Definition of Refractory Plastic
Refractory plastic is an indefinite refractory material which is in the form of hard clay paste and maintains high plasticity for a long period of time, which is made of powdered granular material with plastic clay and other binding agents and plasticizers, with a small amount of water, and is fully mixed and tempered.
It can be made from various materials of refractory raw materials, and is often classified and named according to the materials. As this kind of indefinite refractory material is mainly used in various heating furnaces which are not in direct contact with the molten material, clay clinker and high alumina clinker are generally used, and light granular material can be used for manufacturing light weight refractory. Sometimes for some special requirements, can also be used silica, sintered and electrofused corundum, chrome, silicon carbide, zircon and carbon materials.
Plastic clay is an important part of plastic. Although it only accounts for 10%-25% of the total plastic, but it has a great influence on the bonding strength of plastic and its hardened body, on the plasticity of plastic and the volume stability and fire resistance of its hardened body. In a certain sense, it can be considered that the nature and quantity of clay determines the nature of the plastic.
Properties of plastic
(1) Workability of plastic. Generally, it is required that the plastic should have high plasticity and still have a certain plasticity after a long storage period.
In order to make plastic plasticity in its shelf life without significant reduction, can not use water hard bonding agent. If air-hardened binding agent is used, sealing measures must be taken during storage. When the water content of plastic is high, it is also easy to harden due to water retention and water dissipation. In order to keep the plasticity of plastic in the storage process for a long time, must take slow condensation measures.
(2) The hardening and strength of plastic. Ordinary plastic is fire hardening. Because there is no chemical bonding agent in it, the strength is very low before sintering, but at a certain temperature, the strength increases with the increase of temperature. After sintering at high temperature, the cold state strength increases greatly. The hot state strength decreases with the increase of temperature at high temperature.
The strength of plastic with sodium silicate changes quickly after construction, and it is not easy to produce shrinkage cracks as long as the drying speed is properly controlled, and the mold can be demolded sooner after construction. The plastic containing this bonding agent is suitable for large furnaces with long construction period and for the roof of the furnace, etc.
Aluminum phosphate is one of the most widely used thermosetting agents in plastic. High strength can be obtained by drying and baking after construction.
(3) Shrinkage during the heating of plastic. The plastic contains more clay and water, which often produces great shrinkage during the process of drying and high temperature heating. The plastic without expansion aid will dry shrink about 4%, produce obvious shrinkage above 1000℃, and the total shrinkage in the temperature range of 1100~1350℃ can be about 7%.
Generally speaking, because the plastic contains a considerable amount of clay, its deformation under high temperature load is generally higher than other indefinite materials, so its volume stability is often regarded as an important technical index, and as the main content of quality classification. (National regulations: senior clay can be plastic heated to 1400 ℃ cold shrinkage rate should not be greater than 4%; extra viscous can be plastic heated to 1600 ℃ cold shrinkage should be below 2.5%.)
(4) The thermal shock resistance of plastic. Compared with the same material of sintered refractory products and other irregular refractory materials, the thermal shock resistance of plastic is better. Because of the high thermal shock resistance of plastic, it is more appropriate to be used in places with large temperature fluctuations.
Application of plastic
When it is used to make furnace lining, the plastic is taken out from the sealed container, laid between the hanging bricks or hooks, and pounded in layers (each layer is 50~70mm thick) with a wooden hammer or air hammer to make the desired shape. When the plastic is not yet hardened, the extruded residue is cut off with repair tools, and the shape is repaired and the surface is processed. After repairing, to facilitate the drainage of water, ventilation holes are made at certain intervals. Finally, the expansion and contraction joints are left according to the design. If it is used to make the whole furnace cover, it can be constructed on the bottom mold first, and then lifted after drying.
The plastic is especially suitable for various heating furnaces, even-heating furnaces, annealing furnaces, carburizing furnaces, hot air furnaces, sintering furnaces, etc. It can also be used in cement rotary kilns, small electric arc furnace covers, high-temperature furnace burners and other similar parts. The use of temperature mainly depends on the quality of granular and powder material. Such as ordinary clay material can be used for 1300 ~ 1400 ℃ temperature; high quality material available dry 1400 ~ 1500C; high aluminum material can be used for 1600 ~ 1700 ℃ or even higher; chrome material can be used for 1500 ~ 1600 ℃.
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