A wind turbine is held together by bolts that are inspected and tensioned in a structure that moves in every gust. The thread on those bolts is cold rolled, not cut. Rolling forms the thread by pressing the steel into shape, which leaves the thread root stronger.
Where the bolts sit
Bolted joints run the length of a turbine, and each position has its own size range. Dokka Fasteners, which supplies the wind industry from plants in Dokka in Norway, Brande in Denmark and Klaipėda in Lithuania, lists the picture clearly across its wind power range:
- Tower flange bolts and studs from M36 to M100
- Blade connection kits and blade studs from M24 to M48
- Studs, hex bolts and threaded rods from M24 to M100
- Foundation bolts and kits
- Transition piece and monopile connection fasteners up to M100
The range is supplied in property classes 8.8, 10.9 and 12.9, with coatings from hot dip galvanising and zinc flake through to PTFE.
Why the thread is rolled
A thread can be cut or rolled. Cutting removes material. Rolling presses the steel into shape without removing any, which leaves the thread root stronger, and the root is where a fatigue crack starts. In fatigue testing on bolt steel, rolled threads reached more than twice the fatigue strength of cut threads. For a bolt that is tensioned once and then carries load from every gust, that difference decides how long the joint lasts.
What rolling M100 actually demands
Forming a thread on an M100 bar means driving a rolling head into hardened alloy steel while holding the bar concentric and rigid over its full length. The forces are high, the part is heavy, and any deflection ends up in the thread.
The AKEA GA Series is built for that class of work, combining chamfering, peeling and thread rolling on tube, bar and rebar in one machine:
- Diameters from ø12 to ø100 mm
- Threads from M12 to M100
- Part lengths from 300 mm to 6,000 mm
- 50 to 500 parts per hour
- 1 to 3 spindles and 1 to 3 clamping vices
The rolling heads matter as much as the machine. LMT Fette’s EVOLine axial rolling heads cover F55Evo to F85Evo and threads from M18 to M100x6. The head forms the thread, and our machines do everything around it. LMT Tools Brasil has shared film of an AKEA machine running an F75 EVO head on wind energy fasteners.
Throughput is a supply chain question
Where a line lands between 50 and 500 parts per hour is decided by spindle count, clamping arrangement and how much handling sits between operations, more than by the rolling itself.
A wind fastener line is therefore designed as a whole: cut to length, chamfer, peel, roll, and move the part on without an operator touching it.
Talk to us
AKEA Automation develops and builds special purpose machines and automation for metal processing in the steel and aluminium industries, from stand alone machines through to complete turnkey lines with integrated robot handling. For fastener production projects, contact Kasper Bilstrup.
Frequently asked questions
How are wind turbine bolts made?
The bar is cut to length, chamfered and peeled, and the thread is formed by cold rolling. Heat treatment, coating and inspection bring the bolt to its property class and finish.
Why are wind turbine bolt threads rolled instead of cut?
Rolling presses the steel into shape without removing material, which leaves the thread root stronger. In fatigue testing on bolt steel, rolled threads reached more than twice the fatigue strength of cut threads.
What sizes are wind turbine bolts?
In Dokka Fasteners’ wind range, tower flange bolts and studs run from M36 to M100, blade studs from M24 to M48, and transition piece connections up to M100.
What property class are wind turbine fasteners?
Dokka Fasteners supplies its wind range in property classes 8.8, 10.9 and 12.9.
Can one machine thread up to M100?
Yes. The AKEA GA Series covers M12 to M100 on diameters from ø12 to ø100 mm and part lengths from 300 mm to 6,000 mm, with EVOLine axial rolling heads reaching M100x6.