How to stabilize the hydrogen content and slag inclusion level in the entire process of LPDC aluminum liquid refining, degassing, and slag removal?

How to stabilize the hydrogen content and slag inclusion level in the entire process of LPDC aluminum liquid refining, degassing, and slag removal?
The root causes of the two major defects, porosity and slag inclusion, are mostly in the smelting process. Many factories only perform degassing once, ignoring static placement, slag removal, and liquid level protection. Hydrogen and oxide slag are intermittently released, and the yield is sometimes good and sometimes bad.
1、 Refined degassing quantification parameters (A356)
Rotor degassing speed: 300-450rpm; Argon flow rate of 8-12 L/min, degassing time of 8-12 minutes; The finer the bubbles, the higher the dehydrogenation efficiency.
Refining agent addition ratio: 0.2-0.4% by weight of aluminum liquid, divided into two doses, the first slag removal and the second auxiliary dehydrogenation; A one-time release is prone to slagging and clumping.
After degassing is completed, let it stand for 15-25 minutes and allow hydrogen bubbles and oxidized slag to float up through the window; Insufficient settling, suspended slag and gas enter the mold cavity, and defects randomly erupt.
Slag removal requirements: The floating slag on the liquid surface should be completely removed without stirring the aluminum liquid; Stirring will drag the slag back into the aluminum liquid.
Target hydrogen content: ordinary castings ≤ 0.2ml/100gAl; Automotive X-ray parts ≤ 0.15ml/100gAl; If the hydrogen content exceeds the standard, it will be difficult to eliminate the pores even if the mold is further optimized.
Xinfeng Machinery provides customers with matching melting SOP, distinguishing between adjusting parameters for operating conditions with high proportions of new machines and recycled materials.
2、 Key points for controlling recycled materials
The recommended proportion of recycled materials is ≤ 40%; The recycled material comes with oxide skin, oil stains, and residual mold release agents, and the hydrogen and slag content is much higher than that of primary aluminum.
The recycled materials must be separately crushed and dried, and the surface oil and moisture must be completely removed. Wet recycled materials can be directly fed into the furnace, causing a surge in hydrogen content.
After adding the recycled material, heat it up to 740 ℃, refine it thoroughly, and extend the settling time by 5-10 minutes.
3、 Differences in smelting control among overseas customers
Southeast Asian factories have a high proportion of recycled materials, simplify degassing, rarely measure hydrogen, and rely on infiltration to detect bottom porosity defects.
Tier 1 primary aluminum in North America is given priority, and the proportion of recycled materials is strictly controlled. Each furnace's spectrum and hydrogen measurement records are recorded, and the entire furnace is isolated and scrapped if it exceeds the standard.
European customers continuously measure hydrogen online, and if the hydrogen content exceeds the standard, it will automatically lock and prohibit feeding and die-casting. Melting records will be archived for a long time.
In the high-temperature environment of the Middle East, the hydrogen absorption rate of aluminum liquid is faster, which shortens the insulation time of aluminum liquid in the crucible and reduces the suction window.
4、 Melting defect chain
Insufficient degassing and settling → hydrogen remains in the aluminum liquid → hydrogen gas is released during filling → dispersed pores;
Incomplete slag removal, stirring of aluminum liquid → suspension of oxidized slag → slag inclusion in castings, X-ray judgment of waste;
Wet recycled materials, oily materials → moisture decomposition to produce hydrogen → batch porosity;
Excessive addition of refining agent → residual refining agent, forming salt inclusions.
5、 Long tail traffic layout ideas
Aluminum liquid degassing, rotor degassing, hydrogen content, slag inclusion control, aimed at smelting supervisors and quality engineers.
Keywords: LPDC aluminum melt degrading process, rotor degrading hydrogen content A356;
Problem class: Recycled material ratio limit low pressure casting;
Comparison category: rotor degeneration vs flux degeneration aluminum casting.
Suitable for smelting processes and quality control topics.
6、 Common misconceptions in the industry
Misconception 1: The longer the degassing time, the better. If the degassing time is too long, it will increase the oxidation of aluminum liquid and increase the slag amount.
Misconception 2: Adding more refining agent to remove gas is cleaner, and excessive refining agent forms new inclusions, polluting the aluminum liquid.
Misconception 3: Direct feeding of recycled materials into the furnace, introduction of oil and moisture, and uncontrolled hydrogen content.
FAQ
Q: Recommended rotor degassing speed?
A：300–450rpm。
Q: What is the upper limit of hydrogen content in automotive parts?
A：≤0.15ml/100gAl。
Q: How long should it be left to stand after degassing?
A：15–25min。
Q: What is the recommended upper limit for the proportion of recycled materials?
A：≤40%。
Q: What is the proportion of refining agent added?
A: Aluminum liquid weight is 0.2-0.4%.
Q: What are the hazards of damp recycled materials?
A: Water decomposes, absorbs a large amount of hydrogen, and the pores burst in batches.
Q: Taboo on digging up trash?
A: Do not stir the aluminum liquid to prevent the slag from being re drawn in.
Q: What are the characteristics of European smelting control?
A: Online continuous hydrogen testing, exceeding the standard and locking production.