Pitch Bearing
for Wind Turbines

IMO's  T-Solid pitch bearing –
the solution for prematurely failing blade bearings!

The problem:

Some wind turbine generator platforms do not provide for adequate stiffness to accommodate the widely used 2-row 4-point contact ball pitch bearing.

Issues directly resulting from inadequate stiffness can be clustered as follows:

  • Ring cracking (corrosion fatigue, cracks through filler plugs, cracks next to lifting/stiffening plates, fastening elements & hub cracks)
  • Contact ellipse truncation along with load increase (cage failure, raceway edge & ball fractures and spalling)

As a result several 2-row 4-point (2r4p) pitch bearings fail prematurely and need to be replaced in the field. Neither the blade root nor the hub can be fundamentally reinforced on site – costly multiple replacements are often the consequence. The 45deg contact angle of 2r4p pitch bearings makes it even worse – radial loads resulting from resolution of aero dynamical forces increase the ring separation and cause bearing ovalization.


Lost blade because of cracked outer ring


Blade drop, 2021 in Vienna area


Cage failure due to ellipse truncation


Corrosion fatigue in bolt holes


Cracked outer ring

T-Solid - the solution:

IMO made a change in paradigm: If you cannot avoid the detrimental deformation effects, choose a bearing design which can simply withstand it!

T-Solid, developed and manufactured by IMO, is a 3-ring/3-raceway pitch bearing which has same form, fit & function like the 2r4p pitch bearing to be replaced.

  • The difference comes from the load independent 90deg contact angle: no ellipse truncation effects.
  • No cage – logically no cage issues
  • No filler plugs – logically no cracks through filler plugs
  • Hoop stresses are much lower compared with 2r4p pitch bearings, therefore, T-Solid operational life is much longer.
  • Fatigue issues are history with T-Solid!

T-Solid is field proven in many 1 to 4MW platforms – first T-Solid fielded already in 2016 on a 3-4MW class wind turbine! T-Solid was also chosen by OEM for a 8MW offshore turbine in 2021. T-Solid is available for many platforms including but not limited to hydraulic & electric pitch machines, blade on inner or on outer ring configurations, for OEMs and after sales market.


45deg contact angle in 2r4p


90deg contact angle in T-Solid


T-Solid outline incl. 3 rings | 3 raceways

German engineering, manufacture and quality control. No compromises in design.

Which bearing type to use in which case?

  • In the after sales market T-Solid is first choice for blade bearing field retrofit in turbines which experience a shortfall in fatigue life especially in combination with stiffness issues. As robust as required for 20+ years’ service life at high prevailing hub deformation levels.
  • OEMs use T-Solid for large low wind onshore rotors and large offshore machines.
  • 2r4p pitch bearings (2-row 4-point contact) can be used as replacements in machines in which this susceptible design survived at least half of the service life. IMO 2r4p pitch bearings include a variety of product improvements to address known failure modes.
  • T-Solid remains the better alternative, if life span shall be extended, maybe to 25 years for better return on investment.
  • Never use 3-row roller type bearings for prematurely failing 2r4p pitch bearings! 3-row roller type bearings generally have a much higher demand on stiffness than 2r4p bearings, hence, early failure is almost predictable!


Spare part arriving at site


Field replacement


Retrofit kit swinging in

T-Solid blade bearing
field retrofit kit

Double axial-radial bearing with accessories
for field replacement

Field replacement kit for prematurely failing 2r4p blade bearings

T-Solid blade bearing
general design

Double axial-radial bearing

for OEM collective pitch control


Mr. Hans-Josef Schlicker
Tel. +49 9193 6395 4167