The Development Of The Casting Method Of Refractory Castable

Refractory castable casting form
Refractory castables have been documented to have similar fluidity and castability to civilian Portland cement concrete when mixed and placed. With the advancement of refractory castable technology, other casting methods and techniques have been used. Low cement castables require a lot of vibration to flow and cure when they start pouring. The improved fluidity of the next generation of advanced castables has led to the development of artesian and pumpable refractory castables. Compared with vibrating castable, the advantages of free-flowing castable are fluidity and density without any external force. The ease with which castables were installed in the early days depended on the skill level of the workers, the complexity of the mixture filling and the narrowness of the space.
At present, the installation of refractory castables can be poured or sprayed. The casting method is usually used to build large bricks of definite size; Spraying is often used to coat large surfaces or to repair existing refractory linings.
1 Pour
Before installation after pouring, the material used to make the formwork must be a strong material resistant to moisture absorption. In general, steel fibers are favored for their strength and non-absorbent properties. Before pouring, the raw material is mixed with water in a container, then wet stirred to the right consistency and cast into the mold. In the case of thixotropic mixing, a vibrator (immersion or surface) must be used for venting or expanding the wet mixture to fill the model. In the case of self-flowing castables or pumpable castables, vibrators are not required to fill and smooth the surface of the castables in the model. When pouring multiple layers, the rule of pouring the next layer after the completion of one layer must be followed. In addition, the layer is not bonded to the layer, which will form a non-uniform layered shaped refractory product. Casting techniques can be used to make large (sometimes complex) preforms or to place wet mixtures into templates and make large units where the castables will be used. The concept of so-called "continuous lining" can be applied to steel casks for steelmaking. According to this concept, the slag on the surface of the old steel drum is removed and the rest of the lining is maintained. The gap between the lining surface and the mandrel is filled with thixotropic or free-flowing castable, and then the mandrel is extracted, the steel drum enters the drying stage, and then returns to the operating cycle. Therefore, the residue layer of the old liner near the end of its service life is considered as an extended safety liner.
Artesian slurry casting is a special monolithic casting technology with uniform size of coarse particles and micro-slip. The coarse particles are placed in the template to form the framework and safely impregnated by sliding. Similarly, in SIFCA, the structure is made of steel fibers and then filled with a low cement content refractory slurry, resulting in a unique refractory composite product.
2 Spray and spray
In the 1990s, in order to speed up the pouring of castables and reduce molding costs, injection technology was introduced during installation. Shotcrete is defined by the American Shotcrete Association as "high-speed, pneumatic injection of fire mud or concrete onto an appropriate specially treated surface." Wet spraying as a technique has been effectively used in Portland cement concrete for many years. One of the main obstacles to the early implementation of this method in the refractory industry is the relatively poor rheological properties of refractories. However, this problem has been solved with the invention of free-flowing castables and the high pressure of hydraulic pumps. Any free-flowing castable sprayed by the wet process must have special properties:
(1) The upper particle size of the aggregate must be reasonably selected to prevent nozzle clogging and reduce rebound;
(2) The free-flowing castable must have low expansion, good cohesiveness and low segregation trend. A special nozzle assembly must be installed at the end of the hose for pumping castables. In this assembly, the castable is combined with high-pressure air and a small amount of catalytic or coagulant to cause rigid reinforcement of the castable. The reaction of the added catalyst with the cement causes rapid solidification, but the rheological properties of the mixture are changed rapidly by the formation of gel. The mixture is pneumatically sprayed onto the surface of the device. The castable mixture began to harden rapidly and no accumulation formed on the surface.
One of the disadvantages of jet technology is that installation equipment is more expensive and requires longer installation and cleanup times. To overcome this shortcoming, spraying technology was introduced in castable. It is connected with a standard gas spraying machine and a catalyst added nozzle, the equipment needs are similar to dry and wet spraying, equipped with a mixing machine to extend the wetting time of the injection castable. Compared with wet injection, it does not require a large volume mixing vessel and rotary vacuum pump.