Electrical Contacts from Cr-Cu Materials

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 of the reasons 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.

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 ERCr99.95 chromium is used in production of these parts. The contact material is distinguished by high purity in terms of gas-forming and metallic impurities, outstanding phsyical and mechanical characteristics.

Dimensions:

Grade	Nominal dimensions, mm
	Diameter	Thickness
		Disc	Contact layer	Copper layer
ERCr25Cu75-PM single-layer discs	90	8,0 - 20,0	-
ERCr50Cu50-PM single-layer discs	48, 56, 66, 70, 80	8,0 - 20,0	-
ERCr35Cu65-PM single-layer discs	42,0 - 90,0	7,0 - 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	Density,  g/cm³, min	Hardness НВ, min*	Conductivity %, min**
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 reference copper.

Other types of contact parts:

- ERCr30Cu70-PM made from Cr30Cu70 material. Single-layer disks with the dimensions: Ø 50х16, 70х22 mm.

- 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.

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.

An example of a product grade: ERCr25Cu75-PM, ERCr50Cu50-PM, ERCr35Cu65-PM, ERCr30Cu70-PM, ERCr50Cu50-PM

You can contact our sales managers for more details at:

export_polema@metholding.com,

tel.: +7(4872)25-06-76.

Chemical composition:

Grade, standard	Form and structure		Chemical composition, mass %
			Cr	Cu	O max	N max	S max
ERCr25Cu75-PM Spec. 14-22-146-2002	Single-layer chromium-copper disks		24-27	Base	0,07	0,005	-
ERCr50Cu50-PM Spec. 14-22-146-2002	Single-layer chromium-copper disks		Balance	48-53	0,07	0,005	-
ERCr35Cu65-PM Spec. 14-22-187-2003	Single-layer chromium-copper disks		33-37	Base	0,07	0,005	-
ERCr30Cu70-PM Spec. 14-22-161-2002	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 Spec. 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

Chemical composition of electric contact blanks ERCr30Cu70-PM; ERCr50Cu50-PM (Bimetallic contact discs with a contact layer and a copper substrate):

Goods		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	Bal.	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	Bal.	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	Bal.	0,042	0,002	0,002	8,4	106	41,1
	Copper substratum	<0,05	Base	0,008	0,002	0,001	-	-	-

* ρ - blank density

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

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