CA1048269A - Apparatus for continuous vacuum-refining of metals - Google Patents

Abstract

Abstract of the Disclosure The present invention relates to apparatus for continuous purifying of tin from impurities - lead and bismuth, by refining.
The apparatus comprises a vacuum chamber accommodating a range of trays arranged in succession and fitted each with an overflow conduit disposed in its side wall at a certain distance from its upper end face, with the overflow conduit communicating with the tray space and being positioned parallel to the tray axis and with an overflow conduit outlet being connected to the underlying tray and a tray column being encompassed by an induc-tion is spinning climbing to the level of the overflow conduit.

Description

~0~8~9 APPARATU~ FOR CONTINUOUS V~CUUM-REFINING OF MET~LS
The present invention relates to metal processing equip-ment and more particularly to apparatus for continuous vacuum-refining of metals.
The invention may prove to be most advantageous in produc~
ing tin with a minimum lead and bismuth content.
The now-existing apparatus for continuous vacuum-refining of metals comprises a cylindrical vacuum chamber accommodating a range of graphite trays arranged in succession one above ano-~her in a vertical plane, adapted to receive preliminary melted ' `
impure metal and forming a column~ and an induction heater en~
com~assing the graphite tray column and provided ~ith a current l~ad to feed electric energy thereto. The induction heater' warms up the metal acc,o~modated in the trays to a volatiliza~
tion temperature of low-boiling imp~rities and evaporates them.
~ach tray has in its bottom an internal cylindrical collar with a central hole into which a tapered branch pipe is introduced~
In this case the collar central holes and tapered branch plpes are,aligned axially. ~ , The internal cylindrical collar precludes the draining of metal being refined through its central hole. The collar height is so selected that a clearance for the passage of im-purity vapors, referred to hereinafter as volatilized impuri-ties~ is formed between ~he bottom of the overlging tray and the collar end face. -'~

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~1~41!~;~69 The coaxial centr~l holes of all the trays and tapered branch plpes form a vapor pipe for removing volatllized impuri-ties. ~le length oE the tapered brancb pipe wouLd be such that its lower end face would be spaced at a minimum distance fro~
the central hole of the `underlying tray. This would rule out the ingress of the volatilized impurities from the underlying tray into the space of the over-lying tray and would provide for the ejection of vapors from the underlyin~ trays~
In the zone of molten metal the bottom of each tray has an outlet ensuring a gradual overf~w of the molten metal from the overly~ng into the underlying trayO The lower tray communi-cates via a pipeline with a cooler located outsids the vacuum ~-chamber. The refined metal flows from the lower tray into the cooler where the metal temperature decreases and the metal is `
drained into a receiving tank.
A disadvantage of thi~s present-art apparatus resides in a small open metal surface in the tray9 the area of this sur-,:
face determining the intensity of impurity evaporation. As itis known, dipped impurities are not able to volatilize and can ireach the metal surface only due to diffusion. The process of transfer of such dipped impurities to the metal surface can be ~-intj~e~si~ed by stirring. However~ the known apparatus are not provided with such stirring means. This disadvantage can be partly offset by increasing the number of trays. But it will lead to a considerable lncrease in the overall dimensions of '',..
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Moreover, the now-e~isting apparatus suffars from another disadvantage which lies in the arrangement of the metal over-flow conduit in the tray bottom. ~ith the above arrange~ent the batches of metal, that have not yet been sub~ected to refl-ning, oan overflow through this outlet illtO the next tray, diminishing thereby the degree of metal refining.
The principal ob~ect of the invention ls the provision oE an apparatus for continuous refining of metals, wherein, owing to a modified design of trsys and the use of means increa~
sing an open metal surfaceg the apparatus output and the degree of purifying the metal from impurities by refining are enhanced and overall dimensions of the apparatus are reduced.
Said object is achieved by p~oviding an apparatus for continuous refining of metal, comprising a cylindrical vacuum chamber accommodating a range of trays with central holes arran-ged in succession one above another in a vertical plane, for-ming a column and adapted to receive preliminary melted impure metal, and a heater encompassing the column and provided with a current lead to feed electric energy th~reto for heating the metal accommodated in the trays and evaporatlng low~boiling impurities therefrom~ with the volâtilized impurities being removed via a vapor pipe formed by said tray holes into a con-denser disposed in the vacuum chamber under the tray column, wherein, according to the invention, each tray is fitted with ;

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an overflow condult located in its slde wall at a certain dis-~anc~ from its upper end face~ sald overflow conduit communi~
cating with the tray space and being disposed parallel to the tray axis, with the overflow conduit outlet being in communi-cation with the underlying tray~ and the tray column is encompas-sed by an induction coil establishing a magnetic field under whose effece the molten metal accommodated in the tray rotates climbing to the level of the overflow conduit~ wlth the over-flow conduit outlet of the lower tray com~unicating with a re-fined metal cooler set up under the vacuum chamber.
Owing to the magnetic field established by the coil the -~
metal being refined commences to rotate i~tensively and is in~
ter-mixed. Centrifugal forces urge the spinnlng metal to tlimb along the vertical tray wall with the open metal surface being substantially enlarged as a result. Hence~ the surface firom which volatilization of impurities occurs is considerably in- -creased. Owing to an intense s~irring the dipped batches of me-tal comprising a larger amount of impurities, as compared with the metal disposed on the open surface, move to the volatiliza-tion surface.
Thig intensifies substantially the metal refining rate.
Since the rotating open surface of the metal assumes the shape of a heavily concaved meniscus, the thickness of metal in the upper part of the meniscus is rather small, with the deg-ree of metal refining in thls zone being a maximum one for a ~4- ~

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given tray, and as the overElow conduit is located in the upper part of the ~eniscus, the metal dralned f~om that tray will feature a highest rcfining degree.
Thus, metal spinnining ensures a higher rate and a maxlmum degree of removing impurities from a single tray, this result-ing in a higher output of the apparatus and in a better refining degree. The higher degree of refining achievable owing to in~
tense rotation, which contribu~es to a substantial increase in the open metal surface, does not call for a larger number of trays, the apparatus enabling the above outlined effect to be obtained with a minimum number of the trays. This diminishes the overall dimensions of the apparatus as a whole.
me nature of the invention will be clear Erom the follow~
ing detailed description of the particular embodiment of an ap-paratus for purifying tin~rGmaleàd~ànd bismuth by refining, to be had in conjunction with the accompanying drawings, in which:
Fig. 1 is a longitudlnal sectional view of an apparatus for continuous refining of metal, according to the inv~ntion; `
Fig. 2 is a longitudinal sectional view (scaled up) of trays shown in Fig. 1.

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An apparatus for continuous vacuum-refining of tin compri-ses a c~lindrical vacuum chamber 1 (Fig. 1).
The chamber 1 accommodates a range of trays disposed in succession in a vertical plane~ with the tray 2 being adapted to receive preliminary melted impure metal and trays 3 and 4 - to ~:
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~ 8Z69 refine tin. The tin supply into the tray 2 is shown in the drawing by arrow A. Y
The trays 3 and 4 in their bottoms haYe central holes 5 into which tapered branch pipes 6 are introduced. The holes S
and br~nch pipes 6 are aligned axially and form a vapor pipe for removing lo~-boiling impurities liberated during the tin refining process. The length of the tapered branch pipe 6 in the tray 3 would be such that their lower end face 7 wouid be spaced at a minimum distance fr~m the central hole 5 of the tray 4. This would preclude the ingress of volatilized impuri-ties from the tray 4 into the space of the tray 3 and would provide for vapor ejection~ The branch pipe 6 of the ~ray 4 is connected to a condenser 9 through an additional branch pipe 4~ In the condenser 9 the volatillzed impurities are condensed and cooled to a temperature of 400C~ whereupon they flow ~in , .
a fluid stste) along a pipeline 10 into a condensate tank 11.
The trays 2, 3 and 4 from in conjunction a column encompas-sed by a heater 12 which is an inductor. The inductor has a cur-rent lead to eed electric energy needed for heating the trays

2,3 and 4 together with the tin accommodated therein to an im-purity volatili~ation temperature. The volatilizing impurities are removed, as it has been stated above, via a vapor pipe.
Each of the trays 3 and 4 (Fig. 2) has an overflow conduit 15 located in a tray side wall 13 at a certain distance from its end face 14~ with the inle~ 16 of the overflow~conduit 15 ' ~

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communicating with a space oE the corresponding tray.
The overflow conduit 15 i9 d~sposed parallel to the tray axis and the outlet 17 of this condult 15 communicates with the underlying tray 4. The outlet 17 oE the overflow conduit 15 of the tr~y 4 is connected via a pipeline 18 (Fig. l) to a re-fined tin cooler 19 disposed outside the vacuum chamber 1. Upon cooling~ the refined tin runs off along a p~peline 20 from the cooler 19 into a refined tin tank 21.
The heater 12 is encompassed from the outside by an induc-tion coil 2~ establishing a magnetic fieldO Under the effectof this field the metaloaccommodated in the trays 3 and 4 ro~
tates climbing to the inlet 16 of the overflow conduit 15 in the side wall 13 of the trays 3 and 4.
The herein proposed apparatus functions as follows.
Prellminary melted impure tin is supplied into the intake , : .
tray 2 along a pipeline 23 in the direction shown by arrow A.
~ ~Passlng through a bottom hole 24 in this tray 2 the tin over-~: flows into the upper tray 3 ~here it is heated to an impurity ~i volatilization temperature owing to the energy generated by the heater 12. The induction coil 22 brings the molten metal contained in the trays 3~and 4 into rotation. Stirring and a larger volatilization surface result in an intense evolution of volatilized impurities`from the metal, with these volatili-: zed impurities being passed Yia the vapor plpe into the conden-ser 9 where they are condensed, cooled and discharged along . : : , -7~
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the pipeline 10 into the condensate tank 11~ The metal revolving in the trays a~sumes the shape of a meniscus, reaches the inlet 16 of the overflow conduit 15 and gets into the space of the tray 4.

In the tray 4 the tin is refined to a still higher degree, and then the refined tln flows through the overflow conduit 15 of the tray 4 into the pipeline 1~ Upon passing via the pipeli-ne 18~ it runs off into the cooler 1~ and then to the refined tin tanlc 21.
The tin and condensate from ~he tanks 11 and 21 are cast into pigs.
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Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. An apparatus for continuous vacuum-refining of metal, comprising a cylindrical vacuum chamber; a range of trays, having each a central hole and side walls, said trays being accommodated in said vacuum chamber, disposed in succession one above another in a vertical plane, forming a column and adap-ted to receive preliminary melted impure metal; a vapor pipe formed by the holes of said trays; a heater set up inside said vacuum chamber, encompassing the column of said trays and provi-ded with a current lead to feed electric energy thereto for heating the metal accommodated in the trays and evaporating low-boiling impurities therefrom, said impurities being removed along said vapor pipe; a condenser located under the column of said trays and adapted to receive the impurities emerging from said vapor pipe; each of said trays has an overflow conduit located in its side wall at a certain distance from its upper end face, said overflow conduit communicating with the tray space, being disposed parallel to the tray axis, with the out-let of this overflow conduit being in communication with the underlying tray, an induction coil encompassing the column of said trays and establishing a magnetic field under whose effect the molten metal accommodated in the tray rotates climbing to the level of said overflow conduit; a cooler set up under said vacuum chamber and communicating with said outlet of said over-flow conduit of the lower tray to supply metal therein.

2. An apparatus, as set forth in Claim 1, wherein said induction coil is disposed outside the heater and encompasses it.