GB1594926A

GB1594926A - Method of die casting

Info

Publication number: GB1594926A
Application number: GB9718/78A
Authority: GB
Original assignee: GKN Group Services Ltd
Current assignee: GKN Group Services Ltd
Priority date: 1978-03-11
Filing date: 1978-03-11
Publication date: 1981-08-05
Also published as: FR2419127A2; FR2419127B2; IT7948286A0; IT1162482B

Description

(54) METHOD OF DIE CASTING (71) We, GKN GROUP SERVICES LIMITED, a British Company of Group Head Office, Smethwick, Warley, West Midlands, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to improvements in or modifications of the invention -described and claimed in our prior Patent No.

1 330471. The prior patent discloses a method of pressure die casting ferrous metals which require to be cast at very high temperatures such as cast iron at 1300"C and steel at 1600"C in an apparatus, claimed in Claim 1, comprising: (a) separable repeatedly usable dies de fining in combination a cavity; (b) means for moving said dies relatively towards and away from one another between open and closed positions; (c) an elongated shot duct having at one end a receiving station for receiving shots at an operating temperature sufficient to provide the metal in mol ten condition and at its other end a delivery station communicating with said cavity; and (d) a piston movable in said shot duct to feed said shots of molten metal into said cavity; wherein: (e) said shot duct comprises at least three components disposed in end to end relationship longitudinally of the shot duct, a first component being disposed at said delivery station and being formed of a material whose sur face remains in hard solidified form at the operating temperature resistant to penetration and abrasion as a re sult of fragmentation and displace ment of a solid state skin formed in the metal during casting, a second component being disposed at the re ceiving station and being made from a material which is free from enter ing into chemical and physical reac tion with the ferrous metal being cast and at least one further component intermediate said first and second components and being formed from a material resistant to thermal fatigue.

We have now discovered that metals which require to be cast at lower temperatures lying in the range 9000C to 1 1500C such as copper and copper alloys such as brasses and bronzes can be advantageously die cast by utilising an improvement in or modification of the invention of our prior patent.

According to the present invention we provide a method of pressure die casting metal into a cavity defined between separable repeatedly usable dies provided with means for moving said dies relatively towards and away from one another between open and closed positions, the method comprising the steps of (a) introducing a shot of molten metal, at a temperature lying in the range 9000C to 1150"C, into a first com ponent of a shot duct, located at a receiving station at one end of the shot duct, the surface of the first component contacted by the metal of the shot being free from entering into chemical and physical reaction with the metal of the shot, (b) transferring the shot longitudinally of the shot duct, by means of a piston movable in the shot duct, to feed the shot from a delivery station at the other end of the shot duct into said cavity, (c) the metal of the shot being sequen tially contacted during its passage along the shot duct with the surface of a second component made of a material resistant to thermal fatique and then with the surface of a third component which remains in hard solidified form at the operating tem perature resistant to penetration and abrasion as a result of fragmentation and displacement of a solid state skin formed in the metal during casting.

The method of the present invention can be used to make copper or copper alloy die castings of a wide range of shapes and weights but the method is particularly useful for the manufacture of rotors for electric motors which comprise a plurality of ferrous laminations cast in a copper matrix. Preferably the ferrous laminations are made from low carbon steel sheet of guaranteed composition, Si-free, e.g. Nucore 800.

Thus a further step of the method may comprise positioning a plurality of ferrous laminations on a jig in said cavity prior to introducing and transferring said shot of molten metal.

The invention will now be described by way of example with reference to the accompanying drawings wherein: FIGURE 1 is a diagrammatic side elevation of a rotor for an electric motor made by a method embodying the invention FIGURE 2 is an end elevation of the rotor of Figure 1, FIGURE 3 is a fragmentary sectional view on the line 3-3 of Figure 1, and to an enlarged scale.

FIGURE 4 shows diagrammatically a die casting machine for use in the method embodying the invention, and FIGURE 5 shows a vertical cross section through the axis of the shot duct of the machine of Figure 2 on a larger scale.

Referring now to Figures 1 to 3, a rotor for an electric motor is shown generally at 110 and comprises a plurality of electrical sheet steel annular laminations 111. A pair of diametrically opposite slots 112 are formed in the wall of the central aperture 113 of each lamination and a plurality of circular apertures 114 are formed in each lamination. In the present example 13 apertures 114 are provided.

The laminations are orientated so that each lamination is angularly off-set relative to its neighbours so that a radius Rl through the centre of the aperture 114 in one end lamination is inclined at an angle of 20 to a radius R2 through the centre of the corresponding aperture in the opposite end lamination. Copper is cast around the laminations and passes through the apertures 114 as indicated at 115 to form the rotor for a squirrel cage motor. The angle may be varied from 200 according to the motor design.

In accordance with the method of the present invention the rotor described above is manufactured by assembling a plurality of the electrical steel annular laminations 111 onto a mandrel, not shown with adjacent laminations angularly off-set as described hereinbefore and the mandrel is constructed so as to load the laminations together under pressure. The assembly of mandrel and loaded laminations is then introduced into a die cavity 12 of a pressure die casting machine shown in Figures 4 and 5. The apparatus comprises separable dies 10 and 11 which define a die cavity 12 and which separate along a parting plane X.

Such dies can be moved between a closed position. as shown in Figure 5, and an open position in which the die 11 moves to the left away from the die 10, by any suitable mechanism, either mechanical or hydraulic, of known form.

Figure 4 shows a known form of machine employing a mechanical mechanism for closure of the dies 10 and 11. This machine includes a bed 1 having a mounting member 2 which carries the die 10 in a fixed position. The movable die 11 is carried on a slide plate 3 which is slidable along horizontally extending bars 4 which are fixed in position relative to the bed 1. The slide plate 3 is movable along the bars 4 by means of a toggle mechanism indicated generally at 5. The toggle mechanism 5 is operable by means of a piston and cylinder unit 6 which is carried by a longitudinally adjustable mounting member 7. A connecting rod 6a extends from the unit 6 to the toggle mechanism 5. Also fixedly mounted on the bed 1 there is a piston and cylinder unit 8 having a connecting rod 8a for operation of the shot duct 14 which is hereinafter described in detail.

The dies 10 and 11 are made of a material which is capable of repeated use to form the cast copper rotors in the die cavity 12.

Although in this example the apparatus is described in connection with the performance of the method to make a copper rotor it will be appreciated that apparatus and the method embodying the invention may be utilised to cast other articles in copper than rotors for electric motors and that the method may be used to cast other metals than copper, for example, copper alloys or nickel, or cobalt, based alloys.

The dies 10 and 11 are either made of, or lined with, a metal of a higher melting point than the copper or other metal to be cast, or have a rate of heat dissipation, either natural or produced by cooling means provided in association therewith, which maintain them at a sufficiently low temperature to enable them to withstand repeated use.

Typically the dies may be formed of molybdenum or an alloy thereof.

Preparatory to casting into the die cavity 12 a medium may be sprayed onto the surface of the die cavity to facilitate stripping the cast article therefrom and a suitable medium for this purpose is graphite suspended in a suitable carrier, pr carbon blank deposited from an acetylene torch.

One or both of the dies is formed with a channel or gate 13 by means of which the metal to be cast is fed into the die cavity, in this example, upwardly and preferably into the lowermost part of the die cavity.

In other cases metal may be fed to other parts of the die cavity and in directions other than upwards.

The metal is fed to the lower end of the gate 13 by means of the shot duct 14, and which is formed or constructed to define a horizontal, or approximately horizontal, bore 15 conveniently of circular shape in cross-section and of uniform diameter throughout its length (except for a terminal portion at the forward end as hereinafter described). In some cases the bore 15 could, however, be inclined to the horizontal.

The cast metal is delivered into the bore 15 at a receiving station 16 and is moved along the bore by a piston 17 connected to a suitable operating mechanism, either mechanical or hydraulic, and such as the piston and cylinder unit 8. The metal thus is forced from the bore 15 at a delivery station 18 to pass upwardly through the gate 13 under pressure.

The pressure employed may vary widely but it is contemplated that pressures of as much as 5000 to 6000 lbs. per square inch may be obtained during the operation of feeding the molten metal into the die cavity.

Again delivery of molten metal into the bore may be effected in a variety of ways, one of which is illustrated diagrammatically and consists in pouring the metal from a pot 19 through an opening 20 leading to the re ceiving station 16, the metal being maintained at the required temperature, for ex ample in the region of 1100 to 11500C for copper and 90e1000"C for brass, by any suitable heating means provided in association with the pot.

Referring now specifically to the construction of the shot duct 14, this comprises a plurality of inner components, these being a front liner or insert 21 at the delivery station, an intermediate liner or insert 22, and a rear liner or insert 23 at the receiving station. These inserts are supported collectively partly by an outer casing comprising a front casing component 24 and a rear casing component 25, as well as by the die 10 which, as will be evident from the accompanying drawing, engages and supports the forward insert or liner 21.

The front casing component 24 has at its forward end a flange 30 through respective apertures in which screws 31 are passed to secure the front casing component 24 to the fixed die 10. The front casing component 24 includes a generally tubular body portion within which. part of the generally tubular rear casing component 25 is received. The rear casing component 25 has an external flange 35 mid-way along its length. The flange 35 abuts the rear end of the front casing component 24 and is apertured for the passage of screws 34 whereby the casing components 24 and 25 are rigidly secured together.

The front liner or insert 21 is located in an aperture in the fixed die 10 and is largely supported thereby. However, the insert 21 extends outwardly from the fixed die 10 and at its rearward end is supported particularly by the flange 30 of the forward casing component 24. At its rear end, the insert 21 is formed with an outwardly directed flange 21a which is located between the forward end of the rear casing component 25 and a radially inward extension of the flange 30 at the forward end of the front casing component 24. If desired the flange 21a may be omitted.

The intermediate liner or insert 22 is supported by the forward portion of the rear casing component 25 and at its forward end abuts the flange 21a of the insert 21. The rear liner or insert 23 is supported by the rear portion of the rear casing component 25 and is in abutting relation with the liner 22. At its rearward end, the liner 23 abuts an inturned lip 25a afforded by the casting component 25. The insert 23 is formed with an aperture 20a which registers with a corresponding aperture 20b formed in the rear portion of the rear casing component 25 collectively to define the opening 20 through which the molten metal can be poured into the interior of the bore 15.

As can be seen at 37, the external surface of the forward portion of the rear casing component 25 is somewhat recessed so that there is a small clearance space, extending over most of the length of the forward portion of the front casing component. Additionally, whilst the internal diameter of the rear casing component 25 is nominally uniform throughout its length, the diameter may be locally increased by a few thousandths of an inch in the regions indicated at 38 and 39 so as to allow for a small amount of outward expansion of the liners 22 and 23 in those regions and to prevent undue compressive stress being exerted on these liners at the working temperature of the assembly.

The rate of heat loss from molten metal passing along the bore 15 and situated within the front liner or insert 21 is considerable, since heat is conducted therefrom to the die 10 and there is consequently a tendency for a skin or solidified layer of metal to form immediately adjacent to the interior surface of the front liner or insert 21, particularly in the region indicated at 26. In the course of forward movement of the piston 17, this skin tends to be disrupted and pieces of it may be forced outwardly to penetrate the inner surface of the front liner or insert 21.

Continued forward movement of the piston 17 tends nevertheless to force these pieces forwardly dragging with them particles of metal from the surface layer of the liner or insert 21 leading to rapid erosion of this surface layer.

Accordingly, it is desirable that the front liner or insert 21 should be made of a material which affords relatively low thermal conductivity in order, so far as possible, to minimise the freezing of the metal undergoing casting and avoiding the formation of, or reducing the thickness of, the skin referred to. At the same time it is desirable that the front liner or insert should be in contact with a heat sink so that, despite the low thermal conductivity, heat is conveyed away from this component to an extent which prevents this component attaining so high a temperature that its properties of hardness are so adversely affected as to offset the value of the low thermal conductivity. Accordingly it is contemplated that the optimum values with respect to thermal conductivity and the capacity of the heat sink can be selected.

For casting copper and copper alloys it is contemplated that the front liner or insert may be made of a ferrous metal and in particular a steel of a composition designed to withstand abrasion under conditions of high temperature. One steel suitable for this purpose is steel of the composition utilised for hot working forging dies, preferably the component being subjected to hardening and nitriding. One particularly suitable steel is that of A.I.S.I. specification H13. The composition of this steel is as follows: carbon 0.3 to 0.4%, manganese 0.2 to 0.4 ,Xo, silicon 0.8 to 1.2, chromium 4.7 to 5.5, vanadium 0.8 to 1.2%, molybdenum 1.2 to 1.75%, balance iron.

Alternatively, the front liner or insert 21 may be made of a non-ferrous metal. In this category, it is contemplated that the refractory metals might be utilised such as tungsten, platinum, molybdenum and their alloys, particularly an alloy of molybdenum known by the designation TZM which contains 0.5% titanium and 0.1% zirconium.

Further alternatively non-ferrous metals which might be employed include the socalled "super alloys" which are based on nickel and chromium and the like particularly those known as Rene 41 and Nimonic (Registered Trade Mark).

Another alternative material which may be employed for this component is a ceramic material. Particularly suitable ceramics for this purpose are silicon nitride, and silicon carbide and zerconia. In this case the ceramic material would be in the form of a liner supported externally and maintained in a state of compression by an outer tube made, for example, from a steel such as that mentioned above.

It would also be possible to employ materials of the type known as "cermets" and comprising a mixture of ceramic and metallic components.

All of these materials have ability to maintain a reasonably hard surface to define the bore 15 at the delivery station at the temperature at which the copper or copper alloys are required to be cast. Ceramic and cermet materials especially are also resistant to penetration by any pieces of the skin previously mentioned.

Any deficiency in the matter of transverse rupture strength i.e. the resistance of the shot duct to rupture as a result of internal pressure applied to the walls thereof and acting in a direction transverse to the longitudinal axis of the shot duct, would be made good by the additional complement of transverse rupture strength afforded by the front casing component 24, particularly the flange 30 provided at the forward end thereof and which abuts the die 10 to which it is secured by screws or other suitable fastening elements at the position indicated at 31.

A further factor in the operating conditions is that the corner 27 formed at the junction of the interior surface and forward end surface of the front liner or insert 21 is subjected to severe thermal shock and, to minimise failure from thermal fatigue, it is preferred that this corner be rounded as shown. A typical radius when the bore 15 has an internal diameter of about 1 t inches would be 9 of an inch, the insert 21 having a wall thickness of about k of an inch.

Additionally, on completion of the feeding operation, a plug 28 of metal remains in the bore 15 adjacent to the delivery station 18, such plug being positively expelled by the piston 17 upon solidification of the cast article in the die cavity 12. To facilitate expulsion of this plug and minimise wear on the surface of the bore, the terminal portion of the front liner or insert 21 is made of divergent form, as indicated at 29. A typical divergence (measured as the semi angle of the cone) would be 50, and the axial dimension over which such divergence is present would typically be Q of an inch for a bore of the diameter previously mentioned.

Instead of the forward extremity of the shot duct, in which the solidified plug 28 forms, being formed as an integra] part of the front liner or insert 21, it could be structurally separate therefrom. For example, it could comprise an insert of molybdenum, or the alloy thereof mentioned above, keyed into the die 10 so as to be replaceable.

Alternatively, the die 10 itself might be shaped to afford a part equivalent to the for ward extremity of the insert 21 as shown.

As a further possibility, the front liner or insert 21 might be replaced entirely by a bore formed in the die 10.

The intermediate liner or insert 22 is subjected to somewhat differing conditions, in that the major problem in this case is one of thermal fatigue. Accordingly, whilst any of the materials previously mentioned for possible use in respect of the component 21 may be employed, it is contemplated that advantageously steel of the A.I.S.I. specification H13 may be best suited to this component.

It will be noted, however, that in the event of employing a material having low transverse rupture strength, for example one of the ceramic materials mentioned, again any deficiency in this respect is made good by the presence of both the front casing component 24 and the forward portion 32 of the rear casing component 25 which are-assembled in concentric relation with each other and with the intermediate liner or insert 22.

The degree of radially outward heat conduction may be controlled by selecting the degree of tightness or interference between these concentrically assembled components, or by deliberately providing clearance spaces between them if desired, either along their whole lengths or at selected positions, so as to control the operating environment of the intermediate liner or insert 22.

In respect of the rear liner or insert 23, the conditions of operation again differ, in that the observed area of maximum erosion occurs at the point of impact or the molten metal stream entering the bore 15 through the opening 20, this point of impact coinciding with the forward end of the arrow 33.

Erosion at this position is believed to be due partly to fluid friction but also to an appreciable extent by chemical and/or physical action between the cast metal and that of which the component 23 -is made (assuming that it is made of a metal).

Although, therefore, again it is contemplated that any of the materials already mentioned in respect of the component 21 may be employed it is probable that good results would be attained either (a) by using a metal which does not enter into any chemical and/or physical reaction with the metal to be cast for example the component 23 may be made of molybdenum or tungsten or alloys thereof when cast ing copper; or (b) by using a non-metallic material such as a cermet or one of the cer amics already mentioned.

In either case any deficiency of transverse rupture strength would be made good by the rearward portion of the rear case component 25. Again this can closely embrace the rear liner or insert 23 along the entire length of the latter, or radial spaces may be left if desired to control the rate of heat transfer in an outward radial direction.

It is particularly to be noted that whilst the materials of which the inserts 21, 22 and 23 are made are chosen respectively to suit the different operational conditions encountered by these components, it is possible in some cases for all three inserts to be made from the same material, especially H13 steel, and for the service life of the shot duct thus formed to be materially Im-.

proved relative to prior art shot ducts which are not divided into longitudinally successive sections. Merely forming the shot duct inthree or more sections is believed to improve the thermal stability of the construction and therefore prolong its service life, but where, as in- the embodiment illustrated, the liners are mounted in a casing, the possibility of controlling the rate of outward heat transfer as mentioned above further affords an opportunity to ensure that the optimum environmental conditions exist in all regions of the duct even where all the liners are made of the same material.

It will thus be seen that in accordance with the invention different regions of the shot duct may be formed from different materials and/or the environmental conditions in different regions of the shot duct can be controlled, particularly as regards the rate of outward heat transfer, to suit the particular requirements of the different regions. It is preferred that the delivery station component and the intermediate component are made of steel of AISI H 13 designation or like composition and the receiving station component is made of refractory metal, particularly when casting copper.

The components described may be secured together in- any suitable manner as, for example, by the provision of screws or other fastening element at the position 34 extending through the flange 35 of the rear casing component into threaded bores in the front casing component 24.

Particularly, where one or more of the liners or inserts is formed of a ceramic- ma- terial, or other material having a comparatively low transverse rupture strength, the casing may include an additional sleevelike component which is in direct contact with the liners throughout the whole length of the shot duct. In this case, the liners collectively may present an external surface which tapers slightly from end to end, preferably decreasing in cross-sectional dimensions in a direction from the receiving station towards the delivery station although the opposite taper could be utilised.

The additional casing component would then be of complementary taper so as to be assembled with the liners as a press fit so that the -liner is supported by the casing at all positions along its length. This arrangement is the subject of our Specification No.

1,323,685 which reference may be had for a fuller description.

However, it would be possible for the casing components to be omitted and for the shot duct to be formed from a plurality of longitudinally successive components which are secured directly together without being-supported by such a casing providing such compbnents are designed toafford the requisite transverse rupture strength.

A rotor having a diameter of 48 mm a length of 30 mm and a weight of 335 gins has- been cast using the method of the present invention and has been found to be sound etc. The weight of copper was 105 gums.

Although the particular case of the manu facture - of a rotor -for an electric motor by the rnethod embodying the invention has been described hereinbefore if desired copper die castings of other shapes and weights may be made utilising the method embodying the invention and in addition the methodmay be utilised for other metals and alloys such was brasses or bronzes, which require to be introduced into the shot duct at temperature lying in the range 900--1150"C.

WHAT WE CLAIM IS:- 1. A method of pressure die casting metal into a cavity defined between separable repeatedly usable dies provided with means for moving said dies relatively towards and away from one another between open and closed positions, the method comprising the steps of (a3" introducing a shot of molten metal, at a temperature lying in the range 9000C to 1150"C, into a first cbm- ponent of a shot duct, located at a receiving station at one - end of the shot duct, the surface of the first component contacted by the metal of the shot being free from entering into chemical and physical reaction - with j the metal of the shot, (b) tr nsferring the shot longitudinally of the shot duct, by means of a piston movable in the shot duct, to feed the shot from a delivery station at the other end of the shot duct into said cavity, W the metal of the shot being sequen tially contacted during its passage along the shot duct with the surface of a second component made df a material resistant to thermal fatique and then with the surface of a third component, said surface remaining in hard solidified form at the operating temperature resistant to penetration and abrasion as a result of fragmenta tion and displacement of a solid state skin formed in the metal during cast ing.

2. A method according to Claim 1 wherein the metal of the shot is copper.

3. A method according to Claim 2 wherein the copper is introduced into the first component at a temperature lying in the range 11000C to 11500C.

- A method according to Claim 1 wherein the metal of the shot is a copper alloy or a - cobalt based alloy or a nickel based alloy.

5. A method according to any one of the preceding claims including the additional step of positioning a plurality of ferrous laminations on a mandrel in said cavity prior to introducing and transferring the shot.

6. A method according to any one of the preceding claims wherein at least two of the components are made of different materials.

7. A method according to any one of the preceding claims wherein said delivery station component is formed from a metal.

8. A method according to any one of the preceding claims wherein said receiving station component is formed from a metal.

9. A method according to any one of the preceding claims wherein the intermediate component is formed from a metal.

10. A method - according to any one of Claims 7 to 9 wherein the metal comprises a ferrous alloy.

11. A m

Claims

**WARNING** start of CLMS field may overlap end of DESC **. then be of complementary taper so as to be assembled with the liners as a press fit so that the -liner is supported by the casing at all positions along its length. This arrangement is the subject of our Specification No. 1,323,685 which reference may be had for a fuller description. However, it would be possible for the casing components to be omitted and for the shot duct to be formed from a plurality of longitudinally successive components which are secured directly together without being-supported by such a casing providing such compbnents are designed toafford the requisite transverse rupture strength. A rotor having a diameter of 48 mm a length of 30 mm and a weight of 335 gins has- been cast using the method of the present invention and has been found to be sound etc. The weight of copper was 105 gums. Although the particular case of the manu facture - of a rotor -for an electric motor by the rnethod embodying the invention has been described hereinbefore if desired copper die castings of other shapes and weights may be made utilising the method embodying the invention and in addition the methodmay be utilised for other metals and alloys such was brasses or bronzes, which require to be introduced into the shot duct at à temperature lying in the range 900--1150"C. WHAT WE CLAIM IS:-

1. A method of pressure die casting metal into a cavity defined between separable repeatedly usable dies provided with means for moving said dies relatively towards and away from one another between open and closed positions, the method comprising the steps of (a3" introducing a shot of molten metal, at a temperature lying in the range 9000C to 1150"C, into a first cbm- ponent of a shot duct, located at a receiving station at one - end of the shot duct, the surface of the first component contacted by the metal of the shot being free from entering into chemical and physical reaction - with j the metal of the shot, (b) trànsferring the shot longitudinally of the shot duct, by means of a piston movable in the shot duct, to feed the shot from a delivery station at the other end of the shot duct into said cavity, W the metal of the shot being sequen tially contacted during its passage along the shot duct with the surface of a second component made df a material resistant to thermal fatique and then with the surface of a third component, said surface remaining in hard solidified form at the operating temperature resistant to penetration and abrasion as a result of fragmenta tion and displacement of a solid state skin formed in the metal during cast ing.

2. A method according to Claim 1 wherein the metal of the shot is copper.

11. A method according to Claim 10 wherein the ferrous alloy comprises a steel of the ATSI designation H13.

12. A method according to any one of Claims 7 to 9 wherein the metal comprises a non-ferrous metal.

13. A method according to Claim 12 wherein the non-ferrous metal is one of the "super-alloys".

14. A method according to Claim 12 wherein the non-ferrous metal is a refractory metal or an alloy thereof.

15. A method according to Claim 14 wherein the metal comprises tungsten, platinum, molybdenum or alloys thereof.

16. A method according to any one of the claims 1 to 6 wherein said delivery station component is formed from a nonmetallic material of low thermal conductivity in contact with a heat sink to prevent said delivery station component attaining so high a temperature that its properties of hardness are adversely effected.

17. A method according to any one of Claims 1 to 6 wherein the receiving station component is formed from a non-metallic material.

18. A method according to any one of

Claims 1 to 6 wherein the intermediate component is formed from a non-metallic material.

19. A method according to any one of Claims 16 to 18 wherein non-metallic material comprises a ceramic material.

20. A method according to Claim 17 wherein said ceramic material comprises silicon nitride, silicon carbide or zircoma.

21. A method according to any one of Claims 16 to 18 wherein said material comprises a cermet.

22. A method according to any one of Claims 1 to 9 wherein the delivery station component and the intermediate component are made of steel of AISI designation H13 and the receiving station component is a refractory metal.

23. A method according to any one of the preceding claims wherein one or more of said components are mounted in a casing supporting the components externally and made of a material and dimensions which provide alone, or in combination with the components, the requisite transverse structure strength.

24. A method according to Claim 23 wherein the degree of radially outward heat conduction is determined by the degree of tightness or interference between the casing and said one or more components therein.

25. A method according to Claim 24 wherein the degree of radially outward heat conduction is controlled by providing at least one clearance space between the casing and said one or more components therein.

26. A method according to any one of the preceding claims including a component at the delivery station which is limited in length to that part of the shot duct in which a solid plug of metal forms after casting.

27. A method according to Claim 26 wherein said delivery station component is releasably located in said die.

28. A method according to any one of Claims 1 to 26 wherein said component at the delivery station is integrally formed with the die.

29. A method according to Claim 28 wherein said delivery station component is limited in length to that part of the shot duct in which a solid plug of metal is formed after casting.

30. A method according to any one of the preceding claims wherein the corner and the junction of the bore of the shot duct and the end thereof at the delivery station is radiused.

31. A method according to Claim 30 wherein the internal bore of said slot duct is immediately adjacent to said corner is of forwardly increasing cross sectional dimensions to facilitate removal of the solidified plug of metal after casting.

32. A method substantially as hereinbefore described with reference to the ac companying drawings.

33. A die casting made in accordance with the method claimed in any one of the preceding claims.

34. A rotor for an electric motor comprising a plurality of ferrous laminations in a die cast copper matrix and made by die casting the copper in accordance with the method claimed in any one of Claims 1 to 31.