GB1574711A - Production of metal castings - Google Patents

Description

(54) PRODUCTION OF METAL CASTINGS (71) We, BOC Limited, an English company of Hammersmith House, London, W6 9DX, England, do hereby declare the invention, for which we pray that a patent may be granted to us, to be particularly described in and by the following statement: This invention relates to the production of metal castings.

A known method of producing shaped metal articles involves forming an ingot by casting and then rolling, forging or extruding the ingot. There is a tendency, however, for segregation to occur upon the molten metal solidifying in the casting mould.

According to the present invention, there is provided a process for the continuous production of metal castings -suitable for subsequent formation into shaped metal articles including the steps of causing molten metal to fall in a vertical stream; directing at least one jet of gas at the stream of molten metal so as to atomise the molten metal; collecting the atomised metal.in the mould of a continuous casting machine, the major axis of such mould being vertical, so as to form continuously a longitudinally extending metal casting;-with- drawing said casting continuously from the mould in a vetrical direction, and cutting it into lengths.

Generally the gas chosen for atomisation should be non-reactive with the metal, although the need may occasionally arise to include in the atomising gas a constituent which is reactive with, say, impurites in the metal. Generally, suitable atomising gases are argon, nitrogen and carbon dioxide, and mixtures of at least two of these gases.

The atomisation is preferably formed by allowing a stream of molten metal, typically having a diameter of up to 0.63 inches, to fall under gravity from a tundish into a chamber in which at least one jet of atomising gas is directed at the stream. If desired, they gas from the chamber in which the atomisation is performed may be passed into the mould so as to maintain therein an atmosphere which does not react chemically with the casting. It is of course possible to supply such non-reactive gas to the mould from a source other than the atomising chamber.

The atomising gas is desirably directed at the molten metal from at least one nozzle adapted to form a jet of gas travelling at a high velocity. The nozzles can be-of conventional design. The outlet end of the or each nozzle preferably terminates from 0.5 to 12 inches from the- region at-which the gas impinges upon the stream of metal, the distance -being along the axis of the nozzle. A distance of about 1 to 6 inches is, in particular, often preferred.

The or each nozzle is preferably orientated such that the jet of atomising gas impinges upon the stream of molten metal at- an acute angle, typically less than 30 to the- stream of molten metal in the direction of travel of the stream.

The or each nozzle is preferably movable relative to the mould. The movement of the or each nozzle may be vibratory, the vibration being generally horizontal. This facilitates the deposition of atomised metal evenly over the surface of the casting in the mould. In addition, or alternatively, the or each nozzle is preferably positively displaceable both vertically and horizontally. This helps in controlling the spread of atomised metal particles entering the mould and the points of their impact on the surface of the casting.

The temperature of the atomised metal particles entering the mould is desirably controlled such that when they strike the surface of the casting, they coalesce therewith.

For the coalescence to occur it is desirable that the particles encountering the surface of the casting- should be about the temperature of the solidus temperature (ie the freezing point) of the metal. At such a temperature the particles encountering the casting surface is below the temperature at which they are plastic adequate coalescence with the casting does not occur. If on the other hand the temperature of the particles encountering the surface of the casting are near the liquidus temperature (ie the particles are liquid) segregation in the casting will occur as the temperature thereor falls to below the solidus temperature.

Control of the temperature of the atomised metal upon its contact with the surface of the casting may be exerted by an appropriate choice of the distance between the region where the atomising gas impinges upon the stream of molten metal and of the surface of the casting. This distance is preferably adjustable, for example, by varying, as previously described herein, the position of the or each nozzle employed to form a jet of atomising gas.

The atomising gas is preferably directed at the stream of molten metal at high velocity.

This enables small discrete particles (or droplets) of molten metal to be formed, which particles enter the mould with a large kinetic energy. It is generally preferred that the kinetic energy should be as high as possible so as to facilitate compaction of the particles striking the surface of the casting.

The atomising gas is preferably supplied from the nozzle or nozzles at a pressure in the range 10 to 600 psi (gauge), preferably in the range 50 to 250 psi (gauge). The atomising gas preferably impinges upon the stream of molten metal at a rate corresponding to 5000 to 20,000 standard cubic feet per ton of metal.

The rate at which the atomised metal particles enter the mould may be chosen in accordance with the cross-sectional shape and size of the casting.

A conventional continuous casting machine may be used. The machine may typically have a water-cooled mould from which the casting is able to be continuously withdrawn. The mould may be any convenient shape in cross section. For example, it may be circular, square, rectangular or hexagonal in cross section.

The lengths of castings produced by the method according to the present invention may be formed into shaped metal articles by means, for example, of rolling, forging or extruding.

The method according to the present invention offers the advantage of being able to produce castings of metal, such as high alloy steels, and aerospace alloys, having a density of the order of from 92 to 99.9% of the theoretical density. Moreover, the method according to the present invention makes possible the formation of segregation-free metal articles in a particularly convenient and economical manner.

The method according to the present invention will now be described by way of example with reference to the accompanying drawing which is a schematic view of a continuous costing machine for performing the process to the present invention.

Referring to the drawing, which is diagrammatic and not to scale, a ladle 2 is positioned above a tundish 4 which has in its base an aperture 6. The tundish is seated over an opening 8 in the lop of a chamber 10in which is positioned an atondsing unit including nozzles 12 about a central axis in line with the axis of the aperture 6 and which are supplied with gas which does not react with the molten metal from a source 16 via a conduit 14. The nozzles 12 direct the gas at an angle of less than 30 with respect to the common axis from which they are spaced.

The nozzles 12 form part of a single assembly which is movable in both the horizontal and vertical direction.

The chamber has a sighting port 18 from which atomisation of the stream of molten metal falling under gravity from the tundish 4 may be observed. The chamber 10 also has an outlet 22 connected by a conduit 24 to a shroud 30. The shroud 30 extends around the mould 36 of a continuous casting machine 34. The major axis of the mould 36 is vertically disposed.

The mould 36 is typically water-cooled.

In operation molten metal is poured from the ladle 2 into the tundish 4 and falls under gravity through the aperture 6 as a stream. The nozzles 12 direct jets of atomising gas at the stream. The jets of gas from the nozzles 12 impinge upon the stream of metal at an acute angle of less than 300 and cause the atomisation of the molten metal. Because the atomising gas is supplied from the nozzles 12 at high velocity it imparts a large kinetic energy to the droplets produced by the atomisation and causes these droplets to travel in the form of a fine divergent spary towards the mouth of the mould 36 in which they are received. In the mould 36 the droplets encounter the surface of a casting already formed from previous atomised droplets The droplets coalesce on the casting and thus the casting increases in length. The casting is continuously withdrawn from the mould in the vertical direction as shown by the arrow 38.

Lengths are cut from the casting. In order to ensure that there is adequate coalescence of the droplets with the casting it should be arranged that the droplets on encountering the surface of the casting have a temperature at or about that of the solidus temperature of the metal. In order to ensure that the droplets have this temperature upon their encounter with the surface of the casting the position of the assembly of the nozzles 12 may be adjusted both vertically and horizontally in relation to the mould. Furthermore, the atomisation process can be observed through the sighting port 18 to check that the atomisation is proceeding in the desired manner.

In order to prevent oxidation of the newly formed casting the gas is withdrawn from the chamber 10 through the outlet 22 and passed into the shroud 32.

WHAT WE CLAIM IS: 1. A process for continuous production of metal castings suitable for subsequent formation into shaped articles including the steps of causing molten metal to fall in a vertical stream, directing at least one jet of gas at the stream of molten metal so as to atomise the molten metal; collecting the atomised metal in the mould of a continuous casting machine, the major axis of such mould being vertical, so as to form continuously a longitudinally -extending metal casting, withdrawing said casting continuously from the mould in a vertical direction, and cutting it into lengths.

2. A process as claimed in claim 1, in which the gas is argon, nitrogen or a mixture of argon and nitrogen.

3. A process as claimed in claim 1 or 2, in which a stream of molten metal is allowed to fall under gravity from a tundish into a chamber in which the or each jet of atomising gas is directed from its own nozzle at the stream of metal.

4. A process as claimed in claim 3, in which the outlet of the or each nozzle terminates from 0.5 to 12 inches from the region at which the gas impinges upon the stream of molten metal.

5. A process as claimed in claim 3 or claim 4, in which the or each nozzle directs its jet of gas at the stream of molten metal at an acute angle of less than 30"to the stream of molten metal, the said jet of gas being directed in a downward direction.

6. A process as claimed in any one of claims 3 to 5, in which the or each nozzle is movable relative to the mould.

7. A process as claimed in claim 6, in which the or each nozzle is positively displaceable both vertically and horizontally.

8. A process as claimed in any one of claims 3 to 7, in which the gas is supplied from the nozzle or nozzles at a pressure in the range 10 to 600 psi (gauge).

9. A process as claimed in claim 8, in which the pressure is in the range 50 to 250 psi (gauge).

10. A process as claimed in any one of the preceding claims, in which the temperature of the atomised metal particles entering the mould is controlled such that when they strike the surface of the casting being formed they coalesce therewith.

11. A process for the continuous production of metal castings substantially as described with reference to the accompanying drawing.

12. A casting produced by a process as claimed in any one of claims 1 to 11.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. vertically and horizontally in relation to the mould. Furthermore, the atomisation process can be observed through the sighting port 18 to check that the atomisation is proceeding in the desired manner. In order to prevent oxidation of the newly formed casting the gas is withdrawn from the chamber 10 through the outlet 22 and passed into the shroud 32. WHAT WE CLAIM IS:

1. A process for continuous production of metal castings suitable for subsequent formation into shaped articles including the steps of causing molten metal to fall in a vertical stream, directing at least one jet of gas at the stream of molten metal so as to atomise the molten metal; collecting the atomised metal in the mould of a continuous casting machine, the major axis of such mould being vertical, so as to form continuously a longitudinally -extending metal casting, withdrawing said casting continuously from the mould in a vertical direction, and cutting it into lengths.

2. A process as claimed in claim 1, in which the gas is argon, nitrogen or a mixture of argon and nitrogen.

3. A process as claimed in claim 1 or 2, in which a stream of molten metal is allowed to fall under gravity from a tundish into a chamber in which the or each jet of atomising gas is directed from its own nozzle at the stream of metal.

4. A process as claimed in claim 3, in which the outlet of the or each nozzle terminates from 0.5 to 12 inches from the region at which the gas impinges upon the stream of molten metal.

5. A process as claimed in claim 3 or claim 4, in which the or each nozzle directs its jet of gas at the stream of molten metal at an acute angle of less than 30"to the stream of molten metal, the said jet of gas being directed in a downward direction.

6. A process as claimed in any one of claims 3 to 5, in which the or each nozzle is movable relative to the mould.

7. A process as claimed in claim 6, in which the or each nozzle is positively displaceable both vertically and horizontally.

8. A process as claimed in any one of claims 3 to 7, in which the gas is supplied from the nozzle or nozzles at a pressure in the range 10 to 600 psi (gauge).

9. A process as claimed in claim 8, in which the pressure is in the range 50 to 250 psi (gauge).

10. A process as claimed in any one of the preceding claims, in which the temperature of the atomised metal particles entering the mould is controlled such that when they strike the surface of the casting being formed they coalesce therewith.

11. A process for the continuous production of metal castings substantially as described with reference to the accompanying drawing.

12. A casting produced by a process as claimed in any one of claims 1 to 11.