Induction Coil for Medium Frequency Melting Furnace
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Induction Coil for Medium Frequency Melting Furnace
The induction coil is the core component of the melting furnace.
Cold-extruded copper tubes and cast copper tubes differ greatly in performance and cost. It is recommended to use rectangular T2 cold-extruded copper tubes. The surface insulation of the copper tubes shall be treated with TSC-L ultra-high temperature insulating varnish or APC-H+ high-temperature arc-resistant insulating enamel, with a temperature resistance exceeding 200℃.
Why choose high-temperature insulating varnish?
The induced current passing through the coil has a skin effect, meaning current concentrates mainly on the surface of the copper tube. The higher the frequency of the induced current, the greater the surface current density. As a result, heat generation in the induction coil is concentrated on the surface, so the temperature at the surface in contact with the insulating varnish is much higher than that inside the tube in contact with cooling water. Even under normal circulating water cooling with outlet water controlled at 50–60℃, the copper tube surface temperature can still exceed 80℃.
- Heat conduction from molten steel in the furnaceA new furnace has a relatively thick lining, which effectively blocks heat from molten steel reaching the coil surface. However, as the lining erodes rapidly in later stages and becomes thinner, the heat transferred to the coil surface becomes far greater than with a new lining.Actual measurements show:
New lining (thickness approx. 15 cm): coil refractory layer temperature around 80℃
Late-stage lining (thickness approx. 5 cm): coil refractory layer temperature rises to nearly 200℃
At this point, conventional insulating varnish completely carbonizes and fails.
- Reduced cooling capacity of cooling waterThis is mainly caused by water quality issues. At high temperatures, cooling water tends to form scale, especially in hard water areas such as northern and western China. Severe scaling blocks the copper tubes, reduces water flow and pressure, and significantly lowers cooling efficiency. Higher temperatures further accelerate scaling. Once this occurs, the copper tube surface temperature rises rapidly, and conventional insulating varnish carbonizes and breaks down in a short time.
If ordinary insulating varnish is used, mica tape and alkali-free fiberglass tape can be wrapped separately for insulation protection, followed by moisture-resistant insulating enamel. However, this method is complicated in construction, with high material and labor costs, and its effect is not as effective as directly applying high-temperature insulating varnish.
Why is tape wrapping inferior to spraying high-temperature insulating varnish directly?
Commonly used insulating tapes include mica tape, alkali-free fiberglass tape, and polyimide tape. Although these materials offer good insulation, their adhesion to copper tubes is poor and usually requires an additional layer of insulating varnish or resin for bonding.
During operation, medium frequency furnaces produce strong vibration. Over time, wrapped insulating tapes easily detach from the copper tubes or form gaps. Moisture from the new lining, water vapor, and metal dust can penetrate these gaps, causing short circuits and complete insulation failure.
In contrast, high-temperature insulating varnish forms excellent adhesion on the copper tube surface, creating a dense, hard insulating protective film that avoids the above problems. Meanwhile, fiberglass tape and mica tape tend to become brittle under long-term high temperatures, resulting in a short service life.
A certain gap shall be reserved between coil turns. When applying refractory ramming mass inside the coil, the mass should penetrate these gaps to enhance adhesion. After tamping, the inner surface shall be smooth to facilitate lining removal and protect the coil.Several additional turns of stainless steel water-cooled rings are added at the upper and lower ends of the coil to improve overall rigidity and heat dissipation.
Special attention shall be paid: some manufacturers use cast copper or T3 copper tubes, which have poor electrical conductivity and are prone to cracking and water leakage.
Xi’an Lanhui is one of the earliest professional manufacturers specializing in medium frequency induction heating equipment in China, integrating production and sales.Main products: series-connected one-drive-two furnaces, bottom-pouring medium frequency furnaces, medium frequency furnaces, medium frequency electric furnaces, medium frequency vacuum furnaces, medium frequency sintering furnaces, medium frequency induction heating furnaces, and other medium-high frequency induction heating equipment.