hvof sleeve spraying

[Brent]

I have a sleeve a customer is wanting me to spray that is 12.5"id x 13"od x 12" wide. I will be spraying it with a 86wc 10c 4cr hvof coating. My question is not in the spraying of the piece but more on what is needed to install this sleeve on the shaft after I am done. This sleeve apparently has a lot of press on it and I am unable to spray it on the shaft due to the fact I cannot fit the shaft in the grinder. I am still waiting to hear if it is pressed on or heated then put on. My question is how is the coating and bond going to react to the changes due to press post spraying?? What is the elasticity of the coating if that is the right term to use? What I would like to do is make a mandrel the same size as the shaft, install the bushing on it. Spray and grind it so I know it will be the right size after installation but I am unsure how the coating will react?
Thanks Brent








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[KevGarty]

Just kind of think posting out loud here.......

What is it your coating the ID or OD ?

OD : will you not pre machine it leaving a couple of inlays in it ? If so when it comes to be pressed the pressing will be on the parent material rather than the coating ? As long as there is plenty LUBE should go on fairly easy ?

ID: pretty much the same as above

I've seen people spray bearing areas etc then press the bearing into them (arc spray) but still gets done pretty easily ?

Maybe somebody has done it before or can have a bit more imput than me but if I am understanding what you are trying to do correctly then I cant see a problem ? as long as they dont heat the sleeve up ?? And he wont be pressing directly on the coating ?

have you got a picture ?

[MichiganMan]

Presumably the OD is being sprayed. I'm guessing from the size of the sleeve that this is for a sizeable piece of rotating or reciprocating equipment, and there is some kind of a contact seal riding on this portion of the shaft. If this is accurate, then be careful.

Depending on the thickness of the coating and the spray parameters it may or may not crack if you try to heat it before sliding it onto the shaft. Check coefficient of thermal expansion of the base material, compare to the coating material and if they aren't close, then you most likely have a problem if it is a thick coating and there is a lot of interferance to the fit. If practical for the piece of equipment in question, then you may consider cooling the shaft (as in with liquid nitrogen) rather than heating the sleeve. I have seen it done before, but not on a piece of equipment this large.

If it is a simple press and doesn't require heating, then you are probably in the clear as long as they aren't putting an exceeive point load on a coated surface.

[sreenuvundela]

Hello friend,

From my knowledge, the bonding of the thermal spray coatings is mechanical, hence thermal spray coatings will not work good in shrink fitting applications.

When we heat above 200 degree centigrade, coefficient of thermal expansion differs for base material and Tungsten carbide coating and this difference leads to coating peel off.


Regards,

SREENIVAS

[Brent]

Thanks for the input I was able to get the customer to agree to install the sleeves prior to spraying. The sprayed area ended up being 13.75dia x 20" wide and the shafts weighed in at 3300lbs by far my largest spray job to date. Went well both jobs are done and the customer is happy.