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ITW Plexus has developed fast-curing, 1:1 methacrylate structural adhesives for turbine blades.

These advanced methacrylate adhesives chemically fuse FRP/GRP, composite stiffener spars and perimeter flange joints.

They also give increased peel resistance and cycle fatigue resistance while reducing damage encountered during transportation.

Room temperature snap cure properties have helped to increase production rates and eliminate the high capital expenses and energy costs associated with post-bake ovens that are required to cure some epoxies.

No abrasion or surface preparation is required.

The company’s MA560 and MA590 adhesives are also claimed to increase blade performance and reduce processing time.

Effective resistance to bending and fatigue is a major consideration in blade design as the outer composite shell cannot perform this function without the assistance of internal stiffening.

Box and C-shaped structures are often used to provide the required bending strength and stiffness; these stiffening structures are bonded to the interior of the turbine blade.

As the blade parts are generally bonded together, strength and durability of the adhesive bonds are another design consideration.

This can become a limiting performance factor in conjunction with the performance of the composite itself.

According to blade qualification procedures, the bending strength and fatigue strength must be sufficient for a 20-year life, and part of the procedure requires full-scale test on prototype blades.

Adhesives must withstand the centrifugal forces applied to each blade and display high resistance to stress, fatigue and ageing.

To ensure long-lasting joints, the adhesive must withstand outdoor exposure, significant temperature ranges and lap shear strengths in the range of 4,000psi (27MPa).

As adhesives are used to bond two halves of a blade and the spar while filling substantial gaps on structures up to 60m long, they must maintain the bond strength for the blade’s lifetime.

Bonds must endure lifetime ambient conditions with daily cycling.

Improved cure profiles and reduced peak temperatures.

The adhesives developed by ITW Plexus for the wind sector are able to chemically fuse composites to give strong bonds.

Superior bonding strength is achieved and little or no surface preparation is required.

They give high resistance to stress, fatigue and outdoor exposure, and utilise a room-temperature curing mechanism.

As a result of using these products, ITW said that the manufacturer can expect to experience: reduced production costs; shortened assembly times; increased throughput; reduced component weight; improved blade quality and manufacturing process; plus excellent resistance to water and UV.

Terom Wind Energy, Bologna, Italy, has used the adhesives in a a recent application.

The company designed and manufactured a small-size wind turbine – the ATBV26 – suitable for low wind speed sites, using a wide diameter rotor and a very efficient technology involving a multi-pole direct-drive permanent-magnet generator, variable pitch, active pitch and yaw control system.

Nominal power is reached at a wind speed of less than 8m/s and energy yield is particularly high: 3,000 equivalent hour production in a site with average wind speed of 5m/s.

Glass fibre-reinforced polymer blades have been internally designed and produced using a vacuum-infusion process.

This system allows complete saturation of glass reinforcements with resin and offers a very good fibre-to-resin ratio as the vacuum minimises air pockets forming between fibres and the permeability of the fibreglass.

Blade components, made using special moulds, are then finished and bonded together using a Plexus structural adhesive.

The total result is a strong but light product with very good mechanical resistance properties.

ITW Plexus has also developed some adhesives/fillers that the company said are becoming a standard for servicing wind blades in the field.

Plexus MA530 and MA425 adhesives can fill gaps up to 18mm in depth and are now being used to fill cavities.

Because of their good adhesion they are less dependent on the condition of the surface.

MA530 and MA425 do not require heat for curing, which allows a service engineer to carry out work in the field.

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