ChromeCarbide Porosity Dilema
09-17-2009, 11:13 AM,
#1
ChromeCarbide Porosity Dilema
Hi All. We are having great difficulty in achieving a dense coating through HVOF application of Cr-C TK7184 (JK135) onto 316L Stainless Steel.

We use a UTP Hypersonic uni-spray-jet Top Gun and the parameters are as follows:

Oxy = 560 SCFH
Propane = 140 SCFH
Carrier Gas = 40 PSI
Flow Rate = 30g/min

Our 88/12 and 1350 coatings achieve a porosity level of <1.5% but the Cr-Carbide coating only achieves a density of around 80%?

The experienced operator claims that the flame looks good and care was taken during surface preparation.

Any advice is very well appreciated !

Cheers,
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09-18-2009, 01:06 PM,
#2
RE: ChromeCarbide Porosity Dilema
Hi Batsy

I have no real experience with your equipment so its difficult to comment on gun setting parameters.

Where do your spraying parameters originate?

Have you notice any features from metallography (other than porosity) that might give clues to what is going wrong? Might help to upload photo here.

Are you spraying in confined conditions? like internal diameter bore etc.

Are you spraying at shallow angle (< 45 degrees)?

I would watch the process closely - does the spray look hot or maybe cool? Is it high velocity and can you see shock diamonds? What level of deposit efficiency? Is there much airborne dust/smoke/particles around spray area? etc..

To be honest, I would have though using the exact same parameters as for your WC/Co would give a denser coating than your getting now.
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09-22-2009, 06:35 PM,
#3
RE: ChromeCarbide Porosity Dilema
Thanks Gordon, here is some more information as you suggested:

The spraying parameters we use are the same as our standard WC/CO parameters which originated from our operations manual (although this is quite old now > 12 years)

WRT micrograph, i've tried to upload as an attachment and keep getting the following fault:

Fatal error: Allowed memory size of 262144 bytes exhausted (tried to allocate 26632 bytes) in /home/gordonengluk/public_html/sef/inc/plugins/seo.php on line 424.

I've reduced the size of the micro significantly but still no joy?

We spray four sides of a rectangular bar and the spray angle = 45 degrees

The spray looks good and 8 shock diamonds are clearly visible within the flame plus all work is carried out in an enclosed spray booth which has extraction on the back wall.

I hope this is of help,

Cheers, Batsy.
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09-26-2009, 04:46 PM,
#4
RE: ChromeCarbide Porosity Dilema
Hi Batsy

Quote:WRT micrograph, i've tried to upload as an attachment and keep getting the following fault:

Fatal error: Allowed memory size of 262144 bytes exhausted (tried to allocate 26632 bytes) in /home/gordonengluk/public_html/sef/inc/plugins/seo.php on line 424.

Sorry, this is a known bug that sometimes crops up, try advice given in last post of
image-photos-in-posts-t-58.html or just email image file to me and I will insert it for you.


Quote:We spray four sides of a rectangular bar and the spray angle = 45 degrees
This probably is not helping. Can you spray nearer the 90 degree angle?
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