Preparation and sintering of medium frequency induction heating furnace lining

The lining of the medium frequency induction furnace not only has high operating temperature and large changes in furnace temperature, but also suffers from strong slag erosion, strong electromagnetic stirring and the amount of furnace tribute that determines the longevity of the furnace lining. The furnace lining is the most susceptible to damage. The quality of the furnace lining determines the life of the furnace lining and affects the economic benefits of the plant, so the production of the furnace lining is very important.

1) Preparation for furnace lining. Before making the furnace lining, the stack body, induction coil, etc. must be thoroughly cleaned and inspected. First, ensure that the induction coil should be fixed reliably, with a certain gap between turns, cooling water pipes and induction coils, water-cooled cables and induction coils. The connection must be reliable, and it is especially prohibited to use iron wire and other magnetic materials for binding. If the gap between the turns of the induction coil is too small, it will cause a short circuit and breakdown of the induction coil. Therefore, the defective screws and screws must be matched. If the gap is too small, use insulating materials to isolate it. The matching of coarse and fine lining sand is very important. In order to achieve the ideal furnace lining mission, good sand materials should be selected, but this cost is very high. A reasonable particle size ratio is the key to improving the service life of the furnace lining, because different particle sizes have different effects on the furnace lining. The coarser-grained sand material acts as a skeleton in the furnace lining, giving the furnace lining a certain strength to withstand various forces. The role of medium-grained sand is to fill the gaps of coarse materials, increase the packing density, improve the sintering performance of the furnace lining, and increase the strength; the role of fine-grained sand is to ensure the continuity of the sintering network of the furnace lining, so that the furnace lining has good compactness . Therefore, a reasonable ratio of coarse and fine particle sizes can obtain better tamping density and the lowest gas rate, and improve the compressive strength of the furnace lining. The greater the tamping density of the furnace lining after knotting, the smaller the volume change during sintering and use, the higher the furnace lining's ability to withstand various stresses, being less prone to cracks and having good resistance to chemical attack.

2) Knotting of furnace lining. Use glass fiber cloth of appropriate width, fold it into 4 layers according to the appropriate length and lay it on the inner wall of the induction coil, then fold it into 4 layers according to the appropriate size and lay it on the bottom of the furnace; then pour the mixed sand into the bottom twice and compact it. The height of the bottom sand should be level with the first circle at the bottom of the induction circle, and then follow the following steps to make it:

① Put the crucible into the furnace, keep it flat and straight, and evenly around it. Use inclined wooden blocks to wedge it around, and then add iron material to the crucible to compact it.

② Pour the mixed silica sand evenly around the crucible and press it firmly. The height of each sand addition is 10--15cm, and the sand is poured all the way to the middle layer of the refractory bricks on the furnace surface.

When making the upper layer and the furnace mouth, first mix the silica sand and clay evenly - add an appropriate amount of refractory cement to mix, and then add a small amount of water glass to mix; brush a layer of water glass on the interface, and then mix the mixed Pour in the sand and fill it up.

3) Sintering of furnace lining. After the furnace lining is finished, the oven and sintering can be carried out. The purpose is to fully remove the moisture in the furnace lining, make the silica sand fully and uniformly phase-change, and finally sinter it at high temperature to form a dense ceramic surface with high strength. The quality of the oven will directly affect the life of the furnace lining, otherwise all previous efforts will be wasted. Therefore, the following matters must be paid attention to when drying and sintering.

① The cooling water system, tilt system, control loop and various marks must be inspected in detail before the oven.

② A certain amount of charge must be added to the oven, approximately 70% of the height of the furnace, to ensure uniformity of temperature rise and fall.

③The oven should use low power and slow heating. When power is supplied, cooling water should be passed through the oven. In the early stage of the oven, the heating rate is 100°C/h and rises evenly until 800~900°C.

④ When the temperature of the furnace lining reaches above 1000℃, switch to 50% power supply to slowly heat up the furnace material and the furnace material and melt them slowly to reduce the erosion effect.

⑤Choose clean and rust-free return materials to reduce slag. Large pieces of material should be installed around the crucible wall, and small pieces should be added to the center of the furnace bottom.

⑥The temperature of the molten iron should be about 50°C higher than the working temperature and should be maintained for 1 to 2 hours to allow the furnace to sinter evenly. The entire melting time of the first furnace is about 2 to 3 times the normal melting time.

⑦The molten iron in the first furnace should be full so that the furnace mouth can be sintered satisfactorily, and the entire crucible has a uniform and dense sintering layer from top to bottom.

⑧After the first melting furnace, the sintering layer of the crucible is still very thin, and the sintering process can only be completed after 2 to 3 consecutive furnace meltings. If the sintering temperature is too low and the holding time is not enough, the furnace lining will crack after cooling.

⑨ When drying the oven, voltage regulation and graded power transmission are required. In general, the requirements for the lining oven and sintering are slow baking at low temperature and full furnace sintering at high temperature. The first furnace charge should be clean and free of impurities.