell furnace has much less leakage current, and the service life of the equipment greatly exceeds that of the aluminum shell furnace.

5) Safety performance The steel shell furnace is much better than the aluminum shell furnace. When the aluminum shell furnace is smelted, the aluminum shell is easily deformed due to high temperature and heavy pressure, and the safety is poor. The steel shell furnace uses a hydraulic tilting furnace and is safe and reliable.

Why are the prices of the same model different? How do you choose the “medium frequency melting furnace”?

The price of the same type of medium frequency induction furnace is very different. Take the 1 ton furnace that is commonly used as an example. The market price sometimes differs several times, which is related to the structure of the furnace, component selection, technical content, after-sales service and quality. A multifaceted factor is relevant.

Different materials

Furnace shell and yoke: In the choice of the shell of the aluminum shell furnace, the standard 1 ton aluminum shell furnace has a furnace shell weight of 400Kg and a thickness of 40mm. Some manufacturers often have a weight and insufficient thickness. The most important part of the steel shell furnace is the choice of the yoke. The choice of the same type of steel shell furnace yoke is different. The price difference is very large. Generally, a new high-permeability cold-rolled silicon steel sheet with Z11 should be selected. Silicon steel The thickness of the sheet is 0.3mm, and the contoured structure is adopted. The inner arc surface and the outer circular arc of the induction coil are the same, so that the yoke can be closely attached to the outer side of the induction coil, and the maximum restraint coil is outwardly radiated, and the yoke is bilaterally The stainless steel plate and stainless steel are clamped, welded and fixed, and cooled by water.

(Some manufacturers use waste, no orientation, or even silicon steel sheets removed from used transformers to make yokes,)

Copper tube and the same row: The core of the melting furnace is the effect of the cold extrusion copper tube and the cast copper tube of the induction coil. The T2 cold-extruded copper tube with giant cross-section should be used. The surface insulation treatment of the copper tube is electrostatically sprayed to achieve Class H insulation. To protect its insulation strength, the mica tape and the alkali-free glass ribbon are wrapped and wrapped on the surface once, and then Apply moisture-proof insulating enamel. There is a certain gap between the turns of the coil. When the refractory mortar is coated in the coil, the refractory clay should be infiltrated into the gap to strengthen the adhesion of the glue on the coil on the coil. After the refractory cement is built, the inner surface is smoothed to facilitate the removal of the lining. The coil is protected, and a few stainless steel water-cooling rings are added to the upper and lower ends of the coil to increase the overall rigidity and facilitate heat dissipation.

( Some manufacturers use copper or T3 copper tubes, which have poor electrical conductivity and are easy to break and leak. )

SCR: The thyristor used by various manufacturers is generally of uneven quality. The quality of the thyristor is good, the reaction is fast and the failure rate is low. Therefore, the thyristors of well-known manufacturers are selected, and the quality is reliable and stable.

(When selecting, the manufacturer of the electric furnace is required to indicate the manufacturer of the thyristor, and the product certificate of the thyristor manufacturer is presented. The quality control thyristor of H quality is: Xiangfan Taiwan Semiconductor Co., Ltd., Xi’an Institute of Power Electronics, etc. )

Power cabinet: The regular manufacturer uses the standard spray panel cabinet. Not a tin-painted cabinet. And the size specifications of the power cabinet are standard. Inconsistent manufacturers of power cabinets have also shrunk, height, width and thickness are not enough, and even some of the reactors are placed outside the power cabinet. The regular manufacturer’s IF power supply is equipped with a low-voltage switch inside, which does not require the user to configure the voltage switch cabinet. Some non-regular manufacturers do not have a low-voltage switch installed inside the power supply. Invisible increases the user’s cost (good quality low-voltage switches are Huanyu, Chint, Delixi, etc.).

Capacitor : The most important capacitor cabinet for reactive power compensation must be equipped with a sufficient amount. Generally, the compensation value of the capacitor is 18—-20 times the power of the power supply: Capacitance compensation amount (Kvar) = (20— 18) x power supply. And use the capacitors of regular manufacturers.

Reactor : The main material of the reactor is silicon steel sheet. New products produced by regular manufacturers should be used, and recycled second-hand silicon steel sheets cannot be used.

Water pipe clamp : In the complete set of medium frequency melting furnace, there are a large number of water pipes connected. Strictly speaking, stainless steel clamps should be used. It is better to use copper slip knots. It is convenient to install and disassemble the knots without maintenance. It is especially suitable for application on water-cooled cables, which is conducive to current transmission and does not cause water leakage, which is safe and reliable.

In addition to the above points, there are other components to choose from, such as inverter non-inductive capacitors, non-inductive resistors, water-cooled cables, connecting copper bars, water pipes, etc., which will affect the quality and price of the equipment. Here we do not elaborate, I hope you can pay attention when choosing to buy, try to require the melting furnace manufacturer to provide the details of the main components and manufacturers, can not simply ignore the structure and quality of the equipment than the price.

Since the intermediate frequency furnace is a non-standard product, it is ordered to be remanufactured, and the quality is closely related to the price.

4, technical strength

The regular manufacturers have invested a lot of manpower and material resources for researching advanced technology, with advanced equipment and exquisite technology, reflecting different aspects in terms of melting speed, power consumption and equipment failure. Many manufacturers do not have the conditions for in-plant commissioning, the cost is naturally lower, and the impact of assembly and commissioning processes on quality is very large. Different manufacturers, different processes, and different prices also produce different qualities.

5, after sales service

Good after-sales service is the guarantee of equipment quality. It is inevitable when the electromechanical products fail. This requires good after-sales service. The regular manufacturers have enough technical personnel and ability to guarantee after-sales service. The intermediate frequency induction melting furnace has a one-year warranty period after repeated static and dynamic commissioning before leaving the factory. During this period, any equipment failure caused by non-human responsibility will be the responsibility of the manufacturer.

In short, the foundry enterprise should select the equipment that is most suitable for the current situation of the enterprise according to actual needs. In the selection process, the manufacturer should compare the manufacturing, configuration, technical solutions, and after-sales service attitudes of the equipment to select satisfactory equipment.

The intermediate frequency furnace includes, transformer, air-opening, harmonic filter, inverter cabinet, water cable, induction coil, furnace shell and the like. Different configurations are possible for each production. It may be different depending on the material, form and price. It is best to discuss the price separately. At present, the medium frequency furnace is developing towards high power and large capacity. The 1 ton intermediate frequency furnace is already very small. At present, there are not many new ones, but the technology is mature and cheap.