6328 M/C3VL2071 Insulated Bearing for Motor

High Precision Insulated Bearing 6328 M/C3VL2071 is Deep Groove Ball Bearing design. its dimension is 140×300×62mm, it has the same dimension and the same design with normal chrome steel 6328 M/C3 bearing. but the most different is 6328-J20AA-C3 bearing with Aluminium Oxide Coating. the coating can Electrical Resistance Voltages up to 3000 V DC. This kind of bearing are widely used in high quality demand application like traction motor.

Electrically Insulated Bearing can protect the machine to be exposed to electrical current. In a worst-case scenario, this can damage raceways and rolling elements, which in turn, causes the motor or generator to fail prematurely and without warning. On top of the extra expenses incurred for repairs, this also means additional costs caused by machine downtime and the resulting production losses.

Typical Damage Caused by Electrical Current Passing through the Bearing

Regardless of whether a bearing was exposed to direct current or alternating current (up to frequencies in the MHz range), the resulting changes to the surface are always the same: Uniformly dull, gray marks in the raceways and on the rolling elements. These marks are not very specific and can also be caused by other factors (e. g. lubricating oil containing abrasives).

Principle bearing types for traction motor applications

• cylindrical roller bearings

• electrically insulated EASIER cylindrical roller bearings

• electrically insulated EASIER deep groove ball bearings

• hybrid cylindrical roller bearings with ceramic rollers

• hybrid deep groove ball bearings with ceramic balls

• traction motor bearing units based on cylindrical roller bearings and deep groove ball bearings

• Sensorised traction motor bearing unit

• Regreasable traction motor bearing unit

Electrically Insulated Cylindrical roller bearings and electrically deep groove ball bearings are the most used type, outer ring or inner ring coated is the best choice for insulated function, hybrid cylindrical roller bearing with ceramic rollers and hybrid ball bearings with ceramic balls are higher cost then the bearing rings coating.

Type:

Deep groove ball bearing, cylindrical roller bearing

Inner diameter:

50 mm to 110 mm

Dimensional deviation:

Compatible with traditional bearings

DC resistance

At room temperature, the layer typically has a

DC resistance of 1–10 GOhm, depending on the bearing size. As the temperature increases, the DC resistance

decreases exponentially, typically by approx. 40–50 % per 10 K. But even at operating temperatures of 60 °C

or even 80 °C, the insulating layer still has a resistance of several MOhm. According to Ohm’s law (I = U/R),

this means that voltages of up to 1 000 V only produce currents that are significantly below 1 mA, which are not critical for bearings.

AC resistance

The insulated unit acts like a capacitor (C) which can accumulate charges. When exposed to an AC voltage, this causes an alternating current to flow through the

contact area between the rolling element and raceway.

In the case of a harmonic time dependence with

angular frequency w, the rms values for current and voltage are calculated using the formula

High-quality coating

Insulated bearings feature an insulating layer of aluminium oxide applied by a sophisticated plasma spray process for outstanding quality, which provide the following beneits:

• Resistance to common media used in bearing applications

• Protection over a wide range of operating temperatures

• Minimum electrical resistance of 200 MOhm

• Tested to withstand voltages of 3 000 V DC (coatings that can handle higher voltages can be quoted on request)

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