GB2087271A

GB2087271A - Wear resistant electrical contact

Info

Publication number: GB2087271A
Application number: GB8132791A
Authority: GB
Original assignee: Technical Materials Inc
Current assignee: Technical Materials Inc
Priority date: 1980-11-03
Filing date: 1981-10-30
Publication date: 1982-05-26
Also published as: GB2087271B; DE3143549A1; SE8106463L; CA1226608A

Abstract

Improved contact surface life is provided by annealing a laminate 48 of gold 40 and another precious metal 42 at such a high temperature, viz. 1400 DEG F, that substantial interdiffusion occurs. The laminate is mounted on a base metal, e.g. copper, and rolled prior to the annealing step. <IMAGE>

Description

SPECIFICATION Wear resistant electrical contact This invention relates to electric contact elements, and more particularly to providing the same with highly conductive contact surfaces of improved lifetime under wear conditions.

We have discovered a contact element in which the contact surface is a mixture of gold and another precious metal, and in which substantial quantities of gold are found well beneath the depth corresponding to the distance of gold initially present, with a gradient of relative concentration characterized by a decreasing percentage of gold as distance beneath the contact surface increases. In preferred embodiments the other precious metal is palladium. In another aspect we have discovered a method of making the products above referred to. In this process the gold and other precious metal are brought into close contact and thereafter annealed at a sufficiently high temperature for (with gold and palladium, in excess of 1000"F (537.7"C) and until the desired amount of diffusion occurs.

We have also discovered that in the manufacture of a contact element characterized by palladium diffused to the contact surface, and in which in manufacture said contact surface abuts a base metal surface, it is desirable to space apart said layers using an inert layer.

We have also discovered that, in the production in an electrical contact layer of a diffused two-precious metal contact zone, carried over a base-metal base, the amount of diffusion in the diffused zone may be accurately and inexpensively monitored by monitoring the grain size of the base material.

We turn now to the presently-preferred embodiments of the invention, which will be more particularly described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a partial isometric view of the formation of the three-layer sandwich to be set into a skived zone of a contact element; and Figure 2 is an isometric view, to a smaller scale, of the sandwich of Figure 1 being assembled into the remainder of the contact element.

In a preferred embodiment, layers from rolls of gold 40 (two thousandths of an inch (0.00508 cm) thick by 1.00 inches (2.54 cms) in width), palladium 42 (18 thousandths of an inch (0.04572 cm) in thickness by 1.00 inch (2.54 cms) wide) and nickel 44 (0.056 inch (0.14224 cm) thick by 1.00 inch (2.54 cms) wide) (all three metals 99.99% pure) are put through a compression bonding step in which a sandwich 19 thousandths of an inch (0.04826 cm) in thickness is produced. The sandwich is then annealed at 950"C (510cm). The sandwich is then reduced in thickness in a rolling mill to 0.0052 inch (0.013208 cm), and thereafter annealed again at 9509C (510"C). These two annealing steps do not produce between the gold and palladium diffusion significant from the standpoint of the present invention.

The sandwich is then slit to a width of 0.227 inch (0.57658 cm) and cleaned.

There is now provided a copper alloy base layer (C 72500) (0.125 inch (0.3175 cm) in thickness and 4.297 inches (10.91438 cms) wide, in a surface of which has been skived a groove 46 about 0.0052 inch (0.013208 cm) in depth and 0.227 inch (0.57658 cm) in width (although just enough larger in width than the sandwich so that the fit is not an interfering one).

Thus far the procedure is a typical prior art procedure.

The base layer and the sandwich 48 are then bonded, in a step in which the thickness is reduced from 0.125 inch (0.3175 cm) to 0.039 inch (0.09906 cm). The product is next put through a rolling mill to reduce its thickness still further, to 0.0185 inch (0.04699 cm) in thickness.

The sandwich is then passed through a heat zone furnace in which it is annealed by passing it as a strip over a 90 second period through a heat zone at 1400"F (760"C), producing substantial diffusion of gold and palladium into each other, whereby even though wear occurs to a depth greater than the initial thickness of the gold layer, a fine contact surface still exists. The product is then put through another rolling mill step to reduce its thickness to 0.010 inch (0.0254 cm) and slit.

This annealing step has a further purpose: the recrystallization annealing of the copper alloy base material. Indeed, the adequacy of diffusion can be simply and inexpensively gauged by monitoring the extent of base material recrystallization.

When the alloy of the preferred embodiment is brought to a proper grain size of about 15 microns, the outer surface of the inlay is no longer a gold colour, but rather is in colour metallic silver grey, with a golden hue, and the concentration of the gold at the surface is perhaps 65% on an atomic basis.

Gold reaches a depth of 0.000025 inch (0.0000635 cm), as opposed to perhaps 0.000010 inch (0.0000254 cm) of a prior art electroplated "gold cap".

It is important that an inert interleaf be wound into the roll following the final diffusion step, for otherwise undesirable chemical reactions may take place between the precious metal and the copper back base, in the roll. We prefer a sulfur-free, chlorine4ree paper having a pH of about 7 and a thickness of about 3 thousandths of an inch (0.00762 cm).

1. An electrical contact element comprising a base layer, and a variably diffused layer, said variably diffused layer comprising a contact portion characterized by a major atomic percent of gold and a minor atomic proportion of another precious metal, the proportion of gold decreasing and the proportion of said another precious metal increasing in the direction away from the surface of said element, whereby gold-rich good contact is retained even if wear is to a depth greater than that characteristic of the thickness of a hypothetical pure sheet of gold including all the gold atoms of said variably diffused zone.

2. A contact element as claimed in claim 1, in which said another precious metal comprises palladium.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Wear resistant electrical contact This invention relates to electric contact elements, and more particularly to providing the same with highly conductive contact surfaces of improved lifetime under wear conditions. We have discovered a contact element in which the contact surface is a mixture of gold and another precious metal, and in which substantial quantities of gold are found well beneath the depth corresponding to the distance of gold initially present, with a gradient of relative concentration characterized by a decreasing percentage of gold as distance beneath the contact surface increases. In preferred embodiments the other precious metal is palladium. In another aspect we have discovered a method of making the products above referred to. In this process the gold and other precious metal are brought into close contact and thereafter annealed at a sufficiently high temperature for (with gold and palladium, in excess of 1000"F (537.7"C) and until the desired amount of diffusion occurs. We have also discovered that in the manufacture of a contact element characterized by palladium diffused to the contact surface, and in which in manufacture said contact surface abuts a base metal surface, it is desirable to space apart said layers using an inert layer. We have also discovered that, in the production in an electrical contact layer of a diffused two-precious metal contact zone, carried over a base-metal base, the amount of diffusion in the diffused zone may be accurately and inexpensively monitored by monitoring the grain size of the base material. We turn now to the presently-preferred embodiments of the invention, which will be more particularly described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a partial isometric view of the formation of the three-layer sandwich to be set into a skived zone of a contact element; and Figure 2 is an isometric view, to a smaller scale, of the sandwich of Figure 1 being assembled into the remainder of the contact element. In a preferred embodiment, layers from rolls of gold 40 (two thousandths of an inch (0.00508 cm) thick by 1.00 inches (2.54 cms) in width), palladium 42 (18 thousandths of an inch (0.04572 cm) in thickness by 1.00 inch (2.54 cms) wide) and nickel 44 (0.056 inch (0.14224 cm) thick by 1.00 inch (2.54 cms) wide) (all three metals 99.99% pure) are put through a compression bonding step in which a sandwich 19 thousandths of an inch (0.04826 cm) in thickness is produced. The sandwich is then annealed at 950"C (510cm). The sandwich is then reduced in thickness in a rolling mill to 0.0052 inch (0.013208 cm), and thereafter annealed again at 9509C (510"C). These two annealing steps do not produce between the gold and palladium diffusion significant from the standpoint of the present invention. The sandwich is then slit to a width of 0.227 inch (0.57658 cm) and cleaned. There is now provided a copper alloy base layer (C 72500) (0.125 inch (0.3175 cm) in thickness and 4.297 inches (10.91438 cms) wide, in a surface of which has been skived a groove 46 about 0.0052 inch (0.013208 cm) in depth and 0.227 inch (0.57658 cm) in width (although just enough larger in width than the sandwich so that the fit is not an interfering one). Thus far the procedure is a typical prior art procedure. The base layer and the sandwich 48 are then bonded, in a step in which the thickness is reduced from 0.125 inch (0.3175 cm) to 0.039 inch (0.09906 cm). The product is next put through a rolling mill to reduce its thickness still further, to 0.0185 inch (0.04699 cm) in thickness. The sandwich is then passed through a heat zone furnace in which it is annealed by passing it as a strip over a 90 second period through a heat zone at 1400"F (760"C), producing substantial diffusion of gold and palladium into each other, whereby even though wear occurs to a depth greater than the initial thickness of the gold layer, a fine contact surface still exists. The product is then put through another rolling mill step to reduce its thickness to 0.010 inch (0.0254 cm) and slit. This annealing step has a further purpose: the recrystallization annealing of the copper alloy base material. Indeed, the adequacy of diffusion can be simply and inexpensively gauged by monitoring the extent of base material recrystallization. When the alloy of the preferred embodiment is brought to a proper grain size of about 15 microns, the outer surface of the inlay is no longer a gold colour, but rather is in colour metallic silver grey, with a golden hue, and the concentration of the gold at the surface is perhaps 65% on an atomic basis. Gold reaches a depth of 0.000025 inch (0.0000635 cm), as opposed to perhaps 0.000010 inch (0.0000254 cm) of a prior art electroplated "gold cap". It is important that an inert interleaf be wound into the roll following the final diffusion step, for otherwise undesirable chemical reactions may take place between the precious metal and the copper back base, in the roll. We prefer a sulfur-free, chlorine4ree paper having a pH of about 7 and a thickness of about 3 thousandths of an inch (0.00762 cm). CLAIMS

3. A contact element as claimed in either claim 1 or claim 2, in which said base layer comprises copper alloy.

4. An electrical contact element substantially as described herein with reference to the accompanying drawings.

5. A method of producing an electrical contact element which comprises the steps of laminating gold and another precious metal and thereafter annealing at a temperature to produce substantial diffusion therebetween.

6. A method as claimed in claim 5, in which said another precious metal comprises palladium.

7. A method as claimed in either claim 5 or claim 6, in which said temperature is in excess of 1000"F (537.7 C).

8. A method as claimed in any one of claims 5 to 7, in which said laminate of gold and said other precious metal is mounted on a base metal base before said annealing step.

9. A method as claimed in claim 8, in which the extent of diffusion during said annealing step is monitored by monitoring the grain size of the metal of said base.

10. A method as claimed in either claim 8 or claim 9, wherein after annealing at a temperature to produce substantial diffusion between said gold and said another precious metal, an inert spacer is sandwiched between the gold-containing contact surface of said contact element and the bottom of said base.

11. A method as claimed in claim 10, in which said inert spacer is a sulphur-free, chlorine-free paper with a pH in the region of 7.

12. A method as claimed in any one of claims 8 to 11, in which said base material comprises copper alloy.

13. A method of producing an electrical contact element substantially as described herein with reference to the accompanying drawings.