36 and 60 Grit AlO help!
03-21-2018, 10:52 PM, (This post was last modified: 03-22-2018, 11:18 AM by Carguy1968.)
#1
36 and 60 Grit AlO help!
Hello all!

I am inquiring everyone’s knowledge on the world of grit blasting. What are the pros and cons of grit blasting each 36 Grit AlO and 60 Grit AlO prior to HVOF? Assume the same RA achieved for both followed by an HVOF coating thickness at or below 250 microns.

Background: Embedded 36 Grit particles are currently popping through finished machined coating leaving porosity holes. Would like to evaluate other alternatives, such as finer grit without repercussions.

Thanks!
C
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03-22-2018, 01:39 AM,
#2
RE: 36 and 60 Grit AlO help!
(03-21-2018, 10:52 PM)Carguy1968 Wrote: Hello all!

I am inquiring everyone’s knowledge on the world of grit blasting. What are the pros and cons for each 36 Grit AlO and 60 Grit AlO? Assume the same RA achieved for both as well as a coating thickness at or below 250 micrometers.

Background: Embedded 36 Grit particles are currently popping through finished machined coating leaving porosity holes. Would like to evaluate other alternatives, such as finer grit without repercussions.

Thanks!
C

Dear mr. Carguy

Maybe you can used 60 grit alox for the finishing of machining process, because the fine grit of the alox. i used 60 grit alox for all cleaning in gas turbine in hot gas path part because so fast process when mechanical cleaning.

Thanks, regards.
Achmad
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03-22-2018, 09:31 AM,
#3
RE: 36 and 60 Grit AlO help!
Hi Carguy,

The more fine-grained the spray powder and the thinner the layer, the fine-grained corundum must be used. For HVOF powders with grain size 20-45 microns and layer thicknesses of more than 200 microns, 60 grit of corundum is OK and 36 grit - too coarse. For spray powder < 25 microns you have to choose a corundum with grit 90; the same applies to thin layers (< 150 microns).

Regards
Vadim
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03-22-2018, 12:44 PM, (This post was last modified: 03-22-2018, 12:46 PM by Carguy1968.)
#4
RE: 36 and 60 Grit AlO help!
(03-22-2018, 09:31 AM)Vadim Verlotski Wrote: Hi Carguy,

The more fine-grained the spray powder and the thinner the layer, the fine-grained corundum must be used. For HVOF powders with grain size 20-45 microns and layer thicknesses of more than 200 microns, 60 grit of corundum is OK and 36 grit - too coarse. For spray powder < 25 microns you have to choose a corundum with grit 90; the same applies to thin layers (< 150 microns).

Regards
Vadim

Vadim

Thank you for your honest reply. When you reference coating layer thickness of 200 microns, is this finished (post machining operation), or as sprayed? The powders are of a medium grain size.

Thanks
C
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03-22-2018, 01:48 PM, (This post was last modified: 03-22-2018, 01:50 PM by Vadim Verlotski.)
#5
RE: 36 and 60 Grit AlO help!
Carguy,

I talked about the layer thickness as finished. In your case it is over 400 microns with an allowance for grinding (200 microns must remain on the surface after grinding). With such thicknesses and average grain sizes of the spray powder you can use grit 60.
Also, the hardness of the base material plays a role in blasting before coating: the harder the less rough the surface is at the same grit of blasting corundum. At a hardness of the base material 20 HRC, grit 90 gives practically the same surface roughness as grit 36 at a hardness of 55 HRC.

Regards
Vadim
Reply
03-22-2018, 02:48 PM,
#6
RE: 36 and 60 Grit AlO help!
(03-22-2018, 01:48 PM)Vadim Verlotski Wrote: Carguy,

I talked about the layer thickness as finished. In your case it is over 400 microns with an allowance for grinding (200 microns must remain on the surface after grinding). With such thicknesses and average grain sizes of the spray powder you can use grit 60.
Also, the hardness of the base material plays a role in blasting before coating: the harder the less rough the surface is at the same grit of blasting corundum. At a hardness of the base material 20 HRC, grit 90 gives practically the same surface roughness as grit 36 at a hardness of 55 HRC.

Regards
Vadim

Vadim,

I appreciate all the help. I’m still new to this and any knowledge and experience is greatly appreciated. Do you have any recommendations given this scenario for a surface roughness prior to HVOF given a material around 30 HRC?

Thanks
CG

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03-22-2018, 04:02 PM,
#7
RE: 36 and 60 Grit AlO help!
Carguy,

I, personally, would have used grit 90 in your case, but grit 60 might work as well. To be sure you can compare the layer-adhesivity of these two variants. Find someone doing adhesive pull tests; he should pull your coated samples with grit 60 and grit 90 blasted surface. If the sample with grit 60 shows better adhesion than the sample with grit 90, then take grit 60, if not, then take grit 90 is always better.

Regards
Vadim
Reply
04-05-2018, 05:11 PM,
#8
RE: 36 and 60 Grit AlO help!
(03-21-2018, 10:52 PM)Carguy1968 Wrote: Hello all!

I am inquiring everyone’s knowledge on the world of grit blasting. What are the pros and cons of grit blasting each 36 Grit AlO and 60 Grit AlO prior to HVOF? Assume the same RA achieved for both followed by an HVOF coating thickness at or below 250 microns.

Background: Embedded 36 Grit particles are currently popping through finished machined coating leaving porosity holes. Would like to evaluate other alternatives, such as finer grit without repercussions.

Thanks!
C

check the hardness of substrate, worry about the roughness of the substrate surface, that is what will help with mechanical anchoring, you need to consider the blasting equipment you are going to use, and of course, check the pressures, you need a roughness around 2.5 Ra In.
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