GB2145016A

GB2145016A - Manufacturing a composite tube of dissimilar metals or alloys

Info

Publication number: GB2145016A
Application number: GB08411685A
Authority: GB
Inventors: Clifford John Barfield; Roger Charles Eassom
Original assignee: Darchem Ltd
Current assignee: Darchem Ltd
Priority date: 1983-05-09
Filing date: 1984-05-08
Publication date: 1985-03-20
Also published as: GB2145016B; GB8411685D0; GB8312693D0

Abstract

A tube of the first metal is formed with a recess in which the second metal is applied. Alternatively, two tube sections of the first metal are spaced end-to- end in a mould and the second metal cast into the space. The composite tube is then machined to its final dimensions. In the preferred embodiment the article is a high pressure tube (Fig. 1) for use in a proportional solenoid operated valve where the first metal is a magnetic material (12, 14) and the second metal is a non-magnetic material (10) which may have been cast into the recess whilst the tube is positioned in a mould, or flame- melted into the recess in the tube, the tube then being machined to provide two sections of magnetic material separated by a band of non-magnetic material. <IMAGE>

Description

SPECIFICATION Composite metal articles The invention relates to the manufacture of composite articles comprising dissimilar metals or alloys, more particularly magnetic and non-magnetic metals and/or alloys.

The operation of certain types of electro-magnetically actuated hydraulic valves relies upon the accurately controlled movement of a plunger within a tube of magnetic materials but having one or more "gaps" of non-magnetic material at intervals along its length, the energising solenoid coil being disposed around the tube.

In the past such tubes have been manufactured by brazing or welding together separate components of magnetic and non-magnetic material machined and assembled to fine tolerances but since the contour and definition of the surfaces of transition between the magnetic and nonmagnetic material and the concentricity of every detail is important to the accuracy of the operation of the valve, the procedure is both complex and costly. Furthermore, the quality of the brazed or welded joint must be such as to withstand extremely high operating pressure.

One object of the present invention is to facilitate the manufacture of composite articles of the kind referred to and accordingly we propose a method for manufacturing a composite article comprising dissimilar metal or metals and/or alloy or alloys, in particular magnetic and nonmagnetic metals and/or alloys, the method comprising forming or positioning one or more parts of the composite article so as to define a space corresponding to or including that part of the article to be formed of the metal or alloy having the lower melting point, and applying the said lower melting point metal or alloy in situ.

The said one or more parts may be positioned in a mould so as to define with the mould the space. The lower melting point metal or alloy may be injected into the mould in a molten state or may be in solid form e.g. in the form of a loose or compacted powder, and placed in the cavity for melting during subsequent heating.

Alternatively, the said one part may be formed with a recess into which the metal or alloy or lower melting point is deposited by melting with a high temperature gas flame.

When manufacturing high pressure tubes of the kind described above for proportional solenoids, two or more sections of magnetic material may be joined together in a mould by casting the non-magnetic material in situ therebetween but we prefer to form a recess or groove around either the interior or exterior surface of a tube, apply the non-magnetic material to the recess or groove and subsequently machine away excess magnetic and non-magnetic material to leave two tubular portions of magnetic material connected by a band of the non-magnetic material. Preferably, the recess is formed about the exterior surface of the tube and the method comprises rotating the tube about its axis and applying the non-magnetic material to the recess by flame melting as the tube rotates.

Alternatively, where the non-magnetic material is cast within a mould separate from the article a compact of non-magnetic material having a green density of up to 85-90%, may be formed e.g. as a split-ring, to fit into the recess or groove, in which case the volume of the mould cavity need not be substantially greater than the volume of the recess or groove into which the nonmagnetic material is to be cast. In another arrangement, a mould cavity is provided which is large enough to form a reservoir for a quantity of powder that will produce sufficient of the molten metal metal or alloy to fill the recess or groove and is so disposed that molten metal or alloy will flow under gravity into the recess or groove, and there bond with the host metal on solidification.

However, the preferred embodiment consists of flame-melting comprising feeding a rod of the non-magnetic material towards said recess, and flame heating the end of the rod to melt same so as to apply molten drops thereof to the recess.

Suitable non-magnetic materials include copper and/or nickel with additions of phosphorus, silicon, manganese or zinc. In the case of composite high pressure tubes for proportional solenoids, the magnetic material is usually steel and we prefer to use an alloy consisting of copper and a nickel phosphorus alloy such as Nicrobraz as the non-magnetic material.

The invention also includes a composite article comprising dissimilar metals or alloys, the lower melting point metal or alloy having been applied in situ according to the above method.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross-section through a composite high pressure tube for use in a proportional solenoid operated valve; Figure 2 is a schematic cross-section through a mould for casting a composite blank from which the tube of Fig. 1 is machined; and Figure 3 is a schematic perspective view of an alternative preferred apparatus for producing a composite blank from which the tube of Fig. 1 is machined by flame melting the copper base alloy into the recess.

The finished high pressure composite tube shown in Fig. 1, is formed mainly of steel but has a cast copper alloy band or insert 10 integral with and defining a magnetic 'gap' between, the steel tube portions 1 2 and 1 4. To produce the tube shown in Fig. 1 a recess or groove 20 of a desired shape is machined around the outer periphery of a steel tube 22 as shown in Figs. 2 and 3. The recess 20 is preferably trapezoidal in cross-section, (as seen in Fig. 2) the edge 24 of the recess (the upper edge in Fig. 2) being inclined at 30 to the longitudinal axis of the tube.

In the method of Fig. 2 the tube 22 is first degreased and then painted with Nicrobraz Green stop-off to within 1 /6" to 1 /8" of the recess. It is important not to contaminate surface of the recess.

The tube 22 is then inserted into a cylindrical graphite mould 26 which may be one of a number of moulds formed in a single graphite block, and, Saffil (registered Trade Mark) low density matt 28 is packed into the annulus 30 defined between the exterior of the tube 22 and the bottom of the mould, so as to retain the tube and inhibit the flow of alloy along the tube.

Although not shown in the Figure, suitable graphite packing pieces are used to build up the bottom of the mould to an extent determined by the length of the tube projecting from the bottom of the mould which is then closed by placing a plain graphite platen over the packing pieces. The mould is then inverted to stand on the platen.

The mould cavity 32 including the recess 20, is then filled with a mized powder comprising 90 parts by weight copper and 10 parts by weight Nicrobraz which is a proprietory nickel, phosphorus alloy. To tamp down the powder, the mould is vibrated and more powder added, if necessary, to fill the cavity. The mould is then placed in a vacuum furnace (not shown).

In the vacuum furnace, evacuated to below 1 0 - 3m bar, the temperature of the charge which may comprise a bath of similar moulds, is raised to and held at 900"C for up to 20 minutes to reduce oxides on the parent metal and casting material. After closing the vacuum valve, the furnace is then charged with an atmosphere of nitrogen to a pressure of 20 m bar so as to avoid vapourisation of the copper during melting which is effected by raising the temperature to 1120"C. After maintaining this temperature for up to 10 minutes to ensure equalisation, the heat is switched off and the charge allowed to cool to a temperature below about 900"C. Once the alloy has solidified the nitrogen pressure is increased to 600 m bar and the cooling fan started to bring the temperature below 100 C prior to removing the charge from the furnace.

Finally, the tube 22 is bored out to expose the cast copper alloy band and the exterior of the tube is machined to shape.

In the method of Fig. 3 the copper base alloy infill is applied to the machined recess 20 of the steel tube 22 by flame-melting the infill alloy from a flux coated alloy wire. Thus, in Fig. 3, the steel tube 22 is mounted for rotation in the direction of arrow A and is positioned such that the recess 20 is aligned with a flux coated alloy wire 36 heated to melting point by means of an oxy-acetyJene flame 38. The molten drops of the alloy melted from the wire 36 are deposited in the recess and compressed air jets 40 rapidly solidify the alloy to maintain it within the recess 20 to form a composite with the steel tube.

The oxy-acetylene flame 38 is positioned so as to heat the previously flux-coated tube recess 20 to the required temperature for the alloy to 'wet' and subsequently build up to fill the volume of the tube recess 20. Moreover, the speed of rotation of the tube 22, the positioning and infeed of the flame-melted wire 36 and the air jets 40 are correlated so that drops of the alloy are added to the machined recess 20 during a single rotation of the tube 22. The setting of the air jets 40 and the oxy-acetylene flame 38 are adjusted to hold the molten alloy for a time sufficient to allow the maximum amount of oxides, flux and other deleterious materials to surface from the molten alloy before solidification.

In a particular example a steel tube of length 50mm and diameter 21.4mm is machined to provide a recess 2.2mm deep. The recess is trapezoidal in cross-section reducing from a width of 8mm at the surface of the tube to an internal width of 3.5mm. The recess is flux coated and then the tube is positioned on a rotatable mandrel with the recess arranged relative to an alloy wire and an oxy-acetylene torch.The alloy wire is 3mm diameter and conforms in composition to B.S.1845 Type CiF 6 namely: Copper 58.5-61.5 Tin 0.2 Max Silicon 0.2-0.4 Lead 0.02 Max Aluminium 0.01 Max Arsenic 0.01 Max Antimony 0.01 Max Bismuth 0.01 Max Total Iron 0.25 Max Balance Zinc The alloy wire is provided with a mechanical wire feed arrangement which feeds the wire at a rate of 4mm/sec but with a first pre-heating time delay of 50 secs relative to the start of the oxy-acetylene melting cycle so as to ensure that the tube is at the required temperature (approx 800"C) to receive the molten alloy.The tube is then rotated at an angular velocity of 0.9 mm/sec and the alloy wire fed towards the tube so that the end of the wire is melted at a temperature above 900"C. Compressed air at a pressure of 0.35 bar then issues from the air jets to assist in solidifying the molten alloy in the recess.

The cycle time for the recess to be filled with alloy is 75 sec and a second time delay of 10 sec is incorporated at the end of the wire feed to ensure that the oxy-acetylene flame maintains a pool of alloy in the recess of the final point of application to fill cracks or shrinkage cavities.

Once the recess has been filled with alloy the tube is machined internally to remove the base of the tube and thereby expose the alloy infill. The outside of the tube is then polish-finished.

In the second, preferred embodiment of the invention, we have found that the size of the drops must not be too large in relation to the cross-section of the recess being filled for a cast alloy of the desired quality to be obtained. Thus, for a recess 2.2mm deep and 8mm wide at the surface we have found an alloy rod of 3mm diameter provides the right size of molten drop.

Claims

1. A method for manufacturing a composite article comprising dissimilar metal or metals and/or alloy or alloys the method comprising forming or positioning one or more parts of the composite article so as to define a space corresponding to or including that part of the article to be formed of the metal or alloy having the lower melting point, and applying the said lower melting point metal or alloy in situ.

2. A method according to claim 1 comprising forming a recess in said one part of the composite article and applying the metal or alloy of lower melting point to the recess.

3. A method according to claim 1 or 2 wherein the said one or more parts of the composite article are placed in a mould so as to define with mould and, if needed, core pieces, the said space, and casting the lower melting point metal or alloy in situ in the space.

4. A method according to claim 3 wherein the lower melting point metal is in the form of loose or compact powder and is applied to the space for melting during subsequent heating.

5. A method according to claim 2 wherein the metal or alloy of lower melting point is flamemelted into said recess.

6. A method of manufacturing a high pressure tube of magnetic material having at least one interval of non-magnetic material along its length for use in proportional solenoid operated valves, the method comprising providing a tube of magnetic material, forming a recess around either the interior or exterior surface of the tube, applying a non-magnetic material to the recess, and subsequently machining away excess magnetic and non-magnetic material to leave two tubular portions of magnetic material connected by a band of non-magnetic material.

7. A method according to claim 6, where the recess is formed about the exterior surface of the tube, comprising rotating the tube about its axis, and applying the non-magnetic material to the recess by flame-melting as the tube rotates.

8. A method according to claim 7 wherein the step of flame-melting comprises feeding a rod of the non-magnetic material towards said recess, and heatng the end of the rod so as to apply molted drops thereof to the recess.

9. A method according to claim 8 comprising providing a first time delay in the feed of the non-magnetic material relative to the beginning of the hesting cycle to cause the tube to be heated prior to the receipt of molten non-magnetic material.

10. A method according to claim 9 comprising providing a second time delay in the feed of the non-magnetic material relative to the end of the heating cycle such that the heating cycle continues longer whereby the non-magnetic material remains molten in the recess for a short time after application to fill cracks or shrinkage cavities.

11. A method according to claim 9 wherein the solidification of the non-magnetic material in the cross-sectional area of the recess is controlled by the gas stream such that the non-magnetic material remains molten in the recess for a short time after application and before solidification.

1 2. A method according to any one of claims 1 to 4 wherein the non-magnetic material is an alloy comprising 90 parts by weight copper and 10 parts by weight nickel/phosphorus 1 3. A method according to any one of claims 1, 2 and 5 to 11 wherein the non-magnetic material conforms to B.S. 1845 Type Cl 6.

1 4. A method of manufacturing a composite article substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

1 5. A composite article made in accordance with any one of the preceding claims.