Unshaped refractory materials constructed by ramming (manual or mechanical) and hardened under heating above normal temperature. It is composed of refractory aggregates, powders, binders and admixtures with a certain gradation, and is mixed with water or other liquids. According to the material classification, there are high alumina, clay, magnesia, dolomite and zirconium ramming materials.
①Composition
Ramming materials can be prepared from refractory aggregates and powders of various materials according to the needs of use. At the same time, an appropriate binder is selected according to the refractory aggregate material and usage requirements. Some ramming materials do not require a binder but only add a small amount of flux to promote sintering. Sodium silicate, ethyl silicate and silica gel are commonly used as binding agents in acid ramming materials. Alkaline ramming materials use aqueous solutions of magnesium chloride and sulfate as well as phosphates and their polymers as binding agents. Those with higher carbon content are also often used. Forms carbon-bound organic matter and temporary binders at high temperatures. Glauber's salt is often used as a binding agent in chromium ramming materials. High-aluminum and corundum ramming materials commonly use inorganic substances such as phosphoric acid and aluminum phosphates, sulfates, and chlorides as binding agents. When phosphoric acid is used as the binding agent, the phosphoric acid reacts with the activated alumina in the ramming material during the storage process to form water-insoluble aluminum orthophosphate precipitates that solidify and harden. Loss of plasticity makes construction difficult. Therefore, to extend the shelf life of ramming materials, appropriate preservatives must be added to prevent or delay the occurrence of coagulation and hardening. Oxalic acid is usually used as the preservative.
➁Performance
Generally, ramming materials are mainly used in parts that are in direct contact with the melt. Refractory materials are required to have good volume stability, compactness and corrosion resistance, so high-temperature fired or electrofused raw materials are generally used. The maximum particle size of ramming material is related to the construction method of the used part. Generally, the critical particle size is 8mm. Most ramming materials have low strength at room temperature before being sintered, and some have low medium-temperature strength. Good bonding can only be achieved after sintering when heated. The fire resistance and melt erosion resistance of ramming materials can be obtained through the selection of high-quality raw materials, adjustment of reasonable proportions and careful construction. In addition to having high stability and corrosion resistance, ramming materials have high temperature resistance. Its service life also depends to a large extent on the quality of baking before use or sintering when first used. If the heating surface is sintered as a whole, has no cracks and is not separated from the bottom layer, the service life can be improved.
③ Ramming materials used in glass kilns
a.Zircon sand ramming material
Its main components are (%): Zr02 62, Si02 32, A1203 2, Fe203 0.5, the volume density is greater than 3g/cm3, the refractory degree is above 1790℃, and the maximum particle size is 0.5mm. The binding agent is aluminum dihydrogen phosphate, which is composed of orthophosphoric acid and aluminum hydroxide. It has strong bonding, high strength, and high temperature resistance. However, it is easy to dry and harden, does not store for a long time, and is corrosive to the skin and is inconvenient to use.
b.Zirconium corundum ramming material
(The French brand is ERSOL) AZS brick waste is commonly used as refractory material. The composition of the material is (%): AI203 48, ZrO2 30, Si02 20, the crystal phase is a-AI203, mullite, baddeleyite, glass phase, the maximum particle size is 5mm. When using, you only need to add water and stir. The volume density is 3.2a/cm3, the porosity is 12%, the tendency of bubbles is weak, and it is highly resistant to the erosion of glass liquid at 1400°C. It can also be used as sealing layer and mud material.
c. Low shrinkage AZSC ramming material
It introduces a certain amount of chromium-containing materials into the basic components of AZS. Its volume density is greater than 2.9g/cm3, its reheating line shrinkage (1400'℃, 3h) is less than 0.2%, and its resistance to the erosion of glass liquid is better than the above two methods. Make materials. It can also be used as sealing layer and casting compound.
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