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GB2393451A - A Method of Manufacture of Metal Alloy Sheet - Google Patents

A Method of Manufacture of Metal Alloy Sheet Download PDF

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Publication number
GB2393451A
GB2393451A GB0222358A GB0222358A GB2393451A GB 2393451 A GB2393451 A GB 2393451A GB 0222358 A GB0222358 A GB 0222358A GB 0222358 A GB0222358 A GB 0222358A GB 2393451 A GB2393451 A GB 2393451A
Authority
GB
United Kingdom
Prior art keywords
pellets
metal alloy
sheet
metal
stock
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB0222358A
Other versions
GB0222358D0 (en
Inventor
Charles Malcolm Ward-Close
Alastair Bryan Godfrey
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Qinetiq Ltd
Original Assignee
Qinetiq Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Qinetiq Ltd filed Critical Qinetiq Ltd
Priority to GB0222358A priority Critical patent/GB2393451A/en
Publication of GB0222358D0 publication Critical patent/GB0222358D0/en
Priority to AT03753690T priority patent/ATE452214T1/en
Priority to PCT/GB2003/004093 priority patent/WO2004029332A2/en
Priority to AU2003271852A priority patent/AU2003271852B2/en
Priority to US10/529,234 priority patent/US20060130610A1/en
Priority to DE60330577T priority patent/DE60330577D1/en
Priority to EP03753690A priority patent/EP1543172B1/en
Publication of GB2393451A publication Critical patent/GB2393451A/en
Priority to US13/477,368 priority patent/US20120230860A1/en
Withdrawn legal-status Critical Current

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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D23/00Casting processes not provided for in groups B22D1/00 - B22D21/00
    • B22D23/06Melting-down metal, e.g. metal particles, in the mould
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/06Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
    • B22D11/0622Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Continuous Casting (AREA)

Abstract

A method for the manufacture of metal alloy sheet 5 comprising the steps of: introducing a continuous source of pellets 1 of the metal alloy to a pair of cooled feed rollers 3a, 3b, heating the pellets 1 as they approach and/or pass through the nip of feed rollers 3a, 3b, drawing the metal through the nip of the rollers to form a sheet of metal alloy 5; and, cooling the sheet. The rollers may be water cooled. A drawing process may be performed after partially melting the pellets in a crucible (figure 2, 27) such that the die (figure 2, 29) has a cross section of near net shape and dimensions to the required net shape and dimensions of the required stock and cooling the stock. The method of heating may be via the use of an energy beam 4 or resistance heating.

Description

. 239345 1
METHOD OF MANUFACTURE OF METAL ALLOY STOCK
This invention relates to a method for the manufacture of metal alloy stock, in particular, stock in the form of sheet, plate, bar and wire. The invention is particularly suited to the manufacture of titanium alloy stock.
Conventional methods for the manufacture of titanium and titanium alloy stock involve hot working of large titanium alloy ingots. T he high temperatures and pressures required for these processes contribute to the high cost of this stock compared to other metal products such as steel and aluminium alloys.
Titanium is conventionally obtained from its ore by the Kroll route, a complex chlorination and magnesium reduction method. The purified metal granules, called sponge, are then melted with the alloying additions and cast into large titanium alloy ingots. The metal is melted at least twice and sometimes more, in order to ensure chemical homogeneity and freedom from defects. The large titanium alloy ingots are then hot forged repeatedly to produce the semi-finished alloy stock shapes, such as bar, plate, sheet and wire, required for the manufacture of articles.
The present invention aims to provide novel methods for the manufacture of titanium or other metal alloy stock, which are less expensive and easier to perform.
In accordance with a first aspect, the present invention provides a method for the manufacture of a metal alloy sheet comprising the steps of: introducing a continuous source of pellets of the metal alloy to a pair of cooled feed rollers, heating the pellets as they approach and/or pass through the nip of the pair of feed rollers, drawing the metal through the nip of the rollers to form a sheet of metal alloy, and, cooling the sheet.
The pellets should be heated sufficiently to allow them to coalesce to form a sheet when subjected to the pressure of the nip, and may be heated so that they soften, or, at least partly melt, or even fully melt.
The term "pellet" is used throughout the specification to refer to particles
ranging from powders to granules and should be construed in the claims accordingly.
Preferably either or both of the feed rollers are water cooled by passing a coolant through their centres. One suitable coolant is water, other suitable fluids will
. - no doubt occur to the skilled addressee.
in another aspect, the invention provides a method for the manufacture of a uniform cross-section metal alloy stock, comprising the steps of: introducing a continuous source of pellets of the metal alloy to a shaped crucible, heating the pellets at an exposed surface of the crucible, ideally, to at least partly melt them, drawing the at least partially molten metal from an opposing surface of the crucible through a die, the die having a cross section of near net shape and dimensions to the desired net shape and dimensions of the required stock, and cooling the cast stock.
The sheet or cast stock may be allowed to cool or may be actively cooled.
In either aspect of the invention, the alloy pellets may be conveniently obtained by an electro-deoxidation (EDO) process, such as that described in WO 99/64638, or, in the Applicant's co-pending applications GB2359564 or GB2362164.
As is described in the above specifications, electrochemical reduction may be used to
provide small pellets of alloy having high purity and good grain structure. Thus, heating so as to soften or partially melt the pellets is sufficient to bond the pellets and obtain a mass of alloy having good mechanical properties.
The step of heating the pellets is preferably carried out by means of an energy beam. The energy beam may, optionally, be selected from an electron beam, a laser or a plasma torch. The heating mechanism could alternatively simply be electric heating of the material by passing a large current between the rollers and relying on resistance heating. In a particularly preferred aspect, the pellets are arranged to fall freely through an energy beam heat source, which heats the pellets sufficiently to enable any volatile impurities resulting from the original manufacturing process, such as an electrochemical reduction process, to be removed, further improving the purity of the end product.
It has been found that the kinds of impurities introduced by such electro-
reduction processes are usually more volatile than the metal and may be conveniently removed by the present process. Such impurities may comprise light metals, for example, calcium and magnesium, as well as salts from the electrolyte, such as calcium chloride. For effective removal of impurities without significant loss of
r r r e r ' À À À À r r r À À r metal, the impurities should preferably be more volatile than the metal by at least a factor of ten, or preferably 20, in terms of their respective vapour pressures at the processing temperature. Preferably, the processing temperature and/or heating time should be sufficient to remove substantially all the contaminating impurities, for example, so as to reduce their total level to less than 50 ppm, or less than 10% their initial total concentration. Preferably the process is conducted so that there is little or no evaporation (for example, less than 5%) of the metal. Ideally, the process is conducted in a controlled atmosphere, for example, at low pressure/vacuum and/or in an inert atmosphere. In the case of Ti it is important that the powder particles are kept separate from oxygen or nitrogen while above a temperature of about 500 C. This is achieved in practice either by processing in a vacuum or in an atmosphere of Ar. The use of argon or helium arc torches is particularly preferred.
In either of the methods of the invention, the rolled or cast stock may be further processed, for example, by one or more additional intermediate steps such as further working or heat treatments of the stock, prior to final cooling.
Products of the methods of the invention are comprised of fully dense metal alloy. The homogeneity of the final metal is improved considerably where the pellets are provided via an electrochemical reduction method, compared to the alternative of using Kroll sponge and powder or particles of the alloy additions. The present methods require considerably less cumbersome and costly apparatus compared to conventional methods where the starting materials are introduced to the casting or rolling apparatus fully molten and are particularly suited to the production of small quantities of stock where mechanical properties and metal homogeneity are of importance. The method of the invention is particularly suited to the manufacture of low volume or small size products, which could be prohibitively costly to produce by conventional methods.
For the purposes of exemplification, some embodiments of the invention will now be further described with reference to the Figures, in which: Figure I shows a schematic illustration of an apparatus for the production of titanium metal or alloy sheet; and, Figure 2 shows a schematic illustration of an apparatus for the production of titanium metal or alloy bar stock.
:.; : c' As can be seen from Figure 1, pellets of titanium metal or alloy l are delivered through a hopper 2 to a pair of counter-rotating feed rollers 3a, 3b. The rollers are cooled by a water-cooling system (not shown). An energy beam 4 is arranged to concentrate a beam of energy along a line just above the nip of rollers 3a,3b and causes at least partial melting of the pellets seated on and between the rollers. As the rollers 3a,3b rotate, the at least partially melted pellets are drawn into the nip and are squeezed together to form a solid mass of the titanium or titanium alloy in the form of a sheet 5. The hot sheet falls to a conveyor 6 and is carried away for further processing and/or cooling.
Figure 2 illustrates a similar arrangement for the production of bar stock having a square cross-section. A source of pellets 21 is delivered through a hopper 22 to a shallow crucible 27. A laser 24 is mounted on a track 28 along which the energy beam sweeps back and forth. The energy beam is aimed at the top surface of the crucible 27 and causes at least partial melting of the pellets 21 delivered thereto. The metal is drawn through a square shaped die 29 communicating with a lower surface of the crucible 27 and bar stock 25 of the titanium or titanium alloy emerges. The bar stock may be cut to length by a cutter (not shown). The bar stock is collected by a conveyor system 26 and removed for cooling and/or further processing.
The parameters for a method carried using either of the described apparatus are more generally described below.
The feedstock in the form of pellets (including powder or granules) is stored inside a hopper that is an integral part of a vacuum chamber housing the roller and for example, E-beam (electron-beam) or a laser beam melting assembly. During operation the feedstock is poured over the rollers at a controlled rate using a regulator valve attached to the feeder. The vacuum chamber is desirably at a pressure ranging from 1 x 106 to 1 x 10-s mBar during the operation.
The energy beam directed at the pellets, heats or heats and at least partially melts the titanium feedstock between the roller gap, which either softens it sufficiently for it to be deformed and consolidated as it passes through the roll gap, or melts it then solidifies it instantaneously on contacting the rollers and also gets deformed into a strip subsequently. The temperature of the solid strip coming out of the rollers is in the region of 600 C. Several titanium strips of dimensions in the range 300-900 mm (length) x 60-100 mm (width) x 3.0 mm (thickness) have been produced using this method.
. . À r À This method is not specific only to titanium feedstock, it has potential application for direct production of strips of any metallic powder, and especially those that are very sensitive to the absorption of impurities such as oxygen or nitrogen.
Titanium powder or granules can be produced as feedstock by various methods. Spherical powders (25 to 500 microns) may be obtained by gas atomising (a process consisting of melting pure titanium or titanium alloy and spraying the melt onto a cold substrate using an inert gas). in the HDH process, irregular shaped granules of titanium are obtained by first embrittling titanium sponge or alloy (2 to 20 mm in size) by hydriding, then crushing it to small particles, and de-hydriding (for example by a vacuum anneal) to produce pure titanium or Ti alloy granules. However preferably, titanium powder is produced by the electro- deoxidation (EDO) process, where metal alloy powder or granules of controlled size are produced by electro-
reducing ceramic powder or granules made from sintered mixtures of the oxides of the alloy constituents.
The method of manufacture of strip described above is ideally suited to feed stock of uniformly sized granules of less than about 1 mm dimensions, irrespective of their origin: gas atomised powder, granules made by the HDH process, broken foams or pellets. Larger granules may be optimal for production of thicker sheets by this method. Rollers are desirably cooled through the centre. The primary requirement is that the chamber housing the rollers should be in a vacuum (or very low pressure environment) to stop the molten titanium from picking up oxygen. A water-cooled roller assembly has been developed by the applicants that lets the water flow through the rollers and bearings, while maintaining good vacuum tightness.
For both variants of the invention described here for the production of metal alloy sheet and the production of shaped bar stock by energy beam heating of pellets or granular feed, the process will have the secondary benefit of removing all or part of any volatile contamination that may be present in the feed material. For example, EDO granules may contain contaminants such as calcium chloride, calcium oxide or calcium metal, and powder or granules derived from the Kroll route without any intermediate heating or melting, such as by the HDH method, may contain magnesium metal or magnesium chloride.
In a further aspect, the invention provides a method for the manufacture of a metal alloy article of uniform cross section comprising the steps of;
r introducing a continuous source of pellets of the metal alloy to a processing means; heating the pellets as they approach or pass through the processing means; drawing the metal through the processing means so as to coalesce the pellets to form the desired article; cooling the cast stock...DTD: In this aspect, metal alloy pellets are ideally produced by the EDO process, which provides a method for the direct production of high purity metal alloy articles from metal oxide feedstock. If necessary, further to improve purity, the pellets may be caused to fall freely through the heat source, usually an energy beam, which heat source is arranged to cause impurities introduced by the EDO process to be volatised and removed from the pellets.

Claims (12)

: l À À 1 . CLAIMS
1. A method for the manufacture of a metal alloy sheet comprising the steps of: introducing a continuous source of pellets of the metal alloy to a pair of cooled feed rollers, heating the pellets as they approach and/or pass through the nip of the pair of feed rollers, drawing the metal through the nip of the rollers to form a sheet of metal alloy; and, cooling the sheet.
2. A method as claimed in claim 1 wherein either or both of the rollers are cooled.
3. A method as claimed in claim 2 wherein the rollers are cooled by a coolant continuously flowing through their centre.
4. A method as claimed in claim 3 wherein the coolant is water.
5. A method for the manufacture of a uniform cross-section metal alloy stock, comprising the steps of: introducing a continuous source of pellets of the metal alloy to a shaped crucible, heating the pellets at an exposed surface of the crucible to at least partly melt them, drawing the at least partially molten metal from an opposing surface of the crucible through a die, the die having a cross section of near net shape and dimensions to the desired net shape and dimensions of the required stock, and cooling the cast stock.
6. A method as claimed in any preceding claim wherein the pellets have been manufactured by an electrochemical reduction of mixed oxides of one or more of the metal alloy constituents.
7. A method as claimed in any preceding claim wherein the step of heating the pellets is carried out by means of an energy beam or resistance heating.
8. A method as claimed in claim 7 wherein an energy beam is used and is selected from an electron beam, a laser or a plasma torch.
9. A method as claimed in any preceding claim wherein the sheet or stock is submitted to additional metal working or heat treatment processes prior to
l À e:. À: cooling.
10. A method substantially as described herein and with reference to Figure 1 or 2.
11. A sheet, plate, block, bar or wire of metal alloy manufactured according to the method of any preceding claim.
12. A sheet, plate, block, bar or wire as claimed in claim 11, or a method as claimed in any one of claims 1 to 10, wherein the alloy substantially comprises titanium.
GB0222358A 2002-09-25 2002-09-26 A Method of Manufacture of Metal Alloy Sheet Withdrawn GB2393451A (en)

Priority Applications (8)

Application Number Priority Date Filing Date Title
GB0222358A GB2393451A (en) 2002-09-26 2002-09-26 A Method of Manufacture of Metal Alloy Sheet
AT03753690T ATE452214T1 (en) 2002-09-25 2003-09-24 CLEANING METAL PARTICLES BY HEAT TREATMENT
PCT/GB2003/004093 WO2004029332A2 (en) 2002-09-25 2003-09-24 Purification of electrochemically deoxidised refractory metal particles by heat processing
AU2003271852A AU2003271852B2 (en) 2002-09-25 2003-09-24 Purification of electrochemically deoxidised refractory metal particles by heat processing
US10/529,234 US20060130610A1 (en) 2002-09-25 2003-09-24 Purification process
DE60330577T DE60330577D1 (en) 2002-09-25 2003-09-24 CLEANING OF METAL PARTICLES BY HEAT TREATMENT
EP03753690A EP1543172B1 (en) 2002-09-25 2003-09-24 Purification of metal particles by heat processing
US13/477,368 US20120230860A1 (en) 2002-09-25 2012-05-22 Purification process

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0222358A GB2393451A (en) 2002-09-26 2002-09-26 A Method of Manufacture of Metal Alloy Sheet

Publications (2)

Publication Number Publication Date
GB0222358D0 GB0222358D0 (en) 2002-11-06
GB2393451A true GB2393451A (en) 2004-03-31

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ID=9944810

Family Applications (1)

Application Number Title Priority Date Filing Date
GB0222358A Withdrawn GB2393451A (en) 2002-09-25 2002-09-26 A Method of Manufacture of Metal Alloy Sheet

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GB (1) GB2393451A (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1026768A (en) * 1963-05-27 1966-04-20 Reynolds Metals Co Multitextural metallic strip
GB1091101A (en) * 1963-11-04 1967-11-15 Maurice Donald Ayers Production of powder,strip and other metal products from refined molted metal
GB2004918A (en) * 1977-09-27 1979-04-11 British Steel Corp Production of metal strip
GB2151761A (en) * 1983-12-13 1985-07-24 Daido Steel Co Ltd A melting and casting installation

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1026768A (en) * 1963-05-27 1966-04-20 Reynolds Metals Co Multitextural metallic strip
GB1091101A (en) * 1963-11-04 1967-11-15 Maurice Donald Ayers Production of powder,strip and other metal products from refined molted metal
GB2004918A (en) * 1977-09-27 1979-04-11 British Steel Corp Production of metal strip
GB2151761A (en) * 1983-12-13 1985-07-24 Daido Steel Co Ltd A melting and casting installation

Also Published As

Publication number Publication date
GB0222358D0 (en) 2002-11-06

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