SKF 6316 M/C3VL0241 INSOCOAT Insulated Ball Bearing

An insulated ball bearing that blocks stray current in large motors and generators

The SKF 6316 M/C3VL0241 is an INSOCOAT single row deep groove ball bearing with an electrically insulating coating on the outside surfaces of the outer ring. The coating keeps stray electric currents from passing through the bearing, which protects the raceways against electrical erosion damage and helps prevent the lubricant breaking down from current discharge. The bore is 80 mm, the outside diameter 170 mm and the width 39 mm.

Shaft currents are a known problem in AC motors fed by frequency converters and in generators. The SKF brochure recommends outer ring coated INSOCOAT bearings for medium size motors that use 6215 and 6313 size bearings and larger, and suggests hybrid bearings where smaller bearings are used. The 6316 size falls well within the outer ring coated range.

Technical specifications

What the suffixes mean

Following the SKF brochure: VL0241 identifies a coating on the external surfaces of the outer ring, M is a two-piece machined brass cage, and C3 is a radial internal clearance larger than normal. The coating is an aluminium oxide layer applied by plasma spraying and sealed against humidity and water, and SKF states that it does not influence running accuracy. Performance data and dimensional accuracy are identical to those of standard non-insulated bearings.

The electrical specification printed for VL0241 is a resistance of at least 50 megohms and a breakdown voltage up to a maximum operating voltage of 1 000 V DC. A higher grade, VL0246, is listed with more than 150 megohms and 3 000 V DC, and the inner ring coated variants VL2071 and VL2074 are recommended for the largest motors, starting at bearing sizes such as 6226 and 6324.

Fitting guidance and what to confirm

Outer ring coated INSOCOAT bearings can be mounted with the same fits as a standard bearing and are suitable for all types of housing, without additional mounting precautions. The housing shoulder or spacer sleeve should not be smaller in diameter than the stated minimum abutment dimension; this bearing lists 154 mm minimum, 158 mm maximum on the housing side and a shaft abutment of at least 92 mm. The reference speed is 8 500 r/min and the limiting speed 7 500 r/min.

Confirm the coating variant (VL0241 against VL0246 or an inner ring coated version), the cage, the clearance class and the required voltage rating before ordering, and agree the insulation requirement for both ends of the motor shaft with the motor manufacturer. More bearing products are listed under Electric Motors. An ordinary all-steel sealed bearing for comparison is the SKF 6206-2RS1.

Documents and quotation

The attached SKF brochure on INSOCOAT and hybrid bearings explains the coating, the electrical properties, the design recommendations and the assortment. The dimensions and ratings in the table are from the SKF product page for this designation. Seven Star LLC, an independent supplier in Muscat, will quote on the designation and quantity you send.