{"id":3320,"date":"2026-04-30T11:11:58","date_gmt":"2026-04-30T03:11:58","guid":{"rendered":"https:\/\/www.c-adtech.com\/?p=3320"},"modified":"2026-04-30T11:37:16","modified_gmt":"2026-04-30T03:37:16","slug":"how-does-aluminum-degassing-equipment-work","status":"publish","type":"post","link":"https:\/\/www.c-adtech.com\/de\/how-does-aluminum-degassing-equipment-work\/","title":{"rendered":"Wie funktioniert die Aluminium-Entgasungsanlage?"},"content":{"rendered":"

Aluminum degassing equipment<\/strong> works by injecting fine bubbles of inert gas \u2014 typically argon or nitrogen \u2014 into molten aluminum through a rotating graphite rotor and shaft system. Dissolved hydrogen atoms migrate from the supersaturated melt into the low-hydrogen-partial-pressure bubbles and are carried to the surface, reducing porosity defects in final castings by 50\u201385%.<\/p>\n

If your project requires the use of Aluminum Degassing Equipment, you can contact us<\/a>\u00a0for a free quote.<\/span><\/p>\n

Why Aluminum Needs Degassing: The Hydrogen Problem in Molten Metal<\/h2>\n

Before examining how degassing equipment works, understanding why hydrogen presents such a persistent and serious problem in aluminum production is essential. The physics of hydrogen in liquid aluminum create a defect mechanism unlike anything encountered in steel or copper casting.<\/p>\n

\"Molten
Molten aluminum online degassing unit removing dissolved hydrogen gas from the melt, featuring a rotary degassing system with inert gas injection to improve metal purity and reduce porosity in aluminum casting processes.<\/figcaption><\/figure>\n

Hydrogen Solubility: The Root of the Problem<\/h3>\n

Hydrogen is the only gas that dissolves in significant quantities in liquid aluminum under typical foundry conditions. The solubility follows Sieverts’ law, which states that dissolved hydrogen concentration is proportional to the square root of hydrogen partial pressure in the atmosphere above the melt.<\/p>\n

At 700\u00b0C (1292\u00b0F) \u2014 a typical aluminum holding temperature \u2014 liquid aluminum dissolves approximately 0.65\u20130.69 ml of hydrogen per 100 grams of metal at one atmosphere hydrogen partial pressure (Eichenauer and Markopoulos, Zeitschrift f\u00fcr Metallkunde, 1974). In solid aluminum just below the solidification point, this solubility drops approximately 20-fold to roughly 0.034 ml\/100g Al.<\/p>\n

This dramatic solubility change means that essentially all dissolved hydrogen must either escape from the melt before solidification or nucleate as gas bubbles within the solidifying metal, creating porosity. Industrial aluminum melts rarely contain hydrogen at equilibrium with atmospheric partial pressure \u2014 actual hydrogen levels vary from approximately 0.05 ml\/100g Al in well-treated primary metal to over 0.40 ml\/100g Al in contaminated scrap-heavy charges.<\/p>\n

How Hydrogen Enters the Melt in Production Practice<\/h3>\n

The hydrogen sources in industrial aluminum processing are numerous and persistent:<\/p>\n

Moisture reaction at the melt surface:<\/strong>\u00a0The dominant source in most operations. Atmospheric water vapor reacts with liquid aluminum continuously:<\/p>\n

2Al (liquid) + 3H\u2082O (gas) \u2192 Al\u2082O\u2083 + 6H (dissolved in melt)<\/p>\n

This reaction proceeds thermodynamically at all aluminum casting temperatures. At 50% relative humidity and 25\u00b0C ambient temperature, the equilibrium hydrogen content in aluminum at 700\u00b0C would be approximately 0.25 ml\/100g Al \u2014 far above the 0.10 ml\/100g Al target for most quality specifications.<\/p>\n

Charge material contamination:<\/strong>\u00a0Scrap aluminum carrying surface moisture, machining oils, coolant residues, paint, and anodizing layers releases hydrogen during remelting. Dispinar and Campbell (International Journal of Cast Metals Research, 2006) measured that mixed post-consumer scrap charges consistently produced melts with 0.15\u20130.25 ml\/100g Al higher hydrogen content than equivalent primary aluminum melted identically.<\/p>\n

Cold and damp tooling:<\/strong>\u00a0Ladles, launders, impellers, and refractory components that have not been adequately preheated before contacting the melt release moisture rapidly. A single undried ladle introduction can locally spike hydrogen content by 0.05\u20130.10 ml\/100g Al in the metal volume it contacts.<\/p>\n

Alloying and grain refiner additions:<\/strong>\u00a0Some alloying master alloy additions and grain refiner rods are processed with organic lubricants or have absorbed surface moisture during storage. These release hydrogen during dissolution in the melt.<\/p>\n

Consequences of Elevated Hydrogen Content<\/h3>\n

The consequences of uncontrolled hydrogen in aluminum castings are both diverse and severe:<\/p>\n

\n\n\n\n\n\n\n\n\n\n
Hydrogen Level (ml\/100g Al)<\/th>\nTypical Effect on Casting Quality<\/th>\n<\/tr>\n<\/thead>\n
<0.08<\/td>\nMinimal gas porosity in most alloy systems<\/td>\n<\/tr>\n
0.08\u20130.12<\/td>\nAcceptable for moderate specifications; borderline for critical applications<\/td>\n<\/tr>\n
0.12\u20130.20<\/td>\nVisible gas porosity in sand and permanent mold castings; wire breaks in rod drawing<\/td>\n<\/tr>\n
0.20\u20130.35<\/td>\nSignificant porosity; structural property degradation; pressure tightness failures<\/td>\n<\/tr>\n
>0.35<\/td>\nSevere porosity; surface blistering during T6 heat treatment; casting rejection<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Beyond simple porosity, elevated hydrogen interacts with oxide bifilms (as documented extensively by Campbell at the University of Birmingham) to create the most damaging defect combination in aluminum castings: bifilm-nucleated hydrogen pores that are irregular in shape, preferentially located at critical structural locations, and responsible for the worst-case fatigue and elongation values in mechanical test specimens.<\/p>\n

How Does Rotary Degassing Equipment Work? Core Mechanism Explained<\/h2>\n

Rotary inline degassing (RILD) using a spinning graphite rotor is the dominant degassing technology in modern aluminum production. Understanding the physics of why it works \u2014 and the specific design variables that determine how well it works \u2014 is fundamental to selecting and operating effective equipment.<\/p>\n

\"Schematic
Schematic diagram of AdTech online rotary degassing system illustrating the working principle, where a rotating impeller injects inert gas into molten aluminum to create fine bubbles that remove dissolved hydrogen and inclusions, improving melt quality and reducing porosity in casting.<\/figcaption><\/figure>\n

The Thermodynamic Driving Force<\/h3>\n

The degassing mechanism is governed by the partial pressure gradient between dissolved hydrogen in the melt and the hydrogen partial pressure inside the injected gas bubbles. In a bubble of pure argon just introduced into the melt, the hydrogen partial pressure inside the bubble is essentially zero. In the surrounding melt, dissolved hydrogen exists at a concentration that corresponds to a finite equilibrium hydrogen partial pressure (calculated from Sieverts’ law).<\/p>\n

This pressure gradient drives hydrogen atoms to diffuse from the melt into the bubble along the concentration gradient. The rate of diffusion is described by Fick’s first law:<\/p>\n

J = D \u00d7 (C_melt – C_bubble_surface) \/ \u03b4<\/p>\n

Where J is the hydrogen flux (ml\/cm\u00b2\u00b7s), D is the hydrogen diffusion coefficient in liquid aluminum (approximately 3.2 \u00d7 10\u207b\u00b3 cm\u00b2\/s at 700\u00b0C, from Eichenauer and Markopoulos, 1974), C_melt is the bulk hydrogen concentration, C_bubble_surface is the hydrogen concentration at the bubble-melt interface, and \u03b4 is the effective diffusion boundary layer thickness around the bubble.<\/p>\n

As each bubble absorbs hydrogen during its rise through the melt, it carries that hydrogen to the surface where it escapes into the atmosphere above the melt. The continuous supply of fresh, hydrogen-free bubbles maintains the driving force throughout the degassing treatment.<\/p>\n

Why Bubble Size Is the Critical Design Parameter<\/h3>\n

The total hydrogen removal rate from the melt depends on the total gas-liquid interfacial area available for mass transfer. For a fixed volume of injected gas:<\/p>\n

Total interfacial area = (6 \u00d7 V_total gas) \/ d_bubble<\/p>\n

Where d_bubble is the bubble diameter. This relationship shows that halving the bubble diameter quadruples the available interfacial area for the same gas volume. This is why rotary degassing technology is so much more effective than simply bubbling gas through a lance \u2014 the rotor’s mechanical shearing action breaks the gas stream into bubbles that are orders of magnitude smaller than lance-injected bubbles.<\/p>\n

A lance-injected gas stream typically produces bubbles of 5\u201320 mm diameter in aluminum. A well-designed rotary degassing rotor produces bubbles of 0.5\u20133 mm diameter \u2014 a 5\u201340 fold reduction in bubble diameter that corresponds to a 5\u201340 fold increase in mass transfer surface area per unit of gas consumed.<\/p>\n

Research by Jahn and Schwerdtfeger (Metallurgical Transactions B, 1978) established the bubble size distribution in liquid aluminum as a function of rotor design and speed, finding that bubble diameter scales approximately with rotor tip speed to the power of -0.6. Higher rotor speed produces smaller bubbles up to the point where secondary coalescence limits further size reduction.<\/p>\n

The Rotor Mechanism in Detail<\/h3>\n

The graphite rotor sits at the end of a rotating graphite shaft. As the rotor spins (typically at 200\u2013600 RPM depending on the system), it creates several simultaneous effects:<\/p>\n

Gas dispersion:<\/strong>\u00a0Inert gas fed through the hollow shaft exits from ports in the rotor body. The centrifugal force from the spinning rotor, combined with the shear forces at the rotor-melt interface, breaks the gas stream into fine bubbles and disperses them radially outward through the melt.<\/p>\n

Circulation:<\/strong>\u00a0The spinning rotor creates a circulation pattern in the melt that distributes bubbles throughout the treatment vessel rather than allowing them to concentrate near the rotor. This circulation is critical for treatment uniformity \u2014 without it, metal at the vessel periphery would receive minimal degassing despite the rotor operating at the center.<\/p>\n

Inclusion promotion to surface:<\/strong>\u00a0The melt circulation pattern also promotes oxide inclusions and non-metallic particles toward the melt surface, where they collect as a skim layer that can be removed. This is an important secondary benefit of rotary degassing beyond hydrogen removal alone.<\/p>\n

Surface agitation control:<\/strong>\u00a0The rotor design and speed must be balanced to produce sufficient bubble dispersion without excessive surface turbulence. Turbulent melt surfaces generate new oxide films that both introduce new inclusions and provide additional hydrogen absorption pathways. The optimal rotor operates at maximum bubble production while keeping surface agitation below the threshold for significant new oxide generation.<\/p>\n

What Types of Aluminum Degassing Equipment Exist?<\/h2>\n

The aluminum industry uses several distinct degassing approaches, each with different operating principles, capital costs, and performance capabilities.<\/p>\n

Type 1: Rotary Inline Degassing Units (RILD\/SNIF\/ALPUR)<\/h3>\n

Inline rotary units process metal continuously as it flows from the furnace to the casting station through a refractory-lined treatment vessel. The metal enters one side, receives degassing treatment from one or more rotors, and exits the other side to the filter and casting system.<\/p>\n

Key commercial systems:<\/strong><\/p>\n