GB2516371A

GB2516371A - Upwards continuous casting system

Info

Publication number: GB2516371A
Application number: GB201411963A
Authority: GB
Inventors: Mervyn Cooper; Andrew William Tero; William Elliott Boyle
Original assignee: Rautomead Ltd
Current assignee: Rautomead Ltd
Priority date: 2014-07-04
Filing date: 2014-07-04
Publication date: 2015-01-21
Anticipated expiration: 2034-07-04
Also published as: GB2516371B; GB201411963D0

Abstract

A continuous casting crucible apparatus comprises a charging chamber 14, a casting chamber 22, a passage 24 connecting the charging chamber 14 and the casting chamber 22, and a lid 52 covering the charging chamber 14 and thecasting chamber 22. The lid 52 is provided with a first sealed tubular port 72 in communication with the charging chamber 14 through which copper rod (100, fig 4) is fed, and a second sealed tubular port 72 in communication with the charging chamber 14 through which cored wire (102, fig 4) containing powdered metal is fed. The lid 52 is provided with at least one sealed aperture 76 through which acasting tool 78 extends into the casting chamber 22, the casting tool including a die (80, fig 5) and a cooling system (88, fig 5) for vertical continuous casting of alloy wire rod (104, fig 4). The lid 52 seals to prevent oxygen reaching the melt in the charging chamber 14 and the casting chamber 22, resulting in an improved cast alloy product, particularly when used to cast CuZr wire rod.

Description

UPWARDS CONTINUOUS CASTING SYSTEM

FIELD OF THE INVENTION

This application relates to an apparatus and method for upwards continuous casting of metal rod, particularly copper alloy rod.

BACKGROUND TO THE INVENTION

It is known to produce copper rod or wire by an upwards continuous casting process. Copper cathode and additional metal alloy ingredients (such as Zr, Mg, Sn etc.) are fed into a charging chamber of a graphite furnace crucible where the copper is melted and conditioned by heat from graphite heating elements. The feedstock may be fed manually or automatically. The charging chamber is linked to an adjacent casting chamber by a passage at the bottom of the chambers. Molten copper alloy passes through the passage into the casting chamber, where it passes upwards through a filter bed to form a reservoir of conditioned melt at the top of the casting chamber. One or more water-cooled cooling tubes extend into the conditioned melt, and molten copper alloy is pulled through a die in the cooling tube to form copper alloy strand of the required diameter.

Copper reacts with oxygen to form copper oxide in the melt. The copper oxide, if present in sufficient quantity, impacts both the casting process and the product quality, so it is important to protect the copper melt from excess oxygen.

Traditionally protection is provided by a layer of carbon on top of the molten copper. This layer, which can include carbon in powder or pellet form, and which may also include slag and/or flake, lies on the surface of the conditioned melt and provides a barrier between the atmosphere and the molten copper alloy to prevent oxygen reaching the molten copper, thereby minimising the oxygen content of the copper alloy. Any oxygen already within the molten copper may react with the carbon cover, thus improving the quality of the copper melt.

Typically copper cathode is fed into the charging chamber by an automatic feed.

Typically up to six cooling tubes are provided, and six strands are formed simultaneously. The strands are guided and placed to form wound coils.

The known process is suitable for many copper alloys, but it has been found that specific alloying elements such as zirconium (Zr) are very reactive with oxygen, and will oxidise at the slightest opportunity, forming oxide slag and hence having a deleterious effect on the alloy configuration. The carbon cover on the top of the molten copper in both the charging chamber and the casting chamber allows a limited amount of oxygen into the molten metal, which can be detrimental to the quality of the Zr-containing alloy. Carbon cover is hence less suitable for CuZr. As well as reducing the Zr level available in the copper alloy, referred to as Zr loss, oxidation of Zr results in high levels of slag formation which makes the casting process very difficult to control, since it restricts successful feeding and melting.

OBJECT OF THE INVENTION

It is an object of the present invention to overcome at least one of the aforementioned disadvantages.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a continuous casting crucible apparatus comprising a charging chamber, a casting chamber, a passage connecting the charging chamber and the casting chamber, and a lid covering the charging chamber and the casting chamber, wherein the lid is provided with at least one sealed tubular port in communication with the charging chamber having a sealable aperture therein for the feeding of copper rod therethrough, and wherein the lid is provided with at least one sealed aperture through which a casting tool extends into the casting chamber, the casting tool including a die and a cooling system.

Preferably the charging chamber and casting chamber are of graphite.

The apparatus may include at least one casting tool extending through the at least one sealed aperture into the casting chamber.

The cooling system of the casting tool may comprise a water cooled jacket. The casting tool may include a graphite die. The casting tool may include a ceramic hot end cap through which the graphite die extends into the casting chamber.

The lid may be provided with two sealed tubular ports each having a sealable aperture therein, a first port being adapted for the feeding of copper rod therethrough and a second port being adapted for the feeding of cored wire therethrough. The cored wire may comprise a hoflow copper rod containing a metal powder, for example zirconium powder or copper zirconium powder.

The apparatus may include a first feed mechanism adapted to feed copper rod through the sealable aperture of the first sealed tubular port The apparatus may include a second feed mechanism adapted to feed cored wire through the sealable aperture of the second sealed tubular port.

The lid may be provided with a gas supply port adapted for the supply of an inert shield gas to the casting chamber. The apparatus may further comprise a source of inert shield gas in communication with the gas supply port.

The apparatus may include a temperature probe. The lid may be provided with a sealed aperture through which the temperature probe extends into the casting chamber. The temperature probe may comprise a thermocouple.

The lid may include a sight glass port.

The lid plate may comprise two or more separate lid portions.

The lid may comprise a frame secured to the casting chamber and the charging chamber. The lid may comprise two or more removable cover plates, each removably secured to the frame and/or to each other. Each cover plate may be removed to provide access to one of the casting chamber and the charging chamber.

A first cover plate may include the sealed tubular port in communication with the charging chamber. The first cover plate may include the sight glass port.

A second cover plate may include the at least one sealed aperture through which a casting tool extends into the casting chamber. The second cover plate may include the sealed aperture through which the temperature probe extends into the casting chamber. The second cover plate may include the gas supply port According to a second aspect of the present invention there is provided a method of continuous casting an alloy using a continuous casting crucible apparatus according to the first aspect comprising a charging chamber, a casting chamber) a passage connecting the charging chamber and the casting chamber, and a lid covering the charging chamber and the casting chamber, the method comprising the steps of: feeding copper rod to the charging chamber through a sealable aperture of a first sealed tubular port in the lid; feeding cored wire to the charging chamber through a sealable aperture of a second sealed tubular port in the lid; casting an alloy wire rod by causing molten alloy to pass vertically through a casting tool which extends through a sealed aperture in the lid into the casting chamber, wherein the molten alloy passes through a die in the casting tool and is cooled to solid form with in the casting tooL The method may include the further step of providing an inert shield gas to the casting chamber through a gas supply port in the lid. The gas may be provided at a pressure such as to maintain a pressure in the casting chamber greater than atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention is described, byway of example, with reference to the accompanying drawings in which: Fig. 1 shows a sectional view of a prior art furnace with a graphite crucible; Fig. 2 shows a sectional view of the crucible of Fig. 1; Fig. 3 shows a sectional view of a continuous casting crucible apparatus according to the present invention; Fig. 4 is a perspective view of the lid of the continuous casting crucible apparatus of Fig. 3; Fig. 5 is a schematic sectional view of a casting tool of the continuous casting crucible apparatus of Fig. 3; and Fig. 6 is a perspective view of the lid of another continuous casting crucible apparatus according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to Figs. 1 and 2, there is shown a prior art furnace 10 used for vertical continuous casting of wire rod. Copper cathode and additional metal alloy ingredients are fed through a feeding apparatus 12 into a charging chamber 14 of a graphite furnace crucible 16. The crucible is heated by graphite heating elements 18. Insulation materials 20 surround the crucible 16 and heating elements 18.

The charging chamber 14 is linked to an adjacent casting chamber 22 by a passage 24. The copper cathode and alloy ingredients are melted in the charging chamber 14 and the molten copper alloy then passes through the passage 24 into the casting chamber 22, where it passes upwards through a graphite filter bed 26 to form a reservoir of conditioned melt 28 at the top of the casting chamber 24. The filter bed 26 is held in pbce by graphite filter retainers 30.

A dump channel 32 is provided in the crucible to allow draining or dumping of the chambers 14,22 during maintenance. The casting chamber 22 includes a lower sacrificial graphite liner 34 below an upper ceramic liner 36. As seen in Fig. 2, above the molten copper in the charging chamber 14 is a carbon layer 38 forming a melt cover. The carbon layer 38 typically includes carbon pellets. Above the molten copper in the casting chamber 22 is another carbon layer 40 forming a melt cover.

The carbon layer 40 typically includes carbon flake.

As can be seen in Fig. 1 the tops of both the charging chamber 14 and the casting chamber 22 are open to the atmosphere. Two ceramic liners 42 surround the openings, allowing feeding of the copper cathode from the feeding apparatus 12 through the carbon layer 38 into the charging chamber 14 and the insertion of a casting tool 44 through the carbon layer 40 into the casting chamber 22. Copper alloy wire rod is formed from the conditioned melt 28 by drawing rod up through the water cooled casting tool 44, in which a die forms the molten copper into a wire rod of the required shape and diameter.

Referring now to Figs. 3 and 4, there is shown a continuous casting crucible apparatus 50 according to one embodiment of the present invention. The crucible 16 is similar to the known crucible illustrated in Fig. 2, and similar components are indicated by the same reference numerals and are not described further. However the continuous casting crucible apparatus 50 includes a lid 52 covering the charging chamber 14 and the casting chamber 22.

In the illustrated example of Fig. 3 the lid 52 includes a frame 54 which is fixed by bolts 56 or other fasteners to the furnace structure 58 which surrounds the crucible 16. The lid 52 comprises two removable cover plates 60, 62, each removably secured to the frame 54 by fixing brackets 64 and fasteners 66. Each cover plate 60, 62 includes one or more lifting handles 68so that the cover plate can be lifted and removed to provide access to the casting chamber 22 and/or the charging chamber 14. The cover plate 60 over the charging chamber 14 has hand operable fasteners 66 to facilitate quick removal of the cover plate 60.

In Fig. 4 the two cover plates 60, 62 are shown connected by two edge plates 70, one fixed to each cover plate. However the cover plates 60, 62 maybe connected directly to the frame 54 with an appropriate sealing means (for example ceramic fibre rope, not shown] therebetween, or may be sealably connected in any other suitable manner to the frame 54 or the furnace structure 58. Alternatively the two cover plates 60, 62 may be replaced by a single removable cover plate) or the second cover plate 62 may be formed integrally with the frame 54, so that only the first cover plate 60 is removable separately from the furnace. Similarly, the lid 52 may be formed as a single component without removable cover plates, and attached directly to the furnace structure 58.

The lid 52 has two sealed tubular ports 72 in communication with the charging chamber 14 for the feeding of copper rod 100 and alloy ingredients 102 therethrough. Each port 72 has an aperture 74 provided with a seal, which may be graphite or other suitable low friction material, which provides an efficient seal around the cylindrical feedstock, either copper rod 100 or cored wire feed units 102 which contain the alloy ingredients such as Zr in powder form wrapped in a tubular copper core. Such cored wire feed units may be those provided by Affival ®. The copper is preferably oxygen-free copper.

Typically the copper rod 100 is 8mm diameter copper rod feed. Both the copper rod and cored wire feed 102 are fed automatically by feed machines or mechanisms (not shown). Load cells (not shown) beneath the furnace measure and control the melt levels and feed volumes.

The lid 52 is provided with at least one sealed aperture 76 through which a casting tool 78 extends into the casting chamber. The casting tool is shown in more detail in Fig. 5. It includes a graphite casting insert 80 which extends into the molten alloy and serves as a die for continuous casting of the alloy rod. The casting insert 80 extends upwards through a ceramic hot end cap 82 into the body of the casting tocil 78. Inside the end cap is thermal insulation 84 and a copper alloy primary cooler 86 which is cooled by water passing through cooling water channels 88 from a water inlet 90 to a water outlet 92. As the molten alloy is drawn into the graphite casting insert 80 it is cooled by the copper alloy primary co&er 86 and a secondary cooling system 94 in the upper portion of the casting tool 78 and emerges from the top 96 of the casting tool 78 as solid copper alloy wire rod 104. From there it is transported and coiled in a known manner.

Although in the illustrated embodiment a single casting tool 78 is shown, in practice the apparatus may include more than one casting tool, each arranged to extend into the casting chamber 22. For example six casting tools may be provided, so that six strands of wire rod are formed simultaneously.

The lid 52 is provided with a gas supply port 110 through which an inert shield gas, for example argon or nitrogen, is supplied to the casting chamber 22. The inert shield gas serves to exclude oxygen from the interior of the crucible. Preferably the lid is sealed to the crucible, for example by ceramic fibre rope, so that the inert shield gas can be supplied at a pressure above atmospheric pressure (typically 50 to Pa above atmospheric pressure) to provide a positive pressure differential inside the crucible to prevent the ingress of atmospheric air, which includes oxygen.

Similarly any separate components of the lid 52, such as the frame 54 and cover plates 60, 62, are preferably sealed to each other, for example by ceramic fibre rope, to maintain the pressure in the crucible 16. The source of the inert shie.d gas is not shown, but can be any suitable source, such as a pressurised cylinder with control valve arrangement.

The lid 52 is provided with a sealed aperture 112 through which a temperature probe 114 extends into the casting chamber. The temperature probe is typically a thermocouple probe in a ceramic tube, adapted to measure the temperature of the melt 28.

The lid 52 includes a sight glass port 116 which allows a user to see inside the charging chamber 14.

With reference to Fig. 6, there is shown an alternative arrangement of a lid 52 of a continuous casting crucible apparatus according to the present invention. In this embodiment the furnace structure 58 includes a flange 130 which surrounds the top of the crucible 16 (notvisible in Fig. 6]. A frame 132 is fixed to the flange 130 of the furnace structure 58. The frame 132 includes lifting handles 134 so that it can be lifted away from the furnace structure 58 after releasing fixing bolts 136. Two cover plates 160, 162 are releasably secured to the frame 132 by lever clamps 138. Seals (not shown) are provided around the perimeters of the cover plates 160, 162, so that the cover plates 160, 162 can be sealed to the frame 132.

The cover plates 160, 162 include lifting handles 68 and are in other respects similar to the cover plates 60, 62 illustrated in Figs. 3 and 4, with sealed tubular ports 72 (omitted from Fig. 6) in communication with the charging chamber 14 for the feeding of copper rod 100, at least one sealed aperture 76 (omitted from Fig. 6) through which a casting tool 78 extends into the casting chamber, and optionally with the other components described above with respect to the cover plates 60, 62 illustrated in Figs. 3 and 4.

It will be understood that variations in the arrangement of frame 132 and cover plates 160, 162 are possiffle, and the invention is not limited to the particular arrangements of lid 52 described herein.

The apparatus of the invention overcomes the problems caused by oxygen in the casting process by the provision of a cover plate or lid 52 over the melt in the crucible 16. The cover plate or lid 52 provides maximum sealing of charging chamber 14 and casting chamber 22, whilst allowing the continuous feeding of both copper and alloy ingredients, and continuous casting of the finished alloy wire rod (both of which must be continuous in production).

The invention achieves its objectives by providing a sealed cover plate or lid 52 which provides the highest possible degree of closure over the charging chamber 14 and casting chamber 22. The invention provides further protection of the melt by excluding oxygen through the provision of inert gas under pressure to the casting chamber 22, meaning that the conventional carbon protection cover is no longer required. A camera or sight glass 116 allows the operator to view the melted material levels and quality in the charging chamber 14.

The use of automatic copper rod feed, typically rod of consistent 8mm diameter, which is fed via a suitable feed tube) and the use of proprietary cored wire feed units which also have a consistent diameter, allows the use of effective seals at the apertures 74 of the tubular ports 72, so that the charging chamber 14 is kept free of oxygen. In addition, the apparatus may be fitted with automatic means for melt skimming and/or slag removal (not shown].

The apparatus according to the present invention has been shown to significantly reduce the presence of oxygen in or around the molten material by greatly restricting availability of oxygen in the crucible 16. This results in: * significantly reduced slag * reduced Zr "losses") therefore reduced Zr variability * improved alloy tolerance levels.

These improvements can all be achieved whilst maintaining the advantages of a continuous casting process, with continuous input and output.

Claims

CLAIMS1. A continuous casting cruciffle apparatus comprising a charging chamber, a casting chamber, a passage connecting the charging chamber and the casting chamber, and a lid covering the charging chamber and the casting chamber, wherein the lid is provided with at least one sealed tubular port in communication with the charging chamber having a sealable aperture therein for the feeding of copper rod therethrough, and wherein the lid is provided with at least one sealed aperture through which a casting tool extends into the casting chamber, the casting tool including a die and a cooling system.
2. The apparatus of claim 1, wherein the apparatus indudes at least one casting tool extending through the at least one sealed aperture into the casting chamber.
3. The apparatus of claim 2, wherein the casting tool includes a graphite die.
4. The apparatus of any preceding claim, wherein the charging chamber and casting chamber are of graphite.
5. The apparatus of any preceding claim, wherein the lid is provided with two sealed tubular ports, each having a sealable aperture therein, a first port being adapted for the feeding of copper rod therethrough and a second port being adapted for the feeding of cored wire therethrough.
6. The apparatus of claim 5, further comprising a first feed mechanism adapted to feed copper rod through the sealable aperture of the first sealed tubular port and a second feed mechanism adapted to feed cored wire through the sealable aperture of the first sealed tubular port.
7. The apparatus of any preceding claim, wherein the lid is provided with a gas supply port adapted for the supply of an inert shield gas to the casting chamber.
8. The apparatus of claim 7, further comprising a source of inert shield gas in communication with the gas supply port.
9. The apparatus of any preceding claim, further comprising a temperature probe extending through a seated aperture in the lid into the casting chamber.
10. The apparatus of any preceding claim, wherein the lid includes a sight glass port.
11. The apparatus of any preceding claim, wherein the lid comprises a frame secured to the casting chamber and the charging chamber and at least one removable cover plate removably secured to the frame.
12. The apparatus of claim 11, wherein the lid comprises two removable cover plate removably secured to the frame, a first cover plate being removable to provide access to the charging chamber and a second cover plate being removable to provide access to the casting chamber.
13. A method of continuous casting an alloy using a continuous casting crucible apparatus comprising a charging chamber, a casting chamber, a passage connecting the charging chamber and the casting chamber, and a lid covering the charging chamber and the casting chamber, the method comprising the steps of: feeding copper rod to the charging chamber through a sealable aperture of a first sealed tubular port in the lid; feeding cored wire to the charging chamber through a sealable aperture of a second sealed tubular port in the lid; casting an alloy wire rod by causing molten alloy to pass vertically through a casting tool which extends through a sealed aperture in the lid into the casting chamber, wherein the molten alloy passes through a die in the casting tool and is cooled to solid form with in the casting tooL
14. The method of claim 13, wherein the continuous casting crucible apparatus is a continuous casting crucible apparatus according to any of claims ito 12.
15. The method of claim 13 or 14, including the further step of providing an inert shi&d gas to the casting chamber through a gas supply port in the lid and maintaining a pressure in the casting chamber greater than atmospheric pressure.