Refractories for glass kilns

April 29, 2021

Refractories for glass kilns

Glass kiln has many forms, such as flat tank kiln, horizontal flame flow tank kiln and horseshoe flame flow tank kiln, among which flat glass kiln is divided into three parts: tank kiln, regenerative chamber and tin tank. In addition, there are L hanging wall, electric flux, bubbling and melt division device, tin tank.

The bottom of the pool is made of large clay bricks, which are laid with zirconium or AZS ramming material. The melting part is then paved with 33 AZS bricks by electrofusion without shrinkage hole oxidation method. When the requirements are not high, the bottom of the pool before the hot spot can also be paved with sintered AZS bricks. Cooling section with α-β-Al₂O₃ casting brick pavement, when the requirements are not high available No. 33 shrinkage shrinkage oxidation method electric melting AZS brick.

The wall of the melting pool shall be constructed by the whole No. 33, No. 36 and No. 41 oxidation electrofused AZS bricks. The bricks produced by dense casting or inclined casting can be selected according to the erosion condition, but the No. 41 AZS bricks without shrinkage cavity shall be selected for the corner bricks. The liquid line of the wall brick should be air-cooled or water-cooled, and the other parts can be insulated by non-asbestos calcium silicate board. Cooling part of the pool wall using α-β-Al₂O₃ casting brick, low requirements can also use No. 33 oxidation method inclined casting AZS brick.

The parapet of the melting zone is made of 33 AZS electric fused brick without shrinkage hole. Clarification area and cooling parapet using high quality silicon brick, high requirements can be used β-Al₂O₃ casting brick.

L The nose of the hanging wall is made of 33 electric fused AZS sintered zirconium mullite composite brick. The AZS portion of the brick has a T-hook; Part of zirconium mullite has sigma ─ ─ groove. The two are connected by mechanical occlusion. When the requirements are not high, zirconium mullite bricks with good sintering, normal porosity, good volume stability at high temperature and main crystalline phase of mullite and plagioclase zircon can be used. High quality zirconium mullite bricks are used above the composite bricks. The top layer is made of high-quality silicon bricks. The rear gable of the glass kiln and the traditional front face wall can be made of high quality silicon brick.

L Both domestic and imported zirconium mullite sintered bricks used in the hanging wall have repeatedly spalled off. After spalling occurs, a large number of stones appear in glass products, and the qualified rate of products and the economic benefit of the factory are seriously affected. The main reason is the use of sintered not good enough, high porosity or contain a lot of zirconite brick. Zirconite is an acidic mineral, which will decompose quickly in the presence of high temperature and high concentration of alkali vapor, forming low melt and promoting the mullite Xia petrification reaction. In the presence of zirconite, the volumetric effect of fossilization is +39%. The volume change produces large stresses, which cannot be relaxed, resulting in spalling.

Melted crown using high quality silica brick. High quality silicon brick for SIO ₂ content 96%, melting index (Al₂O₃+2*R₂O) less than 0.5%, true density is not more than 2.34 or 2.35, and has a small size tolerance. Silica brick is sealed with amorphous material first, relay insulation layer. The main mechanism of arch walling damage is through upward droughtings or "rat holes".

The "rat hole" is the alkali vapor that escapes from the kiln condenses in the brick seam and corrodes the silicon brick. The erosion products with low viscosity run off along the brick seam, causing the further expansion of the gap. The key to prevent "rat hole" is to design the temperature field in the refractory in advance, so that the alkali vapor can condense on the amorphous refractory rather than in the cracks of the silicon brick.

The top of the regenerator by NA ₂O, flying material and high temperature compound effect. The erosion of the middle and lower parts of the regenerator is mainly rich in mirabilite.

98%~97% and 96%~95% magnesia bricks are used for the lattice without special requirements at 1300~1100℃. Directly bonded magnesia-chrome brick was used at 1100~800℃. Low porosity clay bricks were used below 800℃. Magnesium chromium refractories in CR ₂O₃ to improve the resistance of materials to mirabilite erosion has a good effect. However, in order to avoid chromium pollution, magnesia zirconium brick (magnesia aggregate + magnesia olivine + plagic zircon matrix) or pure spinel brick can be used instead of magnesia chrome brick.

Tin trough bottom brick is generally composed of large refractory brick, sealing and filling material, graphite products and stainless steel fixed parts. The bottom brick is fixed on the bottom plate by screw; The upper part of the bolt is covered by an inverted tapered amorphous refractory solidified material. In case of tin solution along the edge of the inverted taper hole invasion, it can not make the solidified amorphous material surface, fall off. The main function of graphite powder and graphite gasket is to protect the bolt from the erosion of the leaking tin liquid, so that the bolt can reliably and permanently play a fixed role and prevent the bottom brick from floating.

In addition to the properties of conventional refractories, tin trough bottom brick also requires low fossilization tendency, hydrogen diffusion, high strain rate and surface accuracy. Reduce the trend of Xia petrification method: one is to control the content of Al₂O₃ is 38%~43%, significant porosity is not more than 23%; The second is to control the content of AL ₂O₃ is 43%~48%, and the apparent porosity is not greater than 15%. Hydrogen diffusion is used to characterize the gas permeability index, its value should not be greater than 1.5KPa (150mmH₂O). Strain rate is the maximum percentage of deformation of a material before compression failure. The strain rate is high, the deformation of the material is large after compression, and the brick seam can be left narrow, which can also reduce the possibility of tin leakage and bottom brick being pulled out by buoyancy.

There is a correlation between porosity and strain rate. The porosity and strain rate are high, but the corrosion resistance is poor and the petrifaction tendency increases accordingly. Domestic and foreign products have their own advantages. Foreign bricks are characterized by low aluminum, high porosity, high diffusivity and high strain rate. Domestic bricks are characterized by blast furnace, low porosity, low diffusivity and low strain rate.

The combined modular structure of siliconite brick and insulation brick is used to construct the tin groove roof in foreign countries. In the early stage of our country, prefabricated blocks of heat-resistant reinforced concrete were used to construct the tin groove roof, and then the combined tin groove roof was developed. The supporting module adopts prefabricated parts; The heating module is made of mullite fired brick and the electric heating element is installed on the module. This structure combines the advantages of prefabricated parts and sintered bricks: low cost, easy installation, good flexibility of electric heater arrangement, and long service life. The prefabricated parts used for tin tank top had better be treated at high temperature to completely remove the bound water and obtain stable structure and performance.