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, so that it is sintered with the furnace lining refractory brick to repair the lining. The main raw refractory 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 spray feed of the converter furnace are sufficient refractoriness; it can withstand the high temperature in the furnace, the spray material can be attached to the lining to be sprayed; the refractory material detachment is less; the spray material adhesion layer can be treated The surface of the red hot lining of the spray (800~1000 °C) is well sintered, melted into one body and has sufficient strength, the spray filler layer can withstand the erosion of high temperature slag, molten steel, furnace gas and metal oxide vapor; 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 conveying mechanism, and a nozzle; the spray material in the storage tank is sent to the nozzle through the compressed air, and mixed with an appropriate amount of water (10% to 18%). Sprayed to 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 effect of semi-dry spray is:
(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℃ 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 materials of the spray material are magnesia and magnesium dolomite sand, and the binder is mainly powder. Sodium silicate, sodium phosphate, calcium, potassium 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 composition of the spray material, 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 spraying 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 blended 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. Will be melted and sintered into a whole. The flammable materials and combustible gases to be blended include coke powder, coal powder, propane, methane, oxygen, and the like. The flame spraying is mostly carried out in the working gap after the tapping of the converter. The spraying time is very short, the residual temperature of the lining is relatively high, the adhesion effect is good, and the service life is long. Generally, the spraying 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(MgO) > 85%, C: 7% to 10%) is a dry material. When dry sprayed into a hot lining, it contains a heat generating agent. , causing the bonding agent to melt, and welding the sprayed material sprayed onto the lining to the lining. This 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, the service life increased to more than 30 times.
