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How superfinishing boosts component reliability


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November 19, 2012 by  

Major gearbox component failures entail the largest of wind turbine repair costs. Failures such as overheating and contact fatigue cause turbine downtime and result in a loss of revenue. O&M costs can significantly increase over a turbine’s lifecycle. For example, costs are 10 to 15% of production costs and grow to 20 to 35% later in turbine life. A complete gearbox overhaul is likely needed every five to seven years and carries replacement costs in excess of $250,000 per 1.5MW turbine. With turbines sizes increasing, large-multistage gearboxes are needed that require complex maintenance making traditional repair techniques inadequate. So it is safe to say gearbox reliability is critical to O&M cost reduction.

An Isotropic Superfinished surface has no asperity peaks, only a non-directional surface texture.

A Ground Surface has directionally oriented, parallel rows of surface asperities.

As an alternative to traditional component repairs and replacements, the isotropic superfinishing (ISF) process can reduce wear, overheating, stress concentrations, and thereby extend gearbox component life. REM Surface Engineering’s (www.remchem.com) ISF process produces a chemically-accelerated vibratory finish that reduces surface roughness to <0.1 μm Ra on gearbox components. Typically used for gears and bearings, the process creates a smooth, textured surface. ISF flattens and micro-textures the surface while maintaining a component’s geometry. Unlike a ground surface that is directionally-oriented with parallel rows of surface asperities, ISF creates a surface that has no asperity peaks and only has a non-directional surface texture.

ISF repairs micropitting, scuffing, fretting, corrosion, and foreign object damage.

ISF eliminates stress initiation sites at peak asperities and valleys which increases lubricant life, and reduces gear and bearing viscosity, and friction. As an easy-to-implement option, the process is applied to existing designs without need for design changes,says the company. It also decreases the effect of load and speed variability, and reduces micropitting making the gearbox lifecycle three to five times longer. Ultimately, the process extends the life of the gearbox which increases turbine availability. This reduces maintenance requirements and lowers the costs of operation. Furthermore, larger operating safety margins allow for an increase in load carrying capacity.

ISF repairs micropitting, scuffing, fretting, corrosion, and foreign object damage. Benefits to owner operators are said to include:

  •  Faster turnaround times – About two weeks for a complete 1-stage planetary gearbox
  • No setup loses− No gears are destroyed in the machine setup
  • Flexible stock removal − <10 micron per side (~0.45 thousandths) to >75 micron per side (~3 thousandths)
  • Better final surface finish – An ISF processed WT Gear Final Finish ~0.05 to 0.1 μm Ra (four to five times better than regrinding) WPE

Windpower Engineering & Development

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