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Resin Transfer Molding (RTM)

Vacuum injection with foil

In recent years vacuum injection has played a greater role in the manufacture of fibreglass composites. Instead of manual impregnation of the fibreglass, a vacuum is used, in which the dry glass and any core materials are laid in the vacuum-sealed mould.
Depending on the construction of the laminate and the surface requirements, helping materials may also be layered in. Finally the whole mould is covered with a thin layer of foil. The air is then sucked out, while the vacuum helps suck in the resin to impregnate the fibres. Compared to hand lay-up, this method provides a more even product with fewer air bubbles. In addition, it is possible to achieve a higher fibre percentage and less air containment than with hand lay-up, which makes the finished laminate much stronger.
Vacuum injection with foil is used for the manufacture of prototypes, where greater strength is required, and for medium batch sizes. EM Fibreglass’s main use of this process is in the manufacture of nacelle parts for the windmill industry.

The benefits of RTM:

  • Excellent strength
  • Even quality
  • Low mould expenses
  • Perfect for sandwich constructions
  • Good working environment


Vacuum injection with solid counter mould (RTM light)

This form of injection is very similar to vacuum injection with foil. This also involves laying dry fibres in the mould. But instead of foil, this process uses a semi-flexible or solid counter mould in composite. As with foil moulding, the air is sucked out and, with the help of the resultant vacuum, the resin is injected and impregnates the fibres. A counter mould achieves the same high quality surface on both sides of the laminate.
Counter mould vacuum injection is used for both medium and large batchsizes, and for composite products, which call for a high quality surface on both sides. EM Fibreglass’s use of this process includes the manufacture of nacelle and spinner parts for the windmill industry.

The benefits of RTM light:

  • Excellent strength
  • High quality surface on both sides
  • Perfect for sandwich constructions
  • Even quality and material thickness
  • Quick lay-up
  • Good working environment

EM-fiberglas A/S     »     Hornsyld Industrivej 20 | DK-8783 Hornsyld     »     Tlf.: 7568 7311     »     Fax: 7568 8081