Necessity of aluminum liquid purification and its technical challenges
In the production process of aluminum alloy, molten aluminum liquid is very easy to absorb hydrogen and produce oxidation slag, which will significantly reduce the mechanical properties and processing characteristics of the final product. Studies have shown that when the hydrogen content in aluminum liquid exceeds 0.2ml/100g, the probability of pores in the casting will increase by more than 80%. At the same time, oxidation slag will cause the material strength to decrease by 30%-40%, seriously affecting the service life of the product.
Traditional degassing methods have problems such as low efficiency and high cost. The graphite rotor degassing technology can increase the degassing efficiency to 2-3 times that of the traditional method by rotating and blowing inert gas. However, the durability of the core component of this technology, the graphite rotor, in the high-temperature aluminum liquid environment has always restricted its widespread application. Especially at operating temperatures above 600℃, the oxidation loss of graphite materials has become a technical problem that the industry needs to solve urgently.
Working principle and technological innovation of Graphite Degassing Rotor
In-depth analysis of purification mechanism
The working principle of graphite rotor degassing system is based on multiple basic principles of physical chemistry. When the high-purity graphite rotor rotates at a speed of 500-700rpm, its specially designed impeller structure can break the inert gas (usually nitrogen or argon) into tiny bubbles with a diameter of 0.5-2mm. These bubbles form a huge gas-liquid contact interface in the aluminum liquid. It is estimated that the total surface area of microbubbles dispersed in 1m³ aluminum liquid can reach 200-300m².
According to Henry’s law, these bubbles form a concentration gradient with hydrogen atoms in the aluminum liquid, and hydrogen atoms will spontaneously diffuse into the bubbles. At the same time, according to the principle of surface adsorption, the bubbles will capture the oxidized slag in the aluminum liquid during the rising process. Experimental data show that a well-designed graphite rotor system can reduce the hydrogen content of aluminum liquid from 0.3ml/100g to below 0.1ml/100g in 15-20 minutes.
Major breakthroughs in anti-oxidation technology
In recent years, graphite rotor anti-oxidation technology has made significant progress. The current mainstream technical solutions include:
Chemical vapor deposition (CVD) SiC coating technology
This technology forms a dense silicon carbide protective layer on the graphite surface by decomposing silane gas under high temperature. Tests show that a 50-100μm thick SiC coating can reduce the oxidation rate of graphite in 800℃ air by more than 85%. An application case of a well-known aluminum wheel manufacturer shows that after using SiC coating, the service life of the rotor is extended from the original 15 days to 90 days.
Borosilicate composite impregnation technology
This lower-cost solution uses a vacuum impregnation process to allow borosilicate solution to penetrate into the pores of graphite. When working at high temperatures, these compounds will form a glassy protective layer. Although its temperature resistance is slightly inferior to that of SiC coating (optimal operating temperature below 650℃), its cost is only 1/3 of the former, which is particularly suitable for small and medium-sized aluminum processing enterprises.
Key considerations in practical applications
Optimization of process parameters
In actual production, the use effect of graphite rotors is affected by multiple parameters:
- Speed control: Too low speed will lead to excessive bubbles and reduce degassing efficiency; too high speed may aggravate rotor wear. Experience shows that for most aluminum alloy melts, 550-650rpm is the best speed range.
- Gas flow rate: Usually controlled at 1.5-2.5L/min·ton aluminum liquid. It is worth noting that although argon gas has a higher cost, its dehydrogenation efficiency is 15%-20% higher than that of nitrogen.
- Immersion depth: The depth of the rotor immersed in the aluminum liquid should be maintained at 200-300mm. Too shallow will affect the bubble distribution, and too deep will increase the rotor force.
Strict implementation of operating specifications
To ensure the service life of graphite rotors, a complete operating procedure must be established:
- Preheating system: Use step-by-step heating, first heat to 300℃ and keep warm for 30 minutes, then heat to 500℃ and keep for 20 minutes, and finally heat to the operating temperature. This preheating method can avoid cracks caused by thermal stress.
- Shutdown procedure: When stopping use, the rotor should be lifted above the surface of the aluminum liquid, and the protective gas should be continuously introduced until the temperature drops below 200℃.
- Daily maintenance: Check the rotor diameter every 8 hours, and consider replacing it when the shaft diameter decreases by more than 5%.
Economic Benefit Analysis and Industry Cases
Quantitative Analysis of Cost Savings
Take an aluminum strip production enterprise with an annual output of 50,000 tons as an example:
| Cost Item | Traditional Rotor | Anti-oxidation Rotor |
| Rotor Consumption | 200 pieces (￥6000/piece) | 50 pieces |
| Inert Gas | 25m³/ton | 18m³/ton |
| Aluminum Loss | 3.5% | 2.2% |
Typical Application Cases
Transformation Project of a New Energy Vehicle Battery Shell Production Enterprise:
Before Transformation: Ordinary graphite rotors were used, with an average life of 10 days, unstable hydrogen content control (0.15-0.25ml/100g), and a monthly scrap rate of 3.2% due to pores.
Transformation measures:
- Use SiC coated graphite rotor
- Install nitrogen blanketing system
- Optimize process parameters (speed 600rpm, Ar gas flow 2.0L/min·ton)
Transformation effect:
- Rotor life extended to 75 days
- Hydrogen content stabilized at 0.08-0.12ml/100g
- Scrap rate reduced to below 0.8%
- Annual comprehensive benefits increased by about ￥2.8 million
Future technology development direction of Degassing Rotor
With the continuous improvement of product quality requirements in the aluminum processing industry, graphite rotor technology is developing in the following directions:
Intelligent monitoring system: By integrating temperature sensors, vibration sensors and diameter measuring devices, the working status and loss of the rotor are monitored in real time to achieve predictive maintenance.
Nanocomposite coating: Laboratory test data of graphene-enhanced coating shows that its corrosion resistance is 2-3 times that of traditional SiC coating, and it is expected to be industrialized in the next 3-5 years.
3D printing technology: Using 3D printing to manufacture graphite rotors with complex internal cooling channels can further improve heat dissipation efficiency and service life.
Conclusion
As the core component of aluminum water purification technology, the continuous improvement of the performance of the anti-oxidation graphite degassing rotor is of great significance to the aluminum processing industry. By adopting advanced anti-oxidation technology and optimizing process parameters, enterprises can not only significantly improve product quality, but also achieve considerable economic benefits. It is recommended that aluminum processing enterprises choose the appropriate rotor type according to their own production characteristics and establish a complete use and maintenance system to give full play to the advantages of this technology.
When selecting a supplier, focus should be placed on the company’s technical research and development capabilities, quality control system and after-sales service level. At the same time, it is recommended to conduct a small batch trial to verify the performance of the rotor through actual production data, and provide a decision-making basis for large-scale application.