MechChem Africa September-October 2021

Specialty rotating shaft solutions for the renewable energy sector

MechChem Africa talks to Saien Rugdeo, SKF’s sales and business intelligence manager for Gauteng and North West Province, about specialty solutions and services developed for wind turbines and renewable energy generators.

“G lobally, SKF partners with many of the wind turbine OEMs such as Nordex , Siemens and Vestas. These OEMs use either their own designed com- ponents or they incorporate gearbox and generator units from other manufacturers for installation into theNacelles of theirwind turbines,” begins SKF’s Saien Rugdeo. “Our core focus as SKF is on themaindrive shaft. Depending on the designof the turbine, this is either a direct drive with a large bear- ing connected directly to the generator; or a convectional bearing arrangement with a supported shaft connecting to the generator via a gearbox. “The generator itself, which is the source of the electrical generation as well as the

units for direct drive turbines, which are designed to be integrated into theNacelles, canbe inexcess of 2.0 to 2.5 m in diameter. These bear- ings come with integrated sealing carriers to improve cleanliness and reduce the risk of bearing contamination during the mount- ing process. The integrated seal design alsohelps to reduceweight and associated costs, and it makes seal replacement easier from the topof the turbine,without having to dismount the carrier,” Rugdeo says. “Fostering our industry partner- ship, we also supply a range of spe- cialty products purpose developed for the industry, which trusts us because of our 100-year legacy of developing fit-for-purpose quality solutions and our ability to deliver at the scale and performance levels necessary and ex- pected,” he tells MechChem Africa. A particular innovation with respect to the bearing design for wind turbines is SKF’s black oxide coating. Black oxide is a rolling element coating developed for environments where lubrication requirements are criti- cal, particularly in low lubrication and high moisture applications. This coating, which was originallyaproprietarySKF innovation, is nowwidely used for offshore turbines. “Black oxide coatings enhance grease adhesion to the rolling element surfaces and are ideal for inaccessible environments where regular re- lubrication is prohibitive but critical for long

connecting gearbox, also re- quires high quality precision bearings for the rotating generator coils,” he contin- ues, adding that SKF bearing products supplied to the wind turbine industry are

term reliability. This is now standard onmost main shaft andgearboxbearings,” heexplains. Becauseof theelectrical natureof genera- tors, SKF has also developed speciality prod- ucts to overcome current leakage, which is a common cause of generator bearing failure. “An electrical path coming through the roll- ing elements of the bearing to the outer or inner ring can cause sparking, which causes electrical erosion on the bearing contact sur- faces anddamage to the lubricant. This is very common if steel bearings are used,” he says. SKF offers two potential solutions. The first is called INSOCOAT, which is a INSOCOAT coatings create an electrically insulated barrier to prevent current leakage. Left: INSOCOAT deep groove ball bearing. Right: INSOCOAT CARB toroidal roller bearing.

vital components that keep the turbines ro- tating and generating safely, efficiently and reliably. The bearings used for wind turbines tend to be large, wi th average shaft sizes exceeding 400 mm. “Our Nautilus hub-

physical surface treatment of alu- minium oxide applied to the in- ner or outer racewayusing the plasma-spraycoatingprocess. INSOCOAT coatings produce an exceptional surface fin- ish that creates an electrically insulated barrier to prevent current

leakage from occurring. “We offer specialty SKF Hybrid bearings to solve this problem. These have rings made of steel, but instead of using steel rolling ele- ments, Hybrid bearings use ceramic silicon

Above left: An SKF Hybrid deep groove ball bearing. Hybrid bearings use ceramic silicon nitride rolling elements. Above centre: SKF Nautilus hub units for direct drive turbines can be in excess of 2.0 to 2.5 m in diameter.

28 ¦ MechChem Africa • September-October 2021