From achieved results to new horizonts
» Main » Products » Cr-Cu, W-Cu Contacts
Cr-Cu, W-Cu Contacts

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 development 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 impurity content, outstanding phsyical and mechanical characteristics.

 

Grades, structure and chemical composition

Grade,
standard
Form and structure Chemical composition, mass %
Cr Cu

O max

N max S max
ERCr25Cu75-PM
 

Single-layer chromium-copper disks

24-27 Base 0,07 0,005 ND
ERCr50Cu50-PM
 

Single-layer chromium-copper disks

Balance 48-53 0,07 0,005 ND
ERCr35Cu65-PM
 

Single-layer chromium-copper disks

33-37 Base 0,07 0,005 ND
ERCr30Cu70-PM
 
 Two-layer disks: Cr-Cu and 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
 
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

Grade 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

Grade Minimum
density,  g/cm³
Minimum
hardness ??*
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 ?? 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 50?16, 70?22 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* ??** σ, %***
Cr Cu O max N max

S
max

ERCr30Cu70-PM
Two-layer disk Ø48?10

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 Ø56?6

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 Ø66?6

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

**  ?? - Contact layer Brinell hardness ?? 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

fig. 1
fig. 2

*Fig.1: Complex 2-layer contact material structure ERCr 50Cu50 (fragment) ?r50Cu50 contact layer and Cu substratum.

*Fig.2: Contact layer structure ERCr30Cu70 (fragment) of bimeitalic contact.

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

Grade, 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.

Grade,
standard
Part shape and structure Chemical composition, mass %
W Cu O max N max S max
W70Cu30-PM
(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

Grade 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

Grade Minimum
density,  g/cm³
Minimum
hardness ??*
Minimum
conductivity,
%**
 W70Cu30-PM  11,36 145 55

* Contact layer Brinell hardness ?? 5/250

** Contact layer conductivity in % of standard copper.

fig. 3

Sample structure of complex contacts

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

*Fig.3: Structure of bimetal contact contact layer material W70Cu30-PM (fragment).

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 ?? 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 ??.

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.