How Do I Improve Adhesion in Composite Materials with Flame Treatment?

Composite materials, such as carbon fibre reinforced polymers (CFRP) and glass fibre reinforced plastics (GFRP), are widely used in industries ranging from aerospace to automotive. While they offer exceptional strength-to-weight ratios, one persistent challenge is achieving reliable adhesion for paints, coatings, adhesives, and other bonding processes.

One effective way to overcome this challenge is flame surface treatment. By exposing composite surfaces to a controlled gas flame, the treatment modifies surface chemistry and increases surface energy, creating a more receptive surface for adhesion.

Why Composites Struggle with Adhesion

Composites often contain resin-rich outer layers or release agents used in moulding, which can make the surface chemically inert. This low surface energy prevents adhesives, inks, and coatings from wetting the surface properly, resulting in weak bonds or delamination.

Traditional mechanical roughening can damage fibre structures, while chemical etching may be inconsistent and environmentally hazardous. Flame treatment provides a clean, fast, and scalable alternative.

The Flame Treatment Process for Composites

In flame treatment, a precisely balanced mixture of fuel gas and air (or oxygen) is combusted to form a controlled flame. As the flame passes over the composite surface:

• Polar functional groups are introduced, increasing surface energy.

• Contaminants such as oils, mould release agents, or fine dust are removed.

• Microscopic oxidation improves wettability without damaging fibres or resin matrices.

For production lines, treatment can be automated with burner heads mounted on robotic arms or conveyors, ensuring uniform results across large or complex composite surfaces.

Benefits of Flame Treatment for Composite Adhesion

• Stronger bonding – adhesives, paints, and coatings adhere more effectively.

• Improved consistency – reliable adhesion across batches.

• Non-destructive – no damage to composite fibre structures.

• Scalable – suitable for both laboratory testing and industrial-scale production.

• Environmentally safer – avoids solvents and harsh chemical primers.

Industrial Applications

Flame treatment of composites is increasingly used in:

• Automotive: bonding lightweight body panels, interior trims, and components.

• Aerospace: preparing CFRP for coatings and adhesive joints.

• Marine: treating glass fibre composites for paint and gelcoat adhesion.

• Wind Energy: improving bonding on turbine blades.

Rapidflame systems can be configured to treat both small components and wide panels, offering flexibility for OEMs and integrators.

Next Steps

If your production relies on composites and you face adhesion challenges, flame treatment offers a reliable and efficient solution. Rapidflame provides gas burner systems tailored for composite surface treatment, ensuring high performance and compliance with industrial safety standards.

Contact Rapidflame today to discuss your application.

Learn more about our flame treatment systems for industrial use.

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Frequently Asked Questions (FAQs)

How does flame treatment improve adhesion in composites?

Flame treatment introduces polar groups and increases surface energy, which improves wettability and allows adhesives or coatings to bond more effectively.

Can flame treatment damage composite surfaces?

No, when properly controlled, flame treatment is non-destructive and does not harm the fibre or resin structure of composites.

What gases are used in flame treatment for composites?

Common gases include propane, natural gas, or butane mixed with air or oxygen, depending on burner design.

Is flame treatment suitable for carbon fibre and glass fibre composites?

Yes, flame treatment works effectively on both CFRP and GFRP, improving adhesion for coatings, adhesives, and paints.