Key technical control of oil air lubrication casting process

1. Casting temperature control
The casting temperature is the primary parameter that affects the quality of ingots and the safety of the casting process. The pouring temperature of aluminum alloy round ingots is usually between 680 ℃ and 760 ℃, and the specific value needs to be adjusted according to factors such as alloy type, ingot specifications, and casting speed. Raising the pouring temperature can enhance the fluidity of aluminum liquid, reduce insufficient pouring and cold shut defects. However, excessively high temperatures can increase gas solubility and oxidation reactions, leading to defects such as pores and slag inclusions, while exacerbating solidification shrinkage and increasing the risk of cracking and deformation. Under the conditions of oil and gas slip casting, due to the insulation effect of the air cushion, the temperature distribution of the melt in the liquid cavity is more uniform, allowing for good flowability and filling ability at relatively low pouring temperatures.

2. Casting speed control
Casting speed is the most sensitive process parameter affecting quality in oil and gas slip casting. As mentioned earlier, the casting speed has a significant impact on the solidification structure of the ingot - as the casting speed increases, the proportion of floating grains in the center of the ingot increases, resulting in grain refinement; However, excessive speed may lead to the deepening of liquid voids, increased segregation, and even the formation of central cracks [90]. Oil gas slip casting allows for higher speeds than traditional DC casting due to the air cushion effect, but essentially requires optimization and matching based on comprehensive factors such as alloy grade, ingot diameter, cooling conditions, etc., in order to achieve the best balance between surface quality, internal structure, and production efficiency.

3. Optimization of cooling water parameters
The cooling water flow rate, water temperature, water pressure, and water quality directly affect the solidification rate and temperature field distribution of the ingot. The cooling water flow control accuracy of modern casting machines can reach ± 2%, with an adjustable range of 200-10000 L/min. The temperature of cooling water is usually controlled between 20 ℃ and 35 ℃. In oil and gas slip casting, precise control of cooling water parameters is more critical than traditional casting due to the minimization of primary cooling and the dominance of secondary cooling. Excessive water cooling can cause excessive thermal stress on the surface of the ingot, leading to cracks; Insufficient water cooling can make the solidification shell too thin, which can easily lead to aluminum leakage accidents. Wagstaff's DualJet cooling technology achieves uniform and efficient secondary cooling by optimizing the cooling water spray angle and layout.

4. Accurate control of oil and gas supply parameters
Oil and gas supply is a unique control element that distinguishes oil and gas sliding casting from traditional processes. The oil supply system needs to set the pulse frequency and duty cycle according to the specifications of the ingot and the alloy grade, providing an appropriate and stable flow of pulse lubricating oil for each crystallizer. Excessive oil consumption can cause smoke and surface pollution during oil combustion; If the oil volume is too low, the oil and gas film will be incomplete, leading to surface defects. Compressed air needs to maintain a dry and stable pressure and flow rate. The moisture contained in the gas will decompose and produce hydrogen gas at high temperatures, directly causing porosity defects in the ingot.
The control of oil and gas ratio is the technical difficulty. Oil and gas need to be accurately measured separately before entering the porous structure of the graphite ring. After achieving uniform mixing in the micropores of the graphite ring, a stable gas oil two-phase film layer is formed on the inner surface of the crystallizer. The stability of this process directly determines the uniformity and quality consistency of the entire length of the ingot.

5. Automation and intelligent control
Modern high-end casting machines have achieved full process automation control. Real time closed-loop adjustment of casting speed, cooling water flow rate, water temperature, oil and gas supply parameters is carried out through PLC. All key parameters can be set with process formulas and automatically executed. For example, the curve of slow gradient speed in the initial stage of casting can be preset, and the speed or oil supply parameters can be automatically adjusted when liquid level fluctuations are detected during the casting process. After introducing closed-loop control, the fluctuation of casting speed can be reduced from ± 20% in open-loop control to below ± 0.2%, and the surface quality and yield are significantly improved.