GB2366226A

GB2366226A - Die tooling

Info

Publication number: GB2366226A
Application number: GB0021333A
Authority: GB
Inventors: Martin Jarrett; Glenn Mccrickerd; Cecil Mitchell
Original assignee: Luxfer Group Ltd
Current assignee: Luxfer Group Ltd
Priority date: 2000-08-30
Filing date: 2000-08-30
Publication date: 2002-03-06
Anticipated expiration: 2020-08-30
Also published as: WO2002018071A1; AU2002213926A1; GB2366226B; GB0021333D0

Abstract

A die (2') for extruding aluminium and aluminium alloys in which an upstream entrance section has an entrance surface (13) which diminishes downstream to a downstream diminishing surface (14). A discontinuity (20) may be provided between the first entrance surface and a gap (16) may be provided between a final die surface (19) and a backer (7). A die can be divided into two parts at the discontinuity (20) so that the relative taper angles of surfaces (12 and 14) can be varied without replacing the whole die. This is useful to change the die configuration for a particular alloy to control the microstructure of the extruded material. The first die surface has the effect of suppressing non-preferred grain structures whilst the second surface has the additional benefit of improving the eventual surface finish of the extrusion.

Description

<Desc/Clms Page number 1> "DIE TOOLING". The present invention relates to a method of and die for extruding aluminium and aluminium alloys.

British Patent Specification No. 2285941A describes the use of an extrusion die having a frustro-conical upstream entrant section diminishing downstream followed by a cylindrical or rectilinear bearing section where opposed bearing surfaces are parallel to each other. Such a die is used for hot extruding 2000 series aluminium. alloys and whereas dies of this conformation have reduced peripheral coarse grain banding at certain speeds, it has been found that surface break up and/or deterioration of extruded material can exist under certain conditions.

According to the present invention, there is provided a die having an upstream entrant section diminishing downstream characterised in that the upstream entrant section has a first tapering surface and a second tapering surface downstream of the first surface. Preferably the first surface has less of an angular taper than that of the second surface.

The first surface has the effect of suppressing non- preferred grain structures, for example peripheral coarse grain (P.C.G.), while the second surface has the additional benefit of improving the surface finish of the extrusion.

In one embodiment of the installation, the upstream section is made with a first and a second part, the first part having the first surface and the second having the

second surface, the parts being separable so that the whole die can be adjusted for the particular alloy in use by, for instance, retaining the first part and changing the second part to provide a different taper. This is an economic way of changing the whole die configuration to control the microstructure although it may be preferable to form the die in one piece. in one emiDoctiment or trie invention, tne secona surrace starts upstream from a wider point of the whole die than that at the downstream end of the first surface. Thus the metal being extruded is allowed to preform its shape with the first shape and form the final shape with the second surface, the two surfaces being separated by a gap, the second surface of course being of a smaller cross-sectional area. The first and second surfaces may be rectilinear or be circular in cross-section. The first surface preferably tapers at 2-60 similar to that described in GB 2285941A but within a range of 1.5'-2.61 and within the disclosed range described in '1941A publication whilst the second surface tapers at an angle of preferably 71 and within a range of 30 to 450, but at a greater angle to that of the first surface. Nitrogen inerting and/or cooling ducting may be provided between the first and second parts where these are separate. The first and second surfaces may be nitrided. Upstream entrants to the die parts may be radiused or curved.

According to another aspect of the invention, a method of extruding aluminium and aluminium alloys comprises provided a die as set out above according to the first aspect of the invention and any of its supplementary features, and cooling and/or inerting the die with a flow of gaseous or liquid nitrogen according to a predetermined formula according to the cross-sectional aspect of this backer section, and the extruded shape.

Preferably the predetermined formula for flow rate of nitrogen for round bar is 3.142T (D+T) x 10-5 x 6V in m 3 /hour where T is the distance between the bar and backer, D is the bar diameter in mm and V is the extrusion speed in metres/min.

Preferably the predetermined formula -t-o flow rate Df nitrogen for flat bar is 2T (B + W + 2T) x 10-5 x 6V in M 3 /hour where T is the distance between the bar and backer, B is the bar thickness in mm, W is the bar thickness in mm and V is the extrusion speed in metres/min.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 shows the relation of die surfaces according to one embodiment of the invention where the upper section surfaces are continuous; Figure 2 is a similar view to Figure 1, shows a second embodiment of an invention where the upper secti-on surfaces are discontinuous;

Figure 3 is a similar view to Figure 2, but in a third embodiment where the die of Figure 2 is modified so as to be in two parts; Figure 4 shows the provision of nitrogen ducting for the second embodiment; and Figure 5 shows the provision of nitrogen ducting for a third embodiment. In Figure 1, a longitudinal cross-section of the die 2 shows a first and upstream entrant surface 3 continuing downstream to a second and downstream surface 4. A further downstream surface 5 has no taper. The first surface has a taper within the range 1.51 to 2.6' whilst the second surface has a taper within the range 3' to 45' and preferably 71. The first, second and further surfaces are respectively 20-100mm, 4-20mm and 0-12mm long,,whilst a 1 to 20mm wide gap 6 is provided between the downstream end of the further surface and the backer 7. The tapered form may be applied to a die for round or flat bar. In Figure 2 the first upstream entrant surface 13 of the upstream section 12 continues downstream with a non- tapered surface 18. The second surface 14 has a greater taper and a discontinuity 20 between the surfaces 18 and 14 to preform the extrusion at surface 18 before achieving the final shape at surface 19. The orifice of the die at surface 19 has a smaller cross-sectional area than that at surf ace 18. Surface 19 is non-tapered and is provided downstream of surface 14 with a gap 16

between surface 19 and backer 7. The first, second, third and fourth surfaces are respectively 20-100mm, 0- 12mm, 4-20mm. and 0-12mm. long, whilst a 1-50mm. gap 20 is provided between the second and third surfaces 18 and 14. Although the embodiment of Figure 2 is shown with the die as a single part, the die can be divided into two at the discontinuity 20 so that the relative taper angles of surfaces 12 and 14 can be varied without replacing the whole die. Thus adjustment to the die can be provided for differing aluminium alloys to be extruded. This modification is shown in Figure 3 where die 2 is split into die parts 2a and 2b. In Figure 4, nitrogen inerting or cooling either in gaseous or liquid form is ducted through duct 40 in die backer 71 to a ring feed duct 44 in die backer 71 . The nitrogen duct 44 exits via a number of ducts shown by example as duct 46 in backer 71 within the space between the backer and extruded metal to cool the die and extrusion and inhibit surface oxidation of the aluminium. alloy extrusion (i.e. "inerting"). In Figure 5 which shows two part die #,481', 49' , nitrogen is ducted to duct 56 from feed duct 54 in backer 17, through duct 55 in partr49'.. Duct 56 leads to a space 57 around extrusion 66 then through duct 58 to ring duct 59 in backer 17' Then nitrogen exhausts through a number of ducts shown typically as ducts 60 and 62 into the backer where a cylindrical or rectilinear space 64 is formed between the backer and extruding aluminium. 66.

In Figure 6 three die parts 47, 48' and 491 have nitrogen cooling and/or inerting from entry duct ' 7.) in outer die ring 47 to helical duct 72 also in ring 47. Duct 72 is bounded by the outer surface of inner die part 481. The helical duct 72 communicates with duct 73 between first and inner die part 481 and second die part 491 thence to space 571 around extrusion 66 then through duct 74 in part 49' to ring duct 59 and out through a number of ducts shown typically as 62 as in the embodiment shown in Figure 5. Die surfaces are generally nitrided.

Claims

CIAIMS 1. A die having an upstream entrant section diminishing downstream characterised in that the upstream entrant section has a first tapering surface and a second tapering surface downstream of the first surface.
2. A die as claimed in claim 1 wherein the first surface has less of an angular taper than that of the second surface.
3. A die as claimed in claim 1 or 2 wherein the first surface tapers inwards at an angle of between 1.5* and 2.60 to the axis (A) of the die.
4. A die as claimed in any one of claims 1 to 3 wherein the second surface tapers inwards at an angle of between 30 and 450 to the axis (A) of the die.
5. A die as claimed in any one of claims 1 to 4 wherein the first and second surfaces are on separate die parts.
6. A die as claimed in any one of claims 1 to 5 wherein a die bearing surface or surfaces depending on whether the die is circular or rectilinear has no taper with respect to the die axis (A) and is provided between the first and second surfaces immediately following the first surface.
7. A die as claimed in any one of claims 1 to 6 wherein the first and second surfaces are discontinuous.

<Desc/Clms Page number 8>
8. A die as claimed in any one of claims 1 to 7 wherein a space is formed between the first and second surfaces such as to be closed by an extrusion passing through the die.
9. A die as claimed in any one of claims 1 to 8 wherein the die is fitted to a backer arranged with ducting to direct nitrogen over an extrusion passing through the die.
10. A die as claimed in any one of claims 1 to 9 wherein ducting is provided to pass nitrogen through the die to the space formed between the first and second surfaces.
11. A die as claimed in any one of claims 1 to 10 wherein nitrogen ducting is provided around that part of the die adjacent the first die surface.
12. A die as claimed in claim 11 wherein the nitrogen ducting is helically formed between an outer element and an inner die part on which is formed the first die surface.
13. A die substantially as described with reference to any one or more of the accompanying drawings.