--- title: What is the coating on the shaft when a Carbon Block Brush is used? description: What is the coating on the shaft when a Carbon Block Brush is used? image: https://blog.est-aegis.com/hubfs/Imported_Blog_Media/Carbon-Block-with-patena-film-on-shaft-277x300.jpg --- [![Electro Static Technology](https://blog.est-aegis.com/hubfs/raw_assets/public/public/images/electro-static-technology.svg "Electro Static Technology")](https://www.est-aegis.com/) [![Aegis](https://blog.est-aegis.com/hubfs/raw_assets/public/public/images/Aegis.svg "Aegis")](https://www.est-aegis.com/) - [+1 866-738-1857](tel:+1%20866-738-1857) - [Products](https://www.est-aegis.com/products/) - [AEGIS® SGR – for motors under 500 HP/375 kW](https://www.est-aegis.com/product/sgr/) - [AEGIS® uKIT – for common NEMA/IEC frame size](https://www.est-aegis.com/product/sgr-ukit/) - [AEGIS® RPPR – for reactor recirculating pumps](https://www.est-aegis.com/rppr-resources/) - [AEGIS® EV and EVO Rings - for electric vehicles](https://www.est-aegis.com/product/ev-evo-rings/) - [AEGIS® PRO Series – for motors over 300 HP/225 kW](https://www.est-aegis.com/product/pro-series/) - [Shaft Voltage Testing and Accessories](https://www.est-aegis.com/product/mounting-accessories/) - [Online Product Catalog](https://catalog.est-aegis.com/) - [AEGIS® 2-Year Extended Warranty](https://www.est-aegis.com/product/extended-warranty/) - [Applications](https://www.est-aegis.com/applications/) - [Electric Vehicle Solutions](https://www.est-aegis.com/applications/electric-vehicle-solutions/) - [Food & Beverage](https://www.est-aegis.com/applications/food-beverage/) - [HVAC](https://www.est-aegis.com/applications/hvac/) - [Industrial & Chemical](https://www.est-aegis.com/applications/industrial-chemical/) - [Other Industries](https://www.est-aegis.com/applications/other-industries/) - [Power Generation & Renewable Energy](https://www.est-aegis.com/applications/power-generation-renewable-energy/) - [Transportation](https://www.est-aegis.com/applications/transportation/) - [Water Treatment](https://www.est-aegis.com/applications/water-treatment/) - [Bearing Protection](https://www.est-aegis.com/bearing-protection/) - [Shaft Voltage & Bearing Currents](https://www.est-aegis.com/bearing-protection/shaft-voltage-and-bearing-currents/) - [Fluting & Bearing Inspection](https://www.est-aegis.com/bearing-protection/fluting-and-bearing-inspection/) - [Best Practices & Installation](https://www.est-aegis.com/bearing-protection/best-practices-and-installation/) - [Resources](https://www.est-aegis.com/resources/) - [AEGIS® Bearing Protection Handbook](https://www.est-aegis.com/resources/handbook/) - [IEEE-841, Hazardous Locations, & AEGIS®](https://info.est-aegis.com/technical-codes-and-ieee-841-standards) - [Recorded Webinars Library](https://www.est-aegis.com/resources/recorded-webinars/) - [Installation Instructions](https://www.est-aegis.com/resources/installation-instructions/) - [Videos](https://www.est-aegis.com/resources/videos/) - [Technical Papers](https://www.est-aegis.com/resources/technical-papers/) - [Case Studies](https://www.est-aegis.com/resources/case-studies/) - [Specifying AEGIS®](https://www.est-aegis.com/resources/specifying-aegis/) - [Request Training](https://www.est-aegis.com/resources/training/) - [Product Sheets](https://www.est-aegis.com/resources/product-sheets/) - [About](https://www.est-aegis.com/about/) - [News](https://blog.est-aegis.com/) - [Tradeshows](https://www.est-aegis.com/about/tradeshows/) - [Blog](https://blog.est-aegis.com/) - [Where to Buy](https://www.est-aegis.com/where-to-buy/) - [Distributors](https://www.est-aegis.com/where-to-buy/distributors?type=Distributor) - [Trained Installers](https://www.est-aegis.com/where-to-buy/installers?type=Installer) - [Explosion Proof Installers](https://www.est-aegis.com/where-to-buy/installers?type=Explosion%20Proof%20Installer) - [Motors & Seals with AEGIS® Installed](https://www.est-aegis.com/where-to-buy/oems-with-aegis/) [Contact Us](https://www.est-aegis.com/contact/) - [+1 866-738-1857](tel:+1%20866-738-1857) # What is the coating on the shaft when a Carbon Block Brush is used? [Home](https://www.est-aegis.com/) » [Blog](https://blog.est-aegis.com/) » What is the coating on the shaft when a Carbon Block Brush is used? [AEGIS](https://blog.est-aegis.com/author/estaegis) Nov 3, 2016 A highly resistive glaze may form on brush surface, requiring periodic cleaning.  This is sometimes also called a *patina* and forms a visible black non-conductive band on the shaft.  It is also one of the disadvantages of using a carbon block brush for shaft grounding.  It renders the carbon block brush ineffective.   ![Carbon Block Brush causes Non-Conductive Coating on Motor Shaft "patena film"](https://blog.est-aegis.com/hs-fs/hubfs/Imported_Blog_Media/Carbon-Block-with-patena-film-on-shaft-277x300.jpg?width=277&height=300&name=Carbon-Block-with-patena-film-on-shaft-277x300.jpg) Carbon brush causes nonconductive coating on motor shaft (patina)   What to do? ***Clean the shaft where the carbon block brush contacts the shaft and install the AEGIS Shaft Grounding Ring*** in its place. [VFD Bearing Damage](https://blog.est-aegis.com/tag/vfd-bearing-damage), [Carbon Brush](https://blog.est-aegis.com/tag/carbon-brush), [FAQ](https://blog.est-aegis.com/tag/faq), [Shaft Grounding](https://blog.est-aegis.com/tag/shaft-grounding), [Patina](https://blog.est-aegis.com/tag/patina) ### Subscribe To Our Blog ## Read On ### [What Is the Effect of PWM Drives on Electric Motor Bearings?](https://blog.est-aegis.com/effect-pwm-drives-electric-motor-bearings?hsLang=en-us) **Pulse Width Modulated** (PWM) power sources, also known as variable frequency drives (VFD),... ### [Three Types of Bearing Current: Causes](https://blog.est-aegis.com/three-types-of-bearing-current?hsLang=en-us) ### [To Prevent Bearings from Failing Again, Find Why They Failed in the First Place](https://blog.est-aegis.com/prevent-bearings-from-failing-again?hsLang=en-us) The new motor you installed 6 months ago is making the kind of noise you only hear in horror... 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