DUROCOAT DC77

Electrical Discharge Damage

Electrical erosion (Elektroerosion) is a well-known problem in the rolling bearing industry. Every damage catalogue of reputable rolling bearing manufacturers documents the typical characteristics after current passage:

Microcraters

• Only a few micrometres (µm) in size
• Visible under a microscope
• Raceways appear grey and dull to the naked eye
• Caused by locally high temperatures in the contact zone, where material melts
• Classified as primary damage

Microcrater

Ripple Formations / Washboard Effects

• Appear perpendicular to the raceway direction
• Caused by mechanical vibrations generated as rolling elements pass over microcraters
• Classified as secondary damage following microcraters

Ripple formation

Lubricant Blackening

• Caused by locally high temperatures
• Leads to oxidation of the lubricant
• Changes the composition; oils and components burn or coke
• Reduces service life until lubrication fails completely
• In the final stage, the lubricant turns black and hardens

Solutions Against Current Passage

Solution 1: Ceramic Coating on Outer or Inner Ring

• Available in various coating thicknesses
• Ready-to-install solution
• All bearing tolerances remain unchanged
• No modification of adjacent structures required

Solution 2: Ceramic Coating on Conversion Parts

• Alternative solution when more cost-effective
• Replacement parts receive the same coating as rolling bearings

Solution 3: Hybrid Bearings

• Bearing rings made of rolling bearing steel
• Ceramic rolling elements (typically silicon nitride Si₃N₄)
• Generally more economical for smaller bearings

DUROCOAT DC77

Bearing rings requiring coating are pre-machined to accommodate the required coating thickness. THB is not limited to standard products; DC77 can be applied to virtually all radial and axial bearing types and sizes.

Production Methods

Reworking: Bearing rings requiring coating are machined completely independently of the base manufacturer.

Series Production: For larger quantities, bearing rings are pre-machined at the factory.

Technical and Quality Features

• All tolerances remain unchanged and are 100% inspected
• Bearings are ready to install
• No modification of adjacent structures required
• All coated bearing rings are sealed and resistant to moisture and humidity
• 100% testing of dielectric strength and electrical resistance after coating
• Batch documentation with employee details recorded for every lot
• Further documentation or serialisation available, including per-ring documentation

Coating Colour

Standard colour: medium grey. White is available upon special request (suffix W).

Dimension Specifications

Standard Coatings DC77 and DC77-1

Electrical Resistance

Dielectric Strength

Other coating thicknesses are available on request, up to a maximum of 300 µm. Coatings rated at 500V or 1000V are not produced.

Current-Insulated Abutment Parts

The technical and quality specifications for rolling bearing rings can be applied to any other component surrounding the bearing. Consequently, coating a shaft component may be more efficient than coating the bearing inner ring.

A part inspection is recommended prior to submitting a quotation request.

Packaging / Labelling / Marking

Bearings are not re-marked after coating. The original markings on the coated rings are therefore no longer legible.

Packed in original packaging with an additional adhesive label.

Original packaging with additional DUROCOAT identification label

DUROCOAT DC77 product specification label

Designations of Other Manufacturers

Only the following manufacturers offer comparable systems under protected trade names: