Abradable Coating-Bond Strength

[rayudugirish]

Dear Gordon and Members,

What is the best method to estimate the bond strength of Abaradable coatings. We have tried to follow ASTM C-633 but we are observing cohesion failure. (The top surface of the coating which is exposed to the glue is peeling off). Nevertheless hardness values are all within the specs.

Some one suggested tape type test is required. If yes kindly specify the spec and make.

Thanks and Regards,
Girish

[karunanidhi]

Hi Girish,

the procedure& specifications for performing tape test is given in ISO 2063:1991

with regards
karunanidhi

[TurbineRepair]

Hi Girish,

Do you mean the coating is failing at the glue interface or actually within the coating? What thickness of coating are you applying and is it level?

Jim

[raviswanadha]

Hi Jim,
Coating is failing at the Glue interface(approx 10microns inside the coating). Thickness of coating after grounding is around 1mm. Expected bond strength is 1500psi. Failure at glue interface is around 600PSI. Well how we can report the findings.

Regards
Girish

[landemarre]

Hello

Do you use the same glue as expected in specification coating? This is possible trouble, abradable tensile tests are very high sensitive to glue used.

regards

Hi Jim,
Coating is failing at the Glue interface(approx 10microns inside the coating). Thickness of coating after grounding is around 1mm. Expected bond strength is 1500psi. Failure at glue interface is around 600PSI. Well how we can report the findings.

Regards
Girish

[ykang]

Hi Girish:

You may try to cure your bond specimen with sprayed condition without grind-off. I am not sure if this is accepted in ASTM Spec (not familise with it). Ground surface will make the surface flat but at the same time too smooth for the proper bonding. I did experience before to take much effort to grind the surface and perform the bond test, however it failed most of the time.

After that I realised that with proper spraying condition and robot movement, uniform thickness bond specimen can be obtained and thus can be used for the bond test with better curing result.

I had also experienced on inconsistent bond strength readings due to the improper curing method. So uniform-flat thickness is important.

Regards

[TurbineRepair]

Hi Girish,

The glue needs a rough surface to bond to, if you are grinding the buttons flat after spraying you will destroy the nice rough surface.
Are you spraying directly onto the load cells or onto separate buttons? The way we do this test is to spray 1" dia buttons about 15mm thick and glue them to the load cells. This was we have a greater choice of the substrate material and the 15mm short buttons are less problematic to spray in a circular spray pattern. The buttons must be flat after (and before!) spraying but if you are having to grind them you may need to look at you spraying method to get a nice even coat. Typically 90 RPM with 6.6mm/s traverse works for a 300mm dia test rig.
Does your glue test give a satisfactory result? We use Type FM 1000 which is good for 10000psi (I think, although I would have to check for exact specs!).
How do you cure the glue? have you got the correct preloading curing fixture?
Finally what coating/powder are you testing?

Regards,
Jim

[Gordon]

Hi Girish

I can only echo the helpful replies from Jim, Ykang and Landemarre.

[KevinS]

If the cross-head speed of the tensile test is faster than it needs to be then that condition may be occuring. See if testing at 0.020 in/min corrects the problem. Then see what is the lowest crosshead speed that you customer/specification will allow.

Dear Gordon and Members,

What is the best method to estimate the bond strength of Abaradable coatings. We have tried to follow ASTM C-633 but we are observing cohesion failure. (The top surface of the coating which is exposed to the glue is peeling off). Nevertheless hardness values are all within the specs.

Some one suggested tape type test is required. If yes kindly specify the spec and make.

Thanks and Regards,
Girish

[derek]

The liquid glue is not the best for coating tensile test, please try


 


FM-1000 adhisive film.