oxide stringers and porosity In HVOF WC-CO

[wilfred1963]

Having problems with oxide stringers and porosity in 2005NS running DJ8W with O2andH2 fuel gas

[Gordon]

Hi wilfred1963

to the Surface Engineering Forum.

Quote:Having problems with oxide stringers and porosity in 2005NS running DJ8W with O2andH2 fuel gas

Can you give more details about your set-up/parameters etc. and ideally an image of the coating showing the faults.

[Gordon]

Hi wilfred1963

I will move your thread to "Surface Engineering" as it does not really belong here and hopefully it will get more attention.

[wilfred1963]

(01-14-2011 06:43 PM)Gordon Wrote:  Hi wilfred1963

to the Surface Engineering Forum.

Quote:Having problems with oxide stringers and porosity in 2005NS running DJ8W with O2andH2 fuel gas

Can you give more details about your set-up/parameters etc. and ideally an image of the coating showing the faults.

---

Thanks for the reply,
will try to get a photo of the system but for now i'm running 44 air 32 oxygen and 62 hydrogen problem being is that the parameter that was handed to me really is no good they have an 11.0" stand off and it should be 8-9" were 8.5" is nominal distance i have used the DJ8W in the past but am fighting an uphill battle. the stringers have a lazy s apperence or an elongated c across the horizontal plane with even distrabution, the hardness is low which i can fix and the structure is good as the Dph readings were with in 2.5 points but the spec calls out 1% max voids, oxides,and porosity so i have a bit of way to go any ideas??

[Gordon]

Hi wilfred1963

My advice would be to use the Sulzer Metco recommended parameters for 2005NS. While these parameters may not necessarily always be the best optimised for your purposes, they will be a massive improvement on what your getting now and the best starting point/baseline for further development.

[wilfred1963]

Thanks for the reply Gordon ,
Was thinking same but the powers to be want to do things differently as they sprayed in the past with these parameters and had success but the system was unstable with varying pressuers in air Psi now that i have it running properly will try a parameter change, thaks again for the reply nice to know i'm not losing my mind lol will post later with results thank you again
....Wilfred1963....

[Gordon]

Hi wilfred1963

Good luck and yes it would be nice to know how you get on

[Khairul Anwar]

hi wilfred1963,

did you get any result on this? I was wandering as well, what will be the root cause. I am facing the same problem with Amperit 593.775. I am using HVOF and H2 fuel.

We have run this for years but suddenly this laminar oxides pop up. I did ensure every setting are as before but i guess it's all in vain. Appreciate any advise..and how do i post some pictures here?

[wilfred1963]

Yes i did have good results by going back to basic parameter settings of 32 oxy. 62 hydro. and 44 air this reduced tyhe oxides some what but not as much as needed so i went to 225mm standoff and ramped the hydrogen up to 66 and left the oxygen alone as well as the air left that at 44 as well moved the feed rate to 55 g/m giving me a deposition of .010-.012 mils in 35-45 cycles or passes with a Dph of 1190-1220 VH. also i am usung diamaolly 2005NS(metco) was using starck- Amperit but the powder was comming in the door with contamination from the vendor. the laminar oxides sounds like your running to hot or not traversing fast enough also check your powder for proper micron size.. good luck

[Khairul Anwar]

Thanks Wilfred1963, running to hot is what i am guessing as well. so i did try to increase the cooling rate as well as the transvers rate, but they dosent bring much different. Is it possible this problem comes from extra fuel or O2 during combustion? I am afraid something goes wrong with our mass flow sensor.

[wilfred1963]

try checking your F.M.R for leaks and calibration also break the torch down and check the internals for worn parts and possible leaks, had some issues with the feed tube being oversized due to wear from the powder as tough tungston will chew up these things up just from normal use. would say most likely the issue is in the feeds and speeds as well as cooling during the process. let me know how things turn out for you..

[Khairul Anwar]

i am waiting for machine calibration, as i dont have any instrument to do it in house. but now it far more worse, the coating peel off. and it dosent looks like because of bad surface preparation. anyone can help?

[wilfred1963]

coating peeling off? sounds like yopu coild have some gross contamination in your air supply system such as oil try cleaning your equipment if your using grit type media also make sure your work piece is completly clean and free of anything that could cause poor bonding to the substrate, sometimes it is the simpliest of things that cause this type of problems othet than that recheck your feeds and speeds and take a look at your spray system it is possible that some form of contamination is being introduced at this area of the process

[Khairul Anwar]

Thanks wilfred1963. it might be the simplest things.hum..i ll try to check everythings back.