The strength of casting coating can not be divided into two situations: one is the normal drying strength, the other is the strength after high-temperature scouring. The two cannot be replaced each other. The normal drying strength is high ≠ high-temperature strength. If you misunderstand it, something will happen.
There are three reasons for insufficient drying strength
One is the lack of additive performance;
Second, the amount of additives is insufficient;
Third, there are problems with aggregate powder.
The former two are easy to understand, while the latter one is not generally and truly clear. The following focuses on the problem of aggregate powder.
① The coarseness and fineness of the same aggregate powder will affect the strength of the coating after drying, and the best selection range is 180-250 mesh.
② Lightweight aggregate powder (light weight) is often not as strong as the larger aggregate powder, because its coating density is slightly lower, and its volume and coverage are obviously different under the same weight.
③ Some aggregate powder containing some harmful elements will seriously weaken the dry strength of the coating, such as Cao, MgO and even some inexplicable components. The higher the content, the lower the coating strength, and the longer the slurry storage time, the more obvious the strength decline.
The low strength at high temperature is due to the poor performance of additives
The common casting coating in the world almost has a fatal common feature: it can’t endure high temperature scouring for a long time, and it can’t withstand the high temperature scouring for more than 40 seconds at 1600 ℃, so what kind of porcelain pipe sprue should be made. The key to solve this problem is not the fire resistance of the aggregate powder, but the high temperature strength of the additive: the coating of Guilin No.5 with a thickness of 1-2mm can be washed out for a long time above 1600 ℃, and the strength is not only not reduced, but also the higher the pouring temperature is, the stronger and the harder it is, which is called high temperature vitrification, which is better than the high temperature performance of the ceramic pipe.