Compared with aluminum shell furnaces, steel shell furnaces have five advantages:

1) Sturdy, durable, beautiful and elegant. Especially for large-capacity furnace bodies, a rigid structure with high strength is required. From the safety perspective of furnace tilting, steel shell furnaces should be used whenever possible.

2) The yoke made of silicon steel sheets shields and conducts the magnetic lines of force generated by the induction coil, reduces magnetic leakage, improves thermal efficiency, increases output, and saves energy by about 5%-8%.

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

4) Long service life. Aluminum oxidizes severely at high temperatures, causing metal toughness fatigue. In the actual production site of foundry enterprises, it is common to see aluminum shell furnace shells that have been used for about one year become severely damaged. Due to less magnetic leakage, the service life of steel shell furnaces is far longer than that of aluminum shell furnaces.

5) Steel shell furnaces have far better safety performance than aluminum shell furnaces. During melting, aluminum shells are prone to deformation under high temperature and heavy pressure, resulting in poor safety. Steel shell furnaces adopt hydraulic tilting system, which is safe and reliable.

Why is there a huge price difference for products of the same modeland how to choose “medium frequency melting furnace”?

The price of medium frequency induction furnaces of the same model varies greatly. Taking the widely used 1-ton furnace as an example, the market price sometimes differs by several times,which is related to many factors such as furnace structure, component selection, technical content, after-sales service and quality.

Different material selection

Furnace shell and yoke:For the shell selection of aluminum shell furnaces, the shell of a standard 1-ton aluminum shell furnace is made of 400Kg cast aluminum alloy with a thickness of 40mm. However, many manufacturers produce shells that fail to meet the required weight and thickness; The most important part of a steel shell furnace is the selection of yoke. For steel shell furnaces of the same model, different yoke selections lead to a large price gap. Generally, brand-new high-quality Z11 high-permeability cold-rolled silicon steel sheets should be selected, with a thickness of 0.3mm. The profiling structure is adopted, and the inner arc surface is consistent with the outer arc of the induction coil, so that the yoke can be closely attached to the outer side of the induction coil, and maximize the constraint on the magnetic lines of force diverging outward from the coil. The yoke is clamped by stainless steel plates on both sides, fixed by welding, and cooled by water cooling.

(Some manufacturers use waste, non-oriented silicon steel sheets, even silicon steel sheets disassembled from waste transformers to make yokes.)

Copper tube and copper busbar: The core of the melting furnace is the induction coil. There is a huge difference in performance and price between cold extruded copper tubes and cast copper tubes. Giant-section T2 cold extruded copper tubes should be adopted. The surface insulation treatment of copper tubes adopts electrostatic spraying to reach Class H insulation. To protect the insulation strength, the surface is wrapped once with mica tape and alkali-free glass fiber tape respectively, and then coated with moisture-proof insulating enamel. A certain gap is reserved between turns of the coil. When the refractory mortar is applied inside the coil, the refractory mortar can penetrate into the gaps to enhance the adhesion of the refractory mortar on the coil. After the refractory mortar is built, the inner surface is smooth, which is convenient for removing the furnace lining to protect the coil. Several additional stainless steel water cooling rings are added at the upper and lower ends of the coil to increase the overall rigidity and facilitate heat dissipation.

(Some manufacturers use cast copper or T3 copper tubes, which have poor conductivity and are prone to cracking and water leakage. Special attention should be paid to this.)

Thyristor:The quality of thyristors used by different manufacturers is generally uneven. High-quality thyristors feature good temperature sensitivity, fast response and low failure rate. Therefore, choosing thyristors from well-known manufacturers guarantees reliable and stable quality.

(When selecting, you should require the electric furnace manufacturer to mark the manufacturer of the thyristor and provide the product qualification certificate of the thyristor. High-quality thyristors are produced by manufacturers including Xiangfan Taiji Semiconductor Co., Ltd. and Xi'an Power Electronics Research Institute, etc.)

Power Cabinet:Regular manufacturers use standard spray-treated steel plate for cabinet shells, instead of sprayed iron sheet shells. In addition, the dimensions and specifications of qualified power cabinets are all standard. Unscrupulous manufacturers cut corners on power cabinets, with insufficient height, width and thickness; some even place the reactor outside the power cabinet. Regular manufacturers install low-voltage switches inside the medium-frequency power supply, so users do not need to configure additional voltage switchgear. However, some unqualified manufacturers do not install low-voltage switches inside the power supply, which invisibly increases users' costs (well-known high-quality low-voltage switch brands include Huanyu, Chint, Delixi, etc.).

Capacitor: For the capacitor cabinet for reactive power compensation, the core requirement is to be equipped with sufficient capacitors. Generally, the total compensation capacity of capacitors is 18 to 20 times the power of the power supply, that is: Capacitance Compensation Capacity (Kvar) = (18—20) × Power Supply Power. And you shall select capacitors from regular manufacturers.

Reactor: The main material of a reactor is silicon steel sheet. You should choose new products produced by regular manufacturers, and do not use recycled second-hand silicon steel sheets.

Furnace Shell and Magnetic Yoke:For the selection of the shell of aluminum shell furnaces, the furnace shell of a standard 1-ton aluminum shell furnace is made of 400Kg cast aluminum alloy with a thickness of 40mm, while many manufacturers often produce furnace shells with insufficient weight and thickness. For steel shell furnaces, the most important part is the selection of magnetic yoke. For steel shell furnaces of the same model, different magnetic yoke configurations lead to a huge price gap. Generally, the magnetic yoke shall be made of brand-new high-quality Z11 high-permeability cold-rolled silicon steel sheets with a thickness of 0.3mm. It adopts a profiling structure, and the curvature of its inner arc surface is the same as that of the outer arc of the induction coil, so that the magnetic yoke can fit closely to the outer side of the induction coil, and maximize the constraint on the magnetic lines of force diverging outward from the coil. The magnetic yoke is clamped by stainless steel plates on both sides, fixed by welding, and cooled by water.

(Some manufacturers use waste, non-oriented silicon steel sheets, or even silicon steel sheets disassembled from scrapped transformers to make magnetic yokes,)

Copper Pipes and Copper Busbars: The core of a melting furnace is the induction coil. There is a huge gap in performance and price between cold-extruded copper pipes and cast copper pipes for induction coils. You should select large-section T2 cold-extruded copper pipes. The surface insulation treatment of copper pipes adopts electrostatic spraying, which reaches Class H insulation. To protect the insulation strength, the surface is wrapped once each with mica tape and alkali-free glass fiber ribbon, then coated with moisture-proof insulating enamel. A certain gap is left between coil turns. When coating the refractory clay inside the coil, the refractory clay shall penetrate into the gaps to enhance the adhesion of the clay on the coil. After the refractory clay is formed, the inner surface is smoothed, which is convenient for removing the furnace lining to protect the coil. Several additional stainless steel water cooling rings are added at the upper and lower ends of the coil to increase the overall rigidity and improve heat dissipation.

(Some manufacturers use cast copper or T3 copper pipes, which have poor conductivity and are prone to cracking and water leakage. Special attention shall be paid to this.)

Thyristor:The quality of thyristors used by different manufacturers is generally uneven. High-quality thyristors feature good temperature sensitivity, fast response and low failure rate. Therefore, choosing thyristors from well-known manufacturers ensures reliable and stable quality.

(When selecting, you should require the electric furnace manufacturer to indicate the manufacturer of the thyristor and provide the product qualification certificate issued by the thyristor manufacturer. High-quality thyristor manufacturers include Xiangfan Taiji Semiconductor Co., Ltd., Xi'an Power Electronics Research Institute, etc.)

Power Cabinet:Regular manufacturers use standard spray plastic plate for cabinet shells, instead of spray-painted iron sheet shells. In addition, all dimension specifications of power cabinets are standard. Disreputable manufacturers cut corners on power cabinets, with insufficient height, width and thickness. Some even place the reactor outside the power cabinet. Regular manufacturers all install low-voltage switches inside the medium-frequency power supply, so users do not need to configure an additional voltage switch cabinet. However, some disreputable manufacturers do not install low-voltage switches inside the power supply, which invisibly increases users' costs (Quality low-voltage switch brands include Huanyu, Chint, Delixi, etc.).

Capacitor: For the capacitor cabinet used for reactive power compensation, the core requirement is to be equipped with a sufficient number of capacitors. Generally, the total compensation capacity of capacitors is 18 to 20 times the power of the power supply, that is: Capacitance compensation capacity (Kvar) = (20—18) x power supply power. And you should choose capacitors produced by regular manufacturers.

Reactor: The main material of a reactor is silicon steel sheet. You should choose brand-new products produced by regular manufacturers, and do not use recycled second-hand silicon steel sheets.

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