In recent decades, a number of material and process evolutions have occurred in rotor blade manufacturing, driven by cost optimisation, cycle time reduction and quality issues. Polyethylene terephthalate (PET) is one of the newest foam core materials. Introduced by Armacell to the wind turbine construction industry in 2006, ArmaForm foam cores have followed a steep and successful development curve and experienced rapid growth, taking market shares from PVC and Balsa.
Today, more than 80,000 ArmaForm-cored wind turbine blades are in service around the world. Featuring a unique combination of material performance characteristics linked to its processability, cost and availability, ArmaForm is the preferred core material for blades, nacelles and spinners.
ArmaForm displays excellent fatigue properties, with a threshold level greater than 60%, as compared with PVC - of comparable density - with a limit of approximately 35-40%. The development of blade-manufacturing methods with higher peak exotherm temperatures - to increase curing speeds and improve cure cycles - has pushed the use of PET foam cores. Unlike PVC, ArmaForm has the necessary temperature resistance and allows regular processing temperatures of 150°C with full vacuum.
Due to the extrusion process used to produce ArmaForm - as opposed to the batch process used for most other structural foam cores - the variations in density are markedly low, amounting to less than ±5kg/m³, thereby ensuring more consistent density control and mechanical properties.
Epoxy resin infusion has become the main manufacturing process for modern rotor blades. In contrast to PVC, PET does not outgas during the curing process and provides proper lamination of the sandwich construction with reduced cycle times and increased quality levels.
Armacell has developed a unique quality control system that even exceeds today's quality standards in wind turbine manufacturing. Several inline devices monitor the production line during the entire manufacturing process and allow statistical process control (SPC). Fully integrated ERP enables each individual board to be traced back to the raw material batch used for its production. Several tests are constantly carried out to guarantee that each material property complies with internal and customer specifications. Armacell's quality staff have also been trained to comply with wind energy specific quality requirements such as APQP4.
A wind turbine is designed to produce clean and green energy and, as a logical consequence, environmentally friendly materials should be used for its manufacture. PET is already a sustainable foam core solution, and it was Armacell that paved the way when it supplied the first PET foam to the wind turbine industry in 2006
Armacell did not stop there and now offers PET foam cores made from 100% post-consumer PET materials (recycled beverage bottles). This patented process, called rPET technology, provides a more sustainable alternative to standard (virgin) PET foams: the recycled raw material base reduces CO2 emissions by 33% and ensures an improved - lower - price level thanks to its more economical feedstock. The environmental and economic benefits are even greater when compared with other foam cores, such as PVC.