Apparatus for treating molten metal having a sealed treatment zone

#This invention relates to an apparatus for the treatment of molten metal and, more particularly, for degassing molten metal in a sealed treatment zone.

#When many molten metals are used for casting and similar processes they must be subjected to a preliminary treatment to remove unwanted components that may adversely affect the physical or chemical properties of the resulting cast product. For example, molten aluminum and aluminum alloys derived from alumina reduction cells or metal holding furnaces usually contain dissolved hydrogen, solid non-metallic inclusions and various reactive elements. The dissolved hydrogen comes out of solution as the metal cools and forms unwanted porosity in the product. Non-metallic solid inclusions reduce metal cleanliness and the reactive elements and inclusions create unwanted metal characteristics. This treatment is frequently carried out in a vessel or trough section in-line with the metallurgical trough used to convey the metal from the holding furnace to the casting machine.

#These undesirable components are normally removed from molten metals by introducing a gas below the metal surface by means of gas injectors. As resultant gas bubbles rise through the mass of molten metal, the absorb gases dissolve in the metal and remove them from the melt. This process is often referred to as “metal de-gassing” or “in-line metal de-gassing”.

#FIG. 1 is a plan view in partial section of a de-gassing trough unit;

#FIG. 2 is a vertical section along line A-A of FIG. 1;

#FIG. 3 is a vertical cross-section of the trough unit;

#The drawings show several embodiments of the invention as it relates to a de-gassing apparatus for molten metals. This includes a de-gassing trough unit 10 supported by a framework 11 and being lined by a ceramic liner 12. The trough holds a body of molten metal 13 which is fed in through molten metal inlet 14 and is discharged through molten metal outlet 15. Ceramic or refractory baffles 16 are provided at each end of the treatment zone to act as “air-locks” at the point of metal entry and exit from the vessel. A flat metal flange 17 surrounds the top of the trough 10.

#A cover unit 20 fits over the de-gassing trough unit 10 and sits on the flange plate 17. As seen from FIGS. 4 and 5, the cover unit includes a heavy steel plate portion 21 which includes an edge flange 22. The cover supports downwardly projecting gas injection rotors 26, of which the shafts only are shown. Suitable rotors are described for example in U.S. Pat. No. 5,660,614.

#Fixed to the bottom face of the edge flange 22 are three (optionally two) strips. These strips include a first inner strip 25 which is a solid steel strip of square or rectangular shape. This metal strip acts as a mechanical protection from metal splashing from the de-gassing trough. The metal strip 25 also bears the weight of the cover 20 and allows a predicted amount of compression on strips 24 and 23. The middle strip 24 is made of a metal mesh or ceramic fiber rope wrapped in refractory, e.g. silica, fabric material. Its principle characteristic is its ability to withstand high temperatures. The third strip 23 is optional in some embodiments and is preferably square or rectangular in shape and is formed of an elastomeric material, e.g. a silicon material, and acts as a barrier against gaseous emissions. It is held between shoulder portions 27. The characteristics of this seal 23 are selected for its elasticity and flexibility, and thus ensures a tight seal on the surface of the trough even if the surface is slightly irregular. This third strip is used in situations that require particularly good gastight sealing.