WO1992002322A1

WO1992002322A1 - Casting metals

Info

Publication number: WO1992002322A1
Application number: PCT/GB1991/001305
Authority: WO
Inventors: Philip Graham Enright; Andrew James Hobbis; Stephen Charles Flood
Original assignee: Alcan International Limited
Priority date: 1990-08-07
Filing date: 1991-07-31
Publication date: 1992-02-20
Also published as: ZA916090B; AU8304691A; GB9017319D0

Abstract

A method and device for direct chill casting of light metals and their alloys through an annular mould (1) comprising delivering liquid metal into the upper end of the mould and discharging that liquid metal at a multiplicity of positions adjacent the inner surface of the mould wall (2).

Description

CASTING METALS

This invention relates to a method of and apparatus for the direct chill casting of light metals and their alloys.

Direct chill casting through an annular mould is standard practice and it is common to deliver liquid metal into the upper part of the mould through a float mechanism. Known float mechanisms discharge the liquid metal within the mould around the periphery of the mechanism and generally into a region of the mould lying between its centre and the mould wall.

When direct chill castings are made it is accepted that the surface of the casting will be defective and generally require scalping. Clearly it is desirable to reduce the depth of scalping as much as possible and it has hitherto been thought that the main factors affecting this were not connected with the delivery of liquid metal to the mould.

We have now found that the manner in which liquid metal is delivered to the mould is of considerable importance in minimising surface defects of the resultant casting.

According to one aspect of the present invention there is provided a method of direct chill casting of light metals and their alloys through an annular mould comprising delivering liquid metal into the upper end of the mould and discharging that liquid metal at a multiplicity of positions adjacent the inner surface of the mould wall. The discharge may be only at said positions. Preferably the liquid metal is discharged in a substantially peripherally unbroken stream from a float that extends - ? -

substantially wholly across the mould to position adjacent the mould surface. Alternatively the liqui metal may be discharged through a plurality of tube having lower open ends adjacent the mould surface. Th liquid metal may be discharged downwardly into the moul in a direction parallel with the axis thereof. Alternatively it may be discharged downwardly into th mould in a direction at an acute angle to that axis.

Another aspect of the present invention provides apparatu for the direct chill casting of light metals and thei alloys through an annular mould comprising means fo discharging liquid metal within the mould at multiplicity of positions adjacent the inner surface of the mould wall.

In another aspect the present invention provides apparatus for the direct chill casting of light metals and their alloys through an annular mould comprising a liquid metal input tube having its lower open end disposed centrally within the upper part of the mould and arranged to discharge liquid metal vertically downwardly into the mould, a float device having upper and lower float plates in association with the lower end of the tube and closure means for said open end carried by the lower plate characterised in that the upper and lower plates extend substantially wholly across the mould with their peripheries terminating adjacent the mould wall, the arrangement being such that liquid metal is delivered into the space between the plates and discharged therefrom at a multiplicity of positions adjacent the inner surface of the mould wall. Vaπous embodiments of the invention will now be described by way of example and reference will be made to the single figure of the accompanying drawing which shows diagrammatically in vertical section a simplified view of an annular mould incorporating a float mechanism; the part on the right of the line A-B is a known construction and the part on the left of the line A-B represents one form of the present invention.

Referring to the drawing a conventional water cooled annular mould 1 has a wall 2 extending between an upper end 3 and a lower end 4. Around the lower end a peripheral gap 5 is formed so that cooling water supplied under pressure (by means not shown) to the interior of the mould is discharged as an annular curtain, indicated by the arrows -C- around the upper end of a casting 6 emerging from the mould.

A liquid metal delivering tube 7 is disposed centrally of the mould 1 with its open lower end 8 extending within the upper part of the mould and disposed so that liquid metal is discharged downwardly in the direction of the arrow -D-.

On the right hand side of the line A-B a conventional float mechanism is shown. This comprises an upper, annular, plate 9 floating on the surface 10 of the liquid metal in the mould and a lower plate 11 of generally the same shape and size as the plate 9 and held below the surface 10 by the pressure of liquid metal delivered from the tube 7. A closure 12 is disposed centrally of the plate 11 so that if the level of liquid metal in the mould rises unacceptably the closure 12 seals the lower end of the tube 7 to prevent further flow of liquid metal . With such known construction, liquid metal is delivere by the tube 7 to the space 13 between the plates 9 and 1 and is then discharged as indicated by the arrow -F- int a region of the mould lying intermediate its centre an its wall 2.

The emergent casting 6 is solid downwardly of a regio 14. Above that region there is a liquid core 15 of wel known shape.

With the arrangement described liquid metal is in contac with the mould wall and the emerging casting has a "shel zone" indicated to an exaggerated scale at 16 whic conventionally constitutes the defective surface of th casting usually requiring scalping.

On the left hand side of the line A-B we show a modifie float construction in which the upper plate 9a extends t a position 17 adjacent the wall 2 and has a downwardl turned rim 18. The lower plate 11a extends to a positio just short of the rim 18 to provide an annular gap 1 through which liquid metal is discharged in the directio of the arrow -G- (i.e.) effectively parallel with th axis of the mould.

We have found that with this arrangement the discharge o all the liquid metal from the float mechanism adjacen the cooled mould wall 2 significantly changes the shap and size of the liquid core 15a and, in consequence reduces considerably the thickness of the shell zone 16a. It will be understood that the gap 19 could be disposed so that the liquid metal is discharged more directly at the mould wall 2 (i.e.) at an acute angle to the axis of the mould.

As described the flow of liquid metal -G- is as a continuous annular curtain. The upper surface of the plate 11a could, however, be shaped to provide a multiplicity of discrete streams. In addition some liquid metal could be discharged into the mould at other positions across its width.

In another arrangement (not shown) the float mechanism need not be used and a plurality of delivery tubes 7 could be provided having their lower ends substantially evenly spaced around the mould wall 2 so as to discharge liquid metal directly thereagamst.

On test castings carried out using the float arrangement described above on the left of the line A-B in the drawing we have found:-

1) the effect on macrastructure and surface finish was - (a) to produce a less rippled surface (b) to decrease the shell zone depth from a range of

16 down to 8 mm to 8 down to 4 mm, and (c) to eliminate float patterns in the casting.

The deeper shell zone of the conventionally sized shell zone 15 was a coarse equiaxial structure for the whole width of the shell zone. However the shell zone 15a was less coarse towards the edge of the casting with the exception of the outermost 4 mm.

Claims

1. A method of direct chill casting of light metals and their alloys through an annular mould comprising delivering liquid metal into the upper end of the mould and discharging that liquid metal at a multiplicity of positions adjacent the inner surface of the mould wall.

2. A method according to claim 1 in which the discharge is only at said positions.

3. A method according to claim 1 or claim 2 in which the liquid metal is discharged in a substantially peripherally unbroken stream from a float that extends substantially wholly across the mould to positions adjacent the mould surface.

4. A method according to. claim 1 or claim 2 in which the liquid metal is discharged through a plurality of tubes having lower open ends adjacent the mould surface.

5. A method according to any one of the preceding claims in which the liquid metal is discharged downwardly into the mould in a direction parallel with the axis thereof.

6. A method according to any one of claims 1 to 4 in which the liquid metal is discharged downwardly into the mould in a direction at an acute angle to that axis.

7. Apparatus for the direct chill casting of light metals and their alloys through an annular mould comprising means for discharging liquid metal within the mould at a multiplicity of positions adjacent the inner surface of the mould wall.

8. Apparatus for the direct chill casting of light metals and their alloys through an annular mould comprising a liquid metal input tube having its lower open end disposed centrally within the upper part of the mould and arranged to discharge liquid metal vertically downwardly into the mould, a float device having upper and lower float plates in association with the lower end of the tube and closure means for said open end carried by the lower plate characterised in that the upper and lower plates extend substantially wholly across the mould with their peripheries terminating adjacent the mould wall, the arrangement being such that liquid metal is delivered into the space between the plates and discharged therefrom at a multiplicity of positions adjacent the inner surface of the mould wall.

9. A method of direct chill casting of light metals and their alloys substantially as herein described with reference to the single figure of the accompanying drawing.

10. Apparatus substantially as herein described with reference to that part of the single figure of the accompanying drawing to the left of the line A-B.