Castables have a wide range of applications and are also convenient and fast. Their surface must be smooth, dense, uniform in density, consistent in color and translucent to ensure that the film absorbs ink evenly and the color difference of the same batch of printed products is small. What are the factors that affect the water seepage of this material?
1. Particle size distribution Since most particles are light and hollow, the bulk density is relatively small, and the movement rate is proportional to the square of the particle size, the relative density difference between the particles and the castable, and the viscosity of the castable. Therefore, the larger the particles, the more serious the water seepage of the casting, the greater the relative density difference between the particles and the castable, the more serious the water seepage, and the smaller the viscosity of the castable, the easier it is to seep water.
2. Molding processing Flowability is a process from bad to good and then to bad. If the stirring time is too short, the material mixing is uneven, the fluidity is poor, the material is not dense, and the strength is reduced; if the stirring time is too long, the reaction of various additives has ended, and the effect that should be achieved after pouring is not achieved. In short, if the mixing time is too short or too long, it will affect the concrete after construction and fail to achieve the expected design strength. Therefore, during the entire construction process, when the castable is in a fluidized state, at least the random water at this time is easy to overflow under the action of working pressure.
3. Setting and hardening time
When pouring refractory castables, the vibration time should be controlled well, and the time control point should be when no bubbles appear, and the time is 3 minutes. Too short vibration time will cause a large number of pores in the concrete, and too long vibration time will cause large particles to sink. Castable bleeding usually occurs within 30 minutes after molding, but also occurs after 60 minutes or even 90 minutes after molding. This phenomenon is caused by the use of mixtures in the material. Common admixtures for castables include dispersants, accelerators and retarders, dispersants with retarding properties, and dispersants with accelerating properties, used alone or in combination.
4. Control of layered casting
In castables, layered casting requires a casting of 300-500 mm high at a time, and the entire monomer construction site needs to be completed at one time. Since the concrete body poured in the early stage has initial setting or the setting temperature will rise, the temperature of the newly poured area is low, and the two areas are not synchronized during solidification, the concrete body poured after high-temperature sintering may ooze water.
5. Water addition control
Too much water is added to the castable during mixing. After it is built, the bulk density and strength of the material decrease. If too little water is added, the fluidity of the refractory castable will deteriorate, and it is easy to leave pores of different sizes after the vibration operation, and the strength will be greatly reduced, resulting in bleeding after the strength is reduced.
The castable has the characteristics of corrosion resistance, aging resistance, non-fading, small shrinkage and expansion ratio, and its color registration is unstable, making it difficult to achieve normal printing.
