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How to paint exhaust manifolds & headers

When it comes to high temperature paint, the success of the application depends on the surface preparation, the cleaning of the metal, the application of the paint and the curing of the high temperature coating.  Here is a step by step procedure that will show you how to get the job done correctly the first time and some suggestions what to look for and what to avoid.

Preparing the metal

Abrasive blast surface per specification SSPC-SP 10, “Near-White Blast Cleaning”, or per NACE Standard No. 2 to a profile depth of 1.0 - 2.0 mils minimum, with a 1.5 mil anchor pattern being ideal. Abrasive used in blasting should be selected carefully from materials of mesh size required to produce the desired anchor pattern. If abrasive blasting is not permitted, prepare surface by power tool cleaning per SSPC-SP 11. Use 3M brand “Heavy Duty Roto Peen”, type C flap wheel cleaning system mounted on an air-driven motor. This method will provide a surface equivalent to that provided by commercial blast cleaning per SSPC-SP 6, including the desired surface profile (anchor pattern).

The metal surface should not be bead blasted. It is recommended that the media is 100% grit or 50% grit and 50% shot. Make sure there is no moisture in the air line which could result in rust spots.

If surface prep is performed and the surface gets contaminated, solvent clean the metal with Acetone or Xylene only. Using a wire brush with these two solvents are ideal to remove any grease, rust or other surface contaminants.

Apply one or two very light coats of paint. Applying the paint too thick or with too many coats could lead to a failure resulting in outgassing, cratering, blistering and peeling. High temperature coatings should be applied to a dry film thickness of 1.0 mil (25 microns) per coat. Total recommended dry film thickness is 2.0 mils (50 microns) One or two light coats is better than one thick coat of paint.

High temperature paint should be sprayed from about 12 to 15 inches. If you get too close, the paint will likely drip or run. If you get too far away, the paint will dry in the air and result in a gritty finish.

The paint typically dries to touch in about 20 minutes. When doing two light coats as recommended above, you can apply the second coat after about 15 minutes. The paint will dry to handle in about 2 hours. We recommend waiting for 4 hours before doing the “heat cure process.”

Final curing of the paint

To force all remaining solvent in the paint film, the coated metal must be heated gradually in an oven at 350F for 30-45 minutes. Heating the metal too quickly forcing the solvents out too fast or hotter than 350F could result in a coating failure.

If heat curing in an oven is not possible, installing the metal parts and running them in service that will gradually heat cure the coating film can be done gradually.  Contact Technical Services @ Dampney or any questions or concerns prior to the coating application. www.dampney.com

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