On October 14th, we went to Uddevalla to visit one of our suppliers, Elitkomposit. Elitkomposit is the manufacturer of the blades for our turbine.
This time we went visiting to participate in a test Elitkomposit was about to perform. The test was to infuse a two-meter-long blade section with epoxy. Test is done to see if any defects should occur and if so, try to prevent the defects from happening when the infusion of the 40-meter-long blade is done.
The infusion with epoxy is done through holes in the blade mold, which consists of different layers that together with the epoxy forms the composite material the blades is made of.
The “stack” that lies in the blades during manufacturing consists of dry carbon fibre, a peel ply which is a type of “tear-off fabric”, a distribution net that distributes the epoxy and helps it to better flow through the stack. The airtight layer and the edge around it all act as an “air conveyor” to suck out as much air as possible. It’s important to spread the epoxy well, the composite will be formed under the green area in the picture. The dark part is the epoxy that slowly spreads into the blade.
There is a lot of manual labor preparing for a test like this, it occupies a better part of a day. Elitkomposit is responsible for the building instructions and actual drawings whereas SeaTwirl has calculated and decided how many layers of carbon fibre is needed. Preparing to perform the test for the whole blade will likely take a week or two.
Once the epoxy is infused into the form with the dry carbon fibre it needs to cure for two days until fully hardened. The epoxy, together with the carbon fibre makes for a stiff and light construction. One can compare the process with casting concrete where the carbon fibres are like the steel reinforcing bars in the concrete.
The characteristics of the composite material are decided by the combination of carbon fibre and epoxy. Composites are different in that way that the characteristics aren’t fully decided until the component being manufacturing is done and hardened. For example, same set of components in one form can react in one way but differently in another form. Great knowledge, experience and craftsmanship is therefore required to achieve similar and uniform properties in a series production.
The end goal is to create a complete blade to performer other tests on as well. These tests will be prepared by SeaTwirl and performed together with Elitkomposit.
Picture taken inside the workspace built exclusively for SeaTwirl’s blades. The test was performed at the far end