Metal finishing Q&As since 1989

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Peeling off and brittleness in the epoxy coating

2006

Hi ..
This is the first time I'm posting an enquiry so apologies if I mention something incorrectly. I've just started working with Fusion Bonded Epoxy , which we are using to paint ductile iron pipes and fittings . We follow the International coding of blue (for fresh water) and red (for sewage applications) on our products. Ductile Iron fittings (can also be called pipeline accessories) are of various diameters and shapes( all equal cross,y-shaped,angular bends etc) . We have both flange type and push on joint type fittings . Off late I've been having problems with the red epoxy paint . Our process details can be summarized in the following steps.

1.The surface preparation is done by shot-blasting the fittings.

2. We then heat the product in an combination furnace which has both radiative and convective heating before we paint the job. The job reaches a temperature of around 190 °C before the start of coating .

3. The coating is done by electrostatic precipitation method where the job to be coated is grounded . The thickness of coating varies as per the customer's requirement( 150 - 300 microns) and various international standards like ISO, BSEN etc.

4. Post painting the job is given adequate time to cool down .

While we were able to do the painting properly with both red and blue epoxy , off late the red epoxy paint starts peeling off after the job comes to ambient temperature . This phenomena is being seen only in case of red epoxy paint .

We have also tried to do the post painting curing by re-soaking the job in around 130 °C temperature for around 30 mins.

I would be glad to receive some inputs on the same if possible as I'm not really an expert on Fusion Bonded Epoxy .

Thanks,

Pranav Mimani
Manufacturing Industry - Kolkata , West Bengal, India