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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-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 together.

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

Cr-Cu, W-Cu Contacts

 

Two 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 for making these parts. The contact material is distinguished by high purity in terms of gas-forming and metallic impurity content, outstanding physical 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

Dimensions

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 HB*		 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 HB 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 50x16, 70x22 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* HB** σ, %***
Cr Cu O max N max

S
max

ERCr30Cu70-PM
Two-layer disk Ø48x10

 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 Ø56x6

 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 Ø66x6

 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

**  HB - Contact layer Brinell hardness HB 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). ERCr50Cu50 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 HB*		 Minimum
conductivity,
%**
 W70Cu30-PM  11.36 145 55

* Contact layer Brinell hardness HB 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 layer material W70Cu30-PM (fragment).

3. Chromous powdered bronze CuCr2-PM

Parts made of powdered bronze are also used to equip vacuum arc-quenching chambers. They have an increased softening temperature (more than 100 ºC in comparison with cast chromous CuCr0.7 and chromium-zirconia  CuCrZr bronzes),and are  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 HB.

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 carbon 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.

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