Separation in Silver alloy Wire

[shabisyed]

Hi Gorden and other Members

I have been facing a problem to spray Silver Alloy wire (Braze 300) on 5504 Steel test piece by Metco 14E Gun. I am getting a lot of oxides and Delamination or Separation in this coating.I am using Metco 14E book parameters.i.e Flow of Oxygen=44 Cfh and Fuel= 40 Cfh and distance is 5 inches..I also reduced little Oxygen.I couldn't fix it .Please let me know how can I fix it.
Regard,
SHabi
Email: shabi_riz@yahoo.com

[Gordon]

Hi Shabisyed

to the Surface Engineering Forum.

Is the purpose of spraying silver braze material for pre-placement for post-brazing operation?

What thickness of coating are you aiming for and at what thickness does the coating start to lift away from substrate? Are you controlling substrate/coating temperature well enough?

What substrate preparation are you using?

What is the spray rate/wire speed or more importantly the length of wire tip in flame?

[shabisyed]

Hi GOrgon,
Thanks for reply.
Actually I am using Silver Alloy Wire from Metco 14E gun for the qualification on Aircraft Parts. I spray Silver Alloy wire on Steel Test piece.than Evaluate its Microstructure in Microscope 200X .I get separation layers.I controll the temperature it around 100 to 120F.
My spray rate is 3inches in 5 Sec.and wire burn almost with level of Aircap.
Regard,
SHabi

Hi Shabisyed

to the Surface Engineering Forum.

Is the purpose of spraying silver braze material for pre-placement for post-brazing operation?

What thickness of coating are you aiming for and at what thickness does the coating start to lift away from substrate? Are you controlling substrate/coating temperature well enough?

What substrate preparation are you using?

What is the spray rate/wire speed or more importantly the length of wire tip in flame?

[Gordon]

Hi Shabisyed

I will for the moment assume your metallography techniques are good, but this is an area you could question.

I would try increasing the length of your wire tip in the flame, may be 6, 9 or even 12 mm beyond the air cap. This should give you a coarser, but less well oxidised coating. Try this with everything else as standard and see if has the desired effect. Let us know how you get on May be good to upload some photomicrographs.

[shabisyed]

Hi Gorden,
Thanks for replying.You means I will have to increase the wire speed.I can see wire tip out of aircap 9 to 12mm.I am using CH Air cap.WHich Aircap you would recommond me.Please let me know if I increase the Oxygen what will effect on coating.and If I increase or decrease the Fuel what will effect on Coating.
Thanking you.
Shabi

Hi Shabisyed

I will for the moment assume your metallography techniques are good, but this is an area you could question.

I would try increasing the length of your wire tip in the flame, may be 6, 9 or even 12 mm beyond the air cap. This should give you a coarser, but less well oxidised coating. Try this with everything else as standard and see if has the desired effect. Let us know how you get on May be good to upload some photomicrographs.

[Gordon]

Hi Shabi

Yes, increasing wire speed will increase wire tip length in the flame (assuming this is the only change as other changes like gas flows will have influence).

If you are using 1/8" wire and standard jetted 1/8" nozzle, assuming acetylene fuel (from your flow rates) I would use the EC air cap. The CH air cap is the equivalent, but a non-load version for low melting point wires, which really you should not need for this wire and may in fact be making your problem worse.

I would stick with your standard gas flows, at least until you have sorted other potential causes to your problem. Changing oxygen/fuel ratios (while trying to maintaining total flows) will certainly have significant effects, but effects on the amount of coating oxidation within the coating may be surprising small. There are many other significant factors influencing this, like how the molten particles are atomised (size and velocity), temperature and flight time. So things like air cap, air pressure/flow, total fuel/oxygen flow, wire feed rate and spray distance are among other factors which complicate the overall equation to getting a good coating.

[shabisyed]

Hi Gordon,
Now I got a good result.but I used Oxygen Flow= 42CFH and Acetelene(Fuel) Flow=40 CFH.and wire speed I used 3 inches per 5 Sec. and test piece is stationay and I used gun speed very fast as I can.But I used CH aircap bcoz my supervisor told me to use CH aircap.Thanks you for your guidness.Please let me know what parameter you would recommend to me.also let me know the Parameter of Metco 308NS from Metco 6PII gun and parameter of Metco 450NS from same gun.
Regards,
Shabi

[Gordon]

Hi Shabi

If you don't have specific parameters for that wire, I would start off with the parameters listed for copper in the 14E manual.

For Metco 308 and 450 6P-II parameters, the best place is the 6P-II users manual and I suggest also getting the product technical bulletins from Sulzer Metco. The bulletin for 308NS will also cover the techniques required for adjusting coating hardness, which will be important.

[shabisyed]

Hi,
I am using the same parameters for Braze300(SIlveralloy wire).Gases Flow are same.But I am getting again separation in coating .I thing wire speed is fast thats why I am getting this problem.My wire speed is 3 inches per 5 Sec. as I was using before.Plz let me know the cause of separation.
Thanks,
Shabi

[Gordon]

Hi Shabi

I thing wire speed is fast thats why I am getting this problem.My wire speed is 3 inches per 5 Sec. as I was using before

How far is the wire is the wire tip extending in the flame beyond the air cap? Is the air cap EC or CH?

But I am getting again separation in coating

Could you describe this condition in more detail?