HELP spray over spray

[jtwmc]

HELP !!
we have a roll 16" dia. 5' long
sprayed .100 to .150 total on dia.
with hard s.s.
customer said it is not enough
can you spray over it after it has been ground
with out taking it all off and starting over?
i was told and found out after coolant and oil is on it
it will seep out and new spray will not stick
what would be the best route
bake . sandblast . respray?
startover?
products?

THANKS

[LEN WOOD]

Start Over and put it down to experience - you have to!

[Gordon]

Hi jtwmc

to the Surface Engineering Forum.

Agree with GlenB, I would completely remove coating, re-prep surface and start again.

Some more discussion here re-applying-metco-308

[karunanidhi]

Dear Gordon,

What do you think of blasting with SiC grit for the above case?

[Gordon]

Hi karunanidhi

What do you think of blasting with SiC grit for the above case?

Good blasting media, but I think it changes nothing said above. Coating on top of old coatings is a big risk at the best of times.

[k09]

Hi jtwmc,

I agree with gordon, spray over previous coating is never recommended. BUT...if the "circumstances" are such that you donot have enuf time and you have to return it urgently AND if you do think of spraying over the previous coating make sure you do the following things:

1) Clean the job thoroughly with solvent
2) Ensure that you have good surface roughness (atleast 6 Ra micron)
3) IMP* before you spray give atleast 4 to 6 passes of preheating at normal coating speed. this will ensure that "most" of the oil seeps out and vaporises.
4) then spray without over heating the job ( not more than 100DegC)

All the Best!!