Phosphate high alumina castables are different from other types of refractory castables. The way to eliminate expansion is to trap the material.
Trapping is a simple and effective method. During construction, first add part of the cement to the castable. After trapping for 10 hours, stir the trapped material evenly, add the remaining part of the cement, and continue stirring for 1 hour. It can be used in ~2min. (Each manufacturer will introduce the proportion of cement added in the instructions for use. The part added first can be 50% or 40%)
1. Methods to eliminate expansion phenomenon of phosphate castables
Phosphate refractory castables should be stored indoors for three months. During these three months, the normal temperature compressive strength of the high alumina castables is stable. If it exceeds three, the strength will decrease. Try not to store it outdoors, because the strength of phosphate castables stored indoors after baking will be about 10Mpa higher than that of castables stored indoors. Outdoor storage will be affected by dry-wet cycles due to changes in summer or cold weather. , which reduces the performance of phosphate castables.
When trapping materials, first refractory aggregate, then powder, then add about 40% of cement and mix evenly. The trapping site should be covered with plastic sheeting to prevent the cement from evaporating; during the trapping period, water cannot enter the castable. Let it stand for more than 10 hours above 15℃, allowing the cement to react with the metal in the refractory aggregate and powder to release hydrogen. It can eliminate the expansion phenomenon during construction.
2. Precautions for phosphate refractory castables
What needs to be noted about phosphate high alumina castables is that the raw materials used cannot have too many impurities. The impurities contain iron, potassium, and sodium. Excessive amounts of iron, potassium, and sodium will affect the service life of the castables.
In addition, the amount of cement should not be too much. Too much condensation speed, too fast or too slow, will affect the strength of later use. Special attention should be paid to phosphate castables that they must not be affected by moisture. Deliquescent castables cannot be reused. Not only will they not condense during construction, but they will also have no strength at all in the later stage.
When storing phosphate refractory castables, they cannot be stored under low temperature conditions. White crystals will precipitate on the surface of the castables stored at low temperatures. The castable will have white hairs or even become powdery. As a result, the internal structure of the castable is loose and the compressive strength is reduced.
Therefore, phosphate castables must be trapped before use.
