Temperature plays a vital role in the repair process of wind turbine blades using composite materials. The impact of temperature is multifaceted, affecting the material properties, curing process, and overall quality of the repair. Here are key aspects to consider:
- Curing Process:
- Many composite repair systems involve the use of epoxy resins, which undergo a curing process to harden and bond with the damaged areas.
- Temperature significantly influences the curing time. Higher temperatures generally accelerate the curing process, while lower temperatures can slow it down.
- Careful consideration of temperature is crucial to achieving the optimal balance between curing time and ensuring a thorough bond.
- Material Properties:
- The mechanical properties of composite materials, such as stiffness and flexibility, can be temperature-dependent.
- Extreme temperatures, whether too high or too low, may compromise the material’s integrity and long-term performance.
- Understanding the thermal behavior of the composite materials used is essential to ensure the repaired blades can withstand the dynamic conditions in the field.
- Adhesion and Bonding:
- Proper adhesion between the composite repair materials and the turbine blade surface is critical for the effectiveness of the repair.
- Temperature influences the surface energy of materials, affecting how well adhesives bond to the substrate.
- Ensuring an optimal temperature range during the repair process is essential for achieving strong and durable bonds.
Guidance from expert professionals
Oleg Pilats, blade repair technician, Instructor for GWO BR Training.
Following the rules
First, learn to read the instructions carefully and follow the rules clearly. You don’t have to produce anything when working with composites, particularly if you’re just starting out. Each substance and element in the “chemical cocktail” we use has unique implementation requirements. And the manufacturer’s instructions definitely lay them out in full. It is not a shame to read them (smile).
You might have to use some creativity to adjust the settings so that the materials function as intended. However, take your time—you must first acquire some experience. For my part, I began “inventing” after working for two to three years.
Reaching for the middle ground
The temperature at which working with a particular material is permitted is specified on each safety data sheet. It typically ranges from +5 to +30 degrees Celsius. +20°C is the most pleasant temperature. Every element is in optimal condition: they blend smoothly, disperse effortlessly, and engage with both the surface and one another. However, what can we do when our actual circumstances are far from ideal? I’d like to offer a few life lessons.
Too cold.
Many wind parks are in areas with a predominance of cold and rainy weather. Meanwhile, whether it’s +5°C, 0°C, or even frost, we need to fix blades. We can select a method to adjust the conditions to the ideal ones based on the surroundings. Before combining materials, we can heat them; we can also heart the surface and the chemical mixture when applying it to the surface.
Materials become excessively viscous and challenging to spread across the surface when they are too cold. We might use a construction dryer to solve this. But we must heart our “cocktail” right on the surface, while simultaneously distributing it. Since the components of your mixture will react if you start heating it in a container, that is not what we truly need. My recommendation for studying is to use a hair dryer because of its gentle effect and lower power. This will save the material from overheating by enabling you to feel it and work slowly.
Maintaining composites at work temperature is also crucial. For this purpose, we use warm boxes, which are metallic containers lined with foam plastic in which we put heater inside. The products you use will remain warm. You may also use the rope sack to put bottles with materials and turn on dryer for some time. However, please do not overheat it!
The temperature of the blade surface is another important consideration. It ought to be close to the resin’s temperature. If the blade is cold, it may break due to the impact of warm materials from temperature shock. Prior to applying composites, we additionally warm up the surface using a construction dryer.
Too hot.
When working in the heat, the pot life of chemicals is reduced. Technicians must work more quickly and with greater competence as a result. The turbine can be rotated to shade the area that has to be fixed. However, if it is not feasible or if the repair is scheduled for both sides and must be completed concurrently, the team may assign responsibilities so that a more qualified specialist works on the solar side.
To prevent chemicals from overheating, we could store them in thermos containers or at a minimum shield them from UV rays.
Avoiding thermal shock. Curing
For composites made by different manufacturers, the curing temperature and duration may vary, such as 3 hours at 80°C or 5 hours at 70°C, etc. This mode refers to the line of continuous exposure, which is an important concept that every technician should understand. We must therefore account for heating and cooling times. The process of reaching the temperature needed for curing is called run up. For instance, our epoxy resins require two hours at 80 degrees Celsius to cure manually. To get to this temperature (run up), it will take roughly 40–60 minutes: 20 minutes to heat up to 40 degrees, another 20 minutes to 60 degrees, and another 20 minutes to 80 degrees. After that, we’ll be able to calculate the two hours needed for the curing procedure.
For managing the curing process, we utilise a blanket equipped with an electrical thermostat.
After it’s over, we have to allow our repair area some downtime. Turning off our blanket and leaving it on the surface until it cools fully is all that needs to be done.
It’s critical to “run up” and “run down” to prevent thermal shock.
