Sealant joint used in vacuum molding

      What is the vacuum molding technique?

The vacuum molding technique is a higher-quality process than contact molding. It allows for defect-free moldings of composite products with complex shapes and reduces defects caused by irregularities in manual intervention.

In this production process, atmospheric pressure is used as a counter-mold to eliminate trapped air and improve resin distribution within the laminate. It also helps hold the laminated components in place until the resin hardens.

The range of materials that can be laminated using the vacuum technique is vast, from synthetic fibers to wood veneers.

      Preformed butyl mastic used as a sealing joint

The vacuum technique involves covering the laminated part with a vacuum plastic film sealed all around with a preformed butyl mastic sealant.

The high adhesion and elasticity of butyl mastic ensure a perfect seal, even when the film wrinkles. Once the film is sealed, the air is removed using a vacuum pump. As the vacuum pump removes air, the air pressure inside the envelope decreases. Atmospheric pressure forces the sides of the envelope and everything inside with equal pressure across the surface. The pressure differential between inside and outside determines the clamping force on the laminate.

A drainage fabric is used to trap and retain excess resin in the laminate.

The butyl mastic sealant provides a continuous airtight seal between the film and the mold around the entire perimeter. These strips can also be used to seal where tubing enters the film.

In general, the better the seal between the mold and the film, the less vacuum power is needed.

A poor seal or material that allows air leakage requires a higher-capacity vacuum pump to maintain vacuum pressure.

      Products for ensuring a vacuum seal during molding

There are several types of preformed butyl mastics used for vacuum molding, primarily differing in their ability to withstand higher temperatures and be used in ovens or autoclaves. 

The ADEZIF 350 mastic is designed for high-temperature applications and is effective for baking cycles up to 200°C.

      Examples of applications and products made using vacuum molding

The vacuum technique is used in the production processes of a wide variety of sectors, from automotive (side mirrors) to aerospace (lightweight glider manufacturing) and renewable energy (wind turbine blades), as well as kayak manufacturing.