Amorphous refractory material that is constructed by ramming mass (manual or mechanical) and hardened under heating above normal temperature. It is composed of refractory aggregates, powders, binders, and admixtures with a certain grade, and is mixed with water or other liquids. According to the material classification, there are high-alumina, clay, magnesium, dolomite and zirconium ramming materials.
1. Composition
According to the needs of use, ramming materials can be prepared from refractory aggregates and powders of various materials. At the same time, suitable binders are selected according to the material of refractory aggregates and use requirements. Some ramming materials do not use binders but only add a small amount of flux to promote their sintering. Sodium silicate, ethyl silicate and silica gel are commonly used as binders in acidic ramming materials. Alkaline ramming materials use aqueous solutions of magnesium chloride and sulfate, as well as phosphates and their polymers as binders. Carbon-containing organic matter and temporary binders are also often used at high temperatures. Chromium ramming materials often use Glauber's salt as a binder. High-aluminum and corundum ramming materials often use phosphoric acid and inorganic substances such as aluminum phosphates, sulfates, and chlorides as binders. When phosphoric acid is used as a binder, during storage, phosphoric acid reacts with active alumina in the ramming material to form water-insoluble aluminum orthophosphate precipitation and solidify. Loss of plasticity makes construction difficult. Therefore, to extend the shelf life of the ramming mass, an appropriate preservative must be added to prevent or delay the occurrence of coagulation and hardening. Oxalic acid is usually used as a preservative.
2. Performance
Usually, ramming materials are mainly used in parts that are in direct contact with the melt. The refractory material must have good volume stability, density and corrosion resistance, so high-temperature sintering or electric melting raw materials are generally used. The maximum particle size of the ramming material is related to the construction method of the part to be used, and the general critical particle size is 8mm. Most ramming materials have low room temperature strength before sintering, and some have low medium temperature strength. Only when they are heated and sintered can they obtain a good bond. The refractory performance and resistance to molten corrosion of ramming materials can be obtained by selecting high-quality raw materials, adjusting reasonable proportions and careful construction. In addition to high stability and corrosion resistance at high temperatures, ramming materials also have high service life. To a large extent, it depends on the baking before use or the sintering quality when used for the first time. If the heating surface is sintered as a whole, without cracks and not separated from the bottom layer, the service life can be improved.
3. Ramming materials used in glass kilns
a. The main components of zircon sand ramming mass are (%): ZrO2 62, SiO2 32, Al2O3 2, Fe2O3 0.5, the volume density is greater than 3g/cm3, the refractoriness is above 1790℃, and the maximum particle size is 0.5mm. The binder is aluminum dihydrogen phosphate made of orthophosphoric acid and aluminum hydroxide. It has strong bonding, high strength and high temperature resistance, but it is easy to dry and harden, and it is not suitable for long-term storage. It is corrosive to the skin and inconvenient to use.
b. Zirconium corundum ramming material (French brand ERSOL) often uses AZS brick waste as refractory material. The composition of this ramming material is (%): Al2O3 48, ZrO2 30, SiO2 20, the crystal phase is α-Al2O3, mullite, baddeleyite, glass phase, and the maximum particle size is 5mm. When using, you only need to add water and stir. The volume density is 3.2g/cm3, the porosity is 12%, the tendency of precipitating bubbles is weak, and the resistance to glass liquid erosion is very strong at 1400℃. It can also be used as a sealing layer and slurry.
c. Low shrinkage AZSC ramming mass It introduces a certain amount of chromium-containing material into the basic composition of AZS. The volume density is greater than 2.9g/cm3, the reburning linear shrinkage (1400℃, 3h) is less than 0.2%, and the ability to resist glass liquid erosion is better than the above two ramming materials. It can also be used as a sealing layer and casting material.
