Manufacturers of wind turbine blades need each blade to be released from the mould perfectly. (Picture used under license from Shutterstock.com © cla78.)
Manufacturers of wind turbine blades need each blade to be released from the mould perfectly. (Picture used under license from Shutterstock.com © cla78.)

On the horizons of Iowa and Illinois in the USA, Saxony-Anhalt in Germany and Xinjiang in China, wind turbines are a common sight. Their enormous towers seem to reach the clouds. A single blade can cover the wingspan of an Airbus 380 and spin a dizzying 180 mph at the tips. They are the behemoths of the clean energy industry: literal giants of the green movement.

Immense wind turbines are now the standard in renewable energy production. Wind farms from the plains to the mountains are stacked with these whirling skyscrapers, which provide bulk power to the electrical grid.

The economic equation is simple: the larger the blade, the greater and more efficiently wind energy can be turned into a useable power source. These giant blades provide many benefits by opening the map to geographic locations in the country not formerly viable because of light wind traffic, but they present a number of challenges. First and foremost of these is production.

These blades must endure great physical stress. They take a non-stop beating from the environment, including driving rains, gale-force winds and years of constant motion. They are also designed with exacting geometries to take full advantage of a turbine's sweep area. As such, they are big and bulky, yet nuanced and even delicate.

Building blades that withstand a tremendous amount of force must be done precisely. With blade demand at an all-time high, there is zero tolerance for failure in the production process. Scrapping even a single blade – with a price tag well into the six figures – is not an option. Therefore, every single production operation must focus on eliminating risk, reducing variation and creating the perfect environment for success.

For a relatively modest cost, release agents add value, increase productivity, reduce scrap, perform dependably and keep the pipeline filled with installation-ready blades.
 

To do that, today’s blade manufacturers agree on a form of insurance plan – a process chemical speciality that not only protects the expensive moulds but also assists in extracting the blades perfectly. The product is a release system – a specialised coating designed to prevent the adhesion of moulded articles to mould surfaces. It works as a physical and chemical barrier, a lubricant to reduce friction, and protection against surface abrasion and erosion. These systems ease the release of parts from moulds, while protecting the moulds and improving the blade’s finish. For a relatively modest cost, release agents add value, increase productivity, reduce scrap, perform dependably and keep the pipeline filled with installation-ready blades.

Release agents

In addition to composites applications such as turbine blades, release agents are used in a variety of areas, such as in the die casting process, and in the manufacture of polyurethane, rubber and thermoplastic parts, tyres, and wood composite boards. They improve the production process in a number of ways, including extending the life of expensive tooling, improving part quality and reducing the labour time involved in demoulding parts.

Release agents often come as a system that is applied in steps or layers that work with each other to enhance their attributes and provide benefits greater than can be found with any single component of the system. Chem-Trend produces a system of products that improve the operating efficiency of the blade manufacturing process. This seemingly small process actually extends the life of the mould, literally saving the industry millions of dollars.

The first step of the system features a mould cleaner. This water- or solvent-based cleaner removes mould build-up, providing a sound base for the subsequent application of the release system.

Step two is a mould sealer, also called a primer. This product provides two benefits. Since moulds are often produced of composite materials – as are blades – this chemical seals the mould surface and eliminates the problems associated with microporosity. Put another way, sealers keep the resin from penetrating the mould. They also act much like a traditional paint primer, protecting the mould and ensuring better adhesion for the next layer, which is the actual release agent.

In the final step, the release agent provides a chemical and mechanical barrier between the mould and the outer layer of the blade. This thin layer enables parts to be released with ease, in one piece and with enhanced finish quality. It also prepares the blade for any other post-moulding processes. Some gel-coats are sensitive to the phenomena of ‘fish eyeing’ in which small pinholes appear on the surface of the blade. Chem-Trend has products that address this issue and provide manufacturers with a desirable topcoat – in either gloss or matte – that requires minimal preparation for post moulding operations.

Case study

Problem
A leading wind blade manufacturer was unhappy with the quality delivered by the brand of mould cleaners, sealers and mould release agents it was using. Using a water-based mould cleaner, a solvent-based sealer and a water-based release agent, it found the mould sticking even though it was covered with Teflon® tape and release agents were applied after each demoulding. The company also wanted to use only water-based products in its manufacturing processes.

Solution
Chem-Trend tested the products the company was using against a line of Chemlease® water-based products:

  • Chemlease Cleaner;
  • Chemlease Mould Sealer; and
  • Chemlease Release Agent.

After a thorough cleaning of the mould with the Chemlease product, the Chemlease sealer and release agent were applied. Another mould was prepared with the competitor’s product according to the recommended procedure.

The Chem-Trend products and the competitor products were both applied to a 1 m2 (9 ft2) mould plate. The Chemlease products were found to provide 50% more releases from a single application than the competitor’s product.

The next test involved using the Chemlease products in a 37 m (120 ft) blade mould. The release went so well in this test that the blade manufacturer decided to switch to the Chemlease products.

Benefits
After finding the right product mix to minimise release agent build-up in the mould and reduce time spent cleaning the mould, the blade manufacturer is now running a safe, water-based production without any sticking problems. Chem-Trend was able to go from testing and developing the right products and service to providing a consistent, problem-free release system in a period of six months.

Recently introduced materials such as polyurethane gel-coats present new challenges in moulding and releasing parts. These products are more sensitive than the more traditional epoxy or polyester materials. Instead of covering the surface of a mould in a nice smooth sheet, these gel-coats can be more prone to fish eyeing as described above. Some polyurethane gel-coats simply make it more difficult to extract parts, or to extract as many parts as with other products. Chem-Trend produces specifically formulated release agents that improve the performance of polyurethane gel-coats in the moulding process.

The idea that a part – whatever it is – is of no value stuck in a mould is obvious. Therefore integrating a release system into the production process is critical. It allows massive blades to be manufactured right the first time – a basic requirement for the wind industry to be effective and efficient.

What might not be so obvious is the negative counter effect of demoulding. If parts begin to release before they are fully cured, the blade is also ruined. Therefore, the release agent must provide enough release ease, but not too much.

Further information

Chem-Trend, P.O. Box 860, Howell, MI 48844-0860, USA; tel: +517-546-4520; www.chemtrend.com/contact_us
 

  • PART 2 of this article will be published on ReinforcedPlastics.com next month.


This article will be also published in the July/August 2013 issue of Reinforced Plastics magazine.

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