Fire Resistant Coatings for Composites

Ref. IP117A

Indestructible Paint Ltd, Birmingham, recently carried out a laboratory programme to develop a special coatings system that would meet the stringent fire resistance requirements of an Italian aerospace company.

Based at Casoria, the company manufacture aircraft engine nacelles, for a number of aircraft types, from 2 mm thick GFPM composite.

The specification for these components requires coatings that comply with AC20-135, providing fire protection for five minutes before burn-through.

Indestructible Paint’s laboratories had previously carried out comparative tests with its widely used IP9189 intumescent coating (OMAT N0. 7/28B) against a newly developed formulation.

The new material, code IP1265, proved to have substantially better thermal barrier characteristics than IP9189 with the added benefit that it did not intumesce as much.

In addition, the level of ’char’ was thinner, providing more stability in windy conditions – properties that would be particularly significant for this particular application.

Indestructible Paint’s previous experience in this field indicated that it would be necessary to employ a combination of coatings to obtain the desired level of protection.

Accordingly, a number of composite test panels, were coated on the weave side (hence the use of a primer-filler), with six different systems each in combination with IP1265.

The most successful of these employed:-

• 1 coat IP9064 clear 2 pack epoxy seal coat at 25 microns dry film thickness
• 1 coat 50015 R2 2 pack epoxy primer-surfacer at 50 microns
• 1 coat 50019 2 pack epoxy thermal barrier/filler coat at 350 microns
• 1 coat IP6 2-pack polyurethane finish at 50 microns

Several coats of IP1265 2 pack epoxy thermal intumescent coating were applied prior to the IP6 finishing coat to give a dry film thickness of 1000-1200 microns. This gave a total thickness for the system of at least 1475 microns.

This combination showed no burn-through even after ten minutes, twice that required by the specification.

Even though the flame temperature was measured at more than 900ºC the inside temperature never exceeded a maximum of 350ºC.

As a result of this project, the coatings are now undergoing extended technical assessment and pre-production trials.

Composite Coating Developments

Graham Armstrong -
Technical Sales Manager
Indestructible Paint

In the November 2010 issue of Aerospace Manufacturing Graham Armstrong discusses the latest solutions in over coming the challenges in coating composites.