HVOF coating the bores of thin wall sleeves

[SDA]

Hello All,

I currently have an issue with cracking of 86/10/4 coatings in the bores of thin wall sleeves. We pre-heat to 100 deegrees and run a feed speed of 60mm/min on a 250mm bore. The temperature is kept between 100-160 and the gun angle is approximately 30 degrees whilst keeping to standard Praxair settings. Can anybody help improve this method to reduce the likelyhood of cracking ?

Thanks.

[djewell]

What is the material of the sleeve? Is it stainless steel or carbon steel? Are you seeing compressive or tensile cracks?

[SDA]

Hi,

It is a Stainless Steel and the cracks appear to be tensile.

[djewell]

If the cracks are tensile, then the coating is contracting more than the stainless steel. Therefore, you must get the substrate hotter or cool the coating while spraying to increase compressive stress. If, on the other hand, the cracks are compressive, then you must do the opposite. Are you reporting temperatures in celcius or fahrenheit?

[SDA]

Thanks, temperatures are Celcius. I have also increased the feed rate to achieve 0.00035" per pass and will have the results on Monday.

[kschewe]

try changing your spray angle if you can. hvof likes to be sprayed straight on to the substrate.