Cool Repair – new repair process for low temperatures

Because of their extreme dimensions rotor blades are repaired on site whenever possible. Dismantling the blades would be simply too costly. Therefore, the repair works must be carried out under changing ambient conditions. The minimum temperature for laminating processes specified by the DNV GL is 16 °C. However in wide parts of Europe this temperature is hardly reached during most of the year. For example in almost all Scandinavia the average temperature is below this value, even during the summer months.

To solve this significant problem for rotor blade repair works cp.max teamed up with Süddeutsche Kunststoff-Zentrum. In a project supported by AiF Projekt GmbH within the framework program “Zentrales Innovationsprogramm Mittelstand” a procedure was developed that enables laminating processes at low temperatures. This allows urgent repairs to be carried out faster and more independent from ambient conditions. Therefore the availability of wind energy converters and thus the financial income can be increased. 

The central tool in this process called “Cool Repair” is a silicone vacuum hood with an integrated heating fabric. Similar hoods are used in the production of small to medium-sized fiber-reinforced components. For using them on a hanging rotor blade, the challenge is to make them as light and flexible as possible and to allow easy handling.

The vacuum hood is manually placed over the repair site on the fresh repair hand laminate. Subsequently, the enclosed air is evacuated by a vacuum pump. The hood now gets pressed onto the rotor blade by the atmospheric pressure. No additional tools are needed for fixing it. Thus, a compact composite without air inclusions is produced.

The whole heating system of the device consists of a thin and flexible heating fabric and a temperature sensor in the silicone hood. Both are connected to a digital temperature controller and a small voltage source. The controller and the voltage source are housed in a handy case. This temperature control ensures that the repair laminate absorbs the heat energy required for complete curing. Furthermore it is advantageous that the heating of the vacuum hood is located directly on the repair surface, without any air gap between. In this way, the repair site is reliably shielded from the ambient conditions.

Currently “Cool Repair” is certified by DNV GL. As a result, the benefits of the procedure will be confirmed by an independent institution. In addition, the method can also be used below the common minimum temperature of 16 ° C for repairing rotor blades.