Refractory spray coatings and repairing materials are important varieties of unshaped refractory materials. They are a material that has developed rapidly in the past ten years. In kilns and thermal equipment, the material can be used for spraying new linings, and can also be used for repairing furnace linings. Production practice has proved that this kind of material is an effective technical measure to speed up construction progress, shorten furnace repair time, prolong furnace service life and reduce refractory material consumption.
The refractory spray coating is sprayed with a spray gun to spray the refractory mixture on the surface to be sprayed, that is, the material constructed by spraying is called a refractory spray coating. Spraying is carried out with a sprayer or a spray gun, and is a new process in furnace building and furnace repair. The refractory spray coating can obtain a sufficient speed in the pipeline with the help of compressed air or mechanical pressure, and then spray the sprayed surface through the nozzle to form a solid spray coating. The spraying method is divided into three categories: wet method, dry method and flame method; according to the state of the material received by the sprayed surface, it is divided into two categories: cold material spraying method and molten material spraying method.
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Wet spraying means that the refractory spray coating is sprayed on the surface to be sprayed after adding water or a liquid binder. According to the order of adding water or liquid binder and its dosage, it can be divided into four types: mud method, wet method, semi-dry method and pseudo-dry method. Among them, every two methods are used in combination, which is called mixed method. The mud method is to first stir the refractory mixture into mud and then spray it, which is mainly used for thermal gunning of the furnace lining; the wet method is to stir the refractory mixture into a pumping mud before spraying; the semi-dry method is to add the refractory mixture first. A small amount of water is stirred and wetted evenly, and then it is transported to the nozzle and the remaining water is added for spraying; the pseudo-drying method is to mix the refractory mixture through a mixer, and then transport it to the nozzle and add water for spraying. The last three methods are suitable for spraying the furnace or spraying the furnace lining.
Dry spraying means that the mixed refractory spray coating is directly sprayed onto the sprayed surface through the nozzle, mainly used for furnace repair.
Flame spraying is to use oxygen to transport the mixed refractory spray coating to the nozzle where it meets the combustible gas and spray it together. This method is mainly used for thermal spraying of furnace linings, with less damage to the original lining, easy sintering of the sprayed layer, long service life, but high cost. In addition, the refractory mixture is melted or semi-melted with a plasma gun and sprayed onto the sprayed surface, and the slag with an appropriately adjusted composition in the furnace is sprayed onto the lining (that is, the slag splashing method), which also belongs to this category. method.
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Refractory repair material refers to the material used for repairing kiln and thermal equipment, commonly known as refractory repair material. The material is actually classified by use. The construction methods include spraying, filling, pressing, pumping or grouting. There are many kinds of refractory repair materials, mainly including refractory gunning materials, melt-jet gunning materials, refractory feeding materials, refractory pressing materials, refractory pump injection materials and refractory grouting materials. This material is mostly constructed by spraying method, so it is not included in this chapter, and only important varieties are introduced. The refractory repair material has excellent performance, is easy to use, can improve the service life of the kiln, increase the output, reduce the cost, and has significant economic benefits. Therefore, in recent years, refractory repair materials have developed rapidly, and their output far exceeds that of refractory spray coatings.
Among the refractory spray coatings and refractory repair materials, many materials are common, but the construction methods are different, and their names are different. For example, mud spray paint and refractory grouting material, refractory gunning material and feeding material, etc., have basically the same composition and performance, but the construction methods are different, and the names are also different.
The material composition of refractory spray coating and refractory repair material is basically similar to that of refractory castables of the same variety. The difference is that the critical particle size of refractory aggregate is smaller, generally 35mm, and the combined amount of refractory powder, ultrafine powder and binder is relatively small. More, generally 35%-45%. Since the material composition is similar, the coagulation and hardening mechanism of this type of material and the physical and chemical changes at high temperature are basically similar, so they are generally not repeated.
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The technical keys of refractory spray coatings and refractory repair materials are mainly adhesion, cohesion, strength and sintering. This is also a basic characteristic that the material should have, otherwise the service life of the spray coating and repair layer will be reduced. This characteristic is closely related to the material itself, and more importantly, it is restricted by the sprayer and other equipment and construction process parameters, and is also affected by factors such as the state of the spray body and the conditions of use. These constraints and influencing factors are the basis for the selection of refractory spray coatings and refractory repair materials, and are also the key links to obtain a good spray or repair layer. Therefore, it should be selected reasonably, carefully adjusted, and strictly controlled.
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