Araldite AW 4856 / Hardener HW 4856, a GL approved epoxy adhesive from Huntsman Advanced Materials, is designed to improve productivity and increase fatigue resistance for wind blade shell bonding and repairs.
As a wind turbine 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 adhesive has been formulated to deliver increased toughness. According to Huntsman, the adhesive offers outstanding load bearing strength and a lap shear strength of 22-25MPa.
The two-component structural adhesive is also said to offer improved linear shrinkage (0.2-0.6%) and higher fracture resistance over standard epoxy wind blade adhesives. Its fracture toughness is 2.9-3.2 MPa.m1/2. In the wind industry, the ability to optimise the adhesive application on very large surface areas and minimise labour intensive assembly processes has been identified as a key factor. This is where 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.
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 23°C, fast strength build-up and reduced curing cycle capabilities. The standard recommended cure time of 5 hours at 70°C could be reduced to 2-3 hours at 70°C with the necessary minimal mechanical properties – including lap shear strength, Tg and E-.modulus, Huntsman reports.