Production of the products in the closed molds. First a gel coat is applied (it is also possible to manufacture a version without the gel coat). Next, structural layers are stacked in the mold (glass mats, matting synthetic mats in the form of a sandwich, Coremat, roving, etc.) as well as any strengthening and adaptations.

The use of compressed air, special clamps, cylinders or mechanical press provides the appropriate pressure to the mold. Accordingly, the presence of large closing forces and (during production) a pressure associated with the injection of the resin – the mold in this method must have adequate strength. We therefore use special pastes, composite materials and metal frame structures as well as strengthens. Once the mold is closed resin is injected through a special opening (s) formed in the mold.

Advantages of the method:

• the profitability of large series,
• low emission of volatile substances to the environment,
• very high quality and uniform structure of products,
• further reduction of wall thickness obtained through appropriate mechanical properties,
• high glass content and the highest product durabiity,
• an aesthetic and smooth surface on both sides (with or without the use of gel coat),
• highest process efficiency,
• a wall thickness tolerance up to 0.3 mm,
• low waste and less use of materials,
• very low unit cost of element production – relatively high cost of tooling.

Limitations of the method

Technological limitations (eg. Technological radii, wall inclinations), restrictions on the shape, size and complexity. RTM method may be applied to less complex elements. The relatively high cost of tooling limits the applicability of this method for the production of large-size elements.

Other:

• high cost of production start-up, tooling, equipment
• limited possibility to apply changes to the mold,
• relatively long production preparation time. possibility of getting only one gelcoat surface from the mold side (usually unilateral form).