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Araldite AW 4856 / Hardener HW 4856, a Germanischer Lloyd (GL) approved epoxy adhesive system from Huntsman, is designed to improve productivity and increase fatigue resistance for wind blade shell bonding and repairs.
According to Huntsman, as a wind blade spins, it is subject to static and dynamic forces that vary along the blade from the supporting root to its tip. To account for these diverse loads, Araldite AW 4856 / Hardener HW 4856 has been formulated to deliver increased toughness, offering outstanding load bearing strength and a lap shear strength of 22-25MPa.
Huntsman explains that its two component structural adhesive combines excellent shear strength with improved linear shrinkage and higher fracture resistance to standard epoxy wind blade adhesives. In comparison to the previous adhesive from the range (which had a linear shrinkage of 1.5 to 2.0%), it says this adhesive has drastically reduced linear shrinkage in the range of 0.2 to 0.6%. This would serve to reduce internal stress during curing.
This adhesive’s toughness and fracture properties have also been enhanced. The fracture toughness, in other words the ability of a material containing a crack to resist fracture, has increased from 1.2-1.3 MPa.m1/2 to 2.9-3.2 MPa.m1/2 – a major benefit for the blade service life once installed.
In the wind industry, Huntsman has identified the ability to optimise the adhesive application on very large surface areas and minimise labour intensive assembly processes as a key factor. This is where it says Araldite AW 4856 / Hardener HW 4856’s chemical thixotropy can deliver significant advantages in developing non-slump properties very quickly after mixing and offering controlled flow as well as resistance to sagging. Its low exothermic properties also enhance performance through low shrinkage for thick bond lines, the lessening of residual stress in the finished joint and the possible use of cheaper core material in the composite.
In combination, this system’s good thixotropic and low exothermic properties lead to improved process efficiencies, characterised by easy handling and mixing, a long pot life of 240 minutes at 23C, fast strength build-up and reduced curing cycle capabilities. The standard recommended cure time of 5 hours at 70C could be reduced to 2-3 hours at 70C with the necessary minimal mechanical properties – including lap shear strength, Tg and E-Modulus.
One of the key trends Huntsman has seen in the wind industry is the push to increase productivity as manufacturers strive to reduce cycle times and cut costs. As a result, there’s a need for materials with faster strength build-up and the provision of a resilient bond that consistently delivers end product performance. Araldite AW 4856 / Hardener HW 4856 is designed to be well positioned to meet these requirements.
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