Casting powder
In metal extraction, casting powders are slag formers especially for continuous casting and ingot casting .
commitment
A part of the casting powder melts on the metal melt and forms a liquid casting slag directly on the melt. The casting powder is still in powder form above the liquid layer. There is still a sintered layer between the two layers.
The liquid casting slag is used for lubrication and as a separating agent between the solidifying molten metal and the mold . The casting slag should wet the molten metal as completely as possible and suppress contact with the ambient air. The casting slag serves as thermal insulation and reduces the power loss through thermal radiation.
During the solidification, non-metallic inclusions remaining in the molten metal should rise and be absorbed by the casting slag.
Parameters
In addition to the melting temperature , data sheets often mention the softening temperature at which the powder slowly loses its solid shape and dissolves.
The viscosity is used as a measure of how well the mold is lubricated. Depending on the pouring rate, pouring slag must be able to flow quickly enough into the new gap between the steel and the mold.
The melting rate results from the melting enthalpy of the casting powder and the heat loss of the liquid steel. During the filling of the mold, liquid casting slag is drawn into the gap so that the liquid layer is reduced. Sufficient material must melt from the solid phase in order to continue to ensure a liquid casting slag.
Another parameter that is set in the process is wettability . The liquid casting slag must be able to spread as quickly as possible on the liquid steel. Poor wettability can lead to the casting powder slag cracking open and being in contact with the ambient air for too long or not being able to form a separating joint with the mold. The wettability is set by means of operational tests and is not adjusted based on laboratory parameters.
Components
The composition of the casting powder varies for each application. Important components are clay , lime , carbon and quartz sand .
The raw materials are usually mixed together in powder form, which means that the different phases are present next to each other. Melting in order to obtain chemically homogeneous particles is only carried out in rare cases.