HVOF on CAST IRON ROLL

[Guna]

Dear Forum,
Recently we coated a dia 14" roll which is made of cast iron with Diamally 1008 using HVOF. The coating looked good but, when when approaching +50 micron level while grinding, spot peel-offs appeared. Close inspection(naked eye) indicates/looks like localized bonding problem.(random spot peel off)
Pretreatment: The roll was degreased, torch heated to 200'C and degreased again prior to blasting. No bond coat was applied and the build up was 0.8mm per side.
Any suggestion or precaution when coating cast iron material?
The chrome plating company which did the job previously had some issues with this roll where blackish spot were observed. is it carbon or graphite content of the material or oil which has been there which is not removed sufficiently.

Forum Experts, kindly assist.

Thank you
S.Guna

[Gordon]

Hi Guna

I suspect it will be oil. I think you will need to heat part to higher temperature and for longer time.