Refractory plastic production process

The refractory mortar constructed by tamping method with certain plasticity is called refractory plastic. Refractory plastics can be made into mud billet in general use, when the construction with ramming hammer ramming will produce plastic deformation and do not occur rupture or collapse, after the lifting of the force can still maintain the shape of deformation. In the United States ASTM, it is stipulated that when the plasticity index is used for determination, the deformation index greater than 15% is plastic, and the deformation index less than 15% is ramming material. In our country national standard stipulates: the deformation index is between 15%~40% can plastic. Strictly speaking, refractory plastics should be a kind of semi - hard wet plastic materials. When the plasticity index is more than 40%, the shapeless property is not good, it is easy to collapse under the action of tamping vibration, while the plasticity index is less than 15%, it is easy to rupture when tamping, and it is difficult to tamp compactness.

Refractory but plastic composition is similar to other unshaped refractory materials, is composed of refractory aggregate and powder, binder and plasticizer, according to the use of different requirements can be added special admixtures, such as preservative, shrinkproof agent, antifreeze agent, etc.

Refractory plastic varieties are mainly based on the use of the binder and the main material material to classification, such as by the binder classification of clay binding plastic, phosphate binding plastic, aluminum sulfate binding plastic, tar-bitumen or resin binding plastic and so on. According to the material classification has the silicon, the clayey, the high aluminum, the rigid jade, the zirconite, contains the carbon and/the silicon carbide, the magnesia and the magnesia-chrome and so on, that is to say each kind of nature fire-resistant raw material all can make the corresponding fire-resistant plastic. But the most widely used refractory plastics are mainly aluminosilicate (clayey and high aluminized) plastics.

(1) Clay binding can be plastic

Plastic clay as a binding agent, there are clay clinker or high aluminum clinker processing made of aggregate and powder with a certain size composition, and the mixture of admixture, by adding water to mix into mud, and then by compression or extrusion into a certain plasticity of the brick shape is called clay binding plastic. The characteristics of clay - bonded plastic are: good thermal shock resistance and anti - peeling performance.

As a plastic binder binding clay, ball clay, wood joint clay, kaolin. Generally speaking, the binding clay itself is required to have good plasticity and sintering property. The colloidal particles in clay should be more, the moisture absorption should be large, the humus content should be appropriate, the associated mineral non-colloidal substance should be less and the alkali content should be low. Clay particles should be flat to increase the area of contact between particles. Plasticizers can also be added to improve the plasticity of the binding clay. Plasticizers should be surface active substances that can adsorb onto the surface of clay particles or ultrafine powder particles to form slippable interconnecting bonds between particles. Materials that can be used as clay plasticizer include lignin sulfonate, methyl cellulose, methyl cellulose, polyacrylate, polyvinyl alcohol, naphthalene sulfonate, etc. However, when plasticizers are used, their effects on plasticity energy must be verified through experiments, because some plasticizers can affect the retention period of plasticity and other physical properties.

The composition of clay binding plastic is generally: refractory aggregate 55%~65%, refractory powder 20%~30%, combined

Clay (soft) 10%~15%. The maximum allowable particle size of refractory aggregate is 8mm, and the aggregate particle size composition is 8~5mm, 35%~40%. 5 ~ 3 mm, 30% ~ 35%; < 3mm, 25%~30%. The size of refractory powder shall be less than 0.074mm, accounting for more than 90%. The size of binding clay should be less than 0.074mm, accounting for more than 95%. Shrinkproof agent (e.g., blue SPAR or quartz) is generally added as a refractory powder.

Clay - bonded plastic is mainly used as the furnace top and furnace wall lining of rolling reheating furnace, but also as the lining of various heat treatment furnace. As the lining of heating furnace, the general service life can reach more than 5 years; As the lining of preheating section of heating furnace, the service life can reach more than 10 years.

(2) Phosphoric acid can be bound to plastic

Phosphoric acid or acidic aluminum phosphate as binder and clay clinker, high aluminum clinker or corundum as aggregate. The plastic mud prepared by adding plastic refractory clay and preservative is called phosphoric acid-bonded plastic. Phosphoric acid binding plastic is characterized by good medium and high temperature binding strength, good wear resistance and thermal shock resistance.

With phosphoric acid or acid aluminum phosphate as binder, with phosphoric acid root with the plastic clay in the plastic substrate, or the active alumina powder material, or corundum powder Al2O3 reaction, the production of orthophosphoric acid insoluble aluminium (AlPO4 xH2O) of sediment and cause premature plastic hardening, lose plastic plasticity to construction, so must add preservatives. The experimental results show that the preservation agents that can delay the premature hardening of phosphoric acid binding plastics include oxalic acid, citric acid, tartaric acid, acetone acetate, 5-sulfate salicylic acid, etc. Oxalic acid has a better preservation effect, and the preservation period can be extended from 6 months to about 1 year with the different amount of oxalic acid added (1%~4%).

The bone powder and powder particle size composition of this plastic is similar to that of clay bonded plastic. Its plasticizer (agent) mainly used plastic clay, may also use organic plasticizer. Composition of phosphoric acid-bonded plastics: refractory aggregate greater than 100 m, 53%~65%, refractory powder less than 100 m, 35%~45%. The binder was made of phosphoric acid solution with a density of 1.20~1.35g/cm, with an added amount of 9%~11%, and a small amount of anti-shrinkage agent and preservative.

In the production of phosphoric acid in combination with plasticity material base, the second step should be taken to mix practice process, the first step to use refractory aggregate is equivalent to 60% of the total demand and phosphoric acid solution, powder and plastic clay mixed together, trapped material for 24 h after mixing evenly, so that the refractory aggregate can be fully adsorbed phosphate solution, and makes the metal iron is contained in the refractory aggregate (by broken shattered into) with phosphoric acid root fully reflect the H2 gas release. Then a second mix-match is performed, in which the preservative and about 40% of the remaining phosphoric acid solution are added. When the required plasticity index is reached, the blank is pressed or extruded, and the blank is sealed with plastic film for storage. High temperature wear resistant plastics can be prepared by using aluminum phosphate solution as binder, corundum as aggregate and -Al2O3 fine powder and micro powder.

Aluminum phosphate or phosphoric acid can be used in metallurgy, petrochemical, power and machinery industries and other industrial furnaces, mainly used for heat shock, erosion resistance, wear resistant lining, such as heating furnace burner, cement rotary kiln outlet, vertical kiln feeding mouth, high temperature cyclone separator lining.