Coating thickness

[Arturas]

Hello
I have problem related with coating thickness. After spraying of NiCrBSi coating on stick form part - diameter 300mm I am measuring thickness and it shows me 1mm . Then I perform fusing and when temperature of part is approximately 100C coating thickness decrease to 0.8mm. It looks normal but after part cool down to room temperature I can find only 0.4-0.3 mm of coating. The thickness of coating I am measuring with portable thickness measuring device.. May someone explain this situation?

Arturas

[Vijay Deshpande]

Its a very tricky job as u might not have considered expansion of the substrate. Also always powder shrinks after fusing. One has to expirement to come to proper thickness.
Vijay

Its a very tricky job,
Hello
I have problem related with coating thickness. After spraying of NiCrBSi coating on stick form part - diameter 300mm I am measuring thickness and it shows me 1mm . Then I perform fusing and when temperature of part is approximately 100C coating thickness decrease to 0.8mm. It looks normal but after part cool down to room temperature I can find only 0.4-0.3 mm of coating. The thickness of coating I am measuring with portable thickness measuring device.. May someone explain this situation?

Arturas

[bhellman]

Dear Arturas, you have to calculate with an extra 20+ % for the shrinkgage.
br bjarne

[Gordon]

Hi Arturas

I think the problem must be with your portable thickness measuring device (assuming your spraying and fusing technique is good). These devices actually measure electric or magnetic field strength then convert this to a thickness reading. It is important that these instruments are calibrated to your actual substrate/coating materials and also for temperature. Changes in materials and temperatures will effect the electrical and magnetic properties, thus giving differing readings. Problem here is that you have 3 different stages; an as-sprayed coating, fused coating at 100 C and fused coating at room temperature. Lets say the actual coating thickness is constant for the 3 conditions, your measuring device could be giving 3 different readings.

As said before and I'm sure you are aware that usually coatings will not shrink more than about 20% (barring coating runs and edge pulling).