Cr-Cu, W-Cu Contacts

JSC POLEMA is Russia's largest manufacturer of composite chromium-copper and tungsten-copper materials for high-current contacts in vacuum arc-quenching chambers.

Application

Cr-Cu contacts are used in the vacuum arc-quenching chambers (VACs) of highly dependable, quick-acting vacuum circuit breakers capable of breaking large currents in high-voltage 6-35 kW electrical networks. Contacts are a key element in commutation switches (circuit breakers). Currently, the most common material used in contact pairs in VACs are Cr-(50-75%)Cu composites.

Contacts are subjected to the effects of short-circuit currents and fusing metals in various points of the surface due to the high density of the current in them; as a result, welding joints form in these zones. This problem was one reason that delayed the devleopment of vacuum commutation technology for more than twenty years. The resistance of a VAC's contacts to welding is one of its key characteristics. The problem of welding was solved by developing special contact plates made from chromium-copper composites, which provided a high breaking capacity for circuit breakers in commutation networks, wear-resistance and resistance of contact pairs to welding.

W-Cu contacts are used in VACs of vacuum contactors with a nominal voltage of 1.14 kW and higher in systems for remote control of electric drivers. The contacts are a long-lasting means of switching contactors in electric circuits on and off and ensure a low cut-off current in the system.

1. Characteristics of fabricated parts from chromium-copper materials

 

2 types of products are manufactured: disks made from a composite chromium-copper material, and complex parts consisting of a contact chromium-copper layer and a copper substratum. High-quality POLEMA-produced electrolytic refined ERC99.95 chromium is used in making these parts. The contact material is distinguished by high purity in terms of gas-forming and metallic admixture content, outstanding phsyical and mechanical characteristics.

 

Brands, structure and chemical composition

Brand, standard	Part form and structure		Chemical composition, mass %
			Cr	Cu	O max	N max	S max
ERCr25Cu75-PM ТУ 14-22-146-2002	Single-layer chromium-copper disks		24-27	Base	0,07	0,005	ND
ERCr50Cu50-PM ТУ 14-22-146-2002	Single-layer chromium-copper disks		Balance	48-53	0,07	0,005	ND
ERCr35Cu65-PM ТУ 14-22-187-2003	Single-layer chromium-copper disks		33-37	Base	0,07	0,005	ND
ERCr30Cu70-PM ТУ 14-22-161-2002	Two-layer disks: Cr-Cu и Cu	Contact layer	27-33	Balance	0,05	0,005	0,007
		Copper layer	<1,0	Base	0,02	0,005	0,007
ERCr50Cu50-PM ТУ 14-22-161-2002		Contact layer	48-53	Balance	0,05	0,005	0,007
		Copper layer	<1,0	Base	0,02	0,005	0,007

PM – Powder Metallurgy

Dimentions

Brand	Nominal dimensions, mm
	Diameter	Thickness
		Disc	Contact layer	Copper layer
ERCr25Cu75-PM single-layer discs	90	8.0 to 20.0	-
ERCr50Cu50-PM single-layer discs	48, 56, 66, 70, 80	8.0 to 20.0	-
ERCr35Cu65-PM single-layer discs	42,0 to 90,0	7.0 to 13.0	-
ERCr30Cu70-PM two-layer discs	32	4,0	2±0,5	2±0,5
	48, 56, 60, 66, 80	6,0	3±0,5	3±0,5
ERCr50Cu50-PM two-layer discs	32	4,0	2±0,5	2±0,5
	48, 56, 60, 66, 80	6,0	3±0,5	3±0,5

At the client's request, contact parts of other dimensions can be produced.

Physical and mechanical characteristics

Brand	Minimum density,  g/cm³	Minimum hardness НВ*	Minimum conductivity %**
ERCr25Cu75-PM single-layer discs	8,2	65,0	55,0
ERCr50Cu50-PM single-layer discs	7,8	90,0	40,0
ERCr35Cu65-PM single-layer discs	8,0	72,0	45,0
ERCr30Cu70-PM two-layer discs	8,35	70	55
ERCr50Cu50-PM two-layer discs	8,35	85	40

* Contact layer Brinell hardness НВ 5/250

**Conductivity of the contact layer in % of standard copper.

Other types of contact parts

1. ERCr30Cu70-PM made from Cr30Cu70 material. Single-layer disks with the dimensions: Ø 50х16, 70х22 mm.
2. ERCr30Cu70-PM and ERCr50Cu50-PM Bimetallic disks with a contact layer made from Cr30Cu70 or Cr50Cu50 material and copper substrata.

Nominal product dimensions, mm: diameter 48, 56, 66, 80, thickness (height) 10. Thickness of contact layer 4.5±0.5 mm.

Contact parts with other dimensions can be produced at the client's request.

Controlled parameters: chemical composition, dimensions, density, hardness and conductivity.

Sample actual specifications of contact parts

Part		Chemical composition, %					ρ, g/cm³*	НВ**	σ, %***
		Cr	Cu	O max	N max	S max
ERCr30Cu70-PM Two-layer disk Ø48х10	Contact layer	30,69	Rem.	0,025	0,002	0,001	8,59	79	59,7
	Copper substratum	<0,05	Base	0,009	0,002	0,001	-	-	-
ERCr30Cu70-PM Two-layer disk Ø56х6	Contact layer	30,16	Rem.	0,026	0,002	0,002	8,54	77,1	58,7
	Copper substratum	<0,05	Base	0,01	0,002	0,001	-	-	-
ERCr50Cu50-PM Two-layer disk Ø66х6	Contact layer	50,3	Rem.	0,042	0,002	0,002	8,4	106	41,1
	Copper substratum	<0,05	Base	0,008	0,002	0,001	-	-	-

* ρ - part density

**  НВ - Contact layer Brinell hardness НВ 5/250

*** σ - contact layer conductivity in % of standard copper.

Microstructure

In complex parts, material microstructure is monitored to prevent defects, and the thicknesses of the contact layer and substratum are checked, along with the quality of the composite's transition layer.

Sample structures of complex contacts

2. Specifications of electric contact parts made from tungsten-copper material

Brand, structure and chemical composition

Contract parts consist of two heterogeneous layers (bimetallic structure): a contact layer made from a tungsten -copper material and a substratum made from copper.

Brand, standard	Part shape and structure		Chemical composition, mass %
			W	Cu	O max	N max	S max
W70Cu30-PM ТУ 14-22-162-2002 (elsend)	Bimetallic disks made from W70Cu30 + Cu material	Contact layer	Balance	28-32	0,05	0,005	0,007
		Copper layer	-	Base	0,02	0,005	0,007

PM – Powder Metallurgy

Dimensions

Brand	Nominal dimensions, mm
	Diameter	Thickness
		Disc	Contact layer	Copper layer
W70Cu30-PM	32, 48	4+2,0	2±0,5	2±0,5

Parts with contacts of other sizes can be produced at the client's request.

Physical and mechanical characteristics

Brand	Minimum density,  g/cm³	Minimum hardness НВ*	Minimum conductivity, %**
В70Д30-МП	11,36	145	55

* Contact layer Brinell hardness НВ 5/250

** Contact layer conductivity in % of standard copper.

Sample structure of complex contacts

The parts' material microstructure is monitored to prevent defects, and the thicknesses of the layers and the quality of the composite's transitional zone are checked.

3. Chromous powdered bronze CuCr2-PM

To outfit vacuum arc-quenching chambers, parts made of powdered bronze are also used, with an increased softening temperature (more than 100 ^оС in comparison with cast chromous CuCr0.7 and chromium-zirconia  CuCrZr bronzes), alloyed with 2% chromium: CuCr2-PM with diameters of 48, 56, 66, 80, et al. Conductivity is at least 85%, and hardness at least 115 HB.

 

Typical specifications:
density 8.86-8.88 g/cm³,
conductivity 87-92%,
hardness 130-140 НВ.

Chromous dispersion-reinforced CuCr2-PM bronze in the form of discs with diameters of up to 300 mm are also applied as electrodes for resistance-seam welding of carbonous and low-alloyed steels. Electrodes made from thermomechanically treated CuCr2-PM bronze are distinguished from traditional CuCr1 bronze by increased hardness, resistance to setting and service durability under contact sealing.