APPLICATION TECHNOLOGY
Achieving maximum energy efficiency
The coated fasteners installed in offshore wind energy plants are amongst the most safety relevant components of a wind energy unit. As a consequence, they need to be as maintenance free as possible in order to achieve maximum possible energy efficiency.
T I
he fastener elements in the plants of well-known manufacturers therefore frequently utilise a system structure comprising the basecoat and the topcoat Delta®
-Tone Delta®
& Co KG, based in Herdecke, Germany. Dörken MKS-Systeme has already received various
specifications for this system from well-known manufacturers of wind energy plants. This has also been confirmed by Germanischer Lloyd, which recently issued the certificate for the use on standard bolts in wind energy plants in the onshore and offshore fields. The high strength fastening elements coated with this system, in particular those in the dimension range M24 to M48, have already been successfully employed in gondolas and rotor blade fastening for many years.
Optimal corrosion protection is also required for fasteners -Seal of Dörken MKS-Systeme GmbH
in the onshore field too, because the largest wind energy units of all are employed onshore. These may reach a height of up to 125 metres, with a rotor span of some 100 metres. The largest onshore wind park in Europe is currently under construction in Fantanele, Romania. The 240 x 2.5MW wind energy units incorporated there have a nominal output of 600MW. August Friedberg GmbH supplies various fastener elements for the wind park, coated with Dörken MKS-Systeme products. “Alongside countries such as Latvia, Croatia and Switzerland,
Romania has long been lagging in the field of wind energy in Europe. With the construction of the Fantanele wind park the country has advanced amongst the front runners.”
www.doerken-mks.com
The importance of Compression Limiters
Christie Jones, market development manager at Spirol International, looks at how to ensure correct installation of Compression Limiters and threaded inserts into plastic assemblies.
n applications where the mating component is also plastic, a Compression Limiter is necessary to avoid the creep or stress relaxation in the mating component from reducing the frictional load in the threaded joint. Similar to threaded inserts, Compression Limiters are used to ensure bolted joint integrity in plastic assemblies. As the bolt is tightened to achieve the required friction between threads, the plastic is compressed. The Compression Limiter
absorbs the force generated during tightening of the bolt, and isolates the plastic from excessive compressive loads. Without the Compression Limiter, plastic will creep resulting in the loosening and eventual failure of the joint. The Compression Limiter ensures that the joint remains intact throughout the life of the product. In order for the Compression Limiter to work properly, it should abut the insert, so that the insert and not the plastic, carries
the load. The internal diameter of the Compression Limiter in the mating component must be larger than the outside diameter of the assembly screw, but smaller than the pilot or face diameter of the insert to avoid ‘jack-out’. Headed inserts such as Spirol Series 16,
20, 25, 28, 30 and 51 are designed to increase the contact surface for the Compression Limiters. In addition, Series 14, 19, 24, 41 and 45 generally have adequate surface area. In any event, at the design stage proper contact needs to be evaluated.
If the pilot diameter of the insert being used is too small for the inside diameter of the Compression Limiter, then a special
Compression Limiter with reduced clearance between the assembly screw may resolve the problem. This of course also reduces permissible misalignment. If the surface area of the insert is inadequate for proper contact with the Compression Limiter, then the only solution is
using a plastic in the mating component that has good anti-creep characteristics and using a Compression Limiter with maximum wall thickness for better distribution of the load. Jack-out in these situations will be a concern and needs to be addressed whilst avoiding over-torquing the assembly screw.
134 Fastener + Fixing Magazine • Issue 78 November 2012
www.spirol.com 4.E130
6.N131
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