During the assembly of wind turbines, the crane brings the rotor blades close to the hub so they can be bolted to it.

The effects of the sea (wave motion) and wind make this is a highly delicate process that has to be carried out extremely slowly and can only be done in low winds to avoid running the risk of damaging the rotor blade or hub.

Question

In order to speed up the assembly process, to make it less weather-dependent and to greatly reduce the risk of damage, Buitink Technology was asked to come up with and design a solution.

The following requirements were specified:

• Compact and lightweight (can be moved and fitted by hand);
• Must be capable of being mounted to the hub and easily removed again;
• Must absorb the impact of the rotor blade hitting the hub and provide a “soft landing”;
• The solution should last at least 50 cycles;
• If possible, the solution must guide the rotor blade slightly and bring it into the right position for mounting onto the hub.

Solution – inflatable bumpers

The solution Buitink Technology developed is a mega XL inflatable bumper. This inflatable bumper is lightweight, flexible, compact when deflated and capable of effortlessly absorbing all large shocks during rotor blade positioning. In addition, the inflatable bumpers must help guide the rotor blades to the correct position.

The inflatable shock absorber is a low-pressure system (the internal pressure never exceeds 500 mbar) and is therefore very safe to use.

The inflatable shock absorber is made of an extremely strong TPU-coated canvas (type VII, with a breaking strength of 13,000 N/ 5 cm) with high puncture resistance. Furthermore, the inflatable bumper is fitted with air connections and adjustable pressure relief valves, which let the pressure out of the cushion in the event of an impact.

An inflatable shock absorber including (aluminium) mounting frame weighs only about 17.5 kg (the frame 8 kg and the pad itself 9.5 kg). The frame and cushion can also be fitted to the hub separately.

Using materials with a very high puncture resistance is essential to ensure the inflatable bumpers for a good, safe and long-lasting service. Buitink Technology has done a lot of research on materials to realize a high puncture resistance. See also our website:

puncture resistance

Testing inflatable bumper cushion

Below is a video of testing the inflatable bumper cushion: by means of a water weight (of approx. 1600 kg) the impact of the cushion is simulated as it happens in practice. 

• In order to simulate the impact of a rotor blade during assembly on the hub, a weight of 1600 kg is lowered onto the pad from a certain height
• The bumper cushion absorbs the fall, as seen in the video.
• This is exactly the intention: the hub and the rotor blade will not be damaged during unexpected accelerations if a cushion is used.

The advantages at a glance

Compared to conceivable alternative solutions using, for example, hydraulics or compressed air, Buitink Technology’s inflatable bumper offers several key benefits and properties:

• The bumpers operate at relatively low pressures (maximum 500 mbar), which makes them safe to use;
• The concept has been proven in practice for many years (in the form of catch bags or landing bags for trucks);
• When deflated, these devices are very compact;
• Inflatable bumpers are very light and can be moved and assembled by hand;
• Made-to-measure in our own factory; we can develop and produce a solution for any type of wind turbine;
• All sizes possible, various choices of thickness/height in inflated condition;
• Customized solutions can be delivered quickly;
• The material is soft and flexible, making it relatively safe and thereby preventing impact damage, say, to the hub and the rotor blade;
• Resistant to all weather conditions, even at sea, does not corrode;
• There is no danger of contaminating the environment e.g. through leakage of hydraulic or other oil;
• Quick and easy to assemble and disassemble;
• Ideal for use at sea: very good seawater and salt resistance, easy and safe to handle and takes up very little space.

Based on our landing bags

The solution is based on the catch bags or landing bags developed by Buitink Technology, see also our website:

catch bags for lorries