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New challenges for dosing technology in rotor blade production

DOPAG is one of the companies leading development in the area of dosing technology used in the production of wind turbine rotor blades. As wind turbine technology progresses, the demands placed on dosing and mixing systems are on the rise as well.

The design and construction of wind turbines are more than ever being dominated by extremes. On the one hand, the wind turbines must be able to withstand any weather. The tip of the rotor blade could be facing wind speeds of up to 400 km/h, while leading edges are at risk of serious damage by hail, bird interaction or even raindrops. On the other hand, the boundaries of these systems keep being pushed to new extremes. Currently, rotor blades with the length of about 107 meters are being designed and the resulting rotor diameter will significantly exceed 200 meters. With the constantly increasing sheet size, the wing leading edges need to be protected particularly well to be able to sustain high peripheral speeds. Without this protection, the required rotor blade lifespan of over 20 years could hardly ever be achieved, nor would it be possible to reduce the high level of maintenance needed to keep the power plants in operation.

Understandably, all this presents challenges for the manufacturing of these systems. This is in part down to the fact that the rotor blade components are still being produced manually. Although there have been tendencies to automate the process, they have not yet been acted upon. It is therefore all the more important that the industry works to standardise its production processes, as it has been doing. Only this way will it be able to arrive at an efficient production and ensure consistently high quality of the components. This concerns particularly the reduction of mould cycle times of the investment-intensive blade shapes, which is why the infusion process as well as the blade bonding following the hardening phase must be made more efficient.

Material quantities are rising steadily
That is why, especially in the field of dosing technology, there is a call for solutions which can offer the highest precision, reliability and reproducibility all at the same time. Depending on each application, two-component material - especially epoxies and polyurethane resins – is constantly being processed in both small and very large amounts. For example, the requirements on the quantities of adhesive resin used for bonding of rotor blades have risen significantly to more than 300 liters per metering system. DOPAG takes these requirements into account while designing its dosing and mixing systems. The producer’s comprehensive portfolio has a turnkey solution for any application. The dosing system eldomix processes low to medium viscosity two-component materials based on epoxy and polyurethane, which makes it an ideal option for numerous applications in the production of rotor blades. An example would be Leading Edge Protection (LEP), an application for the effective protection of rotor blade tips. The process involves eldomix metering and mixing a two-component polyurethane, which is then manually applied onto the leading edge.

High volume dosing of infusion resin
For the inner structure of the rotor blade alone, more than 2,000kg of epoxy resin are metered, mixed and infused - an enormous task, for which DOPAG designed the dosing system compomix. It can process up to 60 liters of epoxy resin per minute, while keeping dosing accuracy at up to +/- 1 percent. During the infusion process, semi-finished fiber products and sandwich structures are introduced into an open mould and a vacuum-generating equipment is prepared. The resin is then applied by infusion hoses and valves.

Processing of adhesives in large amounts
DOPAG gluemix is a gear dosing system specifically designed for the processing of large amounts of adhesives in rotor blade production. When bonding rotor blades of the current standard size (55 to 70 meters), over 600kg of glue is required for each blade. The quantities get even more extreme with the newer blade generations, rising to some 1,000kg per blade. For components of greater dimensions and thus higher adhesive quantities, a dosing system is available that can produce over 700kg of resin mixture without needing a drum change. The material is refilled air-free at a refilling station into the permanent containers on the dosing system. Emptying barrels of residual material increases the sustainability of the process, bringing in valued material and cost savings.

High-quality surface protection
In order to ensure a lasting stability and efficiency of rotor blades, the entire surface is treated with a high-quality gel or topcoat. The layer is either applied to the composite or introduced directly in the mould as an in-mould gel coat. DOPAG gelcomix is a dosing system designed precisely with this kind of application in mind. The two-component material, usually a polyurethane, is efficiently prepared by the gelcomix system before it is manually applied.

Conclusion
The composites industry in general has been experiencing a steady growth for years. Components made out of fiber-reinforced plastics, which are used in the manufacture of wind turbines, are in demand in many other industries. Innovation rate is very high and this applies no less in the case of rotor blades production, where the design is aiming at ever larger dimensions. In line with these trends, dosing technology will need to bring more solid solutions in the future. Metering and mixing systems must be able to process the increasing quantities of material reliably and contribute to the standardization of the production processes. Anyone wishing to remain competitive will need to keep pace with this development and offer the market the corresponding solutions.

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