Chrome-Carbide coating issue
10-21-2015, 12:02 PM,
#1
Chrome-Carbide coating issue
Hello all,

I have a problem with Cr3C2-10(Ni-20Cr) coating sprayed with HVOF gun DJ2600 (DJ8W). After sprayed small particales in the shape of "hills" were appeared on the coating texture (on whole outer diameter). After grinding operation these partical pulled-out and overturned to pits (100microns approx.) on the coating (see pic 1). Very interesting fact, that the phenomenon is does not appear on all parts, but only on about 30%.
Prior parts spraying, metallographic specimen sprayed and was approved by MCL for metallography and hardness (approx. 850HV0.3). See the second attachment.

I assume the problem could being from some cases:
1. Dring powder in oven prior spraying is improper.
2. The particals size is 45microns. The powder is in hopper could be for a week and can cause formation of accumulation of powder clusters. During spraying these clusters heated, sprayed on the part and appear like "hills".
3. Poor barrel cooling that leads to barrel loading effect. During spraying, some of the particles that stick to the barrel sprayed on the part.

In conclution, I have two questions:
1. What can cause these "hills" and pits?
2. Why the phenomenon does not appear on all parts?
This looks like something is changing during spraying from part to part (the parts spraed separate one by one) or deterioration of some gun component occur.

If somebody have any idea or had the same issue, I will appreciate to hear your point of view and your suggestion solve the problem.

Thanks!


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10-21-2015, 01:24 PM,
#2
RE: Chrome-Carbide coating issue
(10-21-2015, 12:02 PM)DanyGans Wrote: Hello all,

I have a problem with Cr3C2-10(Ni-20Cr) coating sprayed with HVOF gun DJ2600 (DJ8W). After sprayed small particales in the shape of "hills" were appeared on the coating texture (on whole outer diameter). After grinding operation these partical pulled-out and overturned to pits (100microns approx.) on the coating (see pic 1). Very interesting fact, that the phenomenon is does not appear on all parts, but only on about 30%.
Prior parts spraying, metallographic specimen sprayed and was approved by MCL for metallography and hardness (approx. 850HV0.3). See the second attachment.

I assume the problem could being from some cases:
1. Dring powder in oven prior spraying is improper.
2. The particals size is 45microns. The powder is in hopper could be for a week and can cause formation of accumulation of powder clusters. During spraying these clusters heated, sprayed on the part and appear like "hills".
3. Poor barrel cooling that leads to barrel loading effect. During spraying, some of the particles that stick to the barrel sprayed on the part.

In conclution, I have two questions:
1. What can cause these "hills" and pits?
2. Why the phenomenon does not appear on all parts?
This looks like something is changing during spraying from part to part (the parts spraed separate one by one) or deterioration of some gun component occur.

If somebody have any idea or had the same issue, I will appreciate to hear your point of view and your suggestion solve the problem.

Thanks!

Hi Dan,
What was your spray distance. I've seen this profile before from spraying too close with the DJ2600.

Cheers.
John
Reply
10-21-2015, 05:09 PM,
#3
RE: Chrome-Carbide coating issue
Hi Dany
This trouble is normal for the DJ 2600/DJ2700 and DJP/9MP powder feeder because it's fluidized bed that cause the difficulty to feeding powder with a good combination of carrier gas pressure and flow, and powder feed rate, it can be some problem with the powder injector geometry too, and all this problems cause powder sticking inside the barrel and causing spiting of material, I experienced all this problems with big paper industry rolls, and it was very expensive to rework the rolls rejected, and there wasn't solution, it was possible only changing the spray system.
Best regards
Luigi
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10-21-2015, 10:59 PM, (This post was last modified: 10-21-2015, 11:05 PM by Johnny_Blaze.)
#4
RE: Chrome-Carbide coating issue
Hi Dany,
I would have to agree with Luigi, the loading on the barrel on the DJ 2600/2700 is a problem.

It's intermittent when it spits off, this is possibly why it appears on some parts and not others. I had the same problems with the Miller volumetric HVOF powder feeders, disc type powder feeders, so I wouldn't spend much time worrying if it's a fluidized bed powder feeder.

It's more likely caused by leaving your powder in the hopper for too long and clumping occurs, also barrel condition is a factor.

If it was spray distance it would be consistent and not intermittent.

John
Reply
10-25-2015, 08:59 AM,
#5
RE: Chrome-Carbide coating issue
Hi John and Luigi,

Thank you for all of your professional comments.

My new powder feeder type is Twin 120-AH 1.0 (just 6 months in work). Ar(g) flow is 13 lpm feeding powder appox. 35gr/min.
What are corrective actions could I make in order to prevent or improve this phenomenon?
I have some ideas. What is your opinion?
1. Change the spreader unit. Now 55deg.
2. Empty the powder hopper, dry and blend the powder at list 2 times/day.
3. Clean the barrel periodically.
4. I would like to try change some spraying parameters, but I have a frozen process.

Thanks you in advance
Dany
Reply
10-27-2015, 10:21 PM, (This post was last modified: 10-27-2015, 10:26 PM by Johnny_Blaze.)
#6
RE: Chrome-Carbide coating issue
(10-25-2015, 08:59 AM)DanyGans Wrote: Hi John and Luigi,

Thank you for all of your professional comments.

My new powder feeder type is Twin 120-AH 1.0 (just 6 months in work). Ar(g) flow is 13 lpm feeding powder appox. 35gr/min.
What are corrective actions could I make in order to prevent or improve this phenomenon?
I have some ideas. What is your opinion?
1. Change the spreader unit. Now 55deg.
2. Empty the powder hopper, dry and blend the powder at list 2 times/day.
3. Clean the barrel periodically.
4. I would like to try change some spraying parameters, but I have a frozen process.

Thanks you in advance
Dany

Hi Dany,
Considering you have a process that is frozen, I would agree with steps 2 and 3.

For step 2, be sure to gently rotate the bottle of powder, end over end, to ensure that it is able to flow freely prior to placing it into the hopper.

For step 3, I would pay close attention while spraying to see if the powder is building up and spitting off during spraying if your can actually see the front of the gun while in process.



Regards,
John
Reply
10-04-2019, 09:01 AM,
#7
RE: Chrome-Carbide coating issue
Hello All,

Hope you all are doing fine.

I have also problem with Cr3C2-(Ni-20Cr) coating applied by HVOF gun DJ2600 (DJ8W).
We have cracks that occurs from sub-section of coating to top.
Base Material : Inconel 718
Powder: Cr3C2 -NiCr 90/10 Sintered and crushed
As sprayed thikcness : .020” - .030”

Part temperature is max. 100 C during process. We tried pre-heating and without pre-heating. We changed cooling time between passes, and after spraying.

I'm just wondering if you suggest me some parameters.

Thanks in advance,

Yildirim
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10-07-2019, 08:34 AM, (This post was last modified: 10-07-2019, 09:18 AM by loriolo.)
#8
RE: Chrome-Carbide coating issue
Hi Danny
It's necessary to know very well HVOF settings in order to solve the problems with this systems, and to take care of parameters, the carrier gas flow and pressure define the powder speed and stability inside the barrel, this is one of the important setting for this kind of systems very difficoult to set, low carrier gas flow cause barrel loading, and the other parameters to take care are the stability on gas flow and pressure, because can cause turbulences that cause deviation of the powder flow, so the powder sticks inside barrel, is very difficulty to center the powder flow in order to minimize sticking, so barrel loading cause that larges chunks arrive on the coating that causes hills and after grinding holes, furthermore this cause premature wear in the barrel, in order to minimize this problems, you must take time to set parameters very well, to see if this are correct, you must point the gun to a piece and do spot-test since you obtain a spray spot cylindrical and centered, if spray spot is oval or imperfect you must correct parameters since you obtain a very clean and definite spot

Hi Yildirimn
About your problem with cracks on the coating, this is normal for Gas mix HVOF systems (the best to solve coatings stresses at the moment is HP HVOF systems with O2/Ethanol mix), because the coatings result with high coating residual tensile or compressive stresses, you system normally has compressive stress, and it’s important to minimize this residual stresses, doing a very precise parameters setting, and doing Almen strip test to check this stresses
Best regards
Luigi
Reply
10-07-2019, 11:15 PM,
#9
RE: Chrome-Carbide coating issue
Hi Danny;

Here are the fundamentals to look for with the DJ Hybrid and spitting powder.

1. First confirm by visual examination that the air cap is indeed loading. You will see material adhering to the I.D. of the chrome plated bore.
2. If loading is evident there are several things to check:

A. Powder particle size - if many particles small than 10 micron it will present a problem with the DJ.
B. Air flow - Ensure the air flow parameters are correct. Typical DJC air settings are 100 psi and 44 FMR.
C. Water flow - Ensure there is adequate water flow and that the water is cool. Less than 70F. Water flow should be greater than 3 gpm and preferably upwards of 5 gpm.
D. Check the outside water jacket condition of the air cap. If low water flow or high water temperature are the result of air cap loading you will observe a black oxidized outer surface of the water jacket.

Poor water temperature and flow along with low air flow and sub 10 micron powders are the number one causes of loading in a DJ.
Reply
10-08-2019, 11:03 AM,
#10
RE: Chrome-Carbide coating issue
All of you great folks are very helpful. I just want to point out that the original post is from 4 years past. Big Grin
Reply
10-08-2019, 04:39 PM,
#11
RE: Chrome-Carbide coating issue
(10-08-2019, 11:03 AM)Lemster68 Wrote: All of you great folks are very helpful. I just want to point out that the original post is from 4 years past. Big Grin

Awesome!!! Hahahaha!!!
Reply
10-08-2019, 05:19 PM,
#12
RE: Chrome-Carbide coating issue
The newer post piggy backed onto the old one is kind of discouraged in some forums. It confuses a lot of people, it is sometimes referred to as "grave digging". Better to create your own, unique post, IMO.
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