metalizing

[jtcincy]

this really aint a cnc question but
we thermal srayed a print roll with hard s.s.
16" dia. 5' long
about .100 per side
it is chipping and flaking when grinding it
usually we put .015 per side for journal repairs and it works fine
is .100 too much for good adhesion ?
i was told and found out you cant re- spray after coolant and oil is on it
you have to start over from scratch
is there any way to re-spay or products that can do it
or way to fix that problem it may be too technical but
can anyone help ? ! ?

comments suggestions

thanks

[HuFlungDung]

What kind of metallizing system did you use? Powder metal or atomizing wire?

That is definitely a bit on the heavy side for powder application, because I think the powder skin gets overheated relative to the parent metal, and thermal contraction later causes delaminating of the spray. Bear in mind that the powder is not fused to the surface, so it does not take much to dislodge it. Dull tools/loaded wheels will also break it loose due to inelastic local compression/decompression under the contact point.

How do you guys typically perform the surface prep? Contamination was always a concern, even the preheat oxidation layer was suspect to me. I'd preheat then rough turn then use the bond coat immediately, however I never tackled anything nearly as big as what you have there. I'll bet you've got a few $$ tied up in materials on that one

[jtcincy]

we use wire
we prep by undercuting and chasing threads then wrapping it in newspaper
to keep it clean before spray
we do it all the time no problem
our customer is grinding it we just prepped and sprayed
when we got it it was .090 under fin size
they screwed up and theyre trying to get out of a jam
although we never pre heat
maybe we should have ? ! ?
for something that damn big

[RICHARD ZASTROW]

Back in another life we metalized Yankee Dryers. These are 12-15 ft. dia. cast iron steam heated rolls 12-15 ft long.

The edges would erode within the first 2-6 inches of each end. We coarsely ground the edge area to true it up then grit blasted it. Immediately after blasting, it was wire metalized about .060"-.100" thick.

After metalizing, the rolls were ground till the metalized area blended in with the parent metal. The entire dryer roll face was then finish ground.

10-13 days (sometimes much more) working 24/7 (2 shifts) till finished. 1 day R&R with ample supplies of beer then back home.

Ah, the good ol' days. LOL

Dick Z