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The converter lining may be partially damaged during the service and it is not suitable to be repaired with the charge material, such as the trunnion and the slag line. The refractory material is sprayed on the part with severe local damage, and is sintered with the furnace lining brick to repair the lining. The main raw material for the converter lining spray is composed of magnesia, binder, plasticizer and a small amount of water. Commonly used spray methods include dry spray, semi-dry spray, and flame spray.
The specific requirements for the lining of the converter lining are: sufficient refractoriness; can withstand the high temperature inside the furnace; the spray material can be attached to the lining to be sprayed; the material detachment is less; the spray material adhesion layer can The surface of the red hot lining to be sprayed (800~1000 °C) is well sintered, melted into one, and has sufficient strength; the spray filler layer can withstand high temperature slag, molten steel, furnace gas and metal oxide vapor. Erosion; the spray material can flow smoothly in the spray pipe.
The spraying machine for performing the semi-dry spraying operation includes a storage tank, a compressed air transport mechanism, and a nozzle; the spray material in the storage tank is sent to the nozzle through the compressed air, and the appropriate amount of water (10% to 18%) is mixed. Sprayed onto the working surface of the lining at a certain speed under air pressure, and the sprayed material finally sticks and solidifies. The process factors affecting the semi-dry spray effect are:
(1) The lining spray is carried out in the hot state, so the residual temperature of the working surface has a significant effect on the spray effect, and it is generally considered that 800 ~ 1000 °C is better;
(2) The particle composition, binder, water addition, air pressure, etc. of the spray material have a serious influence on the adhesion rate of the spray material. The basic raw materials of the spray feed are magnesia and magnesium dolomite sand, and the binder is mainly powdered sodium silicate, sodium phosphate, calcium phosphate, chromate and the like. One of the functions of the binder is to make the spray material adhere to the working surface of the furnace lining; the other function is to form a high temperature mineral phase at a high temperature, so that the spray material can not only be firmly sintered with the working surface of the furnace lining In a whole, and make it very resistant to erosion. It is often required to contain a certain amount of CaO in the components of the spray compound, which can improve the high temperature performance and adhesion of the spray material. The effectiveness of the spray material is measured by the adhesion rate and the number of uses. The general adhesion rate requirement is greater than 85% and the number of uses is 3 to 5 times.
Flame spray repair was first applied to the repair of coke ovens, and later extended to the converter lining, which is a new technically difficult technology. It is a simple and convenient method for the semi-dry spraying of the converter lining, but it has a fatal weakness, that is, adding moisture during the spraying process. When the water contacts the repairing working surface, it will generate a large amount due to the residual heat. Water vapor, and will accumulate a certain amount of vapor pressure, leaving a hidden danger to the bonding of the spray and the working surface and the use of the spray. However, the flame spray does not add moisture, but is equipped with flammable materials, flammable gases and oxygen. The spray material burns and heats during the spray process, and some of the materials become molten and contact with a working surface with a relatively high temperature. It will be melted and sintered into a whole. The flammable materials and combustible gases included include coke powder, coal powder, propane, methane, oxygen, and the like. The flame spray is mostly carried out in the working gap after the tapping of the converter. The spray time is very short, the residual temperature of the lining is relatively high, the adhesion effect is good, and the service life is relatively long. Generally, the spray can be used 10 to 20 times.
In order to improve the quality of the spray material, it should be developed in the direction of high-quality magnesia and magnesium carbon spray. The spray method should be developed by semi-dry spray to the direction of flame spray. In recent years, a dry magnesium carbonaceous spray (W(Mg〇)> 85%, C7%~10%) is a dry material, which is burned when it is sprayed into a hot lining. The bonding agent is melted, and the spray material sprayed onto the lining is welded to the lining. In this way, the adhesion rate is more than 90%. This spray material is similar to the flame spray material, plus magnesium carbon, so the effect is very good, and the service life is increased to more than 30 times.
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