The loads placed on the bearing is a factor of concern, but just making a bearing big enough to work with these turbines is a complicated undertaking. Currently, many of the biggest wind turbines require bearings over two meters in diameter, something that according to Lucas, only a very select few manufacturers can even make, Timken among them. However, the industry isn’t stopping there. They already want to go bigger.
Lucas cited one manufacturer that’s already looking ahead and trying to design turbines so large that they would require bearings over four meters, double the size of what’s already the cutting edge of what the bearing industry can handle. The sheer scale is mind-bogglingly massive, something that almost nobody in the industry has ever had to deal with.
“We’re on a size range of bearings that people have never reached before,” Lucas said.
According to Lucas, a major challenge to upsizing these bearings is that the supply chain is pushing their upper size limits. In particular, heat treatment is a primary concern, as the size required for a furnace to be able to treat such massive bearings would be financially prohibitive. Pieces as large as what Timken would need are rare, so it’s understandable that not many heat treaters would have a furnace set aside capable of handling them. However, heat treatment is a must for these bearings to handle the intense loads they do, so even if we can make bearings that large, finding somewhere to heat treat them is a bit of a predicament, and turnaround time skyrockets.
“Once you get up over two meters in size, there are very few heat treat manufacturers or bearing manufacturers around the world that have the size of heat treatment furnaces needed,” Lucas said.
The key operating word here is “currently,” however. So how is Timken, along with other bearing manufacturers, keeping up with demand for increasingly massive bearings to power towering wind turbines?
Some general tactics involve changing over from spherical bearings to cylindrical or taper bearings and sidestepping the issue of size by making two bearings to achieve the same effect.
“As we start seeing turbines grow upwards into the range of 12 MW and beyond, we’re actually seeing that more and more companies are starting to use two single-row pre-loaded tapered roller bearings,” Lucas said. “And as those bearings move further apart, we’ve actually been able to keep the bearing outside diameter down to a range that’s more manufacturable.”
Along the way, Timken’s found that the cylindrical taper bearings just work better in general for wind turbine applications. Spherical roller bearings, according to Lucas, are excellent at carrying radial loads, but they’re less equipped for thrust and overturning moment loads, both of which they must handle when used as wind turbine main shaft bearings.
“Using tapered bearings on larger megawatt turbines has advantages, because that type of bearing is designed to handle those loads,” Lucas said.
