Schaeffler Australia

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Technical Product Information | 2011-04
Current-Insulating Bearings
Rolling bearings for prevention of damage due to current passage

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Passage of electrical current

Irregularities in the winding and motor geometry can cause constant passage of electrical current through the bearings. Current flashover resulting from voltage spikes often occurs in motors controlled by frequency converters. Current densities of more than 0.1 A/mm² can damage the raceways, balls and grease and even cause the bearing to fail.

Figure 1:
Welding beads caused by current flashover

Figure 2:
Fluting caused by continuous passage of electrical current

To prevent such damage, the Schaeffler Group offers current-insulated bearings:

Current-insulated bearings and hybrid bearings

Current-insulated bearings have either an outer ring (J20 A, J20 AA, J20B) or an inner ring (J20C) that is insulated with thin ceramic coating.
Different coating types are available for optimum functional performance.

Types of coatings - Range of Sizes

	J20B	J20A *)	J20AA	J20C
Disruptive Voltage	500 VDC	1000 VDC	3000 VDC	3000 VDC
Environment	dry	dry	dry/damp	dry/damp
Coating Thickness	<100 μm	>200 μm	≈200 μm	≈200 μm
Applicable Dimensions	70…1400 mm outside diameter	70…1400 mm outside diameter	70…500 mm outside diameter	70…340 mm inner ring bore
*) Preferably used for bearings with an outside diameter of at least 500 mm

Current-insulated bearings have the same dimensions and load carrying capacities as those without insulation, which makes them perfectly interchangeable.
The most common type of insulation used in electric motor applications is the J20AA coating. It offers excellent protection against passage of electrical current, even in damp atmospheres.
Bearings with ceramic coating are available with seals also.

Bearings with J20C coating on the inner ring are used in special applications as well as applications where the outer ring rotates. Z shields can be used as well.

Ordering examples:

6220-2RSR-J20AA-C3
Deep groove ball bearing with a coated outer ring, with seals on both sides and radial clearance C3.
NU214-E-M1-F1-J20B-C4
Cylindrical roller bearings with a coated outer ring and radial clearance C4.
6330-J20C
Deep groove ball bearings with a coated inner ring

Hybrid bearings (HC): Hybrid bearings are characterized by the fact that the rolling elements are made of ceramic. They offer maximum protection against passage of electrical current. At the same time, hybrid bearings are suitable for higher speeds and have better dry-running characteristics.

Ordering examples:

HC6214-M-P6-C3
Deep groove ball bearing with ceramic balls; machined brass cage; increased accuracy P6 and bearing clearance C3.
HCN1020-K-M1-SP
Cylindrical roller bearing with ceramic rollers; tapered bore; machined brass cage; increased accuracy SP.