In the section the industrial kiln is subjected to a high temperature atmosphere, the surface of the refractory is often coated with particles such as mullite and alumina as the main components, and a refractory refractory coating agent made of a binder such as clay water glass is added to To prevent the surface of the refractory and the burned material in the kiln to adhere to each other and damage the surface of the refractory. However, when the refractory surface is coated with the above-mentioned refractory coating agent, the water glass binder in the coating agent will vitrify, and it Poor thermal expansion results in cracks that cause the coating to peel off. It cannot fully protect the refractory substrate, and the heat insulation is reduced, the thermal shock resistance is weakened, and the service life of the refractory is shortened. This requires frequent maintenance and repair. It has undoubtedly increased the cost of refractory materials and construction. In order to overcome these defects, a refractory protective coating agent that can effectively protect the refractory is successfully developed.
1. Composition of high temperature protective agent for working kiln
(1) Fire-resistant protective coating agent
The protective coating agent is made of ceramic fiber with a size of 60`300 mesh, silica sol (silica content 5`70%, its particle size) as the main raw material, and an appropriate amount of organic binder.
(2) Ceramic fiber
The ceramic fiber used depends on the use temperature. For example, if the use temperature is 800`1600 ℃, aluminum fiber with alumina as the main component should be used. When used, the fibers used are crushed, iron removed, and sieved into short fibers with a size of 60`300 mesh. The size of ceramic fibers is less than 60 mesh. The thermal shock resistance is reduced. If it exceeds 300 mesh, the adhesion is reduced. % (By weight)
(3) Silica sol
Silica sol is used as an inorganic binder. It contains silica in the range of 5`70% and 10`15%. If the silica content is in this range, either the cohesive strength is reduced, it is easy to peel off, it is coated. The surface of the agent is fused with silica to prevent weak adhesion with the fired product. In addition, in order to improve the uniformity of the silica particle size, it is the adhesion that should be reduced by reducing the binding force between the particles. Should be kept within the range of 5`30 / um. The blending amount of silica sol is 50`65% (by weight).
(4) Organic binder
As the organic binder, powdery carboxymethyl cellulose, polyvinyl alcohol glycerin is used, and the appropriate amount thereof is blended.
2. The use method and effect of high temperature protective agent for industrial kiln
Surface coating method: The refractory protective coating agent can be sprayed, brushed dipped on the surface of the refractory. The thickness of the coating protective layer is generally 0.1`2mm. However, when the substrate used in the kiln wall is lining refractory, in order to improve the heat insulation, the coating thickness can be more than 2mm. In the surface of the refractory, the suitable coating viscosity of the coating agent is 2.5`30 poise.
3. Application effect of paint
The protective coating agent can firmly adhere to the basic surface of the refractory, produce siloxane bonds, and the structure is dense and hard, especially coated with silicon carbide refractory surface, forming a protective layer with an alumina-rich layer and a silicon oxide-rich layer The composition can prevent the erosion of oxygen and combustion gases, has a good anti-oxidation effect, and prevents the refractory deteriorating.
4. Application examples
Alumina ceramic fiber of size 70 mesh is mixed with the same fiber of 150 mesh in equal amount, and then 38% of the mixed ceramic fiber and 61.8% of inorganic binder with silica sol as the main component, and 0.2% of carboxymethyl cellulose The refractory protective coating agent with a viscosity of 10 poises is changed in the thickness range of 0.7-7mm with a thickness of 0.1mm. When the thickness is 1mm, the impact resistance value is 14 times that of the refractory without the coating agent. However, the protective coating should be thick, because the thickness of the coating is too thick, although the impact resistance value needs to be improved, but the peeling rate will increase instead.
In addition, the refractory plate forming the same protective coating is sent to the firing kiln, heated to 300`900 ℃, immediately taken out, quenched at room temperature, and observed the cracking state. As a result, no cracks appeared on the surface of the refractory plate, and it was subjected to rapid cooling and rapid heating After impact, the flexural strength is increased by about 15% at 900 ℃ quenching temperature difference compared with the refractory plate without protective coating. In addition, the refractory plate with protective coating can continue to be used at a high temperature of 1350 ℃, and the service life is unprotected. 2 times the refractory board.
It can be seen the above that the refractory protective coating agent is coated on the surface of refractory materials in kilns, flues and other high-temperature atmospheres, which can form an effective protective layer to prevent basic damage to the refractory materials, extend its service life, and reduce maintenance And the number of repairs, saving refractory materials and construction costs, bringing significant economic benefits, the protective coating agent uses a variety of refractory and heat-resistant metal parts.
