Structure of coreless induction furnace and construction method of refractory lining
The lining structure is shown in Table 1. The coil made of copper tube is outside the lining. The traditional lining structure is to lay a layer of mica paper at the position close to the coil, followed by the alarm electrode, and then lay a layer of Asbestos board (cloth) followed by dry rammed lining. The dry ramming lining gradually forms a sintered layer, a transition layer and an unsintered layer during the baking and use process. The reasonable thickness of the three-layer structure is one of the important factors determining the life of the furnace lining. In order to satisfy the bottom-top-out dismantling method, coil insulating glue appears, which replaces the mica layer and adds a layer of protection to the coil. The cement layer is generally thicker than the mica layer, but the thermal conductivity is higher than that of mica, so the lining structure containing cement is called an improved structure. The composite furnace lining structure is to meet the needs of some metal smelting, and replace the ramming lining with pre-fired crucibles and fillers. This structure solves the problem of difficult sintering of dry materials, and at the same time improves the effect of some metal melts or slag on the lining. Severe erosion condition.
Types of refractory materials for coreless induction furnaces and construction methods of lining
Refractory materials for coreless induction furnaces are classified as follows according to different materials:
(1) Ramming-molded refractory lining: The lining is rammed mechanically or manually. Most of the induction furnaces below 5t use this method to build the lining. It can be said that almost all coreless induction furnaces use ramming materials. The specific methods are: First lay a layer of asbestos board (or glass fiber cloth) inside and at the bottom of the inductor, then knot the bottom of the furnace, put on the crucible model (welded with 5~7mm steel plate), add the mixed ramming material, use gas Hammer or manually ram the crucible wall, and after knotting, first dry naturally, then bake the wood, and then bake it with electricity. The model in it does not need to be taken out, it plays the role of induction heating during the energization, and it melts with the charge when the first furnace is smelted. There are also casting processes, and induction furnaces with a capacity of 100 kg to tens of tons use this method.
(2) Prefabricated crucible or furnace tile: The forming and drying of the crucible or furnace tile lining are carried out outside the furnace. At this time, the coil is protected by insulating cement, and the impermeable dry refractory material is filled between the coil and the crucible placed in it, which is called a composite furnace lining. This structure solves the problem that the dry material is difficult to sinter at a lower temperature, and at the same time improves the situation that some metal melts and slag erode the lining. This method is suitable for induction furnaces with small capacity (generally below 200 kg). Because the prefabricated crucible method is easy to replace the lining, it is mostly used for experiments and smelting of special metals.
(3) Masonry lining: The lining of the induction furnace is layered with refractory bricks, mainly used for large induction furnaces.