Project Description

A View of Curved Surface Coatings

Wind turbine blades are coated to improve performance, where coating thickness play an important role. LINX developed a new method for measuring coating thickness by 3D-imaging.
Wind turbine blades must endure harsh operating conditions and still preserve desired aerodynamic qualities. One ingredient towards achieving this is a surface-coating applied to the blades, a coating which itself need to comply with a set of requirements regarding its thickness. However, it is technically challenging to apply a layer of coating which is absolutely even, and coating thickness will inevitably vary across the surface. Thickness measurements are therefore an important factor in optimizing wind turbine blade production. However, if destructive methods are used, measuring coating thickness after application can be a difficult and a time-consuming process.
In this project, LINX sets out to explore whether X-ray imaging can be used to provide a 3D-picture of the surface region of a wind turbine blade, with sufficient contrast to distinguish the coating from the material underneath. X-ray imaging is a non-invasive and non-destructive — two qualities which all existing methods for estimating coating thickness lack. In LINX, high-quality imaging is supplemented with automated image-analysis methods for measuring coating thickness. The ultimate goal is to produce a map covering the whole surface of the blade, which will reveal the thickness of the coating, for example using a colour code. An approach capable of producing such a map would accelerate and simplify wind turbine blade development.

Techniques and Methods

Prompted by the implementation of a new coating material application technique, LM seeks to improve it’s in-production assessment of coating material thicknesses. Current thickness assessment methods are generally destructive by nature, and include e.g. optical microscopic analysis of cut-outs and electrical impedance measurements allowed by embedding metal foils in the surface structure of the blade, these metal foils then need to be removed afterwards, which is both cumbersome and time-consuming and introduces weaknesses in the structure due to the necessary repairs. For this reason, a fast and non-destructive coating thickness assessment technique is desirable. Furthermore, the technique should be able to map the variations across a large and curved 2D surface.
Some candidates for such techniques have been identified but need to be tested. Testing candidate techniques also involves a applying a reliable reference technique to map surface variations in test samples. If contrast is sufficient, this reference technique could be laboratory-based CT.
Extensive work in the X-ray laboratory were conducted in order to optimize the instrumentation and positioning of the material to obtain the best possible signal. The results from the experiment showed that it was possible to use virtual landmarks to measure layer thickness at different positions.
Using the network involved in the 3D Imaging center at DTU along with the knowledge from LM Wind Power it was possible to tailor an analytical method enabling thickness measurements as a thickness map for the investigated materials.

Project Information

Participants: LM Wind Power, Technical University of Denmark.
Start date, end date: November 2017 – October 2018.
Title: Curved surface coating thickness assessment (FP09.002, Quality Assurance).