There are many types of refractory castables, but there are only four types of calcium aluminate cement castables, phosphate refractory concrete, water glass refractory concrete and Portland cement refractory concrete. Refractory castables will use admixtures during use to reduce the shrinkage of the castables after forming, etc.
1. Common types of refractory castables
1. Calcium aluminate cement castable
Calcium aluminate cement castable is a hydraulic castable made of cement with calcium aluminate as the main component, binder made of alumina clinker as aggregate and admixture. Because calcium aluminate hydrates quickly, this castable is characterized by fast hardening and high early strength.
However, when the crystallization water starts to be removed at 350°C, the volume shrinks and the strength decreases. Therefore, the oven must strictly follow the predetermined curve. Above 1100~1200℃, the strength of aluminate refractory castable has been improved. The composition of aluminate cement refractory concrete is shown in Table 1, and its main performance indexes are shown in Table 2.
2. Phosphate refractory concrete
Phosphate refractory concrete is a new type of material with good performance formed by phosphoric acid or phosphate solution, refractory aggregate and powder in a certain proportion, and after curing or grilling.
3. Water glass refractory concrete
The main component of water glass refractory concrete is sodium silicate (Na2O•nSiO2). When water glass is used as the cement, because it hardens slowly at normal temperature, sodium silicofluoride (Na2SiF6) is generally added as the accelerator.
4. Portland cement refractory concrete
Portland cement refractory concrete is made of portland cement, slag cement, etc. as binders, and clay clinker, waste clay bricks, etc. as aggregates. Portland cement is a fast-hardening, high-strength hydraulic binder, so after adding water and mixing the concrete, it should be pounded quickly, and there should be no pause in the middle, so as to avoid unrealistic pounding. Covered with straw bags after plastic molding, watering maintenance.
2. Types of refractory castable additives
1. Anti-shrinkage agent, also known as volume stabilizer or expansion agent, can reduce or prevent the shrinkage of refractory material during heating and use after molding. Commonly used are kyanite and silicon powder.
2. Water reducing agent, on the premise of ensuring the fluidity of the castable, significantly reduce its water consumption. Common sodium tripolyphosphate, sodium hexametaphosphate, etc.
3. Accelerator can shorten the setting and hardening time of castable. NaOH and aluminum hydroxide are common.
4. Retarder: It can delay the setting and hardening time of castable. Common citric acid, tartaric acid and so on.
5. Plasticizer can enhance the plasticity of castable and improve the strain ability of mud under stress. Clay and bentonite are commonly used.
6. Inhibitors, which can suppress the expansion phenomenon caused by the reaction of the iron or iron compounds contained in the castable ingredients with the acidic chemical binder to generate hydrogen gas. Common are CrO3 and diacetone alcohol.
7. Preservative can keep the casting performance unchanged or not change after storage for a certain period of time. Common oxalic acid, citric acid and so on.
8. Foaming agent can reduce the surface tension of the liquid and produce a large amount of uniform and stable foam. Generally, there are rosin soap and resin saponin.
