How to decide grit size ?
04-01-2010, 12:32 PM,
#1
How to decide grit size ?
Hello forum members,

I'm currently trying to plasma spray T400 & T800 onto Ni-based alloy substrate, and come across this problem.
Although GE specification P16TF5 mentioned the substrate has to be roughened by grit blasting to 80-150 Ra prior to coating, it didn't give the information of how the grit size should be decided. I did find specification D50TF5, which stipulated the grit composiion, but still, it didn't specify what grit size shall be applied in a specific situation.

So I just wondered, is there a GE specification which could answer my question? Or whatever the grit size I chose, it's just OK as long as I could obtain the required roughness defined by specification?

Does anyone have any suggetion?

Thanks a lot.Big Grin
Reply
04-01-2010, 02:00 PM,
#2
RE: How to decide grit size ?
There are a lot of factors that go into that decision. Assuming that you have typical velocities for your blast abrasives, and the alloy in question is not unusual (in terms of hardness or malleability, etc.), then I would say you can probably get this done at a reasonably fast pace with something akin to a 16-40 mesh blend.

**In making this suggestion I have assumed that you reported Ra in micrometers.
Reply
04-05-2010, 03:33 AM,
#3
RE: How to decide grit size ?
Quote:Or whatever the grit size I chose, it's just OK as long as I could obtain the required roughness defined by specification?

For my understanding, it is true with your statement. I am using Mesh#60. Never see any spec to restrict the used grit size, unless there is a call-out in blue print.

For GE spec, personally I think it is more concern with the interface contamination rather than the roughness (of course you have to meet the min requirement, 80 Ra uin), so you have to consider what grit size you wish to use.

Too fine -> take long blasting time to give required roughness -> might give high contamination.

Too course -> also may encounter interface problem with big embedded media.

However, there are many factors to decide the final roughness reading, i.e. distance, pressure, volumetric flow, hardness of media..... you need to experiment it to establish your own matrix. Smile
Reply
04-21-2010, 09:56 PM,
#4
RE: How to decide grit size ?
We use 36 grit with 30 PSI and 7 inch distance on Ni base alloy can get Ra 120-180.
You also can use 60 grit with 60 PSI get Ra 80-150.
Reply
09-30-2010, 10:17 PM,
#5
RE: How to decide grit size ?
Grit blasting
Realization of a roughened surface for mechanical interlocking of spray particles.
Important: Beside roughening intensive cleaning of substrate surface from oxide layers etc. in order to support adhesion mechanisms, metallurgical interaction like micro- welding, diffusion.
The best angel to blast is ca. 20° perpendicular to the surface.


Grit Size ( µm) Application
Coarse -2000 + 600 Coating thickness over 250 µm and best bonding.
Medium -1400 + 425 Coatings lower than 50 µm and sufficient bonding.
Fine -600 + 180 Coatings lower than 250 µm (as sprayed)

*metco 2005 data
Reply
04-29-2011, 03:14 AM,
#6
RE: How to decide grit size ?
Reference GE SPM 70-49-00 which specifies the use of 60 mesh AlO2 grit and allows coarser grit size only if using mechanical work handling.


(04-01-2010, 12:32 PM)bepsi Wrote: Hello forum members,

I'm currently trying to plasma spray T400 & T800 onto Ni-based alloy substrate, and come across this problem.
Although GE specification P16TF5 mentioned the substrate has to be roughened by grit blasting to 80-150 Ra prior to coating, it didn't give the information of how the grit size should be decided. I did find specification D50TF5, which stipulated the grit composiion, but still, it didn't specify what grit size shall be applied in a specific situation.

So I just wondered, is there a GE specification which could answer my question? Or whatever the grit size I chose, it's just OK as long as I could obtain the required roughness defined by specification?

Does anyone have any suggetion?

Thanks a lot.Big Grin

Reply
04-29-2011, 05:56 AM, (This post was last modified: 04-29-2011, 06:15 AM by wilfred1963.)
#7
RE: How to decide grit size ?
36 grit works well for RA requirements as far as grit contamination try using a soft bristle brush after blast with high pressure air to remove excess from hardware have had repeatable results with 1/4 inch blast nozzle(ceramic) at 6 inch stand off
with 50 to 60 psi pressure at a 30-50 degrees deflection manual and automatic and being it's GE set a prescribed amount of git and usage time/pieces before grit change have done lots of GE hardware with plasma and hvof, they do love the full testing of all processes





Hey Gordan you asked me to let you know how things went with the WC-CO hardness that we chatted about a few months ago when i asked about parameters, hardness,and oxide stringers, sorry i didn't get in touch sooner but i was able to produce a coating (HVOF DJ8W) of 1190 to 1230 Dph (ten diamond drop) with Metco 2005NS repeatable with 4 different lots.carbide content was in the 28 to 40 % range, bond tinsel pulls 10500 Avg psi. with 10,000 being the min. and 11,000 being the high now here is the kicker went through all that to learn today that they now want to swap over to propylene for fuel gas.. go figure.. can some one please take me away???
Reply




Possibly Related Threads…
Thread Author Replies Views Last Post
  Roughness and particle size hustzc 5 6,647 07-05-2018, 06:39 PM
Last Post: velocity
  Particle size distributin texnicar 2 3,053 03-04-2015, 07:43 AM
Last Post: texnicar
  After ball milling, is the powder particle size will be changed? fahad03092 1 3,849 11-21-2012, 11:14 PM
Last Post: loriolo
Shy Grit size sam xu 3 5,477 03-23-2012, 04:24 PM
Last Post: sam xu
  Removal of grit after grit-blasting? pulaunias 11 20,212 06-18-2010, 01:52 AM
Last Post: Gordon
  Pore size in carbides Jeff 5 7,168 12-04-2007, 04:39 PM
Last Post: Gordon
Question How to read a Media Size vs. Intensity chart gejohn 2 8,438 02-15-2007, 06:12 PM
Last Post: Gordon



Users browsing this thread: 1 Guest(s)





Surface Engineering Forum Sponsor - Alphatek Hyperformance Coatings Ltd