CA1227642A

CA1227642A - Process and device for feeding metal into a molten metal bath

Info

Publication number: CA1227642A
Application number: CA000460233A
Authority: CA
Inventors: Rolf Roggen
Original assignee: Schweizerische Aluminium AG
Current assignee: Alcan Holdings Switzerland AG
Priority date: 1983-08-04
Filing date: 1984-08-02
Publication date: 1987-10-06
Also published as: AU570060B2; ZA845502B; NO843091L; DE3468275D1; JPH0354169B2; EP0133417A2; NO162487B; AU3090984A; EP0133417B1; ATE31579T1; EP0133417A3; NO162487C; JPS6056029A

Abstract

A B S T R A C T

A process for feeding metal to molten metal, in particular for the purpose of melting solid metal such as scrap metal or dross granules, is such that at least part of the melt is divided and each divided part set into motion rotating in opposite directions so that at least two rotating streams or "rolls" of molten metal are produced; the cen-tral axes of these rotating streams of molten metal form an angle. The metal is charged at the place where the two "rolls" of molten metal meet.

The "rolls" of molten metal are produced by introducing the molten metal into a pair of pipe lengths approximately perpendicular to their central axes and approximately tan-gentially to the cross section of the said pipe lengths, the central axes forming an angle, or by causing the mol-ten metal in the pipe lengths to rotate by means of elec-trodynamic forces.

(fig 1).

Description

~2~27~

Process and Device for Feeding metal into a molten metal bath The invention relates to a process for feeding metal to a molten metal bath, in particular for the purpose of melt-in down solid metal such as for example scrap metal or granular dross, and relates also to a device for this.

With a view to protecting the environment, and in recogni-lion of the limited availability of raw materials, in-creasing efforts are being made to recycle raw materials.
10 This includes metal which appears in large amounts in in-dustrial and household waste and applies in particular to the recycling of used cans as metal cans are being employ-Ed increasingly today as containers for drinks ox various kinds.

15 One possibility for recycling is to introduce the scrap metal into a molten metal bath in order to melt it down.
In that case it is particularly important for the solid metal to be immersed as quickly as possible in a turbulent metal stream in order to minimize oxidation of the metal 20 and to increase the efficiency of melting. Counterproduc-live in this respect is that thin walled metal such as in scrap cans is much less dense than the melt; as a result, the scrap metal tends to remain on the melt surface for a long time. This is unfavorable in view of the above men-25 toned efforts to minimize metal oxidation and to increase melting efficiency.

On the other hand processes exist in which the melt is made to rotate in a container so that a whirlpool is form-Ed near the middle of the melt, and the metal to be melted is introduced into the whirlpool. In practice it has been found that the metal still tends to stay on the surface of the melt, also in the whirlpool. Furthermore, the turbo-fence produced at the surface of the melt and at the place where the scrap is introduced into the container creates an excessive amount of dross. Also, the heat transfer from 10 the melt to the metal is small and the resultant efficient cry of melting is unsatisfactory.

The object of the present invention is therefore to devil-ox a process and device of the above mentioned kind by means of which metal which is to be melted sinks as fast 15 as possible below the surface of the melt and is therefore excluded from contact with air as quickly as possible. The process and the device are, furthermore, intended to be usable in many different ways and in particular should enable better mixing-in of alloying additions made to the 20 melt. Also, it should be possible to melt down granular dross to achieve a high metal yield without the use of salts.

This object is achieved by way of the invention in that at least part of the melt is divided, and each part is made 25 rotate in a direction counter to that of the other part, so that at least two rotating streams or "rolls" of molten metal are produced, the middle axes of which are at an angle to each other, and the metal to be melted is added at that place where the two rotating "rolls" or streams of molten metal meet.

If the scrap, dross granules or alloying additions are fed to the melt from above, then the stream of metal left of the direction of metal flow is preferably set in motion rotating clockwise, the stream on the right hand side of the direction of flow in an anti clockwise rotation (Vega-live kinetic moment opposed to positive kinetic moment).
As a result, at the place where the two whirling streams of metal meet, a channel or furrow is formed into which 10 the scrap, dross or alloying additions that are to be melted are sucked. Also the melt is repeatedly and thou roughly mixed due to this movement; there is no stationary melt surface and so no metal is held there floating on the surface.

15 As soon as the two whirling melt streams meet, additional turbulence is created - which also ensures intimate con-tact between the melt and the metal to be melted down. At the same time thorough mixing of the solid and liquid phases making up the various parts of the melt is promote 20 Ed It must also be mentioned that the oxide skins are de-stroked in the process. Both the heat transfer coefficient an the melting rate are considerably increased. Briefly after the whirling streams strike each other the component of rotation is lost and the melt flows almost without any 25 agitation into the subsequent channel or a subsequent dross treatment station.

In order to split the melt into two counter-rotating streams or "rolls" two versions of the process according 4:2 to the invention can be employed. In both cases the said rotating or whirling streams are produced via two pipe lengths which are joined together in such a manner that their central axes form an angle. The feeding of the metal then takes place at the place where they are joined as it is also there that the two whirling streams meet.

One case is such that the melt is made to flow approxima-tell perpendicular to the central axes and approximately tangentially into the cross section of the pair of pipe 10 sections. The other method makes use of electrodynamics forces, in particular electromagnetic forces, to set the melt into such a motion that it rotates about the central axes. Both methods can also be used in combination.

A device of the kind described above ensures that a supply 15 channel or pipe for the melt is provided, connecting up to a feeder station made up of at least two ridded pipe sea-lions, the central axes of which form an angle such that the feeder station has a Y shape. The melt streams in the two pipe lengths can be made rotate about the middle axis 20 of the pipe length through which it passes. An opening for feeding the metal to the unit is provided at the place where the two pipe lengths meet.

One method for transferring the melt from the supply chant not into the pipe sections is to divide the supply channel 25 into two branches which feed the melt approximately per-pendicular to the central axes and approximately tangent tidally to the cross section of the pipe length. As the metal flows into the pipe length in this manner, it is dip SLY

vented from its original direction of flow, follows thinner wall of the pipe and is thus made to adopt a rotate in, whirling movement.

Another version of transferring the melt is such that the supply channel connects up to the junction point of the two lengths of pipe which are enclosed by two sleeves. As a result of back pressure on the melt, the pipe lengths at-so become filled with melt. The sleeves then generate electromagnetic forces which act on the melt and cause it 10 to rotate. As a result one obtains two standing, rotating streams or "rolls" of molten metal; the scrap added is wet even better due to the direct impingement by the incoming metal from the supply pipe, and is pushed forwards by the two whirling streams of metal.

15 One of the most important advantages of this device is that the melting takes place in the absence of air. Cons-quaintly, the metal loss is reduced because of the Damon-wished degree of oxidation and dross formation. The high relative speed of movement between the solid and liquid 20 phases ensures that maximum heat transfer is achieved with this device i.e. the rate of melting is substantially it-creased. The very small dimension of feeder station ensure that the heat losses are small. Also, because of the skimp-Lucite of the device the investment costs and maintenance 25 costs are insignificant. The device permits conventional scrap metal or other waste to be melted down, and allows alloying elements or other melt treatment substances to be added in any desired form. This applies in particular to the addition of dross granules from treated dross; these can be melted down without loss of metal and without any accompanying addition of fluxing agents such as salt.

Further advantages, features and details of the invention are revealed in the following description of preferred ox-amplified embodiments and with the help of the drawings viz ., Fig 1 A perspective view of a partly sectioned unit formulating metal.

Fig 2 A perspective view of a further exemplified embo-dominate as in fig 1.

A unit for melting metal, for example can scrap, is such that molten metal 1 is taken from a furnace - not shown here - and conducted via supply channel 2 to a feeder stay lion R for the metal which is to be melted. From there the 15 molten metal 1 then flows back into the furnace, or for example a dross treatment station, via channel 3.

The feeder station R according to jig 1 comprises essenti-ally two pipe lengths 4 and 5 arranged in a Y shape; con-netting up to pipes 4 and 5, approximately perpendicular 20 to their central axes A and B, are branches 6 and 7 no-spectively of supply pipe 2. The pipe lengths 4 and 5 meet at an opening 9 which serves as a charging point 8 for the metal which is to be melted down; from that point the pipes 4 and 5 continue as one in the form of a pipe 10 25 which joins up with channel I The central axes A and B
run at an angle w to each other. At the end away from the charging point 8 the pipe lengths 4 and 5 are closed off - by lids 11.

Situated above the charging point 8 or opening 9 is a silo 12 from which metal that is to be melted - not shown here - is introduced by means of screw conveyor 14 to the melt 1 through the opening 9.

The melt 1 enters pipes 4 and 5 via supply pipe 2. As it enters approximately perpendicular and tangential to these pipe lengths 4 and 5 via branches 6 and 7 rest. of pipe 2, 10 the melt is forced into a circular motion inside the pipes 4 and 5 around the central axes A and B.

The direction of flow of the melt 1 into pipes 4 and 5 is such that the melt rotates in the clockwise direction x in pipe and in the anti clockwise direction y in pipe 5.
15 Both streams or "rolls" of melt meet in the region of the opening 9 below the silo 12. Arrows 15 indicate the con-tinted path of the melt 1. If metal from the silo 12 is now added, it inters the furrow formed by the melt streams - for simplicity indicated here by arrows 15 - is "sucked"
20 in by the melt and completely wet by it. As they meet the "rolls" of molten metal destroy each other - which pro-motes further thorough mixing of the metal additions and the molten melt 1. In pipe 10 the rotational movement of the melt is eliminated and the melt flows on quietly into 25 a dross treatment station or the like - not shown here.

In the version according to fig 1 the feeder station R, likewise comprises two closed pipe lengths 4 and 5, the I

central axes A and B of which run at an angle w Jo each other and meet at a point where there is an opening 9 next to a charging inlet 8 for the metal which is to be melted down. Here the melt is introduced to the feeder station I, via pipe 22 which runs in the direction of flow of the melt z and meets the feeder station R, directly at the join 23 of both pipe lengths 4 and 5 below the charging inlet 8.

Provided on pipe lengths 4 and 5 are sleeves 24 and 25 10 rest. which act as stators and induce a rotary field in the melt, and this such that the melt in pipe 4 rotates in the clockwise direction x while the melt in pipe 5 rotates in the opposite direction. The rotation of the melt can also be achieved for example by providing pipes 4 and 5 15 with the rotors of a motor - not shown here.

As a result again two counter flowing streams or "rolls" of melt are achieved and with that the above described gape-city for taking in metal which is to be melted. The sleeves 24 and 25 can according to the invention also be 20 employed to assist in the formation of the "rolls" of melt in accordance with the version of the feeder station R in fig 1.

Claims

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

1. A process for feeding metal to be melted to molten metal in which, at least part of the molten metal is divided and each part is made rotate in a direction counter to that of the other part so that at least two rotating streams or rolls of molten metal are formed, the middle axes of which form an angle to each other, the metal to be melted being added at the place where the two rotating streams or rolls of molten metal meet.

2. A process according to claim 1, in which the molten metal is introduced into a pair of pipe lengths the central axes of which pipe lengths form an angle, said molten metal being introduced approximately perpendicular to said central axes and approximately tangentially to the cross section of said pipe lengths.

3. A process according to claim 1 or 2, in which the melt in the pipe lengths is set into a rotating movement by means of electrodynamic forces.

4. A device for feeding metal to be melted to molten metal in which: a pipe for supplying the melt is provided and connects up to a feeder station comprising at least two lidded pipe lengths, the central axes of which form an angle (w), and the melt in both pipe lengths can be set into rotatory movement about said central axes, and an opening for charging the metal provided at a place where the two lengths of pipe meet.

5. A device according to claim 4, in which the pipe divides into two branches which lead the melt to the pipe lengths approximately perpendicular to the central axes and approximately tangentially to the cross section of said pipes.

6. A device according to claim 5, in which when the metal is charged from above, the two branches are arranged such that the rotary movement in one pipe is clockwise and the rotary movement in the other pipe is anticlockwise.

7. A device according to claim 6, in which facilities for creating electromagnetic forces or the like are provided around said pipe lengths to reinforce said rotary movements.

8. A device according to claim 4, in which the pipe connects up with the feeder station at a place where the two pipe lengths meet, and said pipe lengths have around them rotatable sleeves which create said rotary movements via electromagnetic forces induced in the melt in the pipe lengths.

9. A process for feeding metal to be melted to a stream of molten metal comprising providing a source of molten metal, providing a source of metal to be melted, dividing said molten metal into a first stream of metal rotating in a clockwise direction and a second stream of metal rotating in a counterclockwise direction, joining said first stream and said second stream so as to form a furrow in the region where the counter-rotating streams meet and feeding said metal to be melted to said furrow wherein said metal is sucked down by said counter-rotating streams.

10. A process according to claim 9, including providing a first pipe length having a first central axis for said first stream of metal and a second pipe length having a second central axis for said second stream of metal wherein said first axis intersects said second axis in the area of said furrow.

11. A process according to claim 10, including providing a first molten metal inlet means for tangentially introducing said first stream of metal into said first pipe length and a second molten metal inlet means for tangentially introducing said second stream of metal into said second pipe length so as to form said counter-rotating streams.

12. A process according to claim 10, including providing an electromagnetic force for rotating said first stream of metal and said second stream of metal.