VAP®: Membrane-assisted low-pressure infiltration

Air and reaction gases that are trapped during closed infusion processes can cause weaknesses in lightweight components. In conventional infusion processes, the entire assembly – subjected to low pressure – must be extensively flushed with the infusion medium until it can be safely assumed that there is no more trapped air and gas inside the component.

In the VAP®assembly, the flexible membrane system – which is permeable to gas but impermeable to the resin – is superficially contacted with the component. When the resin is infiltrated, it separates the matrix from the vacuum duct. With the aid of low-pressure, trapped air and gas can then escape through micro-permeability and are purged via the textile layer.

The vacuum acts uniformly, so trapped air and gas can be evacuated across the entire contact surface during and after infiltration.

Improved flow front management

In all conventional vacuum infiltration processes, the difficulty in successfully infiltrating the component lies in determining, or predicting, the flow fronts in order to avoid undesirable areas of occluded air (‚dry spots‘). If the vacuum then also has to be reduced due to the risk of matrix boiling, it becomes almost impossible to eliminate these imperfections. The reduced vacuum also causes substantial fluctuation in the fibre volume content and material thickness, and Airbus to greater porosity in the components.

The matrix´s flow behaviour is much more consistent in the Vacuum Assisted Process (VAP®) process because of the uniform vacuum. The low pressure’s extensive effect on all of the membrane system´s contact surfaces reliably removes dry spots, even after infiltration, without the vacuum having to be reduced.

How the semipermeable VAP® membrane system works

Semi-permeable VAP® membrane systems from Trans-Textil are full of tiny pores. Under vacuum conditions, small molecules of trapped air and gas can be reliably removed, while the large-molecule resin stays stable in the mould.

In the VAP® membrane system, barrier layers are connected (laminated) to a textile substrate. By the optimal combination of components and processing technologies during manufacture, it is possible to accurately control the essential process parameters: air permeability and the resin barrier.

Trans-Textil´s patented quality-assured VAP® membrane systems have been tested for various different resin types and process variants, and the company is continuously developing the technology in close cooperation with Airbus.

VAP® advantages in the production process:

  • High process reliability, consistently stable and controlled results
  • Air and gas removal during and after infiltration
  • Simple process control
  • Achievement of an exact and constant fibre volume content
  • Production of complex 3-dimensional shapes
  • Fast infiltration process through higher vacuum = shorter cycle times
  • Uniform flow rates in the resin
  • Low initial investment: possibility to use tools that are already available
  • Improved worker protection and low emissions due to closed process
  • VAP® membrane systems by Trans-Textil tested and approved for different resins and processes

VAP® advantages in the end product

  • No dry spots or porosity
  • Excellent component quality
  • Highest quality standards
  • Homogenous fibre volume content

The VAP® process proves its strength especially when it comes to the series production of large complex components with a high degree of integration. VAP® offers maximum economy compared to other existing infusion processes:

“A homogeneous fibre volume content and low porosity in the laminate are proven to result in better component characteristics than those produced in any other known injection process.”
CCM University of Delaware