Measuring the effectiveness of a sandblaster?

On Fri, 12 Jun 2009 15:56:48 -0400, Michael Horowitz
wrote:

I know the compressor requirements are stated when considering a
sandblaster, but is there anyway to measure the effectiveness e.g. is
my blaster taking off paint as quickly as someone elses?

As an example, I can take off an 1/8" strip of paint at about
1"/second, but have no idea what should be happening - Mike

mike I never used this because I did all the error and frustration
stuff that went into this.

save up all of your bead blasting work for one big session and go and
hire yourself a trailer mounted diesel engined compressor.
they are not expensive to hire.
one of the brands in australia is Broomwade.

they have the advantage of being able to deliver 120 to 150psi air all
day long.

bead blasting effectiveness is *all* in the pressure.

at 150 psi and using an el cheapo automotive shop style bead blasting
gun you will be cooking!

the same gun at 60 psi will softly polish the surface and remove
nothing.

I used 3 single phase compressors Teed together in the end and the job
still took me 3 weeks.
my mate took my advise and bead blasted his entire fuselage in 1 day
with no time waiting for a pumpup.

by my reckoning an el cheapo bead blasting gun uses about 60cu ft/min
to be effective. if you stick with what you've got, like me you'll be
forever waiting for a pump up.

btw before you start look at the nozzle on your bead blasting gun.
this *will* wear out and the alloy will be shot into the surface of
your aircraft.
it pays handsomly to go and buy a few feet of nylon rod of the same
diameter as the supplied nozzle. cut it all up into the same lengths
and drill out the centre to the same diameter as the supplied one.
the nylon ones will not damage the aircraft and will last marginally
longer. if you've got a supply it is easy to swap in a new one when
they wear out because they are held in place with a set screw.
also if you are using a lathe. machine a little recess in the end so
that they have a small sharp lip. this is incredibly useful for use as
a scraper for dislodging persistent stuff without having to put the
gun down and take the gloves off.
the second most useful tool in bead blasting is a swiss army knife
with a slightly blunt blade. worlds best beadblasting scraper.

......I have the Tee shirt :-)
Stealth Pilot

On Fri, 12 Jun 2009 15:48:21 -0700 (PDT), Bob
wrote:

On Jun 12, 12:56*pm, Michael Horowitz wrote:

As an example, I can take off an 1/8" strip of paint at about
1"/second, but have no idea what should be happening - Mike
-------------------------------------------------------------------------------------------------

Basic test was to paint a 10" x 2" coupon then cure the paint to spec.

Once th paint was cured you masked-off the surface in strips 2"
wide,giving you four square inches of 'sample surface'.

The coupon was then rigged to a rack at a hight & angle convenient for
the blaster, who got thirty seconds before the flag came down,
indicating the next 2" wide 'surface' was being exposed. Flag goes
up, blaster goes back to work, which is trying to remove ALL of the
paint from ALL of the surface.

The blaster is all suited up, inside a helmet or mask. He's as much a
part of the procedure as the rack or the flag or whatever.

What are they testing? Usually they're comparing one paint against
another, or one abrasive against another, or one nozzle against
another. If they were comparing hobby-type sand-blasting rigs, they
probably run the FULL procedure then take a break, roll in a new rack
of samples AND a new compressor, sand bucket, hose, nozzle & so
forth... and do it all over again.

Guy restoring/repairing an airplane? He'd probably RENT the biggest
rig he could afford, hire someone to keep the hopper filled, use lotsa
pressure, a 'sharp' abbrasive, no grit recovery, etc. -- get the job

grrrrrrrrrrrr!!!!
use round glass beads called ballottini on aircraft steel. AH grade
from memory works well.
sharp grit will stuff up the fatigue life. round beads will extend it
because they minutely hammer the surface into compression.

use sharp grit and I'll put white ants in yer woodwork.:-)
Stealth Pilot

On Jun 12, 9:21*pm, Dan wrote:

* * The VW engine idea sounds interesting. Any suggestions where to find
plans? I don't think Id build one, but it should be an interesting read.
------------------------------------------------------------------------------

There used to be a company named 'Dunn-Rite' (sp?) which supplied a
conversion kit, but the idea dates from the 1930's and the conversion
of anu I-4 or V-8 engine for that purpose. The VW is especially easy
to convert and the DIY method has been explained several times on VW-
specific Groups. Basically, you simply select a pair of sequenctially-
firing cylinders as your power pair (ie, 1-3 or 2-4) and use the other
pair as your 'pumping' cylinders. The spark plugs of the pumping
cylinders are modified to act as ball-type check valves while the
exhaust stack is modified to become an input valve by the use of a
flapper valve made of light-gauge spring steel. The push-rods &
rocker arms of the pumping pair are modified so as to always be
open.

---------------------------------------------------------------------------------

* * I would imagine such Navy machines would be a ta
d noisy. I have
never had the pleasure of hearing a rivet gun used in building large sea
going vessels. I have the feeling it also would be a bit loud.

---------------------------------------------------------------------------------------

Actually, they sound remarkably like welding machines :-)

(I don't think the Navy hasn't used riveted hulls since the 1920's)

-Bob

Bob wrote:
On Jun 12, 9:21 pm, Dan wrote:

The VW engine idea sounds interesting. Any suggestions where to find
plans? I don't think Id build one, but it should be an interesting read.
------------------------------------------------------------------------------

There used to be a company named 'Dunn-Rite' (sp?) which supplied a
conversion kit, but the idea dates from the 1930's and the conversion
of anu I-4 or V-8 engine for that purpose. The VW is especially easy
to convert and the DIY method has been explained several times on VW-
specific Groups. Basically, you simply select a pair of sequenctially-
firing cylinders as your power pair (ie, 1-3 or 2-4) and use the other
pair as your 'pumping' cylinders. The spark plugs of the pumping
cylinders are modified to act as ball-type check valves while the
exhaust stack is modified to become an input valve by the use of a
flapper valve made of light-gauge spring steel. The push-rods &
rocker arms of the pumping pair are modified so as to always be
open.

---------------------------------------------------------------------------------

I would imagine such Navy machines would be a ta
d noisy. I have
never had the pleasure of hearing a rivet gun used in building large sea
going vessels. I have the feeling it also would be a bit loud.

---------------------------------------------------------------------------------------

Actually, they sound remarkably like welding machines :-)

(I don't think the Navy hasn't used riveted hulls since the 1920's)

-Bob

I didn't mean to imply the Navy uses riveted hulls. I had just
watched a show on television about Titanic and I was thinking of the
rivets used in that era.

Dan, U.S. Air Force, retired

"Bob" wrote in message
...
On Jun 12, 9:21 pm, Dan wrote:

The VW engine idea sounds interesting. Any suggestions where to find
.. plans? I don't think Id build one, but it should be an interesting read.
------------------------------------------------------------------------------

There used to be a company named 'Dunn-Rite' (sp?) which supplied a
conversion kit, but the idea dates from the 1930's and the conversion
of anu I-4 or V-8 engine for that purpose. The VW is especially easy
to convert and the DIY method has been explained several times on VW-
specific Groups. Basically, you simply select a pair of sequenctially-
firing cylinders as your power pair (ie, 1-3 or 2-4) and use the other
pair as your 'pumping' cylinders. The spark plugs of the pumping
cylinders are modified to act as ball-type check valves while the
exhaust stack is modified to become an input valve by the use of a
flapper valve made of light-gauge spring steel. The push-rods &
rocker arms of the pumping pair are modified so as to always be
open.

-Bob


They are still around, and have improved dtheir system from the one you
describe.

Here is the link, thanks to Leon in this same thread:
http://dunnrightinc.com/

Peter

On Jun 12, 3:56*pm, Michael Horowitz wrote:
I know the compressor requirements are stated when considering a
sandblaster, but is there anyway to measure the effectiveness e.g. is
my blaster taking off paint as quickly as someone elses?

As an example, I can take off an 1/8" strip of paint at about
1"/second, but have no idea what should be happening - Mike

I sandblast for my living (cemetery lettering) and the most common
misconception is more pressure strips/cleans faster.....when actually
the more CFM (cubic feet per minute) is what works best. In the past
when I was an active EAA member I did a few blast jobs on Cub fuselage
structures. I use a 100 CFM compressor, such as used by utility crews
to run jackhammers, etc. Most tool rental places have 85-185 CFM
machines for rent....anything from 50 CFM up will work fine.

There are two "schools of thought" about how much pressure to use when
doing steel tube fuselage. One says use as low pressure as possible to
minimize damage to the tubing.....the other says to use as high
pressure as possible to intentionally blast thru and expose weak (thin
from internal rust) spots, which can then be cut out and new tubing
spliced/welded in. And of course, never blast thin sheet metal (steel
or aluminum) as the frictional heat can warp the sheet metal .
Chemical stripper works better for sheet metal.

On Jun 13, 1:21*pm, Dan wrote:


* *I didn't mean to imply the Navy uses riveted hulls. I had just
watched a show on television about Titanic and I was thinking of the
rivets used in that era.
--------------------------------------------------------------------------

There's still a few structural steel applications that call for rivets
instead of welding. But it's usually on repair work or modifications
to a riveted structure -- lots of railroad bridges came as 'kits' and
quite a few were riveted. But some are bolted together, often with
Sher-Lock (sp?) type bolts

-R.S.Hoover

On Sat, 13 Jun 2009 16:44:50 -0700 (PDT), rckchp
wrote:

On Jun 12, 3:56*pm, Michael Horowitz wrote:
I know the compressor requirements are stated when considering a
sandblaster, but is there anyway to measure the effectiveness e.g. is
my blaster taking off paint as quickly as someone elses?

As an example, I can take off an 1/8" strip of paint at about
1"/second, but have no idea what should be happening - Mike

I sandblast for my living (cemetery lettering) and the most common
misconception is more pressure strips/cleans faster.....when actually
the more CFM (cubic feet per minute) is what works best.

true but all you have is a pressure gauge and whatever the compressor
delivers. usually what you get with a pump system that deliveres
slower than you are using it, is a reducing pressure and eventually
the need to wait for a pump up. with the bigger pumps what you notice
is that the compressor just keeps on delivering at whatever pressure
you dial up.

150psi will remove rust, paint etc almost completely in a single pass.
100 psi will remove slowly
80 psi is a very gentle action if at all.

also you can moderate the "cutting" action (if you'd call it that) by
angling the gun off perpendicular to the job.

blasting thin metal distorts the sheet all right. the surface closest
to the gun is peened into compression and this causes the sheet to
grow toward you. (aluminium sheet -thats a good use for 60psi blasting
and a very gentle touch)




In the past
when I was an active EAA member I did a few blast jobs on Cub fuselage
structures. I use a 100 CFM compressor, such as used by utility crews
to run jackhammers, etc. Most tool rental places have 85-185 CFM
machines for rent....anything from 50 CFM up will work fine.

There are two "schools of thought" about how much pressure to use when
doing steel tube fuselage. One says use as low pressure as possible to
minimize damage to the tubing.....the other says to use as high
pressure as possible to intentionally blast thru and expose weak (thin
from internal rust) spots, which can then be cut out and new tubing
spliced/welded in. And of course, never blast thin sheet metal (steel
or aluminum) as the frictional heat can warp the sheet metal .
Chemical stripper works better for sheet metal.