Composites on the Upturn
27 August 2007
The success of wind energy would not have been possible without the use of composite materials.
Roman Gaugler, owner of company Gaugler & Lutz oHG from Aalen Ebnet says "In the next few years we will see a yearly increase in the number of wind turbines from 15 to 20 percent. Above all this is due to large offshore projects and the now very loud demands for climatic protection." In addition the plants will have continually improved performance. "Currently more and more 5 MW wind turbines are being ordered, the future is likely to be 10 MW wind turbines and 80 metre long rotor blades. Moreover, longer rotor blades mean that more material will be needed - we are counting on this."
In the meantime material deliveries to the wind energy sector form almost 80 percent of the total sales volume of Gaugler & Lutz. Its list of customers includes all the well-known German wind power plant constructors. The company has about 150 employees and is specialised in the processing and fabrication of core materials for light and sandwich construction. Gaugler & Lutz will present an insight into its product range at the coming COMPOSITES EUROPE (6th to the 8th of November 2007, Stuttgart ), the European trade fair for composite materials. As well as special foam materials and balsa woods, the trading company supplies reinforcement fibres for the entire composite sector and operates its own production facilities. The company's processing spectrum ranges from CNC controlled fabrication to hand fabrication, various types of surface processing, the manufacture of kits, and right up to thermoforming.
Low weight but high strength and rigidity – these properties make composites interesting as construction materials. Composites being light weight materials are used in many industries, especially for wind energy generation. The giant rotor blades consist of two half shells, which have the appropriate shape and are made of cross-linked dense, rigid foam in which balsa woods are incorporated and are then glued to another. The balsa wood is grown on plantations in Ecuador and felled after six years. The approximately one metre long tree pieces are cut into square timbers and glued together to form 1.22 meter long and five centimetre wide blocks.
These blocks are cut, in the opposite direction to the grain, into boards and given a fine spraying of resin solution to protect them against humidity. Then on one side a fine glass fabric is laid on which is then punched out from the other side into small square pieces. The rigid foam elements have a density of 60 kilograms per cubic metre and are supplied in 2,450 by 1,150 times 78 millimetre size blocks. Afterwards they are split into boards then cut to size and numbered according to the specified format. After the edges have been trimmed the blocks are packed. Using the help of a layout plan in each box, the respective part is allocated to the rotor blade shape accordingly.
"Currently, vacuum injection is the main processing method used. It offers significantly better industrial safety, an exact dosing of the resin, there are no bubbles produced in the laminate and it adheres better to the core materials", explains Gaugler. About 4,000 rotor blades per year are produced in this way using the help of materials made by this company, which is located in Baden-Wurttemberg. The owner reveals that "at the moment the smallest measures 27, the largest around 60 metres". At the beginning of the 1990's, Gaugler & Lutz introduced the so-called kit construction of light components for the wind energy sector into their product range.
Not only the right raw materials are needed but also their specific composition is an important prerequisite for their use in the wind energy. The industrial production of the giant wings would not be possible without the use of specialist plastics. Neither the model, the moulds for the construction of the rotor shells, nor the rotor blades could be manufactured without these plastics. Also the gluing of top and bottom shells would not be achievable. So that the epoxy and polyurethane resins as well as modelling and adhesive pastes can be prepared in the correct composition for use, two component dosing and mixing plants are necessary such as those manufactured by the company Tartler GmbH from Lützelbach – also an exhibitor at the COMPOSITES EUROPE.
The company has developed special, more efficient, flexible two component mixing plants for the economic production of wind turbine rotor blades. If SMP (Seamless Modelling Pastes) or epoxy pastes are used in large quantities then the Nodopox 200 mixing plant is used during the construction of the models. Depending on the viscosity and composition ratio it can extrude up to five kilograms per minute. The dosing ratio can be steplessly controlled from 100:10 to 10:100. The dosing pumps and mixing heads are driven by frequency regulated motors. There are appropriately alternative uses for PU pastes. Nodopox machines are also used during the construction of laminated shapes for the wing halves, which are made with epoxy resins.
Tartler manufactures Nodopur two component mixing and dosing systems for the production of the two half-shells. They can produce up to 40 litres per minute and can intelligently control the vacuum supported injection of glass fibre reinforced epoxy resins during the vacuum infusion procedure or directly using Resin Transfer Moulding (RTM). Tartler also supplies an acceptable mixing and dosing machine for the adhesive paste used in the "marriage" of both wind wing half shells. If the surfaces of the finished rotor blades are to be given a highly reactive coating the CG 52 machine is suitable for this job.
One of the special features of the machine is its rotating mixing nozzle with rpm control. These in-house developments enable a high rpm and produce an optimal mixing of the components. At the same time stiffeners on the mixer components increase their service life. Furthermore, there is no dead space in which the material can move independently; this is because the mixing components reach right up to the front end of the mixing tube. Also, a premixer directly at the valve outlet ensures an immediate mixing.
However, composites not only help reduce the weight of rotor blades. The company FWT Wickeltechnick GmbH in Neunkirchen in Austria produces drive shafts for wind turbines using glass reinforced plastics (GFC). About 60 units were delivered last year. "Low weight, temperature resistance and reliable transmission of force make this material very interesting for this application", explains managing director Günther Kautz. Another decisive criterion is the electrically isolating nature of the glass fibre.
During the processing the company uses Filament Winding Technology (FWT). Using the help of this winding technology rotationally symmetric components are manufactured by laying resin-soaked fibre rope onto winding mandrels. The manufacture of a shaft or a tube is divided into the steps: winding, hardening as well as parting and removal. Then the fibres with spools weighing between one and six kilograms are placed into the spool spindles. Using pneumatic pressure the spool brake is activated in order to keep the tension in the fibre during the winding process, which helps achieve a good laying.
The fibres are unwound from the spool spindles and through the resin section in which they are impregnated. A dip roller takes resin from the bath and soaks the fibres with it. The pressure of a squeeze roller is used to wipe off excess resin from the fibres and they can then be fed on to proper winding process. The resin bath can be heated according to requirements in order to influence the viscosity of the resin. From there it goes to the winding mandrel, which is coated with non-silicon release agent. The laying of the fibres is carried out on a CNC controlled winding machine with four programmable axes. This guarantees an exact layout and the reproducibility of the components.
After the winding process the wound mandrel is then placed into a circulating air oven and rotated. It is hardened according to a resin-specific hardening cycle. During the process the chamber temperature is recorded using a non interacting recording instrument so that compliance with the hardening cycle can be checked. The hardened tube is cut to the required length and then pulled from the mandrel using the pull-out device. Afterwards the tube is processed further according to the customer's specifications. "In the winding procedure all normal types of fibre can be processed such as glass, carbon and aramide fibres", says Kautz. His company also presents itself at the COMPOSITES EUROPE.
Vestas, Enercon, LM Glasfiber — as well as the top names in the wind energy industry there are also worldwide around 1,500 suppliers from the plastics processing industry that are customers of the company BÜFA Reaktionsharze GmbH & Co. KG from Rastede, another COMPOSITES EUROPE exhibitor. "Over the last few years the subject of wind energy has become more and more important", says managing director Jürgen H. Aurer. In the meantime, twelve percent of the turnover of 70 million euros is generated in this sector. In addition to a special adhesive – an adhesive resins based on vinyl ester, which is used to glue the rotor blade shells together – the most important product in this segment of the market are:above all release agents, glass fibre materials as well as GFC processing machines. "One can say that around 1,000 rotor blades are produced every year thanks to our help", Aurer reckons.
The vinyl ester resins of the company with around 160 employees are custom made according to the requirements of the moulder. These are easy workability, very good physical properties, especially when used with fibre reinforcements, and the endless new ways of customising them according to the changing requirements. They are especially suitable for the manufacture of rotor blades because they can be easily removed from the mould. The moulder must achieve shorter and shorter cycle times. The moulds for the rotor blades are extremely expensive. This means that the mould must be emptied and refilled as quickly as possible", Aurer describes the material specifications.
The managing director of BÜFA expects a rapid growth in wind energy in the next few years. Up to the year 2010, experts predict a doubling of the currently installed power generation capacity of 74,000 megawatt, whereby the USA due to appropriate political decisions will undertake a leading roll. A yearly rate of increase in the double figure percentage range is therefore pre-programmed. "This wind energy sector is a strategic growth segment in our company. Therefore we have formed our own group of experts", says Aurer.
|Dr. Mike Seidensticker |
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Fax: +49 (0) 211 90191-138