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I modified my Paasche AECR canister for more consistent flow


mattbsharks

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I had an issue with my Paasche AECR remote canister where the flow of abrasive (bicarb) was very inconsistent. I had to shake the canister manually every minute or so, and the flow was much more abrasive right after I shook the van because more bicarb was floating in the air, decreasing abrasive ness until I would have to shake it again a minute later. This led to very inconsistent prep results. I decided I needed to take some sort of vibrating device and attach it to the canister containing the abrasive so that it would constantly shake bicarb into the air to be run through the air abrasive system. I settled on an old vibrating head scratcher. I removed the wiring from the device. I built a small wooden box to house it to dampen the vibrations so that the whole prep station would not vibrate, just the canister. I put a towel in the box to further dampen the vibrations. It worked like a charm! The system now runs with a consistent flow of abrasive when I turn the head scratcher on, and I never have to shake the canister manually. I cannot feel the vibrations from the device at all because the towel and box keep them contained. Below are photos of the whole process.

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I had reservoir issues too. I have a lab magnetic stir plate so I had it on that with a stir bar. That helped a bit. I ended up making a dip tube for the inlet hose out of brass hobby tube from the hardware store. That really keeps it stirred up and flowing well.

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1 minute ago, LabRatKing said:

That helped a bit. I ended up making a dip tube for the inlet hose out of brass hobby tube from the hardware store.

I'd love to see some pictures of that, or maybe some additional insight into your process there?

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Now that's  using your :headscratch:

Accomplishing the impossible means only that the boss will add it to your regular duties.

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8 hours ago, LabRatKing said:

I had reservoir issues too. I have a lab magnetic stir plate so I had it on that with a stir bar. That helped a bit. I ended up making a dip tube for the inlet hose out of brass hobby tube from the hardware store. That really keeps it stirred up and flowing well.

Somewhere in my stash I have an old Thermix magnetic stirrer.  I used it with a plastic covered magnet to stir photo developing powder in water for my dark room. It may work for this? Could this issue be the amount of moisture in the airline? Not using a inline filter. 

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13 minutes ago, Bob Saunders said:

 Could this issue be the amount of moisture in the airline? Not using a inline filter. 

Consistent powder flow is a known issue with this unit regardless of how dry the blast media is or number of inline water filters. The Paasche was not designed for use with baking soda or dolomite, but more with hard etching compounds like aluminum oxide. Just like the Paasche with the little cup on the actual pen, there is a "sweet spot" level of blast media where things flow smoothly, but anything above or below that level does require some modulation/agitation to ensure consistent flow. Sometimes it requires fiddling with the pressure to prime the proper flow.

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...How to Philosophize with a Hammer

 

 

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15 minutes ago, Kane said:

Consistent powder flow is a known issue with this unit regardless of how dry the blast media is or number of inline water filters. The Paasche was not designed for use with baking soda or dolomite, but more with hard etching compounds like aluminum oxide. Just like the Paasche with the little cup on the actual pen, there is a "sweet spot" level of blast media where things flow smoothly, but anything above or below that level does require some modulation/agitation to ensure consistent flow. Sometimes it requires fiddling with the pressure to prime the proper flow.

I do not own that brand and have made my own but have not tried it yet. Need a specimen to practice on.. The one model comes with powered dolomite. I do have a air pump for air brushes for art that auto shuts off until you spray again. On a phone call to  Paasche the man said it should be fine with their abrasive units. I assume you may need 2-4 Lbs of air pressure? 

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4 minutes ago, Bob Saunders said:

I do not own that brand and have made my own but have not tried it yet. Need a specimen to practice on.. The one model comes with powered dolomite. I do have a air pump for air brushes for art that auto shuts off until you spray again. On a phone call to  Paasche the man said it should be fine with their abrasive units. I assume you may need 2-4 Lbs of air pressure? 

It can and should work with other blast media (as long as the micron count is appropriate), but it was not engineered with fossil preparators in mind. I would think 2-4 PSI is far too low for most work, and one could possibly go at that pressure for the very finest work if one has a more specialized unit such as a Schwam or Comco. The Paasche operates optimally between 10-40 PSI. It very much depends on the blast media, matrix type, and specimen.

...How to Philosophize with a Hammer

 

 

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A few trade secrets (mostly about abrasive)for those who find this post

 

With the Paasche units you need an inline water trap.. even minimal moisture with these is a killer especially with dolomite or baking soda. Back in the day when I used to use a Paasche(a long time ago) 20 to 25 PSI was the sweet spot for dry baked uniform size dolomite. Dolomite or baking soda in the humid months absorbs moisture so  30 minutes in a 225 degree F. oven then sealed in a glass container can solve most moisture problems.

 

Winter is the best time to do air abrasion. A compressor in the garage that is not heated will add zero moisture if the air temp is below the dew point.

 

In the winter I can successfully abrade down to about 3 PSI with 600 mesh abrasive (22 micron )  on my COMCO unit. In the summer when it is humid outside it is tough to go below about 18 PSI with 120 to 200 mesh dolomite or baking soda.

 

The Paasche units work best with Dolomite that will pass through a 120 mesh screen (200 is even better). Remember as mesh number gets bigger the particle size gets smaller. If you do not sieve then the dolomite will have particles as big as about 40 mesh (420 microns). Generally a bag of dolomite only has about 95% that is less than 100 mesh. I always sieve my dolomite into grades . I throw away anything that wont go through a 120 mesh. I separate as follows:

 

120 to 170 mesh  (general overburden blasting never on a fossil)

170 to 200 mesh  (abrasion on fossil surfaces that do not have fine detail (125 to 88 microns)

200 to 325 mesh  (my everyday general abrasion but not for the most fine detail) (74 to 44 microns)

325 to 400  (mesh my normal super fine detailing media about 44 micron)

<400 mesh I save this for very special delicate fossils that have fine detail. and only sieve as I need from the 325 to 400 segment. (<37 microns)

600 mesh I purchase a 600 mesh for specialty work but generally this abrasive is too hard for most fossils except at super low PSI (about 22 microns)

1200 mesh (I purchase 2 abrasives at this size for specialty work but generally too expensive for most jobs) (about 12 microns)

 

Just for your orientation as to  size a red blood cell is about 12 microns

 

You manufacture your own sub 20 micron baking soda by taking the orange box of arm and hammer food grade baking soda and use a mortar and pestle to crush/ grind the particles smaller. This is very good for the most fragile and extreme detail. You can also use a pumice which is about 800 mesh but it is so soft that it will not really abrade limestone but will clean up the last traces of matrix in deep Cervices on a fossil.

 

The 325 to 400 group probably is less than 5% of a 50 pound bag. I generally end up throwing away about 5% of every bag as it is larger than 120 mesh. 

 

I reuse my blast media by resieving after use. If it makes it to the cyclone or the shopvac bag I throw it away.. Previously used media is gentler on the fossil but takes a lot longer than new media as sharp edges on the particles have been rounded in the blast process. Uniform particle size is extremely important when doing air abrasion. Consistently sized particles clog less than when a media has mixed sizes (think of large and small marbles filling in gaps)

 

Your particle size should never be more than about 1/4 the size of the detail you are trying to clean. If you are trying to clean matrix out of a groove that is 40 microns across it is impossible to clean with a particle bigger than 40 microns. All you are goin to do is shatter the edges of the groove till you get a final groove that is going to be about 100 microns across by the time you get the matrix out. The smaller the particle the better job you will do on fine detail. (Brilliant idea, I should clean 3 eldredgeops eyes using 80 micron, 40 micron and 10 micron dolomite and post micro pics of the results )

 

Here are some of the abrasives that I use:

 

dolomite (a natural mixture of calcium carbonate and magnesium carbonate and some impurities make sure you get super low silica))

calcium carbonate

magnesium carbonate

Pumice

sodium bicarbonate (Food grade Arm & Hammer in the orange box)

iron oxide (black) 325 mesh

aluminum oxide (way too hard but can be mixed in with dolomite for some Moroccan trilos) (240 & 600 mesh)

Nepheline Syenite

Alumina

Silicon Carbide (600 &1200 mesh)

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2 hours ago, FossilDAWG said:

 

That is some really interesting onfo, Malcolm.  I will have to give it a try.  I sieve my dolomite with a 40 mesh and just use it.  I buy bicarb in two grades... "regular" and No 1 food grade which is much finer.  

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12 hours ago, Bob Saunders said:

Somewhere in my stash I have an old Thermix magnetic stirrer.  I used it with a plastic covered magnet to stir photo developing powder in water for my dark room. It may work for this? Could this issue be the amount of moisture in the airline? Not using a inline filter. 

I must confess that I do not have an inline filter and need to get one. That was a possible culprit that crossed my mind while diagnosing the issue, but like @Kane said, this is a general issue with the Paasche model. I will be getting an in-line filter because that can only help!

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1 minute ago, mattbsharks said:

I must confess that I do not have an inline filter and need to get one. That was a possible culprit that crossed my mind while diagnosing the issue, but like @Kane said, this is a general issue with the Paasche model. I will be getting an in-line filter because that can only help!

Sieve your media and bake it.. get it to a uniform size under 120 mesh

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On 12/23/2020 at 5:54 AM, Bob Saunders said:

Somewhere in my stash I have an old Thermix magnetic stirrer.  I used it with a plastic covered magnet to stir photo developing powder in water for my dark room. It may work for this? Could this issue be the amount of moisture in the airline? Not using a inline filter. 

A thermix is what I have. Worked best with the 4 blade disc type stir bar. Added bonus- if it’s also a hot plate you can set it on low to evacuate moisture.

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On 12/22/2020 at 8:54 PM, Huntonia said:

I'd love to see some pictures of that, or maybe some additional insight into your process there?

I’ll post up some how to drawings in a bit. I don’t want to take apart the reservoir as I just filled it up right before reading this!

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I have a inline air filter for 1/4 inch air hose. You need brass hose fittings, slip on with ridges is best with small fuel line hose clamps. Menards has them around $10 US "hint" I got mine at  Harbor Freight and looks like the same maker. Used the usual %20 off online coupon so with tax under$8. For air operated model live steam engines at tractor shows I made a air manifold of 5 using refrigerator ice maker water valves with 1/4 inch out. Also for the real small ones I used brass air pump valves for fish aquariums, came with Three  and likely a garage sale. Most today may be plastic. Thanks for the tip on using a mortise and pestle to grind finer. and screen sizes.   

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