Casting Porosity Caused by Excess Hydrogen in Molten Aluminum: In‑line Dual‑Rotor Degassing Unit for Stable Hydrogen Control

Molten aluminum readily absorbs hydrogen generated from moisture in the surrounding environment. Hydrogen solubility in solid aluminum is much lower than in the liquid state. During solidification, dissolved hydrogen precipitates into bubbles and forms porosity defects inside finished castings.

On continuous melting and casting lines of 25–35 t/h, raw material variation and ambient humidity fluctuations lead to unstable hydrogen levels in molten aluminum. Hydrogen removal via static holding alone is inconsistent. Unstable hydrogen control increases the risk of non-conforming castings during ultrasonic inspection and results in billet scrap.

The FDUII-30 box-type dual-rotor in-line degassing unit uses high-speed rotating graphite rotors to shear inert gas into micro bubbles. Rising bubbles capture dissolved hydrogen and carry it out of the molten aluminum. The sealed chamber maintains an inert shielding atmosphere to prevent re-absorption of hydrogen. Installed in series within the melting-casting workflow, the unit continuously treats flowing melt and stabilizes the hydrogen level at the outlet.

Source: Document "Dual-rotor In-line Degassing Parameter Sheet"

• Composite graphite rotors feature good high-temperature resistance and thermal shock resistance. They split gas into fine bubbles to maximize gas-liquid contact area.
• Submerged inlet and outlet ports reduce surface turbulence and limit re-hydrogen absorption from entrained air.
• Integrated temperature control system stabilizes melt temperature, preventing solubility shifts of hydrogen caused by thermal fluctuation.
• Equipped with an adjustable gas flow control module, the system adapts gas supply parameters according to production capacity changes to meet refining requirements for different raw material batches.

The in-line degassing unit removes dissolved hydrogen only; it cannot eliminate solid contaminants from feedstock. Furnace materials should be dried before melting to reduce incoming moisture. Regular hydrogen sampling and rotor wear inspection are recommended to sustain consistent degassing performance.