A portable rotary degasser can treat aluminum melts in 1–5 minutes for crucibles of 70–500 lb, while tablet treatments commonly use a 0.1–0.2% dosage and a 5–10 minute reaction interval [S1][S5].
The decision rests on heat size, melt-chemistry sensitivity, fume control, operator skill, and the need to switch quickly between short production runs.
Decision Criteria for Aluminum Melt Degassing
Rotary inert-gas degassing with dry nitrogen or argon is the stronger choice when melt quality, repeatable hydrogen removal, and environmental control dominate the purchase decision. Published process data places the practical rotary treatment time at 1–5 minutes for a 70–500 lb crucible and 5–10 minutes for a 500–3,000 lb crucible [S5].
Tablet degassing remains appropriate where low capital cost, simple handling, and short intermittent heats outweigh consistency and environmental performance. Tablet guidance specifies 0.1–0.2% dosage per ton, 5–10 minutes of reaction time, and hydrogen removal rates stated as up to 90% when correctly matched to the alloy, temperature, and handling protocol [S1].
The practical split is straightforward: buy tablets for occasional small heats and simple workflows, but justify a rotary degassing unit when porosity rejects, inconsistent results, or fume exposure make melt treatment a process-control problem.
Process Performance Compared
Rotary equipment improves hydrogen transfer by breaking the inert gas into small bubbles, and its effectiveness depends on gas-liquid transfer rate and the total bubble surface area exposed to the melt [S4]. A 1-inch bubble has about 6 square inches of surface area, while the same gas volume divided into 0.0625-inch bubbles has about 96 square inches, a 16-fold increase [S4][S5].
Tablet degassing reaches the melt through a different mechanism. The compacted chemical product is plunged into the bath, reacts to release gas, collects dissolved hydrogen in the bubbles, and helps flux oxide fragments into the surface dross [S1]. One manufacturer identifies hexachloroethane, C₂Cl₆, as the principal active ingredient in many conventional aluminum degassing tablets [S2].
On these figures, a rotary unit wins on treatment speed, bubble control, and repeatability. Tablets win on purchase simplicity and the absence of a powered rotor, gas supply, lance, and compressed-air service requirement. For more detail on equipment economics, compare degassing unit price per ton of melt throughput.
Tablet Economics and Chemical Trade-offs
Tablet dosing scales directly with melt weight, and 50 g packs are reported to be more economical for small foundries, while 500 g tablets provide better unit-weight economy for larger heats [S2]. The product format therefore matters: a small shop should compare total treatment cost against usable tablet mass and reaction control, not assume that a larger pack is automatically cheaper.
Conventional tablets create a chemical and ventilation burden. Chlorine-family products can provide rapid hydrogen removal and some grain-refining benefit, but they require effective extraction because chlorine compounds can form fumes [S1]. A nitrogen-family tablet produces lower fumes and is described as more suitable for well-ventilated small shops [S1].
Chlorine-free engineered tablets are available to reduce fume and environmental impact, but published claims still require validation against the actual alloy, melt temperature, tablet chemistry, and foundry ventilation arrangement [S1]. Tablets are therefore not automatically the low-emission option merely because they are simple.
Rotary Equipment Fit for Small Furnaces
Portable rotary equipment can cover a credible small-foundry range: one documented unit handles dip-out and crucible furnaces from 40 to 3,000 lb, weighs less than 50 lb, and uses 24-inch or 36-inch lances [S4][S5].
Its utility requirements are specific: the cited portable design uses a 0.75 hp variable-speed air motor, 90–100 psi compressed air, and dry nitrogen, argon, or a proprietary dry gas, with an overhead hoist required for positioning [S4]. A separate published installation reference lists 90–120 psi compressed air and a regulated gas supply [S5].
These details make a rotary unit more than a consumable purchase. The foundry must provide compressed air, dry gas, lifting equipment, lance handling, and controlled treatment time. A casting ladle may suit a simple manual workflow, but rotary treatment is usually most practical when the melt is held in a crucible or dip-out furnace and the equipment can be suspended over the bath.
Application and Maintenance Constraints
Rotary systems are the better fit for porosity-sensitive aluminum, production foundries, and heats large enough to justify equipment setup, but they are not automatic solutions for every small order. Tablet treatment is more appropriate for a foundry running occasional heats, changing alloys frequently, or operating where fume extraction, gas supply, and maintenance infrastructure are limited [S1][S3].
Process failure modes differ. With tablets, poor placement or shallow immersion can produce uneven bubble distribution, localized over-treatment, and inconsistent results across the melt column [S1]. With rotary equipment, dirty or wet gas, an incorrect lance depth, insufficient treatment time, or unstable lance rotation can reduce the effective gas-liquid interface and hydrogen pickup from the atmosphere.
Temperature and melt condition must also be controlled. Hydrogen solubility in liquid aluminum rises from approximately 0.04 mL/100 g in solid aluminum to about 0.70 mL/100 g at 750°C, a 17-fold increase [S3]. Clean charge, dry tools, and low moisture exposure reduce the treatment burden, but they do not remove the need for a controlled degassing step before casting.
Selection Rules by Foundry Operating Model
Choose tablets when the expected heat is small, production is intermittent, operator training is limited, and the foundry accepts responsibility for dosage, immersion, reaction time, dross handling, and fume control. The published guidance supports 0.1–0.2% dosage, 5–10 minutes of reaction time, and treatment placement matched to melt depth [S1].
Choose a rotary unit when short cycle time, repeatable gas dispersion, reduced chemical handling, or lower environmental impact justifies capital equipment. For a 70–500 lb crucible, the documented treatment window is 1–5 minutes; for 500–3,000 lb, it is 5–10 minutes [S5]. The installation must also support 90–120 psi compressed air and regulated dry nitrogen or argon [S5].
Neither option should be selected from generic porosity claims. A small foundry should record starting hydrogen level, treatment duration, tablet mass or gas flow, melt temperature, dross behavior, and reject rate on the same alloy. For rotary equipment, set degassing gas flow by melt volume and RPM provides a separate process reference.
The next decision point is the next production heat: compare tablet cost and handling time with the rotary unit's 1–10 minute treatment window, then track hydrogen results, porosity rejects, gas consumption, and fume exposure over at least three comparable heats.