Vacuum Assisted Resin Transfer Moulding (VARTM)

Vacuum infusion since 1997

LM Glasfiber uses Vacuum Assisted Resin Transfer Moulding (VARTM) to manufacture wind turbine blades. This is a closed process in which resin is pulled into the mould by negative pressure, and impregnates the fibres already laid out in the mould.
LM Glasfiber presented the first 29-metre blade produced using vacuum infusion in 1997. Since then, we have continued to develop this production technology still further in order to manufacture blades of steadily increasing length and with thicker laminate, meeting escalating demands for improved quality and shorter process times.

Increased flexibility and reduced process time

Vacuum technology provides us with considerable flexibility, because we are able to choose between more materials and material combinations than if we had based our production on preimpregnated materials (prepregs), for example. The fibre mats we use are also easier to handle and considerably cheaper than prepregs.
VARTM also provides better control of the impregnation and hardening processes, as well as faster throughput. Using polyester as a saturation material avoids the need for expensive, advanced heating chambers or other equipment for heating the mould. Using this technology means that we can easily switch production from one type of blade to another, and thus exploit our facilities to the full.
Because production takes place in a closed process, VARTM also helps to improve the working environment.

Simulating resin infusion

Dry spots and air bubbles in the laminate can significantly reduce the strength of the blade and its reliability.  LM Glasfiber has therefore implemented a computerised model for simulating resin infusion. This model provides a precise picture of the way the resin spreads and saturates the laminate in the mould. This enables us to optimise the entire VARTM process, because the program reveals any weak spots. It also calculates the number of filling points that are required.
While resin infusion is taking place, we collect process data that we use to constantly fine-tune the process.

Special infusion machines

Both timing and volume are crucial for quality in the complicated infusion process, and LM Glasfiber uses 40 specially developed machines to control these parameters. Detailed data from the process is used to control the actual infusion procedures, and is also linked up to the LM Glasfiber control, adjustment and monitoring system.
The infusion machines have been automated to save process time, and the infusion time alone has been reduced by 15–20%.