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Aluminum alloy die-casting degassing process, practical points for rotor degassing and argon purificationAluminum alloy die-casting degassing process, practical

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  • เวลาเผยแพร่: 2026-11-07

Aluminum alloy die-casting degassing process, practical points for rotor degassing and argon purification
The hydrogen content in aluminum liquid is the source of porosity and pinhole defects. Many factories only focus on molds and ignore degassing at the melting end. Xinfeng Machinery explains the degassing logic and standards clearly.
1、 Source of hydrogen gas from aluminum liquid
Moisture is the main source of hydrogen: recycled materials with water, oil stains, wet crucibles, wet furnace linings, and wet refining agents. When water encounters high-temperature aluminum liquid, it decomposes and hydrogen gas dissolves into the aluminum liquid; The higher the temperature, the higher the solubility of hydrogen, which precipitates and forms pores during solidification. A356 is more sensitive to hydrogen, and the hydrogen content control requirements for airtight components are much stricter than those for ADC12 ordinary shells.
2、 Principle and parameters of rotor rotation degassing
Rotor degassing (rotary blowing) is carried out by introducing argon gas, which is dispersed into small bubbles. Hydrogen gas diffuses into the bubbles and floats up, carrying out the aluminum liquid. Conventional speed of 400-600rpm, argon flow rate of 8-15L/min; The duration of degassing is based on the furnace capacity, typically 8-12 minutes for 500kg of aluminum liquid. The larger the bubbles, the lower the degassing efficiency. After the rotor head wears down, the bubbles become larger and the degassing effect rapidly deteriorates.
3、 Online hydrogen testing and control objectives
The target hydrogen content of airtight and pressure bearing parts is within 0.15ml/100g; Ordinary non pressure bearing shells can be relaxed to 0.25ml/100g. Factories without online hydrogen testing equipment rely on visually judging the pore level using pressure reducing test samples (RPT samples). The A356 material for alloy wheel mold wheels is generally subject to mandatory RPT sampling by the host factory.
4、 Filtering and refining matching combination
After degassing, a ceramic filter plate is used to remove alumina inclusions. Inclusions not only cause slag holes in castings, but also become nucleation points for hydrogen evolution, making it easier for pores to form. The production line with a high proportion of recycled materials needs to increase the frequency and duration of degassing. If the recycled material exceeds 40%, the single furnace degassing time will increase by about 30%.
5、 Differences in degassing between die-casting and low-pressure casting
Low pressure casting insulation furnace is left to stand for a long time, making it easier for hydrogen to accumulate. Regular degassing of the entire furnace is essential; Long term immersion of aluminum liquid in the riser will also introduce water vapor. The turnover of high-pressure die-casting furnaces is fast, but the transfer of material packages and the presence of water in pouring spoons can also increase hydrogen production. No matter how good the mold exhaust design is, if the aluminum liquid hydrogen exceeds the standard, the pore defects cannot be eliminated. Google's "aluminum degreasing for die casting" is aimed at smelting engineers.
FAQ
Which is better, nitrogen or argon, for degassing?
Argon is more inert and does not react with aluminum; Nitrogen is prone to form aluminum nitride inclusions, and argon gas is preferred for die casting.
How long does it take to replace the rotor head?
High temperature oxidation loss of graphite rotor, usually 7-15 days, depending on the duration of use.
How long can it be stored after degassing?
The longer the standing time, the more hydrogen should be absorbed and used within 30 minutes after degassing as much as possible.
How to determine the qualification of RPT samples?
After vacuum solidification, the cross-section of the sample has fewer and finer pores, and no large pores.
5. Does the ADC12 shell have high requirements for hydrogen content?
The ordinary appearance shell requires looseness, while the water-cooled shell requires strict airtightness.
Can degassing simultaneously remove inclusions?
Dehydration is the main method for degassing, while impurity removal relies on filtration and refining agents.
What are the disadvantages of adding too much refining agent?
Defects such as slag and inclusion will occur, and it will also increase the gas content of the aluminum liquid.
8. Should the low-pressure furnace be continuously degassed during the insulation stage?
No need, regularly remove gas from the entire furnace and keep it sealed daily to reduce water vapor inhalation.

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