Grit Blasting

[Airline]

I don't seem to be able to find any documentation on the standards of how much deterioration of grit is allowed before we need to change. I am using grit 60 aluminium oxide for plasma spray surface preparation.
Can someone point me to the document and method to determine.

[Gordon]

Hi Airline

Welcome to the Surface Engineering Forum.

Must admit I could not find much information on this subject either.

Alumina grit does not suffer from loosing or dulling of sharp cutting edges as many other abrasive grits, but it does readily breakdown to finer grits. The important aspect really, is your process and grit producing the required etch and cleaning on your substrates. Quality control via blasting test plates and evaluating the results periodically is good. Also, testing your grit through a series of sieves to establish the amount of breakdown.

[Airline]

Hi Airline

Also, testing your grit through a series of sieves to establish the amount of breakdown.

I had bought a size 70 sieve for the test. The problem is base on what documents or standard do I fail the sieve test. How many percent of grit must stay in the sieve to qualify a pass.

Thanks.

[Vladimir]

I don't seem to be able to find any documentation on the standards of how much deterioration of grit is allowed before we need to change. I am using grit 60 aluminium oxide for plasma spray surface preparation.
Can someone point me to the document and method to determine.

Hallo Airline,

exists one very easy method. Take the 2 selfsome containers, volume about 5 liters. In the first you give the new blasting material and in the second the deterioration blasting material. If the weight diference between the 2 containers is greather than 20%(30%,40% - to your needs) than the blasting material is bad and you must change it.

[Airline]

Hallo Airline,

exists one very easy method. Take the 2 selfsome??containers, volume about 5 liters. In the first you give the new blasting material and in the second the deterioration blasting material. If the weight diference between the 2 containers is greather than 20%(30%,40% - to your needs) than the blasting material is bad and you must change it.

Do you know of any documentation that I can refer to for the standard of acceptance of deteriorated grit?

[Vladimir]

Hallo Airline,

exists one very easy method. Take the 2 selfsome??containers, volume about 5 liters. In the first you give the new blasting material and in the second the deterioration blasting material. If the weight diference between the 2 containers is greather than 20%(30%,40% - to your needs) than the blasting material is bad and you must change it.

Do you know of any documentation that I can refer to for the standard of acceptance of deteriorated grit?

Sorry, I don?t know it. Its internal method from Honeywell.

[bhellman]

Hallo Airline,

exists one very easy method. Take the 2 selfsome containers, volume about 5 liters. In the first you give the new blasting material and in the second the deterioration blasting material. If the weight diference between the 2 containers is greather than 20%(30%,40% - to your needs) than the blasting material is bad and you must change it.

Do you know of any documentation that I can refer to for the standard of acceptance of deteriorated grit?

Sorry, I don?t know it. Its internal method from Honeywell.

Dear Vladimir,
To my 40 yrs experience in TS, I can tell that aluminium oxide (corundum) is a tricky blasting material for high quality processes. The main problem is the breaking down of AlOx blast particles, creating a lot of dust size sharp particles, which like to wedge themselves into the base surface.
One has to ensure that as little as possible of undersized grit particles are left in the blasting media.
"Old fart's" story from the past:
One unit in the Swedish Air Force was fighting with too low bond strength. When investigating the surface of the blasted object they found that
~17 % of the surface was polluted with AlOx-debris. The solution was to modify the blasting system = adding an extra sieve based classification device into the circulation system. The outcome was acceptable, debris level decreased to about 5 %. Hint: Chromium Oxide do not cause same amount of technical disadvantages.
bhe

[bhellman]

Hallo Airline,

exists one very easy method. Take the 2 selfsome containers, volume about 5 liters. In the first you give the new blasting material and in the second the deterioration blasting material. If the weight diference between the 2 containers is greather than 20%(30%,40% - to your needs) than the blasting material is bad and you must change it.

Do you know of any documentation that I can refer to for the standard of acceptance of deteriorated grit?

Sorry, I don?t know it. Its internal method from Honeywell.

Dear Vladimir,
To my 40 yrs experience in TS, I can tell that aluminium oxide (corundum) is a tricky blasting material for high quality processes. The main problem is the breaking down of AlOx blast particles, creating a lot of dust size sharp particles, which like to wedge themselves into the base surface. This is same reason AlOx is not recommended for pretreatment of self-fluxing fused coatings. One has to ensure that as little as possible of undersized grit particles are left in the blasting media.
"Old fart's" story from the past:
One unit in the Swedish Air Force was fighting with too low bond strength. When investigating the surface of the blasted object they found that
~17 % of the surface was polluted with AlOx-debris. The solution was to modify the blasting system = adding an extra sieve based classification device into the circulation system. The outcome was acceptable, debris level decreased to about 5 %. I don't think there are any standards covering this subject in detail. Hint: Chromium Oxide do not cause same amount of technical disadvantages.
bhe

[Vladimir]

Hallo Airline,

exists one very easy method. Take the 2 selfsome??containers, volume about 5 liters. In the first you give the new blasting material and in the second the deterioration blasting material. If the weight diference between the 2 containers is greather than 20%(30%,40% - to your needs) than the blasting material is bad and you must change it.

Do you know of any documentation that I can refer to for the standard of acceptance of deteriorated grit?

Sorry, I don?t know it. Its internal method from Honeywell.

Dear Vladimir,
To my 40 yrs experience in TS, I can tell that aluminium oxide (corundum) is a tricky blasting material for high quality processes. The main problem is the breaking down of AlOx blast particles, creating a lot of dust size sharp particles, which like to wedge themselves into the base surface. This is same reason AlOx is not recommended for pretreatment of self-fluxing fused coatings. One has to ensure that as little as possible of undersized grit particles are left in the blasting media.
"Old fart's" story from the past:
One unit in the Swedish Air Force was fighting with too low bond strength. When investigating the surface of the blasted object they found that
~17 % of the surface was polluted with AlOx-debris. The solution was to modify the blasting system = adding an extra sieve based classification device into the circulation system. The outcome was acceptable, debris level decreased to about 5 %. I don't think there are any standards covering this subject in detail. Hint: Chromium Oxide do not cause same amount of technical disadvantages.
bhe

Hi Bhellman,
I know this situation. Look at the photo. Its corund grid (down left) on surface and WC coating. (link dead)

[Gordon]

Thank you for showing the photo Vladimir. A good picture can be worth more than many words

[Madila Awalini]

Dear All,

(Hi Gordon, I don't know if my question is still related to this thread or not).

I got a suggestion from someone who's having experience in aircraft engine repair shop that should never use "REUSED GRIT MATERIALS (ALOX)" for thermal spray coating preparation due to contamination / poor quality.
From the previous discussions this is absolutely understandable.
But in my shop, this is a little bit difficult to be applied due to the high cost.
If I want to make a classification for using grit materials in accordance with the base material of the metal parts, will this help with the possibility of having contamination on the prepared surface which will adversely affect the coating adhesion?
What classification of base material should I use then?
Any body can help with the standard perhaps?
The quality (particularly the size) of the grit particles can possibly be controlled by what Gordon, Vladimir and Bhellman suggested.
Another question is : does anybody know the humidity requirement for Alox grit blast storage? or other recommendation for grit storage?

Sorry for having lots of questions...
I know a lot of you out there have far more experiences in thermal spray than I do....

Thanks

[Gordon]

Hi Madila Alwalini

I got a suggestion from someone who's having experience in aircraft engine repair shop that should never use "REUSED GRIT MATERIALS (ALOX)" for thermal spray coating preparation due to contamination / poor quality.

Probably good general advice. But, it does depend on how you define ?reused?. Strictly speaking that means using the grit only once with no recycling, which from a technical point of view only is an ideal situation (least possibility of contamination, no grit break down). This is obviously not a very economic use of grit. Most processes continually recycle the grit and I assume the term ?reuse? in this context is when the grit is removed from the machine and reused at a later date. In facilities where the number of grit blasting machines are limited and there is a need to change the grit type or grade to suit substrate/thermal spray process, a point comes where you are removing grit that may have seen little use. If proper monitoring and storage of partially used grit is done carefully, there should be no reason not to reuse the grit (risk of contamination is potentially increased though).

If I want to make a classification for using grit materials in accordance with the base material of the metal parts, will this help with the possibility of having contamination on the prepared surface which will adversely affect the coating adhesion?
What classification of base material should I use then?
Any body can help with the standard perhaps?

My first and probably most critical comments on this would be:

The grit blast machine used for the final substrate preparation prior to thermal spray should be strictly limited to that use alone. Parts should be clean (free from grease, paint, and scale etc.) before blasting. Strict measures needed to avoid unauthorised use. ?Joe Bloggs? pops in to clean dirty car components or remove paint from part, unaware or just does not care about the potential damage this could cause. Believe me, this does happen.

Using different batches of grit for say for steel/nickel or aluminium or copper based substrates may be wise, though I am not aware of many people doing this.

The quality (particularly the size) of the grit particles can possibly be controlled by what Gordon, Vladimir and Bhellman suggested.
Another question is : does anybody know the humidity requirement for Alox grit blast storage? or other recommendation for grit storage?

Not sure on exact humidity requirements, but it is important to store in dry and isolated conditions. It should also be well labelled with information of prior use. If steel or chilled iron grit goes rusty, you know it's not been kept dry.

[Alexangel1226]

To Madila and all,

If I want to make a classification for using grit materials in accordance with the base material of the metal parts, will this help with the possibility of having contamination on the prepared surface which will adversely affect the coating adhesion?
What classification of base material should I use then?
Any body can help with the standard perhaps?

Do your intention of classification here means collecting data on blasting different grit size/type on metal part, obtain the different RA reading, outcome data?

Normally, to be representative to the blasting outcome, you blast onto a sample substract which if of the same or able to represent the part you are going to blast and spray. If you part to repair is of Nickel base alloy, what is the point of you blast/check sample using a Aluminum sample test piece? It will not give you the same surface profile and roughness you want. Then no control can be meted.

My point here is to use the RA/RZ value to determin and control your blasting process, paramter setting, substract selection and hardware control.

Hope this help

Regards,
Alex

[shabisyed]

Hi Airline,
The only method to check the grit which I have been using is that 1st take 5504 steel test piece and blast it with 30psi and check the roughness. and than contineus the blasting on same test piece for half an hour than check its roughness again if its same than continue again for 15 minute if its reduce ,its means you will have to change your grit after 45 minute.and if its not reduce continue this process till the rougness getting degrease.
For me I change grit after 45 minute.
Thanks.

[Arturas]

Hello
We do a lot off spray/fuse work and I read that it is not recomend to use Al2O3 grit material for blasting operation due to a lot off material remain on the blasted surface. Which material do You recomend in this case . As base material we use simple carbon steel (0.3 C)
Thank You
Best regards
Arturas

[Gordon]

Hi Arturas

Angular chilled iron grit

[Steph]

Hi Arturas

Angular chilled iron grit

Silicon Carbide works well for spray and fuse...

It is true that there are no standards in aerospace for grit deterioration, besides visual on the surface to determine the grit efficiency. If this is a big concern, then change the grit every Monday morning!
Most places will do a "preventive maintenance" and change it weekly.