GB2078784A - Alloying Additive - Google Patents

Abstract

An alloying additive comprises a coilable rod of a metal or metal alloy having at least one continuous core of a metallic alloying constituent enclosed by the metal or metal alloy, and is made by boring a longitudinal hole in a billet, filling the hole with the constituent and extruding the billet to form a rod. The additive may be made to a melt by feeding the rod to the melt flowing along a launder from the furnace to a casting machine.

Description

SPECIFICATION Multiple Alloy Extrusion This invention relates to metal alloys and is particularly although not exclusively concerned with non-ferrous light metal alloys such as those of which the base metal is aluminium.

It is often desired to add to aluminium alloying constituents having a greater density than aluminium. It is well known that in such circumstances difficulties arise since the heavier constituents tend to settle in the melting furnace to contaminate the latter. Examples of such alloys include those produced for their free machining properties containing, for example lead and bismuth.

In the casting of billets of aluminium alloys it is normal practice to locate the casting machine as close as possible to its associated melting furnace in order to reduce the length of launder along which molten metal flows from the furnace to the casting machine. It is known to add to the melt minor constituents in small quantities by supplying these to the launder and particularly where such minor constituents are metallic it is known to feed them into the launder in the form of a thin wire uncoiled from a reel at a rate appropriately related to the flow rate of molten metal in the launder. Such arrangements have proved satisfactory and it has been found that distribution of such added constituents in the resultant cast billet has been satisfactory.

The problems outlined above concerning the addition of alloying constituents more dense than aluminium are heightened when the metals concerned, such as lead and bismuth, have melting points considerably lower than that of aluminium.

It is an object of the present invention to provide an improved method for casting metal alloys containing metallic alloying constituents. Another object is to minimise problems associated with the production of such alloys where added alloying constituents have a melting point lower than that of the metal or metal base alloy.

A further object is to provide an improved alloying additive and a method of making such additive.

According to one aspect of the present invention there is provided an alloying additive to be supplied to a metallic melt comprising a coilable rod of a metal or metal alloy having at least one continuous core of a metallic alloying constituent enclosed by the metal or metal alloy.

The additive is preferably made by preparing a billet of the metal or metal alloy boring at least one longitudinal hole therethrough filling the hole with the metallic alloying constituent and extruding the billet to form the rod. When a constituent has a melting point below that of the metal or metal alloy the hole is preferably filled with molten constituent.

According to another aspect of the present invention there is provided a method according to claim 8 in which the hole is filled with molten constituent.

The above and other aspects of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a cross section of an extruded aluminium rod with a core magnified five times and Figure 2 is a similar view of a rod with lead and bismuth cores.

In this specification where reference is made to a 'rod' this may be of circular or non-circular cross-sectional shape and includes wire, strip and ribbon and where reference is made to a 'billet' this may be of circular or non-circular cross-sectional shape.

Extrusion Using Lead and Aluminium Six 10 mm diameter holes were drilled 95 mm into a 100 mm long 67 mm diameter aluminium billet. The holes were filled with molten lead using argon shielding to prevent oxidation. When the lead had solidified the holes were plugged with 10 mm lengths of aluminium bar. The lead cored billet was then extruded through a 16 mm die at a starting temperature of 2500C. Details of typical extrusion conditions are given in Example 1.

Example 1 Extrusion of Lead Cored Billet Weight of billet 350 g Die diameter 16 mm Extrusion ratio 17.5 Billet temperature 2500C Extrusion pressure 1 9 mn/m2 (constant) Die temperature Cold Ram speed slow Follower pad 2500C Lubricant graphite Chamber temperature 2500C The resulting extrusion was 14 m long and had a smooth bright finish. It was cut into seven equal lengths and the transverse sections examined (Figure 1 and Example 2).

Example 2 Section Details of Lead Cored Extrusion Mean diameter of Section Pb strands % Pb by weight Start of extrusion 1 2.8 mm 49% 2 2.5 mm 42% 3 2.7 mm 47% 4 2.7 mm 47% 5 2.7 mm 47% 6 2.7 mm 47% End of extrusion 7 Pb ends These results showed a reasonably even dispersion of lead within the extrusion. They also indicated that the technique of extruding cored billets could produce aluminium rod containing large quantities of another metal evenly distributed through the length of the extrusion.

Extrusion of Lead/bismuth Cored Billet Following the aluminium-lead trial a billet containing alternate cores of lead and bismuth was produced. It was made in the same way as previously except that the lead cores were 9 mm diameter and those of bismuth 10 mm. This difference was necessary to achieve correct alloy composition in view of the density differences between the two metals.

The cored aluminium billet was extruded at a temperature of 2300C to avoid melting the bismuth although the die itself was preheated to 3500C to lower the starting pressure required. Details of the extrusion conditions are given in Example 3.

Example 3 Extrusion Data for Lead/bismuth Cored Billet Weight of billet 350 g Billet temperature 2300C Die diameter 12 mm Die temperature 3500C Extrusion ratio 31 Follower pad 2300C Extrusion pressure 26 mn/m2 Chamber temperature 230"C Ram speed very slow Lubricant graphite The transverse sections showed reasonable distribution of lead and bismuth (Figure 2).

Three sections were removed and their densities determined (Example 4). The differences in density noted were probably the result of local melting of the bismuth.

Example 4 Density of Three Sections of Pb/Bi Cored Extrusion Section Density 1 4.29 g/cc NB Theoretical density of 20% Pb, 20% Bi Alloy=3.85 g/cc 2 4.00 g/cc 3 4.23 g/cc A further series of tests was subsequently carried out using 99.8% aluminium cored with lead and bismuth to produce a suitable length of extruded bar for a coiling trial. Example 5 gives details of the conditions used for extrusion of billets 100 mm long and 67.5 mm diameter.

Example 5 Extrusion Data-Final Test Series 1st Run 2nd Run Weight of billet 360 g 350 g Die diameter 12 mm 12 mm Extrusion ratio 31 31 Extrusion pressure 1 6 mn/m2 19/25 mn/m2 Billet temperature 2200C 1800C Die temperature 2000C 1800C Follower rod temperature 2200C 1 800C Ram speed slow slow Lubricant graphite graphite+ The first test run again produced some surface defects in the form of bulges and slight tearing of the outer skin.

In the second test at a lower temperature a greater than normal application of graphite was made to the die. Approximately 12 metres of rod was extruded with only slight surface bulging occuring on the last 200 mm, possibly resulting from an excessive rise in temperature at the die face towards the end of the run.

The length of rod obtained from the second trial was easily formed into a coil of approximately 200 mm diameter.

Cored rod formed by the processes set out above can be fed to molten aluminium or aluminium base alloy flowing along a launder from a melting furnace to a casting machine to provide even dispersion of the alloying constituents in the resultant casting. The rate of feed must be appropriately related to the flow rate in the launder and variations in the proportions of alloying constituents may be obtained either by varying the feed rate or using different rods. More than one rod may be simultaneously fed to the launder.

Although primarily intended for non-ferrous light metal alloys such as aluminium it will be understood that the present invention is applicable more widely. For example in the casting of steels containing aluminium and manganese rods of aluminium containing manganese cores would be added to the launder.

Claims (12)

Claims

1. An alloying additive to be supplied to a metallic melt comprising a coilable rod of a metal or metal alloy having at least one continuous core of a metallic alloying constituent enclosed by the metal or metal alloy.

2. An additive according to claim 1 in which the rod is of a non-ferrous light metal or metal alloy.

3. An additive according to claim 2 in which the rod is of aluminium or aluminium alloy.

4. An additive according to any one of the preceding claims in which the rod has cores of different alloying constituents.

5. An additive according to claim 4 in which the rod has more than one core of at least one constituent.

6. An additive according to any one of the preceding claims in which at least one of the constituents has a higher density than the metal or metal alloy.

7. An additive according to any one of the preceding claims in which at least one of the constituents has a lower melting point than the metal or metal alloy.

8. A method of making the additive of any one of the preceding claims comprising preparing a billet of the metal or metal alloy having at least one longitudinal hole therethrough filling the hole with the metallic alloying constituent and extruding the billet to form the rod.

9. A method according to claim 8 in which the hole is filled with molten constituent.

10. A method of casting a metal alloy in which a metallic melt flows along a launder between a furnace and a casting machine comprising continuously feeding the rod of any one of the preceding claims to the melt in the launder.

11. A method according to claim 10 in which the melt is of the same metal or metal alloy as the rod.

12. An alloying additive substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawing.

1 3. A method of making an alloying additive substantially as herein described.

1 4. A method of casting a metal alloy substantially as herein described.