Classification of Unshaped Refractory Materials

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Unshaped refractory materials, also known as bulk refractory materials or monolithics refractories, are composed of bulk particles and fine powders. They do not require firing or forming before use. Depending on the requirements, the composition and properties of the material can be flexibly changed, including the refractory material’s components and particle size, the type and amount of binders, the selection and adjustment of additives (such as plasticizers, setting agents, hardening agents, water reducers, etc.), and the diversity of construction methods (casting, ramming, spraying, shotcreting, plastic construction, etc.). This advancement in shaping refractory materials into larger, irregular, and integral structures is referred to as the second generation of refractory materials.

Unshaped refractory materials are essential foundational materials in the application of refractory linings in high-temperature kilns and furnaces. Refractory castables, an important type of unshaped refractory material, have a short supply cycle, are not restricted by equipment shapes, and can be used directly after on-site forming and baking without pre-firing. Refractory castables can be used to create seamless linings, also known as integral refractory materials. High-alumina castables, high-alumina low-cement castables, steel fiber wear-resistant castables, and mullite castables are examples of unshaped refractory materials widely used in the design of linings for cement kilns, operating in various parts of thermal equipment over the years.

Unshaped Refractory Materials Classification


A material with good fluidity after mixing with water, also known as pouring material. After molding, it needs proper curing to solidify and harden. It can be used after baking according to a certain schedule. Castables use alumino-silicate clinker, mullite materials, or alkaline refractory clinker as aggregates. Lightweight castables use expanded perlite, vermiculite, ceramic granules, and alumina hollow spheres as aggregates. Binders include calcium aluminate cement, sodium silicate, ethyl silicate, polyaluminum chloride, clay, or phosphate, among others. The use of additives depends on the specific situation, aiming to improve construction performance and enhance physical and chemical properties.

Construction and forming methods for castables include vibration, pumping, ramming, spraying, etc. When castables are used as integral linings, they often need to be used in conjunction with metal or ceramic anchor components. Adding stainless steel fibers can improve their resistance to mechanical vibration and thermal shock. Castables are used as linings for various heat treatment furnaces, ore roasting furnaces, catalytic cracking furnaces, conversion furnaces, etc. They are also used as linings for smelting furnaces and high-temperature molten metal troughs, such as lead-zinc smelting furnaces, tin troughs, salt baths, steel or iron tapping troughs, steel ladles, and nozzles for steel vacuum circulation degassing devices.

Plastic Refractory

Malleable clay or mud. It is easily deformable without cracking under appropriate external force and does not deform further after stress relief. Plastic refractories include semi-silica, clay, high-alumina, zirconite, carbonaceous, and lightweight plastics. Plastic refractories must include plasticizing materials, often high-plasticity clays, and plasticity can be improved using plasticizers. Plasticizers include carboxymethyl cellulose, starch, lignosulfonates, etc. Binders used for plastic refractories include plastic clays, phosphates, aluminum dihydrogen phosphate, aluminum sulfate, etc. Aluminum oxide plastic refractories with added phosphoric acid or phosphate binders undergo a chemical reaction with aluminum oxide during storage, producing insoluble aluminum orthophosphate that hardens the mud, so preservatives such as oxalic acid, citric acid, acetone, etc., need to be added.

Construction methods generally use ramming or vibration. When plastic refractories are used to construct integral furnace linings, it is necessary to use metal or ceramic anchor components. Plastic refractories are used as linings for annealing furnaces, heating furnaces, boilers, and other thermal equipment, and are also used for wrapping water-cooled pipes in heating furnaces.

Spraying Repair Material

A refractory mixture used for spraying or coating with a spray gun. According to the spraying method, it can be divided into wet spraying (or slurry spraying), semi-dry spraying, and flame spraying. Wet spraying utilizes compressed air to spray a slurry containing 20-40% refractory powder, achieving high atomization, high adhesion, and uniform thin-layer spraying. Semi-dry spraying wets the refractory powder sprayed by compressed air with water at the nozzle, with a water addition of 11-14%, resulting in lower adhesion and the ability to perform thicker layer spraying. Flame spraying belongs to dry spraying, where the repair material is sent into the flame of the fuel-oxygen spray gun, and the repair material partially melts in the nozzle flame and adheres to the brick lining.

Materials for spraying repair include alumina-silica, alumina-silica-zirconia, magnesia, magnesia-calcium, magnesia-chrome, etc. Binders used include sodium silicate, phosphates, polyphosphates, asphalt, resin, etc. To improve adhesion, additives such as clay, expanded (swelling) clay, lime, etc., are added. To ensure good sintering of the repair material, sintering aids such as serpentine, pure olivine, lime, refractory clay, iron oxide, etc., are added.

Refractory Coating

Material applied to the surface of refractory bricks. Depending on the usage requirements and construction methods, refractory coatings can be prepared in the form of pastes or slurries. The binders used vary according to the material, such as alkaline coatings for continuous casting ladles using phosphates, polyphosphates, and magnesium sulfate; high-alumina coatings are prepared using clay, aluminum dihydrogen phosphate, aluminum-chromium phosphate, and sodium silicate, among others. Additives such as plasticizers may be added to improve the spreadability of the coating. Coatings are mainly used as protective layers for the lining of various thermal equipment or for repairing localized damage to brick linings.

Ramming Material

A type of non-plastic refractory material with extremely low or no plasticity. Materials include silica, clay, high-alumina, corundum, zircon, silicon carbide, carbon, and magnesia, among others. Depending on the material and usage conditions, inorganic binders similar to those used in castables or organic binders can be used, such as water-soluble materials like gum, carboxymethyl cellulose, lignin, sulfonates, and polyvinyl alcohol. Water-resistant, thermoplastic materials like paraffin, asphalt, tar, phenolic resins, and isotactic polypropylene can also be used.

Ramming material is applied using forced ramming construction, resulting in lower porosity and higher density. Therefore, among the unshaped refractory materials, ramming material is particularly suitable for lining various containers for holding high-temperature molten metals in smelting furnaces, such as the lining of melting furnaces and containers for holding molten steel in applications like hearths, various induction furnace linings, iron tapping troughs in blast furnaces, and steel ladles.

Gunning Material

A semi-dry refractory material sprayed onto the lining using a gunning machine. It is mainly used for repairing the lining of ladles for holding molten steel. Materials include silica, magnesite, clay, high-alumina, and zircon, among others. High-silica and high-alumina gunning materials are commonly used.

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