The core of the induction melting furnace is the induction coil. The effect and price of cold extruded copper pipe and cast copper pipe are very different. T2 cold extruded copper pipe with a rectangular section shall be used. The surface insulation treatment of copper pipe shall be treated with TSC-L ultra high-temperature insulation paint or APC-H+ high-temperature arc resistant insulation enamel, and the temperature resistance shall exceed 200 ℃. Why choose high-temperature insulating paint?
The induced current passing through the coil has a skin effect, that is, the current is mainly concentrated on the surface of the copper tube. The higher the frequency of the induced current, the greater the surface current density. Therefore, the heating of the copper tube of the induction coil is concentrated on the surface, and the surface temperature in contact with the insulating paint is much higher than the temperature of the part in contact with the cooling water in the copper tube. Even under normal circulating water cooling conditions, the outlet water temperature is controlled at 50-60 ℃, and the temperature of the copper pipe surface will exceed 80 ℃.
The new furnace lining is thicker, which can effectively prevent the heat of molten steel in the foundry melting furnace from being transmitted to the induction coil surface. However, with the rapid erosion of the furnace lining in the later stage, the furnace lining becomes thinner in the later stage, and the heat of molten steel transmitted to the coil surface is much higher than that of the new furnace lining. The actual measurement surface shows that the temperature of the coil slurry layer is about 80 ° when the furnace lining is new (the thickness of the furnace lining is about 15cm). By the late stage of the furnace lining (the thickness is about 5cm), the temperature of the coil slurry layer has risen to nearly 200 ℃, and at this time, the conventional insulating paint has been completely carbonized and failed.
The cooling capacity of cooling water decreases, which is mainly caused by the impact of water quality. The cooling water is easy to scale under high-temperature, especially in the northern and western regions where the water quality is relatively hard. The scaling phenomenon of the cooling water is prominent, blocking the copper pipe, reducing the water pressure, significantly reducing the cooling capacity, and increasing the temperature in turn accelerates the scaling. Once this happens, the temperature of the copper pipe surface will rise rapidly, and the conventional insulating paint will be carbonized and damaged in a very short time.
If ordinary insulating paint is used, in order to protect its insulation strength, mica tape and alkali-free glass ribbon can be wound and wrapped on the surface respectively once, and then moisture-proof insulating enamel can be coated. However, the construction of this method is complex, the material cost and labor cost are high, and the effect is not as obvious as that of directly applying high-temperature insulating paint. Why is it better to spray high-temperature insulating paint directly than to wrap the insulating tape?
At present, the commonly used insulation tape is mica tape, alkali-free glass ribbon or polyimide tape. These materials have good insulation performance, but the adhesion wrapped on the copper pipe is not ideal, which is mainly bonded by brushing another layer of insulating paint or resin. However, the medium frequency furnace has strong vibration in the production process. With the passage of time, the wrapped insulating tape is easy to fall off from the copper pipe, or form many cracks. The moisture or other water vapor of the new induction furnace lining has metal dust, which will penetrate into these gaps, forming a short circuit and completely destroying the insulation effect. The high-temperature insulating paint has good adhesion on the surface of the copper pipe, forming a dense and hard insulating protective film on the surface, which will not happen.
At the same time, glass ribbon or mica ribbon is easy to become brittle in the long-term high-temperature environment, and its effective use time is not long. There is a certain gap between the turns of the coil. When applying the fire-resistant plaster in the coil, the fire-resistant plaster should penetrate into the gap to strengthen the adhesion of the plaster on the coil to the coil. After the fire-resistant plaster is built, the inner surface is smooth to facilitate the removal of the furnace lining to protect the coil. After the fire-resistant plaster is built, the inner surface is smooth to facilitate the removal of the furnace lining to protect the coil. Several turns of stainless steel water-cooling rings are added at the upper and lower ends of the coil, Increase the overall rigidity, which is conducive to heat dissipation. Some manufacturers use cast copper or T3 copper pipes, which have poor conductivity and are easy to crack, so special attention should be paid to water leakage.
Under What Circumstances Is the Induction Coil of Foundry Melting Furnace Easy to Burn out?
1. Pay attention to the direction of the water inlet and outlet. The correct way is to enter from the bottom and exit from the top. In this way, you can ensure that there is full cooling water in the induction coil, and you have to pay attention to the water flow.
2. The working conditions of the induction coil are relatively poor, so we should pay attention to the short circuit between smashes, which is generally caused by the carbonization of iron filings or iron dregs and insulating strips. In the case of a short circuit between smashes, even if the cooling water supply is normal, the induction coil will be burnt out. Unless the intermediate frequency power cabinet reports a fault.
3. I don’t know whether your foundry melting furnace is used for diathermy or smelting. If it is smelting, you should pay attention to threading the furnace (because the furnace lining becomes thinner, the molten steel flows through the furnace lining to the induction coil). The induction coil in this case must be broken. If this situation is avoided, furnace piercing protection can be installed. But this kind of protective device is rarely used in domestic furnaces.
Insulation Scheme of Medium and High-Frequency Electric Furnace Coil
Ignition or arcing of inductors (coils) in medium-frequency smelting furnaces and high-frequency heating furnaces is a common phenomenon, which seriously affects equipment safety and production efficiency. The consequences are as follows: the production efficiency of the equipment is reduced, the equipment is damaged, or the production accident and life and property safety are serious. Therefore, enough attention must be paid!
A large number of facts have proved that the direct cause of coil ignition is the damage to the insulation layer on the coil surface, which is caused by a short circuit under the condition of high voltage and large current. Therefore, ensuring long-term and effective coil surface insulation is the only way to solve this phenomenon.
One of the main reasons for the damage of the insulation layer is that the equipment has been operating at high temperatures for a long time. The higher the temperature, the faster the aging speed of the insulation layer, resulting in the insulation coating with low-temperature resistance losing its insulation performance in a short time. And too high temperature, such as the structure in the coil, the cut-off of cooling water, or the thin lining at the end of the furnace life, will lead to too high temperature. Exceeding the limit withstand the temperature of the insulation layer will directly lead to irreversible damage to the insulation;
In addition to temperature resistance, the insulation performance, adhesion, strength, toughness and workability of insulating paint are also important considerations.