SOS !!! yellow stain on WC coating

[zhuminkun]

hello all, i have a big issue on carbide tungsten coating. we met a issue on the roller coating surface, it appears some yellow stain, vendor told me this is due to waters or moisture.
my question is, WC coating suppose to have a corrision resist why this happen? is this related to the porosity seal not good?
how can we fix this issue? if need disassemble the roller will take me 2 wks, this is a pain work

question 2: we have strick roughness requirement on the coating surface, 225 - 275 μin. what kind of seal is recommended to use, our normal use is phenolic seal, it will make roller shining, customer want a matte looking, any suggestion?

https://drive.google.com/file/d/16tBwvsS...sp=sharing

https://drive.google.com/file/d/1yAT_WaK...sp=sharing

[zhuminkun]

online waiting!!

[sprayloud]

(03-29-2018 02:14 PM)zhuminkun Wrote:  online waiting!!

From pictures it looks like coating peeled off in these areas. Is it just a stain ? If it peeled off i'm afraid there's not much you can do but to recoat.
But that's just me - you should wait for the other replies.

[Gordon]

Hi zhuminkun

to the Surface Engineering forum.

What type of WC coating?
What process type used to produce coating?
Was coating sealed?
Coating thickness?

It appears that the coating is not impervious to the environment and has allowed corrosion of the substrate underneath coating causing coating damage and the rust staining.

[zhuminkun]

(03-29-2018 04:46 PM)Gordon Wrote:  Hi zhuminkun

to the Surface Engineering forum.

What type of WC coating?
zhu:HVFO
What process type used to produce coating?
Was coating sealed?
zhu: need to check with vendor
Coating thickness?
zhu: 0.12mm.

It appears that the coating is not impervious to the environment and has allowed corrosion of the substrate underneath coating causing coating damage and the rust staining.

i assume the seal may not good, got lots of porosity not sealed.

[Stephen Booth]

I agreee with Gordon, seems that the coatings was not gas tight, or liquid tight, and corrosion has come through the surface.

Has this happened before? Did you coat in house?

(03-29-2018 04:46 PM)Gordon Wrote:  Hi zhuminkun

to the Surface Engineering forum.

What type of WC coating?
What process type used to produce coating?
Was coating sealed?
Coating thickness?

It appears that the coating is not impervious to the environment and has allowed corrosion of the substrate underneath coating causing coating damage and the rust staining.

[zhuminkun]

(04-01-2018 11:09 AM)Stephen Booth Wrote:  I agreee with Gordon, seems that the coatings was not gas tight, or liquid tight, and corrosion has come through the surface.

Has this happened before? Did you coat in house?

(03-29-2018 04:46 PM)Gordon Wrote:  Hi zhuminkun

to the Surface Engineering forum.

What type of WC coating?
What process type used to produce coating?
Was coating sealed?
Coating thickness?

It appears that the coating is not impervious to the environment and has allowed corrosion of the substrate underneath coating causing coating damage and the rust staining.

it is coated in-house for sure, i suspect the seal is not spray properly, that's only reason i doubt. the trick thing is we require the seal is transprant seal, means we need to keep the orginal color of the carbide tungsten. do you have any recommendation about the seal can meet this spec.?

[ThePlummer54]

(03-29-2018 12:12 PM)zhuminkun Wrote:  hello all, i have a big issue on carbide tungsten coating. we met a issue on the roller coating surface, it appears some yellow stain, vendor told me this is due to waters or moisture.
my question is, WC coating suppose to have a corrision resist why this happen? is this related to the porosity seal not good?
how can we fix this issue? if need disassemble the roller will take me 2 wks, this is a pain work

question 2: we have strick roughness requirement on the coating surface, 225 - 275 μin. what kind of seal is recommended to use, our normal use is phenolic seal, it will make roller shining, customer want a matte looking, any suggestion?

https://drive.google.com/file/d/16tBwvsS...sp=sharing

https://drive.google.com/file/d/1yAT_WaK...sp=sharing

Consider other material, maybe a nickel based alloy/super alloy applied through HVOF. Sealing could work but i`m not related with the seal application, so i can`t help with that, sorry.