REPLACEMENT OF CHROMATE AND HIGH VOC COATINGS SYSTEM FOR

 AIRCRAFT PAINTING

    PROJECTS LAUNCHED (Aeronautical Maintenance) 

C3P Joint Projects with TAP Portugal and OGMA – Indústria Aeronáutica de Portugal are:

1. Identification of Suitable Alternatives to Hexavalent Chrome (Cr6+) in Conversion Coating Alodine 1200/1000 on AL 2024, 7075 and 6061;

2. Replacement of High Volatile Organic Compounds (VOC) coatings for aircraft painting, in general painting scheme;

3. Demonstration/Validation of suitable alternatives to Hexavalent Chrome in primer
coatings (AL 2024, 7075, 6061).

The C3P TAP/OGMA project team, lead by the initiative of TAP engineers, have decided to perform an application and flight testing of hexavalent-chrome-free alternative coating systems that could potentially meet the requirements of the above projects – Replacement of Chromate and High VOC Coating Systems for Aircraft Painting.

Introduction

A common coating system on aluminium substrates consists of a chromate conversion coating, a primer and a topcoat.

Chrome conversion coating involves the treatment of a metal substrate with a chrome solution to produce an adherent coating. The metal substrate is changed to a layer of chromium salts to produce the desired decorative or functional properties. Chrome conversion coatings are used for three general purposes:

• Increase corrosion resistance

• Improve paint (primer) adhesion

• Minimize electrical resistance.

Chrome primers are commonly applied to surfaces as a protective coating offer significant corrosion protection.

Although chrome conversion coating and primer coatings offers many advantageous coating properties, its use of hexavalent chromium is strictly regulated due to the compound's toxicity and suspected carcinogenicity. For this reason, manufacturers have begun to identify, evaluate, and implement acceptable alternatives for chrome conversion coating and primer coating where feasible. These alternative technologies commonly generate less pollution than chrome conversion coatings and chrome primers, and have fewer associated health and safety risks.

Also traditional coatings are paints containing high amounts of volatile organic compounds (VOC), such as methyl ethyl ketone, toluene, and xylene, and some percentage of solid components. Alternative coatings seek to reduce the amount of VOCs, and yet retain or improve the ability of the coating to protect metallic or composite surfaces.

At TAP Portugal and OGMA – Indústria Aeronáutica de Portugal, S.A., chrome in chemical conversion coatings and primers coatings, as well as VOC found in paints, were identified as a hazardous material of concern, and targeted for elimination or reduction.

Objective

Test and implement chrome free and low VOC coating systems in aircraft painting scheme at TAP Portugal and OGMA.

Achievements

• Arrangements were made to apply two alternative coating systems on a TAP Airbus A319 over the period of Oct. 16 through Nov. 5, 2004.  Due to limitations on the supply of sufficient materials to paint the entire aircraft, TAP engineers elected to apply the alternative coating system on a service door of the TAP Airbus A319.  The applied coating materials were provided at no cost to TAP, and the coating supplier Pantheon Chemical provided technical expertise to ensure that materials were properly applied as well as provide applicator training to the representatives of TAP, OGMA and the PoAF.

• The two alternative painting schemes were applied as described below:

Upper half: AKZO NOBEL High Solids Painting Scheme:

- M790E, for surface preparation

- Aviox CF Primer

- Aviox Finish 77702

Lower Half: Pantheon Chemical PreKote SP plus AKZO NOBEL High Solids Painting Scheme:

          - PreKote SP

- Aviox CF Primer

- Aviox Finish 77702

Figure 1 – Service Door painting schemes.

The two alternative painting schemes were tested against AMS3095 specification (Aerospace Material Specification that defines requirements for a high gloss paint system for use in civil aircraft) for suitability as a replacement of currently used coating technologies (Table 1). 

• OGMA painted and prepared all test panels.

• The Laboratory tests were conducted by ISQ and NASA at their facilities, as in-kind contribution.

• The test results showed that one coating system pass all the tests and the other failed some. There was no evidence that that can demonstrate that the restored systems performed better that the normal ones. In some cases that was true, but many external factors can affect that decision, such as the coupons preparation conditions.

• The major conclusions were that one painting system performed better or equally than the other.

• Regarding the field test, 3 follow-up reports of the TAP Airbus A319 service door were conducted at TAP facilities, and showed that, after 2 years and 8 months in service, both painting systems to date are in perfect conditions:

         - No peeling-off;

         - No defects were observed;

         - Present high gloss and DOI (Distinctness of Image).

• More detailed information on the tests results can be found in Final Project Report - Replacement of Chromate and High VOC Coating Systems for aircraft painting.

Project Team

Sandra Margarida da Costa (OGMA)
Carla Jesus (OGMA)
Pedro Martinho (OGMA)
Ana Paula Matos (TAP Portugal)
Ana Paula Ricardo (TAP Portugal)
Vítor Morgado Gonçalves (TAP Portugal)
Eduardo Dias Lopes (ISQ)
Rolim do Carmo (ISQ)
Matt Rothgeb (NASA TEERM Principal Center)
Erica Sá (C3P)

Points of contact

Mariana Alves-Pereira  (mariana@c3p.org)

E-mail for contact: Mariana Alves-Pereira  mariana@c3p.org

Last updated: 20/08/2011