Rotary impeller with porous head for dispersing gas treatment of molten metal

Abstract: Usually, for the purpose of impurities removal out of the molten metal such as Al, etc., the treatment gas is blown into the molten metal located in a vessel, the rotor is high-speed revolved; in such a molten metal treatment, the article is aiming at the homogeneity of the treatment gas, and the eddy current and the rippling preventions at the surface of said molten metal. The present application, for the purpose of the above described purposes, comprises such structures and/or materials as a gas chamber (gas reservoir) at a treatment gas outlet section, a porous (with many pores in nature) material at the outlet which composes the outer periphery of the said gas chamber, moreover, an impeller having a weak agitation power aiming at only the dispersion of the treatment gas is used, or the diameter of the rotary axis of the rotor is made slender, or either some tapered portion is installed at the outlet of the treatment gas of the porous material, or a taper or reverse "R" is set at the side of the rotary impeller, and the lower portion of the vessel is also made capable of making -the said dispersion.

Description: The present invention relates to a rotary injector used during a molten metal treatment of Al, etc., for the removal of impurities such as hydrogen gas, oxides, and other non-metallic interposing substances. The rotating injectors are widely being utilized at present in industries for the purpose of floating separation of the impurities in the molten metal such as Al, etc. in the vessel by blowing dispersion of the inert gas which comprises Argon, Nitrogen, Chlorine, etc. A rotaty injector usually comprises a hollow rotating shaft and a rotating mixer made of sintered carbon or ceramics; an inert gas flows out of holes of more than lmm  installed at the down section or side of the rotaty mixer which rotates at a higher speed. As a result of the hole diameter through which the inert gas flows (more than lmm), the particular inert gas diameter flowed through said hole is made as large as more than 5mm  in case when the rotaty injector is not rotated. For obtaining an efficient molten metal treatment capability (removal of the impurities), the predominant premise there shall have to make as much as the contacting area as possible between the inert gas and the molten metal, for which the rotaty injector is being rotated at a higher speed (200 - 800 rpm) contemplating the inert gas micronization and the dispersion of the said gas over the vessel entirely. The said micronization of the inert gas by the higher rotation of mixer is possible viewed from the macro standpoint and is therefore an effective art, on the one hand; however, the inert gas among itself made "sticky" and also by the volume expansion of the inert gas itself inviting the undesirable lowering of the contacting area with the molten metal as a result of the agitation, during the floating process of once micronized inert gas while it is being dispersed upwards to the surface of the molten metal. On the other hand, as a result of the higher agitation force of the rotating injector, the molten metal in the vessel is agitated, causing either eddy current or ripples on the surface of the molten metal, forming oxides due to the contact with the atmospheric air and rolling the hydrogen gas into the molten metal; all of these phenomena have long been regarded to be vital and grave issues. In view of the above cited conventional technological issues, extensive researches and developments were carried out in respect of said issues such as the micronization and homogeneity of the inert gas, and, the preventions of both eddy current at the surface of the molten metal and the rippling. According to the present invention, there is provided a rotary injector for molten metal treatment as defined in claim 1, comprising: an inert gas outlet section made of a porous material, and a gas chamber having a periphery formed from said porous material. According to the present invention, there is also provided an apparatus for molten metal treatment, comprising a vessel, a rotary injector immersed in said vessel, an inert gas being generated inside said vessel while said rotary injector is being rotated, said rotary injector comprising: a rotary shaft, a rotary mixer connected at the lower part of said rotary shaft above an inert gas outlet section. The generation of the micronized and homogeneous inert gas was made possible by the adoption of a porous (preferably multi-porous in nature) material which has a pre-heating effect installed at the gas chamber (gas stay) of the inert gas in the outlet section, but not by the conventional prior high speed rotation of the rotating injector. On the other hand, the particular rotaty mixer with preferably less than 25mm thickness was adopted to curb down the agitation force of the molten metal not to change the inert gas size over the vessel and to uniformly disperse the inert gas. As a result of the less agitation force of the rotaty injector, the present invention successfully resolved the preventions of the eddy current over the molten metal surface and the rippling, hence all the above cited technological issues were totally resolved. Preferred embodiments will now be described as examples without limitative manner having reference to the attached drawings, wherein: Fig. 1(i): is a front elevation view of a first embodiment of a rotary injector according to the present invention; Fig. 1(ii): is a bottom view thereof; Fig. 2(i): is a front elevation view of a second embodiment of a rotary injector according to the present invention, Fig. 2(ii): is a bottom view thereof, Fig. 3(i):is a front elevation view of a third embodiment of a rotary injector according to the present invention, Fig. 3(ii): is a bottom view thereof, Fig. 4(i): is a front view of a rotary mixer used with the rotary injector of the present invention, Fig. 4(ii): is a bottom view of such rotary mixer, Fig. 5: shows a dispersion apparatus according to the present invention,, and Fig 6: shows another embodiment of the dispersion apparatus. Fig. 1 is a front view showing a rotary mixer of the molten metal treatment of the present invention, where A stands for the sleeve for the installation of the rotaty mixer, B hollow rotary shaft, C rotaty mixer with less than 25mm in height, D an outlet section of the inert gas using the porous material (multi-porous in nature), Da gas chamber (gas stay), and E the screw to fix both the rotary mixer C and the inert gas outlet section D onto the hollow rotary shaft B. Fig. 2 is a front view of another embodiment of rotary injector according to the present invention: showing a gas chamber with a slope or slant surface spreading towards downside with respect to the configuration for the inert gas outlet section D. By virtue of and with the benefit of said slant, the mutual sticking of the inert gas immediately upon flowing out of the slant is prevented. Fig. 3 is also a front view of another embodiment of a rotary injector according to the present invention. The function is the same as with the rotary injector of Fig. 1, but with the provision of the protection of the inert gas outlet section D using a porous (multi-porous in nature), Da gas chamber (gas stay) is installed, making the screw E outer diameter identical with that of the disposal gas outlet D, at the partial section of the hollow rotary shaft B. Fig. 4 shows the presence of either a taper or reverse R at the side of the impeller of the rotating mixer C. Fig. 5 shows an inert gas dispersion apparatus for molten metal treatment according to the present invention, having a vessel F into which the rotary injector is immersed, the inert gas being generated while the rotary injector is being rotated; B stands for the rotary shaft, C for the rotary mixer, D for the inert gas outlet section. Also in Fig. 5, 1 stands for inert gas supply pipe, 2 for a driving motor, 3 for an inert gas dispersed in the vessel F, and, 4 for a metal. Fig. 6 shows another embodiment of the apparatus for the molten metal treatment according to the present invention, wherein the rotary injector is immersed into a crucible furnace G. G is the crucible furnace, and 5 is Al molten metal. The inert gas is being generated while the rotary injector is rotating. As a result of the experiments, the superiority of the present invention was apparently substantiated. 1. Results of Test in Al Molten Solution Kind of Rotary Injector Rotary Injector of this Invention 1 Rotary Injector of this Inv. 2 Rotary Injector Conventional Condition for Rotary RPM 250 250 500 Condition for Inert Gas Volume l/min 20 20 20 Result on Inert Gas Bubble Size 1 - 2mm  1mm  1 - 5mm  Results: Inert Gas Dispersion in Vessel There is no change in the gas size as it uniformly disperses - ditto - The dispersion is not uniform and I the gas size varies Eddy Current & Rippling on the Water Surface Eddy current-none Rippling-none - ditto - Eddy current - 30-40mm Rippling - 10-15mm 2. Results of Tests in Al Molten Metal Condition for Ar Gas 1/min 15 15 15 Condition for Rotary RPM 250 250 500 Time for the treatment (min) 7 7 7 Results: H2 Gas Volume prior to treatment cc/100g ALU 0.35 0.35 0.35 H2 Gas Volume after treatment cc/100g ALU 0.09 0.08 0.14 As a result of installation of the gas chamber (gas stay) at the outlet section of the inert gas in the rotary injector, use of the porous (multi-porous in nature) at the peripheral outlet section, and the adoption of the agitation-force-relaxed rotary mixer and the slender rotary shaft, the present invention was successful in the generation of the micronized and uniform inert gas and also totally dispensing with the eddy current at the surface of the molten metal and the rippling thereof; by which in the actual metallic molten metal treatment (A356 Aluminium), about 30% reduction of the use of inert gas was made achievable in comparison with the conventional rotary injector, the nature of the dross generated during the treatment, compared with the currently used rotary injector in the industry, is extremely dry, almost not containing any oxide at all, and the prevention of the oxide formation coming from the atmospheric contact was made possible. LEGEND A Fixing sleeve for the rotary injector B Hollow rotary shaft C Rotating mixer Ca Tapered section of the rotating mixer D Inert gas outlet made of porous material Da Gas chamber (gas stay) E Screw F Vessel G Crucible furnace 1 Pipe for supplying the inert gas 2 Driving motor 3 Inert gas 4 Metal 5 Aluminium molten metal

Claims: Rotating injector for dispersing gas into a molten metal comprising a rotating mixer immersed in the liquid metal, fixed at one end of a hollow rotating shaft (B) and having vertical star-mounted blades (C), characterized in that a gas chamber (Da) having peripheral walls made of porous material (D) is fixed at the hollow end of the rotating shaft under said mixer blades, whereby a treatment gas provided by said hollow shaft in said gas chamber is uniformily dispersed in the liquid metal through said porous material along the periphery of said gas chamber. Rotating injector according to claim 1 characterised in that the gas chamber having walls of porous material has a tapered form, the small base being upward and the large base being downward. Rotating injector according to any one of claims 1 or 2 characterized in that the gas chamber is fixed to the hollow shaft by means of a screw having holes for gas passage from the hollow shaft to the gas chamber. Rotating injector according to any one of claims 1 to 3, characterized in that the mixer blades have a height of at most 25 mm. Rotating injector according to any one of claims 1 to 4, characterized in that the shaft has an outer diameter comprised between 25 and 50 mm. Apparatus for molten metal treatment, comprising : a vessel, a rotary injector according to claims 1-5 immersed in said vessel, an inert gas supply connected to the hollow shaft of said rotary injector, an inert gas being penetrated inside said vessel while said rotary injector is being rotated. Apparatus according to claim 6, wherein said vessel has a curbed bottom.

Inventors: MUKOHDA TAKAAKI, MUKOHDA, TAKAAKI
Applicants: PECHINEY JAPON, PECHINEY RHENALU
Application year: 1997
Main classification: C22B9
IPC codes: B01F3, C22B21, C22B9, B22D1