WO2001090428A1

WO2001090428A1 - Copper-based contact material, contact slug and procedure for making the contact slug

Info

Publication number: WO2001090428A1
Application number: PCT/HU2001/000059
Authority: WO
Inventors: Szergej Ivaskevics; Borisz Judin; Konstantin Kourganov; Alexander JUDIN
Original assignee: JUDINA, Olena
Priority date: 2000-05-23
Filing date: 2001-05-23
Publication date: 2001-11-29
Also published as: AU2001274349A1; HUP0001984A2; HU0001984D0; HUP0001984A3

Abstract

The object of the invention is a copper-based contact material containing the following components (mass percents): graphite 0,5-5,0 %, cadmium 0,1-0,5 %, 0,2-0,5 %, zirconium 0,2-0,5 %, indium 0,1-0,3 %, tantalum 0,05-0,2 %. Further aspects of the invention are a contact slug made of the above contact material prepared by powder metallurgical method, and a procedure for preparing contact slugs by powder metallurgical method, by which granules of 50 um size or smaller are prepared from the above defined composition, mixed and pressed into slugs with a typical specific pressure of 0,4 gPa, the slugs are then baked with the addition of graphite and cadmium-oxide at a temperature of 1223+/-10 K in a vacuum at alumina-spraying, the baked slugs are then re-pressed and sintered at a temperature of 723+/-10K.

Description

Copper-based contact material, contact slug and procedure for making the contact slug

The invention relates to composite materials used for the manufacture of copper-based, silver-free contacts for low-voltage electric switches. The object of the invention is the copper-based contact material containing graphite, cadmium and chromium, as well as the contact slug prepared from this contact material and the powder-metallurgical procedure for making the contact slug.

BACKGROUND OF THE INVENTION

The contact materials used conventionally in low-voltage electric switches are based on silver with additives such as cadmium, copper, zinc, lead, tin, zirconium, hafnium and thorium-oxide, as well as tungsten, molibde- num, nickel, zirconium, cadmium, carbides of metals with high melting point, etc.

Copper-based alloys are also known to be used as contact materials in electric switches. Such an alloy has e.g. the following composition (in mass%): chromium 0,2 - 0,35 cadmium 0,2 - 0,35 copper and other metals.

(Arensburger, D. Sz.: Properties of copper powder alloys of dispersion hardening, Powder Metallurgy, 1988, (2) pp. 37-41)

Another alloy used for electrodes and rollers in contact-welding machines has the following composition: chromium 0,4 - 0,65% cadmium 0,3% copper, other materials (SU 105348 1955).

These alloys possess high hardness, strength and conductivity. Their draw-back is that they easily agglomerate and have high contact resistiv- ity.

Copper-based electric contacts with mass percentual composition of gaphite 0,5% cadmium 0,5% copper, other materials are known (MG0,5Kg0,5 ZSBDC 25.36500001 Technical Conditions, Contact, PO "HEMZ", Harkov, 1985.01.02).

This contact material is characterised by the following properties: density: 8,6 kg/m^ x 10-3, hardness: 76-96 newton/m^ x ( , breaking load: 360 mPa, specific resistance: 2,0 μΩ x cm, contact resistivity: 0,043 mΩ, specific wear of contacts: 0,085 g/cycle x 10^~6.

A serious draw-back of the above silver-free contacts is that they easily sinter, that hinders their application as high-voltage switch-overs in automatic switches. A technical solution against the tendency to sinter (low resistance against baking) might be the use of a copper-based composite material of the following composition: graphite 0,0 - 2,0% cadmium 0,8 - 1,0% chromium 0,5 - 2,0% copper, other materials.

However, disadvantages of this material are that contacts made of them have low operation reliability, and their field of use is limited. For exam- pie, at switching at low and medium voltages their wear-resistance is low, whereas their contact resistivity is high. Their resistance against baking-in and corrosion is not satisfying, thus they cannot be applied as contacts for switch-overs in automatic switches or in contacts under very high load.

In US patent 4,517,033 a copper-based contact material used in vacuum interrupter switches is described which contains, in addition to copper, only less than 10% alloying metals, from which not more than 35% is chromium and not more than 50% is tantalum, and besides it may contain alloying materials of low melting point, such as bismuth, antimony, tal- hum, lead, selenium, cerium and calcium. However, even these contacts show satisfying operation only in vacuum.

SUMMARY OF THE INVENTION

The objective of the present invention is to eliminate the above mentioned draw-backs of contact materials of known compositions, and to provide a widely applicable, optimum contact material, contact slug and procedure for manufacturing the formers.

We have discovered that this objective can be achieved by the application of a copper-based raw material differing in its composition from the earlier ones, so that we use also materials known till now only as impurities in a certain, predetermined ratio, starting from composite materials containing graphite, cadmium, chromium and copper by adding zirconium, indium and tantalum to them as additives.

The invention relates to a copper-based contact material containing graphite, cadmium and chromium, together with the above additives in the following mass percents: graphite 0,5 - 5,0% cadmium 0,1 - 0,5% chromium 0,2 - 0,5% zirconium 0,2 - 0,5% indium 0,1 - 0,3% tantalum 0,05 - 0,2%.

A further aspect of the invention is a contct slug made of copper-based contact material, manufactured by powder-metallurgical method, the material of which consists of the following metals (inmass%): graphite 0,5 - 5,0% cadmium 0,1 - 0,5% chromium 0,2 - 0,5% zirconium 0,2 - 0,5% indium 0,1 - 0,3% tantalum 0,05 - 0,2%

A further aspect of the invention is a procedure for making contact slugs by powder-metallurgical method, in the course of which a contact metal containing copper and at least the following additional components is obtained: graphite 0,5 - 5,0% cadmium 0,1 - 0,5% chromium 0,2 - 0,5% zirconium 0,2 - 0,5% indium 0,1 - 0,3% tantalum 0,05 - 0,2% so that granules of 50 μm or smaller particle size are prepared from the components, then they are mixed. From this mixture, slugs are pressed typically by a specific pressure of 0,4gPa, then the slugs are baked out in vacuum, at alumina-spraying at temperatures of 1223±10 K, by adding graphite and cadmium-oxide, then the baked slugs are pressed again, and finally sintered at 723+10 K.

Baking is preferably performed at a residual pressure of 0,1 -1,0 Pa. Repressing is carried out preferably at a pressure of 0,8 - 0,9 gPa. Sintering is performed preferably at a residual pressure of 0,1 - 1,0 Pa.

DETAILED DESCRIPTION OF THE INVENTION

In what follows, the invention will be described in detail on basis of em- bodiments.

The percentual values given for the compositions are mass percents.

The invention has been realised starting from the following considerations:

The addition of chromium in an amount of 0,2 - 0,5% ensures an increase in the strength, erosion- and corrosion resistance, and the abrasion- resistance of the material. With addition of more than 0,5% of chromium, specific and contact resistivity increase, as well as the heating up of the contacts, worsening thereby the technological properties. In case of addition of less than 0,2% chromium, the above advantages fail to appear.

Addition of zirconium in an amount of 0,2 - 0,5% provides the material with better erosion- and corrosion-resistance, as well as with an increase in re-crystallisation temperature due to the better distribution of materials in the matrix. By addition of more than 0,5% of zirconium, the specific resistance (resistivity) and heating up of the contacts increase. By applying less than 0,2% zirconium, no improvements can be achieved.

Addition of indium in an amount of 0,1 - 0,3% ensures an increase in cor- rosion-resistance and improves the technological features of the material. In addition, the wetting ability of the components increases, which contributes to an increase in erosion-resistance, especially if the graphite content is at its upper limit (5%). By adding less than 0,1% of indium, no advantages can be indicated.

By adding tantalum in an amount of 0,05 - 0,2% we can ensure a uniform distribution of components in the matrix, an increase in the strength of the material, corrosion-resistance and resistance against arcing, and besides, it raises the re-crystallisation temperature. It is disadvantegeous to add more than 0,2% tantalum, since it increases the electric resistivity and thus the heating up of contacts, deteriorates the technological properties, whereas an addition of less than 0,05% does not ensure the above desired advantages.

The copper content of 93 - 98,85% provides the material with a very good electric conductivity and plasticity, as well as with a low and stable con- tact resistance at switching on the current. A copper content higher than 98,85% does not ensure the above advantages, and less than 93% causes a worsening in the technological properties of the material.

Addition of graphite in an amount of 0,5 - 5,0% ensures an increase in the resistance against arcing and getting stuck (baking in?) thereby allowing for a broadening of the application field of contacts. In addition, their abrasion-resistance is larger under short-cut switching conditions. An ad- dition of less than 0,5% of graphite decreases the resistance against baking in, that of more than 5% decreases the strength, erosion- and corrosion-resistance at disconnection or commutation of a current of 50-630 A nominal current strength.

Addition of cadmium in an amount of 0,1 - 0,5% improves the arc- quenching property of contacts, whereas at switching, it decreases their contact resistance. In case of the presence of more than 0,5% of cadmium, the melting temperature and heat-resistance of the material decreases, and its resistivity increases. Addition of less than 0,1% cadmium has no ef- feet, it does not ensure the advantages.

For preparing the contacts, the raw material of a composition given in Table 1 is used. For comparative studies, six experimental group of contacts and mixtures are prepared, the composition of which are shown in Table 2. For studying physical and mechanical properties, experimental samples are manufactured.

Table 1

Components Raw material

Graphite Cl colloidal graphite GOST 17022-76

Cadmium Cadmium powder, TU-6-OC-3096-73. or cadmium-oxide GOST 11120-75

Chromium Chromium powder PH 1 M TU 1-14-74-75

Zirconium Electrolytic zirconium powder TU 95 259-77 (No 1)

Indium Indium powder GOST 10297-75 (No 1, No 2)

Tantalum 1 ^st class powder GOST Copper PMC-1 GOST 4960-76 electrolytic powder. Table 2

Components Sample Sample Sample Sample Sample Sample

1 2 3 4 5 6

Graphite 2 2 2 2 2 0,5

Cadmium 0,2 0,2 0,2 0,2 0,2 0,2

Chromium 0,3 0,3 0,3 0,3 0,3 0,3

Zirconium 0,1 0,2 0,4 0,5 0,6 0,5

Indium 0,05 0,1 0,2 0,3 0,4 0,3

Tantalum 0,01 0,05 0,1 0,2 0,3 0,2 Copper and others (all data in mass %) where samples 1 and 5 contain components outside the limit values, samples 2, 3, 4 inside the limit values, and sample 6 contains only a very small amount of graphite.

All sample mixtures were prepared by mixing the dry starting powders in a ball drum mixer for 6 hours obtaining thus a particle size of not larger than 50 μm. Samples were pressed from the mixtures thus obtained by a specific pressure of 0,4 gPa (4gE/cm²). Baking of the samples occurred with the addition of graphite and cadmium-oxide at a temperature of 1223 ±10 K in vacuum, at a residual pressure of 0,1-1 Pa, at aluminium- spraying. The contacts thus baked were re-pressed with a pressure of 0,8- 0,9 gPa, then sintered at a temperature of 723±10 K for 30 minutes at a residual pressure of 0,1-1,0 Pa.

In Table 3, results of the laboratory tests of the experimental contacts determining the operational properties and safety parameters are shown. Table 3

Composit density strength HV tensile strength spec. el. res. of contact unburnt unburnt kg/m xl0~³ H7m³xl0⁷ MN/m² μΩ.c

1.beyond limit 8,52 112 310 2,4

2. min. graphite 8,7 130 420 2,06

3. inside limit 8,6 116 330 2,30

4. inside limit 8,65 125 350 2,35

5. inside limit 8,68 128 356 2,32 6.beyond limit 8,56 114 320 2,42

7. comparing sample 8,5 80 280 2,60

Experimental results shown in Table 3 illustrate that the component content in the suggested composite material as compared to a known material increases the following physical-mechanical properties: hardness: 44%, tensile strength: 33%, electric conductivity: 21%, as well as the electric- physical properties: electric wear-resistance increases by a factor of 2,9- 5,5, whereas the contact resistance decreases by 30-48%. Consequently, the suggested copper-based composite material improves the operational safely of electric contacts, as well as it broadens the field of their applicability.

Contacts according to lines 2. and 5. in Table 3 were tested as slugs of 16 x 15 x 2,5 mm size on the model contact type KT 5013. Conditions and results of tests are summarised in Table 4. Table 4

Contact slug voltage current no. of cycles resistance wear

V A xlO³ xl0⁴Ω xl0⁶g/c line 2 220 100 20 0,055 0,160 line 5 220 100 20 0,040 0,063 compar. sampl. 3 220 100 20 0,078 0,350

As is seen from Table 4, contacts made of the suggested material have higher conductivity and lower contact resistance as compared to the known contact slug. In addition, the wear of their mobile and fixed com- ponents is uniform. The working surfaces are also differing: the surface of the known contact slug melted after current break-up, especially in its central part, whereas the abrasion of the contacts made of the suggested material is uniform on the whole surface; no craters and pits could be observed. Thus the experiments performed prove the higher operational reli- ability of contacts made of the suggested material.

Contacts made of the suggested material can find application in interrupter switches, self-starters, control switches, different kinds of switching automata, as well as in relays under high load, power switches, and in other switches switching currents of 1-1000 A intensity at 40-1000 V (KVK) as end contacts instead of silver, silver- containing, copper and copper-containing contacts closing with a pressure of higher than 30 g/cm2. The use of these contacts in KVK's improves their reliability, broadens their field of application, as well as it ensures higher cost efficiency by sparing silver and other expensive metals in their production.

Claims

1. Copper-based contact material containing graphite, cadmium and chromium characterised in that its composition is the following: graphite 0,5 - 5,0% cadmium 0,1 - 0,5% chromium 0,2 - 0,5% zirconium 0,2 - 0,5% indium 0,1 - 0,3% tantalum 0,05 - 0,2%

2. Contact slug made of copper-based contact material manufactured by powder metallurgic procedure characterised in that the composition of its material contains the following materials: graphite 0,5 - 5,0% cadmium 0,1 - 0,5% chromium 0,2 - 0,5% zirconium 0,2 - 0,5% indium 0,1 - 0,3% tantalum 0,05 - 0,2%

3. Procedure for manufacturing contact slugs in powder metallurgical process characterised in that a copper-based contact metal is prepared containing in addition to copper, at least the following components: graphite 0,5 - 5,0% cadmium 0,1 - 0,5% chromium 0,2 - 0,5% zirconium 0,2 - 0,5% indium 0,1 - 0,3% tantalum 0,05 - 0,2% so that from the components granules of 50 μm particle size or smaller are prepared, then mixed, slugs are pressed from this mixture with a specific pressure of tipycally 0,4 gPa, these slugs are baked with the addition of graphite and cadmium-oxide at a temperature of 1223+10 K in vacuum, at alumina-spraying, then the baked slugs are pressed again and subsequently sintered at a temperature of 723+10 K.

4. Procedure according to claim 3 characterised in that baking is performed at a residual pressure of 0,1 - 1,0 Pa.

5. Procedure according to claim 3 characterised in that re-pressing is performed with a pressure of 0,8 - 0,9 gPa.

6. Procedure according to claim 3 characterised in that sintering is performed at a residual pressure of 0,1 - 1,0 Pa.