Molten aluminium degassing system (rotary degasser)

01

Size rotor speed, gas flow and treatment time

A Foseco International patent on rotary degassing rotors states that rotors of 175–190 mm treat batches of 250–600 kg and 200–220 mm rotors 600–900 kg, with minimum speed around 300–350 rpm, preferred 400–600 rpm, gas flow of 12–30 L/min (the patent says “more usually 22-24 litres per minute”) of argon, nitrogen, their mixtures or inert gas with 1–10% chlorine, and treatment times of 1–10 minutes. Rotors of 300 mm or more for continuous treatment run at a minimum of about 225 rpm (preferred 400–450 rpm) with 30–80 L/min (“typically 60 litres per minute”), treating up to 500 kg of metal per minute with a residence time of about 2–10 minutes. Faster rotation pumps more metal and improves gas–metal contact. [1]

Jinan Hydeb's XC(P) 200 unit, a linked supplier, drives a graphite rotor immersed in a crucible or transfer ladle while feeding high-purity nitrogen or argon and fluxing agent, to remove hydrogen and oxides. [3]

Editorial note: the patent's figures are for its rotor design; ask suppliers for rotor diameter, speed, gas flow and time for your vessel size and alloy, and whether the unit can record them per treatment.

Give the supplier the alloy and scrap content, batch weight or casting flow rate, vessel type (crucible, transfer ladle, in-line box), purge gas available, flux addition, cycle time available, density index or hydrogen target, rotor and shaft material, lifting and positioning needs, and power and gas supplies.

02

Prove melt quality with density index

The Foseco patent notes that degassing effectiveness can be judged by density index before and after treatment without measuring hydrogen directly — a higher density index meaning more hydrogen — and lists the values castings "should have": wheels 5–8, cylinder head castings below 5, sand castings below 2 and vacuum or pressure die castings below 1. [1]

Kutsal and co-authors (Cevher Jant and Bayburt University, Archives of Foundry Engineering, 2026) treated A356 with 80% scrap using a side-perforated rotor, 0.1 wt% cleaning flux and 700 °C pouring, varying rotor speed (200 or 500 rpm), time (5 or 10 min) and gas flow (5 or 10 L/min). Density index — the difference between densities of reduced-pressure and air-solidified samples as a percentage — ranged from 4.35 at 200 rpm, 5 min, 5 L/min to 0.89 at 500 rpm, 10 min, 10 L/min. Raising rotor speed gave a sharp drop in density and bifilm indices; longer time and higher gas flow gave secondary gains; and tensile strength and ductility improved. [2]

Editorial calculation: density index = (air-cooled density − vacuum density) / air-cooled density × 100. Samples of 2.68 and 2.60 g/cm³ give (2.68 − 2.60) / 2.68 × 100 ≈ 3.0 — within a wheel target of 5–8 but above a sand-casting target of 2. The densities are assumed examples. [2] [1]

03

Compare an in-line compact degasser with a refractory box degasser

STAS describes its ACD (Aluminium Compact Degasser) as smaller and more flexible than conventional in-line degassers built as refractory-lined steel boxes, while working on the same metallurgical principles. Because no metal is held in the machine at the end of a cast, alloy changes are easier and no heating is needed between casts; the unit operates in sealed mode with little dross, eliminates the cost of heating elements, thermocouples and refractory relining, and STAS claims more than a 60% reduction in overall operating and maintenance costs. It lists high hydrogen removal, good alkali and inclusion removal when chlorine or flux is used, chlorine elimination where required through its Flux Feeder for Degasser, and says the ACD suits batch casting or frequent alloy changes. [4]

Set this against the batch rotor sizing and density-index checks above: a ladle or crucible unit treats a batch, while an in-line unit treats metal flowing to the caster, so the choice follows the casting route. [1] [2] [3]

Editorial note: the 60% figure is the maker's claim and the page does not state its baseline; ask for the comparison data before using it in a cost case.

State whether degassing is batch (ladle, crucible) or in-line, the metal flow rate and alloy-change frequency, and ask for hydrogen removal data and operating costs on the same basis.

04

Crucible and ladle units and in-line degassing boxes with filter boxes in the linked listings

Listings include stationary rotary degassing and fluxing units for crucibles and ladles and online degassing units with filter boxes for casting lines; ask each for rotor size, speed, gas flow and achieved density index.

05

Graphite rotor, shaft drive, gas control, flux feeder and lift of a rotary degasser

06

Capacity, gas flow, rotor speed, power and rotor material values for a degassing quotation

Published values in this table come from the Foseco patent, the Kutsal et al. study, STAS and Jinan Hydeb; where none states a value, the row says what to obtain from the supplier.

07

Send the alloy, vessel and quality data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Alloy: [grade; scrap share]
Vessel: [crucible; ladle; in-line box; size]
Batch or flow: [kg; kg/min]
Gas: [N2; Ar; mix]
Flux: [type; dose]
Time: [available minutes]
Target: [density index; hydrogen]
Utilities: [power; gas supply]

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