Secondary Pollution of Molten Aluminum in Casting Process

The secondary pollution of molten aluminum mainly occurs in the insulated washing tank from the furnace to the casting machine. On-line degassing and filtering equipment is installed on the insulating launder to purify the aluminum melt. As the melt passes through the tank system, it absorbs hydrogen to varying degrees when it comes into contact with moisture in the air. When the aluminum melt comes into contact with moisture, hydrogen atoms are absorbed by the surface of the aluminum melt and then diffuse into the melt. The entire dissolution process includes: physical adsorption, chemical adsorption, and diffusion.

Secondary Pollution of Molten Aluminum

Secondary Pollution of Molten Aluminum

According to the hydrogen absorption characteristics of the metal transfer channel, two channels have been compared and tested: one is used to produce an ordinary open channel, where the aluminum melt is in direct contact with the environment, and the melt protection depends only on the oxidation of the surface membrane. The other is an improved runner, which is improved on the basis of an open runner. The depth of the runner remains unchanged. The upper mouth of the runner is reduced by 4 cm, and the width of the lower bottom is reduced by 2 cm. In addition, heat preservation is performed on the runner. After the casting material is formed and installed, the insulation material is added to the outside of the package. The purpose is to reduce the heat dissipation of the runner and reduce the contact between the melt and the air, thereby reducing the temperature of the aluminum melt and the hydrogen absorption capacity.

Compared with the open runner, the improved runner has a smaller cross-sectional area, the melt flows faster in the runner, and the residence time is shorter. The sealed flow channel isolates the melt from the moisture in the air, effectively preventing the generation of high-temperature aluminum and moisture reactants, reducing the hydrogen concentration at the vapor-liquid interface of the aluminum liquid, and effectively preventing the melt Absorb hydrogen. After improving the flow channel, the residence time of the melt in the flow channel is shortened, the system temperature is lowered, the hydrogen concentration at the gas-liquid interface of the aluminum liquid is reduced, and the hydrogen content of the casting point is reduced.

In actual production, it is necessary to control the secondary pollution of the molten aluminum from the outlet of the degassing device to the casting point. Effective control method: First, speed up the flow rate of the melt in the runner and filter box. The second is to reduce the contact area between molten aluminum and air. The third is to reduce the humidity in the air. Take the filter box as an example, a filter box with strong sealing should be used and the residence time of the aluminum melt in the filter box should be reduced. Especially when the hydrogen content in the melt is low, a higher sealing effect is required, otherwise the subsequent secondary pollution will reduce the effect of the online degassing treatment, and the ideal aluminum melt will not be obtained in the melt.