Refining of melts
For refining aluminum (aluminum melts) from dissolved metallic impurities (sodium, magnesium, iron, zinc), non-metallic inclusions (mainly oxide films) and dissolved hydrogen, purging with inert and active gases, settling, treatment with chloride salts and fluxes (self-melting flux, universal flux, coating-refining flux, modifying flux, flux for processing aluminum) , vacuuming, electroflux treatment and filtration through mesh, ceramic and foam ceramic granular filters are used.
Often, one of the listed methods is sufficient, for example, refining and degassing with the “Degassing Tablet” or “Complex Tablet Preparation”, which is used for refining and degassing treatment of aluminum-based melt. The preparation provides increased aluminum fluidity and improved mold filling compared to untreated aluminum melt; creates a protective furnace atmosphere; helps reduce metal losses with slag, as well as remove non-metallic inclusions and gases from the aluminum melt due to chemical binding of hydrogen dissolved in aluminum.
Flux “Complex Tablet Preparation” is introduced into the melt at a temperature of 720 – 750 ° C in an amount of 0.05 – 0.08% of the melt mass. They are introduced into molten aluminum using a “bell”. The bell with the tablet or preparation is immersed in the bottom of the melt and for more complete refining and degassing it is continuously stirred until the release of gaseous products ceases according to the reaction 3MeCl2 + 2Al = 2AlCl3 + 3Me. In this case, chloride salts interact with aluminum according to the reaction. When sulfur is introduced into the melt, approximately 90% of it interacts with hydrogen, the remaining sulfur modifies the Al-Si eutectic.
The released gas bubbles with non-metallic inclusions float to the surface of the melt. In doing so, they entrain non-metallic inclusions suspended in the melt, and the dissolved hydrogen diffuses into the bubbles and is carried out into the atmosphere.
Pouring of moulds
Aluminium alloys are poured into sand or permanent (metal) moulds from ladles lined with refractory material, or from steel ladles coated with zinc oxide and liquid glass paint. Before pouring, ladles with fresh lining are dried and calcined to remove moisture at 700–800 °C. The temperature of the poured alloy depends on the thickness of the casting walls.
After pouring, solidification and cooling of the castings, the moulds (sand) are knocked out. Cooled moulds are knocked out using special machines called knockout grates. The knocked out moulding mixture is returned for subsequent regeneration after adding fresh materials to it. Gating systems and risers from castings made of non-ferrous alloys and steels are cut off, and from cast iron castings they are knocked off. Sand that has adhered (burnt) to the surface of castings is cleaned off with metal brushes and cleaned using special equipment in foundries.