Industrial Verification of One- and Two-Chamber Siphon Degassing

Removal of dissolved Hydrogen from liquid Aluminium prior to casting is industrial standard today. This is done mainly to reduce porosity in the cast product but also to reduce hot tearing during casting and to improve mechanical properties of the finished product. The challenge the casthouses face is to remove as much Hydrogen as possible with as low cost as possible. Cost drivers for degassing is energy and Argon consumption in addition to drain metal, maintenance and consumable parts. Hycast has for almost two decades supplied a drain free two-rotor siphon degassers for metal flow rates up to 75 mt/h (I-60 SIR), and has recently launched a one-rotor version for metal flow rates up to 25 mt/h (I-25 SIR). This paper is a summary of the industrial results gained over these years. The effect of the relative Argon flow rate to the metal flow rate, the alloy composition and the rotor speed on the removal efficiency is investigated. An analytical model is developed to estimate the effect of different process parameters and number of degassing chambers on the removal efficiency. One conclusion found from the measurements is that the Hydrogen concentration within one degassing chamber is close to constant - thus very close to complete mixing.