This is Part 3 of a 4-part series explaining recent strides in acrylic adhesives. The case study of a bonded wind turbine shroud shows that adhesives are performing in applications that might once have been deemed impossible.
Some wind turbine designs incorporate shrouds, or rings that increase airflow through the blades by mixing slow and fast air and creating a vortex. Having a shroud increases the turbine's efficiency. One manufacturer decided to use next-generation acrylic adhesives to bond shroud components, knowing that stringent strength and performance requirements would be needed from the adhesive.
Wind turbines must tolerate extreme vibration, temperature fluctuations and environmental exposure. To accommodate such conditions, an adhesive must exhibit:
- Excellent failure mode (even on tough-to-bond substrates)
- High fatigue
- Environmental resistance
- High elongation
- High strength
Making for an even bigger challenge, bonded shroud components were made of two different metals: hot-dipped galvanized metal and aluminum. These metals expand and contract at different rates as the temperature changes; that is, they have different coefficients of thermal expansion (CTEs). The “mismatch” between substrates’ CTEs can put extreme stress on bonded parts, so in addition to being strong, adhesives must be flexible and able to cross-bond different substrates.
The very large parts involved in shroud construction presented another challenge, increasing the risk of variable bondline thickness across the length of the assembly. Because of this, an adhesive must deliver good sag resistance to accommodate large applied beads, have cure kinetics to allow for the longer time required for application, and be able to deliver high performance at variable cured film thickness.
Several tests were performed to prove the efficacy of the chosen adhesive. A failure mode robustness test demonstrated that the next-generation acrylic adhesive outperformed second-generation adhesives across a variety of substrates. The next-generation adhesive also demonstrated superior results in a fatigue resistance test.
Check out Parts 1-2 of our series on next-generation adhesives and watch for our final installment, a case study featuring elevator manufacturing.