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Hardening of slewing rings

Wind is the ideal energy source. It’s safe, it’s clean, and there’s an endless supply. But harvesting and converting it into electricity poses challenges. The large slewing bearings used in wind turbines, for example, are subject to extreme loads and near-constant operation. Such conditions mean the slewing rings must be hardened without producing so-called ‘soft spots’ or ‘soft zones’. These zones are caused by unintentionally heating already hardened areas—in effect tempering, or softening, the metal.

Induction hardening of slewing ring 

 

Wind is the ideal energy source. It’s safe, it’s clean, and there’s an endless supply. But harvesting and converting it into electricity poses challenges. The large slewing bearings used in wind turbines, for example, are subject to extreme loads and near-constant operation. Such conditions mean the slewing rings must be hardened without producing so-called ‘soft spots’ or ‘soft zones’. These zones are caused by unintentionally heating already hardened areas—in effect tempering, or softening, the metal.

 

One way of achieving seamless hardening (i.e. rings hardened without any soft zones) has been to use furnaces. But the drawbacks are significant. Furnace hardening is a slow, energy inefficient process. And unlike induction, furnaces cannot deliver precise and customized heat patterns. Induction’s minimal heat input results in considerably less torsion in the ring compared to furnace hardening. At the same time, the risk of soft zones has limited the potential for induction hardening. But not anymore. An EFD Induction patented solution now brings the benefits of induction hardening to even the biggest rings.

 

The solution is our multi-coil Seamless Hardening Process (SHP). A technology that has already been used for some of the world’s most demanding engineering companies, SHP uses several independent coils to move around a stationary ring. The end result is a perfectly hardened ring free from soft zones. Of course, the SHP is not limited to the seamless hardening of wind turbine slewing rings. The solution can also be used to seamlessly harden any large ring.

 

Business opportunities

For Helmut Schulte of EFD Induction Germany, SHP is much more than exciting technology: “It’s another example of EFD Induction technical excellence. But the true importance of SHP lies in the commercial benefits it brings to our customers. For example, SHP makes it easy to harden rings to the specifications of the wind turbine market. And that’s a market with a huge growth potential.”

 

‘Huge’ is an understatement. In fact, wind is perhaps the world’s most dynamic energy industry. According to the World Wind Energy Association, the number of wind installations in the world more than doubled between 2005 and 2008. In the US alone, 8,358 MW of new generating capacity was added in 2008—a 50 per cent increase in the country’s total wind power generating capacity. And in China, installed wind power capacity surged from a mere 1,260 MW in 2005 to 12,210 MW in 2008. “Of course,” continues Schulte, “the current economic climate may dampen wind energy growth in the short-term. But there are still very positive signs. For example, the British government recently earmarked GBP 525m (EUR 589m, USD 800m) for offshore wind projects over the next two years.”