Types And Roles Of High-temperature Protective Agents Commonly Used in Industrial Furnaces

High-temperature protective agent

The refractory surface of the section of the industrial kiln subjected to high-temperature atmosphere is often coated with mullite, alumina and other particles as the main ingredient, with the addition of binder such as clay or water glass and other refractory coatings, in order to prevent the surface of the refractory and the kiln firing material fused with each other and the surface of the refractory material damage. However, when the refractory surface is coated with the above coating agent, the water glass binder in the coating agent will be vitrified, and the refractory substrate will have thermal expansion difference, forming cracks and causing the coating to spall off, which will not give full play to the function of protecting the refractory substrate, and the heat insulation will be reduced, and the effect of thermal shock resistance will be weakened, so as to shorten the service life of the refractory material, and this requires frequent maintenance and repair, and will undoubtedly increase the cost of refractory materials and construction. This requires frequent maintenance and repair, and undoubtedly increases the cost of refractory materials and construction.

Fire-resistant protective coatings

The protective coating agent is made of ceramic fiber with a size of 60~300 mesh, silica sol (silica content of 5~70%, its particle size 5~30/um) as the main raw material, and the appropriate amount of organic binder and become.

1,Ceramic fiber

The ceramic fiber used depending on the use of temperature to determine. Such as the use of temperature 800 ° ~ 1600 ° C, it is appropriate to use alumina as the main component of the aluminum fiber. When used, the use of fiber crushing, iron removal, sieving into the size of 60 ~ 300 mesh short fibers. Ceramic fiber size less than 60 mesh, thermal shock resistance is reduced, more than 300 mesh, adhesion is reduced. Fiber with the amount of 30 ~ 50% (by weight).

2, Silica sol silica sol as an inorganic bonding material used, containing silica in the range of 5 ~ 70%, the best 10 ~ 15%. If the silica content is not in this range, either the bonding force is reduced, easy to peel off, that is, the surface of the coating is easy to melt out of silica, to prevent the fusion effect with the sintered material is weakened. In addition, in order to improve the uniformity of silica particle size, not to reduce the bonding force due to the reduction of inter-particle bonding, silica particle size should be maintained in the range of 5 ~ 30 / um. The matching amount of silica sol is 50~65% by weight.

3, Organic binder organic binder using powdered carboxymethyl cellulose, polyvinyl alcohol or glycerin. The amount of cooperation is appropriate.

The protective agent can be sprayed, brushed or impregnated on the surface of the refractory. The thickness of the coated protective layer is generally 0.1 to 2 mm, but when the substrate used in the kiln wall is a furnace lining refractory, the thickness of the coating can be more than 2 mm to improve thermal insulation. On the surface of the refractory, the suitable coating viscosity of the coating agent is 2.5 to 30 Po.

The protective coating agent can be firmly adhered to the surface of the refractory substrate, generating siloxane bonds, dense and hard structure, especially coated with silicon carbide refractory surface, the formation of a protective layer composed of alumina-rich layer and silica-rich layer, which prevents oxygen and combustion gases from erosion, has a good effect of oxidation prevention, to prevent deterioration of refractory.

The 70 purposes of alumina ceramic fiber and 150 purposes of the same fiber mixed in equal quantities, and then take the mixed ceramic fiber 38% with silica sol as the main component of the inorganic binder 61.8%, and then with 0.2% carboxymethyl cellulose with a viscosity of 10 poise refractory protective coating, in the range of 0.7-7mm coating thickness to every 0.1mm thickness of the Variation, respectively, coated in the silicon carbide refractory plate surface, sent to the highest temperature of 1350 ℃ kiln firing 12 hours, take out, determination of impact resistance value. Measurement results show that when the thickness of the protective coating is 1mm, the impact resistance value is 14 times that of the uncoated refractory. However, the protective coating should not be thick, because the coating thickness is too thick, the impact resistance value is to be improved, but the flaking rate on the contrary will increase.

Another will form the same protective coating refractory plate into the firing kiln, heating to 300 ° ~ 900 ° C, immediately removed, room temperature cold, observe the cracking state, the results of the refractory plate surface cracks did not appear, and after a sharp cold and thermal shock, flexural strength of 900 ° C under the temperature difference between the sharp cold compared to the refractory plate without a protective coating to increase by about 15%. In addition, the refractory plate with protective coating can continue to be used at a high temperature of 1350 ℃, and its service life is twice as long as that of the refractory plate without protective coating.

As can be seen from the above, the refractory protective coating is applied to the surface of kilns, flues and other refractories under high-temperature atmospheres, forming an effective protective layer, preventing damage to the refractory substrate, prolonging its service life, and at the same time reducing the number of maintenance and repairs, saving refractory materials and construction costs, and bringing significant economic benefits. The protective coating is used on all kinds of refractories and heat-resistant metal parts.

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