Pretreatment of Carbon Composites

Q. I work for an aerospace metal finishing company, and my question pertains to pretreatments of carbon composites prior to primer and paint. Many companies are looking to replace aluminum and other metals with carbon composites in aircrafts to reduce weight. While the cost of fabricating composite brackets from molds is cheaper than forming and machining aluminum, the high cost to apply the primer and paint seem to be a hurdle driven by the pretreatment.

The three pretreat options we’ve been using are MEK wipes only, hand sand with 220-grit sandpaper and pumice blasting. While the pumice blasting provides the best adhesion, it’s also the most expensive option since it’s a manual operation done in a blast cabinet where the aluminum can get piled in a 12-foot basket and run through a chemical treatment or anodize bath. The primers to be applied are all aerospace material, such as BMS10-79 corrosion-resistant primer or BMS 10-103 nonchromated primers.

Is there a type of chemical bath or similar option that carbon composites can be processed through to improve paint adhesion? This is, of course, after mold release has been cleaned from the parts. J.S.

A. Unfortunately I do not have any direct experience with cleaning or pretreatment of carbon composites, however the limited information I have read about them would suggest the cleaning and pretreatment process you are doing is economical by comparison. For instance, some of the earlier methods suggested for the pretreatment of carbon composites for adhesive bonding (which should be similar to that needed for paint) include chemical vapor deposition (CVD) or possible electrolytic processes. If any readers have more direct experience with this I would like to hear about it and would collect the responses and share them in a future column.