SKF INSOCOAT Bearings Explained: Features, Advantages, and Selection Guide

Is your motor frequently shut down due to bearing erosion caused by shaft currents, leading to production disruptions and high maintenance costs?

TFL Insulated Bearings, an outstanding alternative to SKF INSOCOAT bearings, completely solves the problem of shaft current erosion in VFD-driven motors with their superior insulation performance and cost-effectiveness. Our products offer an insulation voltage of up to ≥3000V (or an insulation resistance of ≥200MΩ), effectively preventing current flow through the bearing raceways. This fundamentally eliminates electrical erosion and extends bearing service life by over 300%.

SKF INSOCOAT Bearings

SKF INSOCOAT Bearings are one of the industry’s earliest and best-known series of electrically insulated bearings, designed to combat the electrical erosion of bearings caused by shaft currents generated by Variable Frequency Drives (VFDs).

Technical Structure and Working Principle

SKF INSOCOAT bearings are a type of standard precision bearing with a built-in electrical insulation layer. The key principle is the application of an aluminum oxide (Al₂O₃) ceramic coating—formed through plasma-spray technology—on the inner or outer ring surface. This coating electrically isolates the rolling elements from the shaft and housing.

This aluminum oxide coating not only provides excellent insulation performance (capable of isolating voltages from hundreds to thousands of volts) but also possesses good hardness and wear resistance, without significantly affecting the bearing’s installation fit precision.

In VFD-driven motors, this insulation layer effectively blocks the shaft current generated by the PWM (Pulse Width Modulation) waveform, preventing the current from forming “electric pitting” as it passes through the raceway.

Typical Structures:

• Outer Ring Coated Type (Often used in applications where the stator side is grounded)
• Inner Ring Coated Type (Suitable for scenarios requiring rotor-side insulation)

Performance Parameters and Manufacturing Process

SKF INSOCOAT series is designed to maintain the same geometric dimensions and load ratings as standard bearings. Their performance parameters typically include:

• Insulation Resistance: ≥200MΩ (at ambient temperature in a dry environment)
• Dielectric Breakdown Voltage: Approximately 1000V∼1500V DC
• Coating Thickness: Approximately $50\sim100\text{\mu m}$
• Coating Hardness: HV ≥1200
• Operating Temperature Range: −25∘C to +150∘C

The coating is formed using the Atmosphere Plasma Spray (APS) process, followed by grinding and a sealant treatment to prevent moisture penetration. This helps maintain stable resistance performance in humid or condensing environments.

Applicable Fields

SKF INSOCOAT electrically insulated bearings are widely used in motor and generator systems requiring protection against shaft currents, including but not limited to:

• Industrial AC asynchronous motors (especially systems used with VFDs)
• Wind turbine main shafts and excitation systems
• Railway traction motors and high-speed electric vehicle drive units
• High-power industrial pumps, compressors, and paper-making machinery

In these applications, the insulation layer can significantly extend bearing life, reduce lubricant degradation, and improve overall system operating reliability.

INSOCOAT Bearings Product Selection Guide

The SKF INSOCOAT series covers the most common bearing types in motors and generators and is an important reference for selection:

Common SKF INSOCOAT Product Types

TFL: Beyond SKF’s Flexibility in Customization and Cost-effectiveness

With years of expertise in insulated bearing manufacturing, TFL Bearing Factory offers products that are fully comparable to SKF INSOCOAT bearings in performance. TFL delivers significant advantages in supply flexibility and total cost of ownership (TCO). For engineers and procurement professionals focused on technical performance, data, and solutions, TFL represents a strategically superior choice.

Key Comparison: TFL vs. SKF INSOCOAT

TFL is more than just a substitute for standard SKF INSOCOAT; our core value lies in rapid response to customer needs and professional customization.

• Non-Standard Bearing Insulation: We can apply insulation coating to customers’ non-standard bearings (such as special sizes or complex geometries), solving the pain points of equipment modification.
• Custom Coating Thickness: Insulation thickness can be customized to 50 μm or 500 μm to meet applications up to 1000V AC or higher.
• Material Standards: Using high-purity GCr15 bearing steel combined with advanced plasma-spray technology and ISO9001-certified quality management, TFL ensures each bearing meets international precision and insulation standards, available up to P5/P4 accuracy grades.
• Competitive Pricing: While guaranteeing product quality and performance, TFL provides more attractive pricing through efficient production management and supply chain optimization, helping customers reduce operating costs.

TFL Insulated Bearings’ Excellent Performance: Wind Turbine Application

Challenge: An important 5MW offshore wind turbine generator, located on the North Sea coast of Germany, had been long experiencing shaft current challenges induced by its frequency converter drive. In the high humidity, salt spray, and vibration environment prevalent for years, the main shaft bearings typically required expensive downtime for inspection and replacement due to electrical erosion damage every 15 months on average. Each maintenance event (including the dispatch of a professional technical team, spare parts replacement, and significant power generation losses due to downtime) was estimated to cost approximately €40,000.

Solution: In pursuit of a more reliable and cost-effective solution, the wind farm decided last year to replace the original bearings and introduced TFL’s custom-manufactured insulated main shaft roller bearings. After 20 months of continuous rigorous offshore operation monitoring, the main shaft bearings of this turbine have performed exceptionally well, with no further recorded electrical erosion-related failures or performance degradation.

This custom bearing maintained the same installation dimensions and load rating as the original model, ensuring seamless replacement in the existing position. Unlike traditional models, TFL applied an aluminum oxide (Al₂O₃) ceramic insulating layer with a thickness of 200 μm on the outer surface of the bearing’s outer ring using the Atmospheric Plasma Spray (APS) process. This layer provides an insulation resistance of ≥ 500 MΩ and a dielectric breakdown voltage of up to 3000V DC.

To maintain long-term insulating performance in high salt spray and condensation environments, TFL implemented multiple optimization processes for the insulating layer:

• Precision Grinding and Fit Correction: Ensuring that the outer ring’s dimensional accuracy after spraying meets ISO P5 grade requirements, with a fit clearance controlled within ±5 μm.
• Nanopore Sealing Treatment: Using a silicone-modified sealant to seal the pores, preventing moisture ingress into the micropores of the insulating layer.
• Withstand Voltage and Insulation Testing: Each bearing set undergoes a 2.5kV DC withstand voltage test and ≥200 MΩ insulation resistance test before leaving the factory.
• Lubrication and Maintenance: Utilizing synthetic-based high-load bearing grease (NLGI 2 grade), maintaining a good oil film under low-speed, high-load conditions, supporting an expected lifespan of over 5 years.
• Roller and Cage Optimization: Employing super-finished roller surfaces and polyamide cages to further reduce the risk of electrical erosion and improve lubrication conditions.

Results: Since commissioning, online monitoring data shows that the peak shaft current of the main shaft system has decreased by over 90% compared to before the modification, with no further characteristic vibration or noise signals related to electrical erosion. After 20 consecutive months of operational validation in the offshore wind farm, TFL’s insulated tapered roller bearings have demonstrated exceptional reliability and stability. Monitoring data shows:

• Shaft current leakage was reduced from the original 20–30 mA to <1 mA.
• Electrical erosion-related failure rate decreased from approximately 1 per year to 0.
• Bearing operating temperature rise decreased by approximately 8°C, and vibration RMS values dropped by 15%.
• Turbine availability improved by over 3%, leading to significant additional power generation revenue.

This project fully validated the superior performance of TFL’s electrically insulated tapered roller bearings in high-load, frequency converter-driven, and extreme offshore environments, proving their complete substitutability for comparable products from international brands, and offering an innovative solution that combines reliability with cost-effectiveness for the wind power industry.

TFL Bearings – Professional Insulated Bearing Manufacturer

Don’t let shaft currents compromise your equipment reliability. If your motors, wind turbines, or rail systems still suffer from electrical erosion, premature bearing failure, or frequent maintenance, it’s time to upgrade to TFL Insulated Bearing Solutions.

Contact us today for:

• Free bearing selection and technical consultation
• Compatible model cross-reference with SKF INSOCOAT
• Customized coating samples and performance test reports

Email: info@insulated-bearings.com

Our professional team will provide timely technical support and quotations tailored to your needs.