The degassing in the furnace is mostly in the static furnace. The refining media used for degassing are: flux, carbon tetrachloride, hexachloroethane, chlorine and other mixed gases. It is a good method for semi-continuous production. However, for continuous production, refining when the charge is transferred or half-charged will easily stir up the precipitated impurities, which will affect the quality of the melt, and the bubble size is not easy to control during refining in the furnace, and the refining effect is not ideal. It is recommended to use online degassing. If you need to degas in the furnace, it is best to refine in the smelting furnace to make the static furnace stand. At the same time, it is recommended to make corresponding improvements to the flow supply system between the smelting furnace and the static furnace to reduce air suction and slagging when the furnace is turned down.
At present, the commonly used online degassing methods at home and abroad are: SNIF method, ALPUR method, RDU method, IMT method, etc. No matter which degassing unit is used, and which degassing medium, the mechanism is the same, that is, the melt degassing is realized according to the partial pressure difference.
When the gas used for refining and degassing is blown into the melt, a large number of bubbles will be generated or reacted. On the contact surface between the bubble and the metal, there is a partial pressure difference between the inside of the bubble and the hydrogen in the metal at the beginning. Due to the partial pressure difference, the hydrogen in the melt penetrates into the bubble. When the bubble rises to the metal surface, the hydrogen is Bring into the atmosphere to achieve degassing. Related impurities are also brought to the surface of the melt to achieve melt purification.
Factors Affecting Degassing of Aluminum Shrinkage
Degassing medium. The passion gas in the degassing medium is mainly N2 and Ar2, which does not chemically react with aluminum. The active gas is mainly Cl2, which chemically reacts with aluminum to form aluminum vapor, and directly chemically reacts with hydrogen, its purification effect is better than purely using emotional gas.
Diffusion rate. If the hydrogen concentration in the bubble reaches equilibrium quickly during degassing, the diffusion speed of hydrogen is the key. Under the same conditions, melts with less impurities diffuse faster and degas better than melts with more impurities.
Degassing time. When the degassing time is short, the hydrogen in the bubbles and the melt will not reach the balance, that is, escape the surface, and the effect is not ideal. Increasing the degassing time is conducive to the further diffusion of hydrogen atoms into the bubbles and increases the degassing effect. For this reason, the degassing molten pool needs to have a certain depth.
Bubble surface area. Under the same conditions, the smaller the bubble, the larger its surface area, the larger its contact area with the melt, and the better the degassing effect. Therefore, how to obtain tiny bubbles and increase the surface area of the bubbles are the key to degassing.