Theoretically speaking, the purity of aluminum alloy melt should reach a high level after refining in the furnace and on-line degassing and slagging. However, the actual results are often not ideal. One of the important reasons is that the aluminum liquid passes through the launder. The slagging and gas suction conditions during the casting process. At this time, the aluminum melt is in an “unprotected” state, and the absorbed gas and the generated non-metallic inclusions are more likely to flow into the casting rod, forming “secondary pollution”. The longer the launder, the greater the probability and degree of secondary pollution.
In view of the above problems, three measures can be taken when designing and purification:
- Shorten the length of the runner. Enter the mold from the casting water outlet, and the length of the launder shall not exceed 2 m. When dealing with the flow trough drop, the method of over-tilting is not adopted, but the method of overlapping two sets of launders is adopted to ensure the stability of the liquid level to the greatest possible extent and prevent the aluminum melt from rolling and slagging.
- The integrated design of filtration and degassing system saves the transfer process and shortens the length of the flow trough as much as possible.
- The filter plate of the secondary filtration is directly placed on the crystallizer to ensure that the aluminum liquid is filtered directly into the casting, reducing the incidence of secondary pollution. When refining in the furnace, the amount of refining agent is sufficient to ensure refining time and avoid refining dead ends. Strictly implement the baking system of the casting system. These measures will have a positive impact on purity control.
In order to make aluminum rods with higher purity of aluminum alloy, there are several points to note:
- When the alloy grade is changed, drain the aluminum liquid in the purification device and clean it up.
- The runner tray must be thoroughly baked.
- When smelting in the furnace, a covering agent is used to prevent inhalation.
- The runner tray must be installed in the previous shift and fully baked.
- The production and maintenance of the runner mold plate adopts light-weight refractory insulation material, which has good air permeability, which is conducive to thorough drying and prevents air inhalation.
- Blow off the scum on the surface of the filter before loading it, and check the blind porosity.
It is worth noting that the degassing purification equipment was put into use in an aluminum material factory in March and has been operating stably, and the degassing and slagging effect is ideal. But after the rainy season in June, the purification effect is greatly affected. It can be seen that environmental factors are an important factor affecting the purity of the melt. Melt purification is not a problem that can be solved by advanced equipment alone. It requires comprehensive consideration and overall planning from production management, equipment maintenance, process specifications, etc., to achieve a more ideal effect.