AU682531B2

AU682531B2 - Method and device for melting metal, especially non-ferrous metal

Info

Publication number: AU682531B2
Application number: AU74442/94A
Authority: AU
Inventors: Daniel Jafs; Lars Henrik Mikael Jafs
Original assignee: Jafs Export Holimesy Oy AB
Current assignee: Jafs Export Holimesy Oy AB
Priority date: 1994-10-05
Filing date: 1994-10-05
Publication date: 1997-10-09
Anticipated expiration: 2014-10-05
Also published as: AU7444294A

Description

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AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): AB JAFS EXPORT QY HOLIMESY Invention Title: METHOD AND DEVICE FOR MELTING METAL, ESPECIALLY NON-FERROUS METAL The following statement is a full description of this invention, including the best method of performing it known to me/us: .00.

0.0 0 1A METHOD AND DEVICE FOR MELTING METAL, ESPECIALLY NON-FERROUS METAL The invention relates to a method and a device for melting metal and to furnaces for processing molten metal, especially non-ferrous metal.

The purpose of the invention is to achieve a method for melting and for processing molten non-ferrous metal, yielding a better melt quality than equivalent, previously known methods. The melting of metal in melting furnaces comprising circulation and batching of the metal by means of pneumatic pumps is previously known, cf. for instance SE pAtent specification 437339. Degasification of the metal e.g. by means of nitrogen gas, optionally combined with filtration, to enhance melt quality, is also previously known. The present invention provides a technique for enhancing melt quality by reducing turbulence in the chambers.

According to a first aspect of the present invention there is provided a method for melting metal and for processing molten metal comprising introducing a solid metal material into an inlet chamber; circulating the metal to": material through one or more melt chambers, one or more pump chambers and/or one or more splash chambers, each 25 chamber having a chamber lid, through ducts connecting the 0 0* chambers, with simultaneous melting or processing by thermal radiation from the chamber lids; wherein pump means acts on an inert gas filling the space above the molten metal in the or each pump chamber connected with the pump 30 means to increase or decrease the pressure within the pump chamber space above the molten metal, said increase or decrease being made by the controlled supply of said inert gas to the pump chamber space; the or each of said pump chambers being connected near its base through a duct with a melt chamber which supplies molten metal to the pump chamber and being connected through a duct with a splash V. 1 chamber from which splash chamber molten metal is removed \\HELBOI\honeS\Chelley\Kep\83N\74442.94.doc 10/07/7 2for consumption or recycling; characterised in that from approximately three to approximately fifteen times more melt per unit of time is transferred between the or each pump chamber and the or each splash chamber connected thereto, than between each pump chamber and the melt chamber connected thereto, in accordance with increase or decrease respectively in the pressure within the pump chamber space above the molten metal.

Thus, the innovation of the melting process in a melting furnace, and in the processing of molten metal in a furnace, respectively, consists in that the amount of molten metal pressed under increased pressure prevailing in the space above the melting surface in the pump chamber into the splash chamber is substantially greater than the amount of molten metal simultaneously pressed back into the melting chamber connected with the pump chamber. At the same time, there are provisions to prevent the melt flow transferred from the base of the pump chamber to the splash chamber from returning to the duct and hitting the melt in the melt chamber, should a sudden drop of pressure occur in the pumping chamber. These provisions avoid turbulence and increase melt quality. The duct between the pump chamber *bottom and the splash chamber is preferably oblique upwards, so that melt is discharged near the upper end of the splash chamber, slightly above the melt level.

Typically an 4 nert gas fills the space above the melt and the space above a pump piston in a pump cylinder connected with the pump chamber. Preferably, the inert gas, is nitrogen. Advantageously, the pressure increase 30 and decrease are controlled to avoid that a vacuum is generated.

The level of the furnace and the outlet pipe is preferably adjusted so as to allow minimum variations in the level of the molten metal. In continuous consumption, the introduction of metal material must also be continuous and adapted to consumption.

R According to a second aspect of the present \\lELBlO\home$\Che1Iey\eep\BJ\7444294.dQc 10/07/91 3 invention there is provided, comprising a melting furnace comprising an inlet chamber for the introduction of solid metal material; one or more melt chambers for melting said metal material; one or more pump chambers which receive molten metal from said melt chambers; one or more splash chambers; pump means adapted to act on an inert gas filling the space above the molten metal in the or each pump ciamber; each of said pump chambers being connected near its base through a duct with the melt chamber that supplies it with molten metal and being connected through a duct with the splash chamber from which splash chamber molten metal is removed for consumption or recycling, wherein said pump means circulates molten metal through said ducts; each of said chambers having a heat-radiating chamber lid; wherein the ratio of the cross-Lectional area of the ducts between the or each pump chamber and the splash chamber connected thereto and between the or each pump chamber and the melt chamber connected thereto in between 3:1 to 15:1.

Preferably, the pump cylinders cil culating the molten metal in the melting furnace are vertically arranged pump cylinders divided by a horizontal, solid partition into an upper and a lower pump space. A pump shaft is fitted movably through the partition and the pump shaft is provided with a pump piston at either end. The partition 25 appropriately divides the cylinder space into two equal parts.

The space above the upper pump piston communicates via a pipe with the space above the molten mtal in the pump chamber connected with the pump. The communicating spaces are appropriately filled with an inert gas, preferably nitrogen. To achieve a controlled increase and decrease of the pressure in the pump chamber above the melt, the communicating space above the upper pump piston is provided with a manometer and a valve leading to a gas source, appropriately a nitrogen source.

The space between the horizontal wall of the pump K cylinder and the upper pump piston and also the space \\HELBoI\home\Chelley\Keep\BR\74442.94.doc 10107/97 4 between the horizontal wall and the lower pump piston are adjustably connected to a respective compressed air source, whereas the space below the lower pump piston communicates with the surrounding atmosphere. A pump cylinder equipped in this manner makes it possible to increase and to decrease the pressure in the space above the melt in the pump chamber, and thus the melt is smoothly transferred to the splash chamber, and the melt remaini-g in the duct is allowed to return smoothly to the duct. Without controlled pressure conditions, underpressure may arise in the pump chamber under the effect of the reverse motion of the pump piston, resulting in a sudden return flow and impact against the melt in the pump chamber. The turbulence which would then arise would affect the melt quality considerably.

A preferred embodiment example of the melting of metal and of a melting furnace according to the invention will be described below with reference to the enclosed drawings, in which: Figure 1 is a schematic view of a melting furnace according to the invention seen from above with the covers removed, and with the associated pump cylinders shown, and Figure 2 shows the cross-section of a vertical pump cylinder with the connection to the pump chamber in the 25 melting furnace schematically drawn.

The melting furnace is divided into several separate chambers by means of partitions equipped with openings, through.which the chambers communicate with each other. The heat for melting the metal derives from the electrically heated cover of the melting furnace, which is not shown in the figures. Ingots and/or scrap metal are batched after preheating into the inlet chamber 1, from where the molten metal flows through an opening near the bottom to the first melt chamber 3. The opening is not shown, but the flow transfer through the opening is indicated with an arrow 2. From the melt chamber 3 the metal flows through an opening near the bottom, marked with \\4ZLBO1\hmeS\Che ley\KeeP\B3N\74442. 4 .dce 10/07197 I~ 5 the arrow 4, to the following melt chamber 5. Between the melt chambers 3 and 5, the melt can be degasified and/or filter in order to enhance the melt quality. In that case, melt flows from the first melt chamber 3 through an opening indicated with the arrow 6 to degasification and filter chambers 7 and 8, and from there on through an opening, arrow 9, to the second melt chamber 5. The degasification and filtering chambers 7 and 8 have a greater depth than the melt chambers in order to make reverse flow possible.

The melt chamber 5 communicates with two pump chambers 10 and 11 through two ducts marked with arrows 12 and 13. The openings of the ducts to the melt chamber are located near the base of the melt chamber and their openings to the pump chambers 10 and 11 are located near the base of their respective pump chamber. From the pump chamber 11, molten metal is pressed through a duct, marked with the arrow 14, to the splash chamber 15. The opening of the duct to the splash chamber 15 in the pump chamber 11 is located near the bottom of the pump chamber and its opening in the splash chamber 15 near the top of the splash o'*i chamber. The ratio of the cross-sections of the ducts 14 and 13 is preferably 8:1, but may vary in the range from 19:1 to 5:1, even from 15:1 to 3:1. Owing to friction 25 against the pipe walls, the volume amount of melt per time unit does not vary with the same ratio as the crosssections. The friction action on the flow increases in inverse proportion to the cross-sectional area. A higher ratio than 15:1 entails oxidation, and a lower ratio than 30 3:1 results in malfunction or non-function of the system.

From the splash chamber 15 the molten metal flows through an opening near the bottom, arrow 16, to the inlet chamber 1, where it joins ingots and scrap metal batched into the furnace.

Meanwhile, a controlled amount of molten metal is pressed correspondingly through a duct 17 to a splash chamber 18, from where it is discharged for consumption \\MetB01\home\Ch1tley \Keep\BJN\74442.94 ,doc 10/07/97 I C s~I _I II 6 through an electrically heated pipe 19.

Both the circulating and the pumping out of molten metal is accomplished by supplying an inert gas, for instance nitrogen, under control to the respective pump chamber 10, 11 through an inlet duct 20, 21 in the respective pump chamber lid from an external, vertically positioned pump cylinder 40, 41. The two pump cylinders are identical and control their respective pump chambers in an identical manner. Tte pump cylinder, as best seen in Figure 2, has a horizontal partition 22 dividing the cylinder into two, preferably equal spaces 23 and 24. On either side of the horizontal wall 22 pistons 25 and 26 respectively are provided, which are each firmly connected with a piston arm 27 passing through the partition 22. The space between the partition 22 and the upper pump piston is marked with reference 28 and the space between the partition and the lower pump piston with 29. An inert gas, preferably nitrogen gas, fills up the upper cylinder space 23 and the space above the molten metal in the pump chamber 10, 11, communicating with said space 23 through the pipe 20, 21. The pump cylinder space 23 is provided with a valve 30 leading to a nitrogen gas source and a manometer 31. Pumping and thus circulation of molten metal is achieved by allowing compressed air to flow into the 25 cylinder space 28 through a pneumatic valve, marked with a two-way arrow 32. In this situation, the cylinder pistons and 26 are pressed-upwards, overpressure being generated above the metal surface in the pump chamber 10, 11. A specific greater amount of molten metal is then pressed 30 through the opening 17, 14 to the splash chamber 18, whereas a specific smaller amount is pressed back to the melt chamber 5 through the opening 12, 13. After a certain period of time the air pressure in the space 28 is allowed to drop, whereas the pressure in the space 29 is raised so as to make the cylinder pistons 25 and 26 move downwards.

The nitrogen gas in the uppermost part of the space 23 of the pump expands, the manometer 34 being set to control the \\HLBQ1\hrwS\Chelley\KeQP\BJ1\7 4 442.

9 4.doc 1OO7/97 7 valve 30 to let more nitrogen gas through if the pressure in the space 23 drops below a given minimum limit. The lower cylinder space 24 contains air and communicates with the surrounding atmosphere through a pipe 31. In this manner, the pressure above the melt surface in the pump chamber 10,11 is also maintained above the specific limit and no under pressure will arise. This arrangement results in smooth and controlled pressing of molten metal into the splash chamber, avoiding a sudden return flow hitting the molten metal.

The pumping through the pump chambers 19 and 11 produces a circulation through the melt chambers so that ingots and metal scrap join the molten metal in the inlet chamber 1, resulting in rapid and efficient melting, molten metal being pumped out from the splash chamber 18 through the duct 19 to be consumed.

All the covers of the melting furnace, especially the pump chamber lid, must be tightly sealed. The melting furnace and pipe levels are preferably adjusted so as to allow minimum level variation.

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Claims

1. A method for melting metal and for processing molten metal comprising introducing a solid metal material into an inlet chamber; circulating the metal material through one or more melt chambers, one or more pump chambers and/or one or more splash chambers, each chamber having a chamber lid, through ducts connecting the chambers, with simultaneous melting or processing by thermal radiation from the chamber lids; wherein pump means acts on an inert gas filling the space above the molten metal in the or each pump chamber connected with the pump means to increase or decrease the pressure within the pump chamber space above the molten metal, said increase or decrease being made by the controlled supply of said inert gas to the pump chamber space; the or each of said pump chambers being connected near its base through a duct with a melt chamber which supplies molten metal to the pump chamber and being connected through a duct with a splash chamber from which splash chamber molten metal is removed for consumption or recycling; characterised in that from approximately three to approximately fifteen times more melt per unit of time is transferred between the or each pump chamber and the or each splash chamber connected 25 thereto, than between each pump chamber and the melt *chamber connected thereto, in accordance with increase or decrease respectively in the pressure within the pump chamber space above the molten metal.

2. A method according to claim 1 wherein from o. 30 approximately six to approximately ten times more melt per unit of time is transferred between the or each pump chamber and the splash chamber connected thereto than between the or each pump chamber and the melt chamber connected thereto.

3. A method according to claim 1 or claim 2, characterised in that the pump chamber space above the molten metal in the or each pump chamber is filled with \\MEL~BO1\home$\Che1ey\Keep\BJN\74442.94.dcC 10/07/97 L I 9 nitrogen.

4. A method according to any of the preceding claims, characterised in that the pressure drop in the or each pump chamber space above the molten metal is controlled so that no vacuum is generated.

A method according to any of the preceding claims, characterised in that the level of the molten metal is maintained approximately constant.

6. A method according to any of the preceding claims, characterised in that introduction of the metal material is carried out continuously.

7. A method according to any of the preceding claims, characterised in that the transfer of molten metal from the or each pump chamber to the or each splash chamber is obliquely upwards from near the base of the or each pump chamber to near the lid of the or each splash chamber.

8. A device for implementing the method according to any one of the preceding claims, comprising a melting furnace comprising an inlet chamber for the introduction of solid metal material; one or more melt chambers for melting said metal material; one or more pump chambers which receive molten metal from said melt chambers; one or more splash chambers; pump means adapted to act on an inert gas filling the space above the molten metal in the or each pump chamber; each of said pump chambers being connected near its base through a duct with the melt chamber that supplies it with molten metal and being connected through a duct with the splash chamber from which splash chamber molten metal is removed for consumption or recycling, 30 wherein said pump means circulates molten metal through said ducts; each of said chambers having a heat-radiating chamber lid; wherein the ratio of the cross-sectional area of the ducts between the or each pump chamber and the splash chamber connected thereto and between the or each pump chamber and the melt chamber connected thereto is between 3:1 and 15:1.

9. A device according to claim 8 wherein the ratio a en. a a a a.. a a.. a a a a li d oo *I *o oooo e ooee oo \\HELB301\hoem\Che11ey\Keep\B3N\74442,94 .doc 10/07/97 I 10 of the cross-sectional area of the ducts between the or each pump chamber and the splash chamber connected thereto and between the or each pump chamber and the melt chamber connected thereto is between 5:1 and 10:1.

10. A device according to claim 8 or claim 9, characterised in tha.- the duct between the or each pump chamber and the connected splash chamber extends obliquely upwards from near the bottom of the pump chamber to near the splash chamber lid.

11. A device according to any one of the preceding claims, characterised in that the pump means comprises one or more pneumatic pumps each comprising a vertically disposed pump cylinder, divided by a horizontal solid partition into an upper and a lower cylinder space, and having a pump shaft passing freely through the partition, said pump shaft having a pump piston at either end.

12. A device according to claim 11, characterised in that the solid partition divides the pump cylinder volume into two equal parts.

13. A device according to claim 12, characterised in that the space above the upper pump piston in the pump cylinder is connected, through a pipe, with the space above the molten metal in the pump chamber connected with the pmp.

14. A device according ho claim 13, characterised in that the space above the pump piston in each pump cylinder and the space above the molten metal in the pump chamber connected with the pump cylinder are filled with inert gas.

15. A device according to claim 14 wherein the inert gas is nitrogen.

16. A device according to any one of claims 11 to characterised in that the space above the upper pump piston is provided with a manometer and with a valve leading to a gas source for controlling gas pressure.

17. A device according to any of claims 11 to 16, characterised in that the space between the horizontal ,solid partition and the upper pump piston and the space \\MELBOI\honmeS\Chei 1\Kep\BJN\ a444294,doc 10/0719' a 11 between the horizontal solid partition and the lower pump piaton are each connected to a respective compressed air source and the space below the lower pump piston communicates with the surrounding atmosphere through a pipe. 0.. 600 a *&009 \\HELBOI\home$\Che11oy\Keep\WJN\74442.94 .doc 10/07j1 I N s Abstract The invention relates to a method and a device for melting or processing metal. The metal material is batched into a chamber and circulated from one chamber to anothler 5, 10, 11, 15, 18) with simultaneous melting under the effect of thermal radiation from the chamber lids. One or more pumps act on the pressure above the molten metal in one or more pump chambers (10, 11), connected with a melt chamber and with a splash chamber (18, 15), from where the melt is discharged or recycled. The object of the invention is to upgrade melt quality by reducing turbulence in the melt chambers. This object has been achieved by transferring, at an increased pressure in the pump chamber, a substantially greater amount, approx. three to fifteen times more melt per time unit from each pump chamber (10, 11) to the splashi :caber (18, 15) than from the same.pump chamber.to the splash... chamber This arrangement has been implemented in a device in which the ratio between the cross-sectional surfaces of the ducts (12, 17; 13, 14) between a. pump chamber (10; 11) and the preceding melt chamber or the same pump chamber (10; 11) and the consecutive splash chamber (18; 15) is in the range from 3:1 to 15:1, preferably from 5:1 to 10:1. F..4r Figure 1 I I IRI