Cracks! in bond coat

[Christine]

Hi all!

I need some advice....

My customer is spraying NiCoCrAlY (bond coat) onto nozzle guide veins with a multicoat system using DJ2600 and twin powder feeders.

Recently they have been experiencing cracks on the thinner edge of the veins and we cannot resolve this issue

parameters are as follows:

O2: Pressure: 11.7 bar Flow: 147.2 nlpm F.M.R: 22
H2: Pressure: 9.6 bar Flow: 705 nlpm F.M.R: 60
N2: Pressure: 6.9 bar Flow: 398.1 nlpm F.M.R: 50
Shroud gas is Nitrogen
Spray rate on the low side at 20g/min

The parts are grit blasted before they coated. Im guessing parts which were not blasted properly are causing these cracks to occur. But these crack are pretty consistent and the most of the whole batch sprayed showed cracks...what can be done to eliminate these cracks?!!! help!!!

Also something else that's adding to the confusion is the width/length of the flame thats producing varied deposit efficiencies resulting in a variation of the weight gain of these parts. Could this be in turn causing the cracks?

[ServiceTech]

[quote='Christine' pid='6446' dateline='1321621728']
Hi all!

I need some advice....

My customer is spraying NiCoCrAlY (bond coat) onto nozzle guide veins with a multicoat system using DJ2600 and twin powder feeders.

Recently they have been experiencing cracks on the thinner edge of the veins and we cannot resolve this issue

parameters are as follows:

O2: Pressure: 11.7 bar Flow: 147.2 nlpm F.M.R: 22
H2: Pressure: 9.6 bar Flow: 705 nlpm F.M.R: 60
N2: Pressure: 6.9 bar Flow: 398.1 nlpm F.M.R: 50
Shroud gas is Nitrogen
Spray rate on the low side at 20g/min

The parts are grit blasted before they coated. Im guessing parts which were not blasted properly are causing these cracks to occur. But these crack are pretty consistent and the most of the whole batch sprayed showed cracks...what can be done to eliminate these cracks?!!! help!!!

Also something else that's adding to the confusion is the width/length of the flame thats producing varied deposit efficiencies resulting in a variation of the weight gain of these parts. Could this be in turn causing the cracks?



Christine;

The nlpm flows listed are WAY out of proportion in regards to Oxy / Fuel ratio. Why is the customer referencing Flow Meter Reading (DJC or DJF) with a MultiCoat? Is this used with an additional flow system? I probably have the DJC / DJF parameters for low oxide bond coats, I'll need to look it up.

Cracks are usually caused by excessive coating thickness deposit per pass or temperature issues.

[Christine]

(11-20-2011 01:27 AM)ServiceTech Wrote:  [quote='Christine' pid='6446' dateline='1321621728']
Hi all!

I need some advice....

My customer is spraying NiCoCrAlY (bond coat) onto nozzle guide veins with a multicoat system using DJ2600 and twin powder feeders.

Recently they have been experiencing cracks on the thinner edge of the veins and we cannot resolve this issue

parameters are as follows:

O2: Pressure: 11.7 bar Flow: 147.2 nlpm F.M.R: 22
H2: Pressure: 9.6 bar Flow: 705 nlpm F.M.R: 60
N2: Pressure: 6.9 bar Flow: 398.1 nlpm F.M.R: 50
Shroud gas is Nitrogen
Spray rate on the low side at 20g/min

The parts are grit blasted before they coated. Im guessing parts which were not blasted properly are causing these cracks to occur. But these crack are pretty consistent and the most of the whole batch sprayed showed cracks...what can be done to eliminate these cracks?!!! help!!!

Also something else that's adding to the confusion is the width/length of the flame thats producing varied deposit efficiencies resulting in a variation of the weight gain of these parts. Could this be in turn causing the cracks?



Christine;

The nlpm flows listed are WAY out of proportion in regards to Oxy / Fuel ratio. Why is the customer referencing Flow Meter Reading (DJC or DJF) with a MultiCoat? Is this used with an additional flow system? I probably have the DJC / DJF parameters for low oxide bond coats, I'll need to look it up.

Cracks are usually caused by excessive coating thickness deposit per pass or temperature issues.

Hi!

Its always great to hear from you

I re-checked the flows, oxygen is at 140nlpm, hydrogen has increased from 670nlpm to 700nlpm. Nitrogen reduced from 650 to 550nlpm.

we aim to achieve 25microns per pass, but now, we cant even achieve this with a feedrate increase from 20g/min to 38g/min!

These new spray parameters and some changes to the robotic programme has been successful in eradicating the more major cracks. Now the problem we face is hairline cracks at the trailing edges of these multi aerofoil components. Plllllleaseee send me the parameters if you do find them? you can email them to Christine.Francis@sulzer.com

Im ever so grateful to your reply! thanks once again

[derek]

Christine, I had similar problem as you do. Please see attached picture. The vane was repaired by welding, braze, blending etc. and go to coating shop for bond coat, in the specific area we have the same problem on 1/3 of the parts. The reason is the thermal stress created during coating process, I try so many different ways (strong air cool, pre-heat, change the program sequence etc.) to solve this problem but still can't get it. Hope here some coating export can help me out. If you can send your picture out, maybe someone can help you.

[Christine]

(11-21-2011 03:54 PM)derek Wrote:  Christine, I had similar problem as you do. Please see attached picture. The vane was repaired by welding, braze, blending etc. and go to coating shop for bond coat, in the specific area we have the same problem on 1/3 of the parts. The reason is the thermal stress created during coating process, I try so many different ways (strong air cool, pre-heat, change the program sequence etc.) to solve this problem but still can't get it. Hope here some coating export can help me out. If you can send your picture out, maybe someone can help you.

Thanks derek

its a long process, they changed the robot programming from traversed vertically over the component to spraying horizontally across the aerofoils to get more control in the fillet areas...

then tried fine tuning the spray parameters...

now.... although we've eliminated the major cracks...there is still hairline cracks!!!

i really hope someone who has overcomed something similar to this shares their experience with us....

ill post a picture as soon as i can..

[landemarre]

(11-18-2011 02:08 PM)Christine Wrote:  Hi all!

I need some advice....

My customer is spraying NiCoCrAlY (bond coat) onto nozzle guide veins with a multicoat system using DJ2600 and twin powder feeders.

Recently they have been experiencing cracks on the thinner edge of the veins and we cannot resolve this issue

parameters are as follows:

O2: Pressure: 11.7 bar Flow: 147.2 nlpm F.M.R: 22
H2: Pressure: 9.6 bar Flow: 705 nlpm F.M.R: 60
N2: Pressure: 6.9 bar Flow: 398.1 nlpm F.M.R: 50
Shroud gas is Nitrogen
Spray rate on the low side at 20g/min

The parts are grit blasted before they coated. Im guessing parts which were not blasted properly are causing these cracks to occur. But these crack are pretty consistent and the most of the whole batch sprayed showed cracks...what can be done to eliminate these cracks?!!! help!!!

Also something else that's adding to the confusion is the width/length of the flame thats producing varied deposit efficiencies resulting in a variation of the weight gain of these parts. Could this be in turn causing the cracks?

Hello,

I can't find same value between FMR and nlpm in your parameters
O2 flow rate (nlpm) is very low (is it the good value?), stoechiometry is at 0.4 only, is it possible to use this gun at so low oxygene flow? If it work with so low oxygene flow, speed of particule should not as high it should, temperature of powder should be relatively low (good for oxydation) but heat transfert on the part should be high (not good for strength).

There is no information on spray distance, this is an important parameter for heat transfer and strength. Wich is relative speed? Do you have cooling system?