EP1935064A1

EP1935064A1 - Slip ring for continuous current transfer

Info

Publication number: EP1935064A1
Application number: EP06806060A
Authority: EP
Inventors: Bernd Gehlert; Rolf Paulsen
Original assignee: WC Heraus GmbH and Co KG
Current assignee: Heraeus Deutschland GmbH and Co KG
Priority date: 2005-10-05
Filing date: 2006-10-05
Publication date: 2008-06-25
Also published as: US20090058219A1; WO2007039302A1; JP2009533544A; CN101278449A; DE102005047799A1

Abstract

The invention relates to a slip ring consisting of a substrate material and a sliding contact surface made of gold or a gold alloy, the sliding contact surface being stabilised by a support base, and to the use of a slip ring in slip ring transmitters (in particular in wind power plants or industrial robots), for transmitting control signals and control currents and generator currents.An extended service life, in conjunction with improved quality, a reduced drop in voltage and considerable savings in the amount of gold used can be achieved with the invention.

Description

Slip ring body for continuous power transmission

description

The present invention relates to slip ring bodies for slip ring transformers for continuous power transmission and a galvanic process for their preparation.

Rotary current transformers with contact systems made of stainless steel or precious metal coatings are mainly used when high demands are placed on the quality (voltage fluctuation during rotation) of the current transmission, service life and ease of maintenance. There is a distinction between sliding contacts with and without power interruption:

^■ Uniform movement of the sliding contacts via an interrupted grinding path (DC micro motors)

^■ sliding of the tapping contact under current flow via contact segments to a new neutral position (rotary, sliding switch)

^■ Uniform movement of the sliding contacts via a closed grinding path (slip ring transmission)

Typical designs for continuous power transmission are cylindrical slip ring transformers or flat transmission systems with printed circuit boards. The electrical load spectrum ranges from data (<1A) to power transmission (100-500A). For transferring higher currents (> 2A), depending on the application, several precious metal sliding contacts are arranged in parallel on a grinding path. In line drums of crane systems, welding robots or generator applications in wind turbines, load currents of up to 500 A can be transmitted. A simple gold-cobalt plating on a nickel-plated copper-based support exhibits variations in voltage drop and thus interferes with transmission performance. After about 3 to 5 million revolutions, the voltage drop increases very significantly, so that the slip ring is no longer useful.

Galvanic layer systems have at least two different layers on a support. Conventional galvanic layer systems for power transmission have on a brass substrate on an approximately 0.5 micron thick copper layer and applied thereto 2 to 5 microns thick nickel layer on which in turn a gold-copper-cadmium layer is applied in a thickness of 5 to 15 microns , With this layer system, a longer service life is achieved compared to simple galvanic layers on a carrier. However, a significantly increased voltage drop is tolerated compared to a simple gold-cobalt coating. In addition, cadmium is undesirable for environmental or health reasons.

It is the object of the present invention to make the voltage drop smaller and more uniform and to further increase the life of the system.

The solution of the problem is described in the independent claims. Advantageous embodiments are described in the dependent claims.

According to the invention, the sliding contact surface on a hard base is made thinner than hitherto usual. This allows the voltage drop with previously unattainable quality (variations in voltage drop) to 5 000 000 revolutions to a constant value well below 0.5 V at 2 A to lower. In the course to at least 10 000 000 revolutions is still at least as good a quality achieved, as was previously achievable in the prior art for the first 1 000 000 revolutions.

The hardness must in any case be higher than the hardness of the nickel previously used as a diffusion barrier layer. Platinum group metals and phosphorus doped nickel have sufficient hardness for the present invention. The slip ring transformers according to the invention are suitable for all applications of electrical energy and data transmission for rotating systems, in particular wind turbines, robots, welding robots, cable drums and radar systems, for all of which a permanently routed electrical connection would be unusable. Preferably, the layer thickness of the sliding contact surface made of gold or a hard gold alloy is significantly reduced. According to the invention, not only a considerable reduction of the gold consumption is made possible, but also a prolonged duration. In this case, the present invention enables a reduction of the suitable depending on the application layer thickness of the sliding contact surface of gold or hard gold by at least 30%, in particular by at least 50%. Layer thicknesses of less than 10 .mu.m, in particular 1 to 5 .mu.m, preferably 2 to 3 .mu.m, have proven successful, in particular when using noble metal grinder wires made of Hera 277 (AuPdAg alloy). Over 15 microns, the gold order is increasingly uneconomical. The abrasion determines a minimum layer thickness with regard to the service life.

The sliding contact surface of a sliding contact track is expediently web-shaped. The web may be disposed axially on the surface of a disk or radially on the outside of a ring.

The sliding contact surface as a web on a sliding contact disk is usefully disc-shaped. On a disc, several tracks can be arranged radially next to each other. Circuit boards have proven themselves for this design.

The sliding contact surface as a track on a sliding contact ring is usefully ring-shaped. Several rings can be arranged axially on one axis.

Sliding contact surfaces made of a gold alloy, which has cobalt or nickel, have proven successful. Suitable gold-cobalt alloys or gold-nickel alloys have 50 to 99.8% by weight of gold, 0.2 to 20% by weight of cobalt or nickel, and 0 to 30% of other alloying constituents. Other noble metals, copper and dopants with boron, carbon, silicon or phosphorus are suitable as further alloy constituents.

The supporting base, in particular an intermediate layer arranged on a nickel-plated carrier, consists of a hard material which supports the sliding contact surface, in particular the hardest material of the composite. A supporting base, in particular an intermediate layer made of one or more platinum group metals (PGM) or alloys thereof or hardened nickel, has proved suitable. As subordinate alloy constituents, nickel, cobalt and iron and boron, carbon, silicon or phosphorus dopants for saving PGM are suitable. A galvanic Pd deposition on a nickel-plated carrier has proved successful from a copper alloy such as brass, bronze or CuZr. To a limited extent, platinum group metals can be replaced by ferrous metals. A doping with B, C, Si, or P increases the hardness.

It has also been proven to apply on a diffusion barrier layer of nickel, the harder intermediate layer. If the intermediate layer of phosphorus-hardened nickel is carried out, the platinum group metals can be saved. In a preferred embodiment, supported on a copper-based support, e.g. Brass arranged a diffusion barrier layer of nickel. An intermediate layer of phosphorus-hardened nickel is deposited on the nickel diffusion barrier layer. On the hardened nickel, a nickel-containing hard gold layer is applied as a sliding contact surface. These three layers are characterized by their simplicity. Nickel diffusion does not matter because all three layers contain nickel. Phosphorus diffusion is unknown.

Intermediate layers having a layer thickness of less than 10 μm, in particular 2 to 7 μm and especially 3 to 4 μm, have proven useful.

It has been proven to make the intermediate layer thicker than the sliding contact surface.

Advantageously, the electrically conductive composite of sliding contact surface and the supporting intermediate layer in a thickness between 3 and 10 .mu.m, in particular between 4 and 8 microns and more preferably between 5 and 7 microns.

The electrically conductive carrier is preferably a copper alloy. Proven copper alloys for continuous power transmission include zinc (brass), tin (bronze) or zirconium.

The supporting base may be separated from the sliding contact surface by a thin layer, for example a diffusion barrier layer or an adhesion promoter. It is recommended that such a layer does not run over 1 micron thickness, since with increasing layer thickness of the thin layer, the supporting function of the supporting base is impaired.

The sliding contact surface with hardened underlay according to the invention is used as the surface of a slip ring transmitter (in particular in wind turbines or industrial robots) for the transmission of control signals, control and generator currents. In the following the invention will be clarified by means of examples with reference to the figures.

FIG. 1 shows the voltage drop as a function of the revolutions for the sliding contact surface according to the invention;

FIG. 2 shows an oscillogram at the beginning of the current transmission in accordance with the invention;

Figure 3 shows an oscillogram after 4,000,000 revolutions;

Figure 4 shows an oscillogram after 10 000 000 revolutions;

Figs. 5a and 5b show slipring assemblies;

FIG. 6 shows a test arrangement for determining the voltage drop and the quality;

FIGS. 7 to 9 show comparative diagrams to FIG. 1;

FIGS. 10 to 12 show comparison oscillograms to FIG. 2;

Figs. 13 to 15 show comparative oscillograms to Fig. 3;

Figures 16 to 18 show comparative oscillograms to Figure 4;

Examples:

In a simple embodiment (FIG. 5b), a current transformer is designed as a ring, wherein the sliding contact surface is arranged on the outer surface of the ring. For the production of such a ring, 2 .mu.m nickel are galvanically deposited on the outside of a brass or bronze ring and then 5 .mu.m nickel phosphorus. In the nickel-phosphorus layer, the nickel is doped with phosphorus, making the layer significantly harder than the nickel layer underlying the nickel-phosphorus layer. 4 μm of a gold-nickel alloy are deposited galvanically on the phosphorus-doped nickel layer. Compared to a slip ring without hardened nickel layer better quality of power transmission and higher wear resistance is achieved.

In a further embodiment (FIG. 5b), a brass ring is galvanically provided on its outside with a 4 μm nickel layer. On this nickel layer, a 5 .mu.m thick palladium layer is applied galvanically. On the palladium layer, a hard gold alloy of gold and cobalt is applied in a thickness of 5 microns. The current transformer produced in this way is evaluated in an arrangement according to FIG. The two wiper wires are driven on different tracks.

Test Parameters:

Electric load: 24 V DC / 2A / ohms,

Contact force: 2 to 3 cN,

Spring length: 45 mm,

Grinder wire: d = 0.5 mm,

Slip ring body: d = 60 mm,

Speed: 300 / min.,

Greasing: none,

Number of revolutions: 10,000,000

The sliding contact consists of Hera 277 (AuAgPd alloy).

In the oscillogram of Figure 1, the voltage drop is shown at the beginning of the experiment. The oscillogram according to FIG. 2 shows the voltage drop after 4 million revolutions and the oscillogram according to FIG. 3 shows the voltage drop after 10 million revolutions. In all oscillograms, the trigger signal is recorded as a square pulse. The zero line for the voltage signal is always the top line of the second box from below.

The voltage drop as a function of the revolutions is shown in the diagram according to FIG. The dotted line represents the upper value from the oscillograms, the dotted line the lower and the solid line the average.

For comparison, according to Figure 5a, three slip ring body with 10 microns sliding contact surfaces of AuCo, AuCuCd and Pd each on a nickel-coated brass substrate under the same experimental conditions studied. Since the slip ring bodies with the AuCo and Pd sliding contact surfaces could not withstand 10 million revolutions, oscillograms were compared with correspondingly lower revolutions (Figures 15, 16 and 18). The oscillograms of Figures 10, 13 and 16 are made with an AuCo sliding contact surface, the oscillograms of Figures 11, 14 and 17 with an AuCuCd sliding contact surface and the oscillograms of Figures 12, 15 and 18 with a Pd sliding contact surface.

The voltage drop as a function of the revolutions is shown analogously to FIG. 1 in FIGS. 7 to 9.

Next embodiment:

It can be several slip ring body stack axially on an axis. This provides several current paths. For the application of high currents, several current paths are closed in parallel. In an alternative arrangement, a plurality of slider tracks can be arranged radially on a disk. In this case, the disc is similarly coated on one of the disc surfaces, as previously described for the outer surfaces of the rings.

Claims

claims

1. slip ring body of a carrier material and a sliding contact surface made of gold or a gold alloy, characterized in that the sliding contact surface is stabilized with a supporting base.

2. slip ring body according to claim 1, characterized in that the supporting base is harder than nickel.

3. slip ring body according to claim 1 or 2, characterized in that the supporting base is an intermediate layer between the slip ring contact surface and a support.

4. slip ring body according to one of claims 1 to 3, characterized in that the hard gold has nickel or cobalt.

5. slip ring body according to claim 4, characterized in that the hard gold alloy 50 to 98 wt .-% gold, 0.02 to 20 wt .-% cobalt or nickel or cobalt and nickel, 0 to 30% further alloying constituents, in particular selected from the group copper, silver, palladium, platinum, rhodium, iridium, ruthenium, boron, carbon, silicon and phosphorus.

6. slip ring body according to one of claims 1 to 5, characterized in that the supporting base, in particular the intermediate layer based on one or more platinum group metals or nickel phosphorous (phosphorus-doped nickel) or a double layer of nickel and nickel phosphorus.

7. Use of a slip ring body according to one of claims 1 to 6, for slip ring transmission (especially in wind turbines or industrial robots) for the transmission of control signals, control and generator currents.

8. Use of a slip ring body according to one of claims 1 to 6, characterized in that the layer thickness of the gold application for a specific application is reduced to at most 70% of the hitherto lowest thickness for the corresponding application, in particular to 10 to 50%.

9. A method for producing a slip ring body for continuous power transmission with a sliding contact surface and an electrically conductive carrier and an interposed between the carrier and the sliding contact surface intermediate layer in which the intermediate layer is electrodeposited on the carrier and on the intermediate layer of gold or hard gold is electrodeposited, characterized characterized in that the intermediate layer is formed of a material which is harder than nickel.