Rotary Degassing Unit is used to complete degassing operation. Inert gas is introduced to produce efficient small bubbles. Short processing time and reduced gas use can save a lot of cost. The degassing treatment of the melt causes the injector immersed in the melt to rotate so that the scavenging gas (usually inert gas) is distributed in the melt as small bubbles. Rotary degassing or impeller degassing is mainly used for aluminum melt purification and hydrogen degassing.
Molten aluminum is highly reactive, so when it comes into contact with moist air or wet tools, water will decompose and release hydrogen from the melt. A large amount of this dissolved gas has a documented harmful effect on the mechanical properties of the final aluminum castings. For anyone who makes castings, it is well known that dissolved gases play an important role in the distribution and quantity of porosity and shrinkage. The level of dissolved hydrogen must be controlled to reduce waste. In order to control the gas in aluminum, the caster must do two things: prevent and minimize the introduction of hydrogen into the melt, and measure and remove hydrogen before pouring.
The ability to degass molten aluminum is usually achieved by using inert gas that is usually introduced into the melt by rotary degassing unit. The degassing process is limited by the laws of thermodynamics; when bubbles are introduced into the melt, they float toward the surface to collect hydrogen. In the best case, these hydrogen saturated bubbles leave the melt and reduce the hydrogen content. In this case, from a thermodynamic point of view, the treatment efficiency is 100%. However, with the decrease of gas content in the melt, the equilibrium pressure of hydrogen in the bubble will also decrease, so the amount of purge gas needed to remove residual hydrogen must be increased.
The alloy elements also affect the solubility of hydrogen. Fortunately, in most cases, these factors can be controlled and the gas content and process required to eliminate excessive porosity in aluminum castings can be achieved without undue difficulty.