TItle：How does the mold powder provide lubrication?
Description：Good lubrication must be ensured between the blank shell and the copper wall, and this effect can only be achieved by mold flux. This article briefly describes the formation of a lubricating slag film.
During the pouring process, the mold vibrates up and down, and the casting billet moves downwards, creating friction between the surface of the solidified shell and the copper wall, causing the billet shell to bond with the copper wall, which increases the drawing resistance, and the lighter causes the billet shell to crack , The heavy ones will cause the shell to crack. Therefore, lubrication must be carried out between the blank shell and the copper wall, and this effect can only be realized by the mold powder.
To ensure good lubrication, there must be a layer of liquid slag film with suitable properties and uniform thickness between the solidified shell and the copper wall. The liquid slag layer on the liquid surface of the mold steel is the source of continuous supply of the liquid slag film. For this reason, it is necessary to ensure that the passage between the liquid slag near the meniscus of the crystallizer flows into the blank shell and the copper wall is unblocked, and is not blocked by the slag ring around the copper wall.
So how is the lubricating slag film formed? When the molten steel is poured into the mold, a primary green shell is formed. When the powder of protective slag is added to the liquid surface, the slag powder is melted to form a layer of liquid slag, which is close to the liquid around the copper wall. The slag is cooled to form a slag ring. As the crystallizer moves downward, the slag is gradually squeezed between the shell and the copper wall to completely fill the slag. The temperature of the copper wall is low, and the slag shell on the side close to the copper wall remains a solid slag skin, while the surface temperature of the condensation shell is high, and the slag on the side close to the green shell is a liquid slag film, which has fluidity. In this way, the liquid slag film between the copper wall and the shell of the mold is smoothed, and it is consumed as the cast slab is drawn out, while the solid slag attached to the copper wall is basically not consumed with the vibration of the mold. While the slag film is continuously consumed, the molten steel surface liquid slag is continuously replenished downward through the meniscus channel, forming a stable liquid slag film.
The thickness of the slag film is related to the slag viscosity, pulling speed, mold vibration and other factors. Knowing that the slag viscosity is constant, the drawing speed increases, and the slag film thickness increases; while the drawing speed is constant and the viscosity increases, the slag film thickness decreases. Generally, the thickness of the slag film is 50-200μm, and the slag consumption is 0.4-0.6kg/t. Therefore, to make the lubrication of the slag film to the solidified shell in the best state, the thickness of the slag film, the consumption of the slag, and the viscosity of the slag should be properly matched. When the mold vibration is constant, the viscosity (η) and the drawing speed (V) should be matched properly. Low viscosity and low drawing speed, or high viscosity and high drawing speed are not advisable. The product of the two is η·V As an index to evaluate the lubrication status, if the η·V value is too small or too large, it means that the slag film thickness and consumption are inappropriate, and the lubrication status is poor.