Cleaning with compressed air

Mike Stimmann

1. Flying chips are a safety hazard (wear goggles, make sure no one else nearby);
2. Cutting oils, etc may be vaporized, also a potential health hazardl
3. the air may drive chips into inaccessible places, making more work to remove them.

Other than that, I can't envision other problems.

JK

Why not, it works great! :-)

Seriously, compressed air can easily cause personal injury or damage equipment
if it is not treated with respect, so some cautions are in order.

I'll try a few off the top of my head, maybe others can add some more warnings.

Never blow dirt or chips off a machine tool unless you are wearing eye
protection. Never blow anything in the direction of another person.
Never put an air nozzle into your mouth, nose, ear, or any other body orifice
(don't laugh, there have been some horrible incidents!).

Be careful to blow grit where it won't get into bearings or other places
where it could be harmful.

Never blow toxic or caustic liquids or dust.

Be really careful when using air to clean small parts, they can fly away
to where you'll never find them again (until after you buy replacements,
of course :-) ).

It's a lot of fun to hold ball bearings in your hand and spin them with
compressed air, and it makes a great noise, but this shouldn't be done
for two reasons. First, it ruins the bearing in a very short time, spinning
it without lubrication and often far faster than is good for it. Second, and
more important, the excessive speed can cause the bearing to explode, with
a risk of personal injury. So even if the bearing is a junker, don't play this
game.

Don't play childish dart-gun games with air blowers. I have to include this,
because in every shop I've ever worked we played various shoot-the-projectile
games with the air blowers :-). They're dangerous, though, so be careful.
I worked one place where we used to turn wooden plugs that slip-fit into
EMT conduit, and fitted the plugs with 6 or 8 inch long darts of SS welding
rod, sharpened to a point. Using a 6' long "dart-gun", we could put these
darts through 3/4" plywood at 100 feet. Compressed air is some powerful
stuff!

All this being said, compressed air is excellent for cleaning up machines.

Regards,

Jay Keller
Sunnyvale, California
bad...@netcom.com

That reminds me of a story...about 30 years ago, two students in a college advanced
physics class decided they needed a high-speed air-motor, and proceeded to build one
in the machine shop. They tried machining a number of rotors, but couldn't get the
cone-angle right. I finally suggested that they try a large bearing-ball, because
SOMEWHERE there would be a correct angle, and it would at least tell them if their
idea could *ever* work. So, the put a 1" diameter ball in the hub, and turned on
the air pressure. At 100 lbs pressure it was spinning about 7000 revolutions per
SECOND. One of the students got so excited he started jumping around and got
tangled in the air line, toppling the setup off the bench.
The ball bounced a few times, then shot off down the shop, rolling on the floor.
We estimate it was traveling in excess of 100 MPH when it hit the cement-block wall
and burried itself therein. We decided it was a good thing it didn't richocet.

JK

I dunno, unless I got the geometry wrong (possible), or flubbed
the calculation (entirely possible), I make the tangential
velocity at the surface of the ball about 1250 miles per hour, or
about mach 1.67 (assuming 1100 ft/sec = mach 1 at room temp and
pressure (which might not be a valid assumption in the close
neighborhood of the surface of the ball))

It still seems awfully fast to me.

I do remember once when the bearings on a Burroughs disk drive
let go, and the spindle waltzed it's way through the cabinet, the
cpu cabinet adjacent, and two cinderblock walls...

--
David Kassover "Proper technique helps protect you against
RPI BSEE '77 MSCSE '81 sharp weapons and dull judges."
kass...@aule-tek.com F. Collins
kass...@ra.crd.ge.com

[discussion of bearing speeds]

Playful people in the machine trades know that a bearing can explode
if you get it going with compressed air. This sometimes happens
inadvertently when you're blowing out a bearing after cleaning
it with solvent.

John Morton University of California
jmo...@euler.berkeley.edu Mechanical Engineering
{decvax,cbosgd}!ucbvax!euler!jmorton Machine Shop

: [discussion of bearing speeds]

John,

What do you mean "playful people" ? This is science damn it! You should
have been around when we experimented with propulsion through a tube and an
alumina ball. We used the pressure in a Nitrogen bottle. Every now and
then that little sucker is seen, still bouncing around the lab.

You university types... ;-)

Dave Parsons
:-

I've got to jump in here. (again).

Not too long ago, I had an office across the hall from a
laboratory. One day I heard:

Ping!!! Clang, Clang, rattlle rattle rattle.
<giggle, guffaw>
Scrape, shuffle...

PING!!! CLANG, Clang, rattlle rattle rattle.
Oooh, that was a good one! <giggle...>

So I bravely stuck my head in the door, and found two guys in
spectacles, beards, and lab coats in front of the Gleeble,
holding an oddly shaped piece of metal.

The explanation was that they were using the Gleeble to make
welds in experimental alloys, and, since the welds were tested by
a different lab with a different budget, it made no sense to send
the samples out if they could break the welds themselves.

So they cleared out the end of the lab, drew a target on the
wall, toed the line at the other end, and heaved.

"I'm not making this up, you know"
A. Russel

Thoroughly flubbed, as a matter of fact. Here's the calc.

Given: 1" diameter
7000 rpm

Circumference == pi * D

3.14159 * 1 = 3.14159 inches

Multiplying by 7000 revolutions per minute gives 21,991 inches/minute.

Divide by 12 to get feet/minute == 1,832.6 feet/minute

Referring to "Engineering Units Coversions", the conversion from
feet per minute to miles per hour is 0.011364.

1,832.6 * 0.011364 == 20.8 miles per hour

Back to the original post, I suspect the bearing was turning MUCH faster
than 7000 rpm. As much as an order of magnitude faster.

A similar story.

One of the motorcycle race engines I used to race required main bearing
changes after every race. As a result, I had a large surplus of slightly
worn, approx 1" diameter bearings. A fairly long road used to dead
end onto another road that went in front of our house. Our driveway
was on the other side of the road. I used to spin these bearings
up with 175 psi air and release them to run down the road.

The bearings would EASILY outrun cars driving at ordinary residental
street speeds, spraying sparks all the while. When it hit a gravel or
other debris, it would jump high into the air. Which resulted in
some funny instances. Like when it chose to leap while under a car.
Or when it hops up in front of a car. Driver reaction was interesting.
I learned several things from this experience:

* This is a lot of fun.

* It is fairly hard to turn the bearing while is is spinning due to
gyroscopic effect. Turning the bearing can make it seize from the
high side loading.

* When the bearing seizes up while you're holding it, the friction heat
makes a nasty burn on your fingers.

* If you happen to have your finger securely inserted into the hole
when the bearing seizes, the torque will likely dislocate your finger.

* When the outer race explodes from over-speed, the particles that fly off
are whizzing and can cause injury. The incident - which ended my
career as a "bearing whizzer" - did not injure me but it DID dig
significant sized divots out of the concrete.

If anyone really wants to try this, stand perpendicular to the bearing
so esplosive debris won't impact your body and have it aimed in the direction
you want to release it. Wear a leather glove and hold the inner race by
only the fingertips.

John
--
John De Armond, WD4OQC |Interested in high performance mobility?
Performance Engineering Magazine(TM) | Interested in high tech and computers?
Marietta, Ga | Send ur snail-mail address to
j...@dixie.com | per...@dixie.com for a free sample mag
Need Usenet public Access in Atlanta? Write Me for info on Dixie.com.

20.8 x 60 = 1248, last I looked.

I still may have had the geometry wrong, but at least I read the
problem correctly...

Hmm, as your own post quoted, the original poster said 7000 rev per second,
capitalized, not 7000 rpm as you proceed to calculate with. Looks more
like 1200 miles per hour, multiplying your result by 60.

I also think some folks are confusing the act of spinning a ball bearing,
complete with inner and outer race, versus spinning just a single steel
ball all by itself.

Jim

Yes, but remember that the tangential speed HAS TO BE LESS THAN THE
AIR SPEED comming out of the hose. 7000 rps and 1" dia is about
1830 ft/s. Aint no way you are getting supersonic flow out of a
100 psi air hose. (without a pretty trick nozzle!)

The original poster has to have meant 7000 rpm, or if they did mean
7000 rps, I'd like to buy their air hose!

--Soren laf...@xenon.arc.nasa.gov

I would like to see the bearing that would stand 420,000 rpm. That
sounds a bit high, even for high cost jet engine bearings.

Bill

Well since we're posting our Adventures with Science, I thought I'd dig
into my archives for an article I originally wrote several years ago.

This is absolutely true to the best of my (intentionally fading) memory.

From: j...@rsiatl.UUCP (John G. De Armond)
Newsgroups: rsi.postings
Subject: jgd; rec.models.rockets; Re: A tale of [nuclear] model rocketry
Date: 13 Dec 89 09:36:45 GMT
Lines: 92

In article <37...@ames.arc.nasa.gov> mi...@ames.arc.nasa.gov (Mike Smithwick) writes:
>
>Ok guys, you want great model rocket stories? I got great model
>rocket stories. . .

[a GREAT story deleted ]

>Beat that guys! :-)

Hey, with a challenge like that, who could resist :-) Betcha can't
beat this one.

This story involves TRULY internal combustion propulsion - as in internal
to the atom.

The setting is the Sequoyah Nuclear Plant in Chattanooga, TN. The date is
about 1979 or 80 and we're starting that sucker up for the first time.

I was the shift test engineer, running the startup test program on the evening
shift. Most testing is conducted from the control room. In order
to get to the control room, a stroll across the turbine deck is necessary.
This deck contains the huge (1200 MWe) turbines and a variety of support
equipment. The floor is tiled and the 10 story tall walls are slightly
tinted glass. A glorious sight when bathed in the afternoon sun.

As I was strolling toward the control room, I noticed an Aux. Operator
standing near a device called a moisture separator/reheater. This device is a
large heat exchanger, about 40 feet long and 20 feet in diameter. Its
purpose is to reheat the steam exhausting from the high pressure turbine
in order to dry it before being introducted into the low pressure turbines.
On top of this device is a large safety relief valve with a tailpipe
that extended almost 10 floors through the roof. When this valve opens,
steam at about 900 psi exhausts to atmosphere through this ~36" tailpipe.
The tailpipe is hung from spring hangers and simply floats on the exhaust
flange of the safety valve which allows the pipe to move under
thermal expansion.

Anyway, this operator was standing along side the reheater. In one hand
was a walkie-talkie and in the other hand was a lanyard that ran to the
manual trip lever on one of the safeties. This was not unusual, as the
functionality of these critical valves is tested fairly often. Normally
when the valve trips, there is some steam escaping around the valve, a
loud shreik and a large steam cloud on the roof.

As I was almost to the control room, the operator got some activity on
the handi-talkie and pulled the manual trip lanyard. The noise
from the H-T had gotten my attention and I looked around just in time
for the valve opening. FOOOMsssss!!!! The whole damn tailpipe jumped
up about 6 inches in the air before settling back down.

Since this behavior was quite abnormal, I asked the operator what was
going on. He pointed to the elevator and suggested I go to the roof
to find out. I rode the elevator 5 floors and hoofed it up 5 flights
of stairs and onto the roof. I noticed about 10 guys standing around
near the tailpipe.

As I stepped out, I saw about 6 guys hoisting A 55 GALLON DRUM up and over
the tailpipe. Whoosh. It hit bottom 10 floors below.

A message on the handi-talkie and BOOOMssss!!!!!!!! That damn 55 gallon
drum full of 600 pounds of water had been launched literally out of sight
by 900 psi of steam.

It stayed out of sight a good 30 seconds before it came into view again,
hurtling down over the Chickamauga lake. When it hit the lake, it looked
like a depth charge going off.

I did a 180 degree twist and headed back down the stairs as fast as my
little feet would carry me. As Shultz on Hogan's heros used to say,
"I saw notsing.. I hear notsing.. I know notsing..". I did keep
a piece of strip chart recording that showed the dip in steam pressure
that documents the launch :-)

I heard a few days later that one of their ICBD (Inter County Ballistic
Drums) had been caught by a gust of wind and had come down on a car in
the parking lot, thus ending the era of the nuclear powered missile.
The funny thing is, no one would ever admit to knowing how that drum
ended up on the car, which ended up about 6 inches tall :-)

So if anyone asks if America has ever launched a nuclear powered
missile, you can answer truthful YES!

[BTW, I've waited 10 years to tell this story to ensure that my
memory of the names of those involved has thoroughly faded just in
case the nuke police were to get interested.]

John
--
John De Armond, WD4OQC | The Fano Factor -
Radiation Systems, Inc. Atlanta, GA | Where Theory meets Reality.
emory!rsiatl!jgd **I am the NRA** |

>Hmm, as your own post quoted, the original poster said 7000 rev per second,

No, I didn't miss it. I presumed he had made a typo or mistake. Ain't
no way you're gonna spin a 1" ball bearing to 420,000 rpm using an
air hose. 50,000 rpm (maybe doable) works out to a surface velocity
of 149 mph. I always figured that the bearings I spun up hit maybe 25,000
rpm which would give a surface speed of about 75 mph.

A
A
A

With a gas welder, you can also weld stainless, but I have had better
results with stick (SMAW). Anyway, to do it with gas, get some stainless
wire at the welding supply shop that is usually used in TIG welding, and
use a reducing flame. I am a lot better with a stick than gas, and my
gas welds usually had a lot of heat distortion, but they were strong.

Hessel

I posted the original story, and meant 7000 revolutions per SECOND! (We estimated
this from the fact that the spinning ball was putting out a pure tone of ~7000cps,
and couldn't come up with any reason why this was not the RPS of the ball -- rather
than some high harmonic of it).

Also, the tangential speed does NOT have to be the air speed -- a sailboat can
travel much faster than the wind when moving at right angles to the wind.

In the case of the ball, it was floating within a cone, with the air entering near
the virtex. The actual point of "contact" was thus about 1/2 the radius. ALso,
the air here was passing through a constriction (a venturi), which causes the air
to speed up.

JK

And John posted - there is no way you would be able to spin it anywhere close
to that fast. I can think of a couple of way that a 7000 hz tone could be
produced - all of them only incidentally linked to the rotation speed of the
ball.

: Also, the tangential speed does NOT have to be the air speed -- a sailboat can

Sorry, the travel is due to a different principle. The boat is actually moving
far less than the wind speed, in the direction the wind is flowing.

: In the case of the ball, it was floating within a cone, with the air entering near

Whether the air was passing through a venturi or not is almost immaterial.
The ball was not in the venturi, by your own description. It was in a cone
outside the venturi. There may be some "jetting" that would produce increased
air speed, but it would be minimal.

Also, remember that rotational speed depends on differential air flow. If the
air flow, on one side of the ball was 50 feet/sec and 25 ft/sec on the other
side - then the maximum rate of movement of the ball surface in relation to
those two air flows would be 25 ft/sec. The flow rate will actually be less,
since you cannot get perfect coupling between the air flow and the ball. There
is always a stagnation/friction zone near the surface where there is slippage.

Bill

I seem to be making a habit of quoting from books on the subject of soldering
and brazing. Argus Books (Argus publishes the "Model Engineer", the address
is available in the FAQ) publishes a useful handbook entitled "Soldering and
Brazing" in their Workshop Practice Series (ISBN 0 85242 845 6). My copy was
first printed in 1985, last printed in 1990. The following excerpt relates to
the brazing of Stainless Steel. (Before I start, I have the feeling that the
flux is a major player in this. We shall see... ;-)

---
Chapter 8: Brazing Techniques

Brazing Stainless Steel

The Term 'Stainless Steel' covers scores, if not hundreds, of alloy steels,
and brazing alloys which will serve for some will be quite unsuitable for
others. Thus, AG9* will serve for most Austenitic (so called '18-8')
steels but not for the Ferritic types. It is imperative that the alloy
makers advice be sought for any important joints. (For plain water-tanks
etc, soft soldering should be quite adequate.) The brazing alloy can then
be tailoed to the base metal, and to the intended service of the joint.
This is especially important when considering superheater joints. You will
find that the manufacturers are quite happy to advise, as a joint failure
in such an important situation is a matter for concern for all. However, do
be reasonable ! Don't expect a firm to engage in lengthy correspondence
over a job which may use perhaps 10 grams of alloy ! Make your enquiry
brief and to the point, and you will get a careful reply.

The very nature of stainless steel makes the choice equally important.
Fortunately proper grades of flux are readily available, but it is wise to
avoid prolonged heating. A general recommendation when brazing drawn tube
or cold-rolled sheet is that the stock should be stress-relieved before
brazing. Remember that stainless steel is a poor conductor of heat and that
most of the special brazing alloys have poor fluidity, so that wide lap
joints can present difficulties. There should be no need for wide laps, as
the shear strength of the brazing alloys is quite high and in any case
these alloys all tend to form fillets.

Having said all that I must confess that I have made scores of joints for
small components in stainless steel using nothing but AG1* or AG2 and
'ordinary' flux. The few failures - usually refusal of the rod to wet the
parent metal - have been traced to the fact that one of the parts was of a
'stainless' steel of unknown origin and composition. It is the parts which
are subject to fatigue stress, high (up to 100 deg. C) temperatures, or
which are to spend most of their time in mucky water that need 'care and
attention' in the brazing.

---

From the tables in the appendix of Johnson-Matthey metals.
Note that AGx refers to a BS (British Standard) 1845 definition.

*AG1: Johnson-Matthey Easyflo 1
Melting range (deg. C) 620/630 50% silver
Remarks: Higher ductility, finer fillets and better corrosion resistance
than the number 2 alloy.

*AG2: Johnson-Matthey Easyflo 2
Melting range (deg. C) 608/617 42% silver
Remarks: Good general purpose alloy suitable for most applications.

*AG9: Johnson-Matthey Easyflo 3 (Special Purpose Alloy)
Melting range (deg. C) 634/565 50% silver
Remarks: Nickel bearing. For carbide tool tips. Short melting range.
*contains cadmium*

Yes, before everyone starts screaming about it, the book has an entire
appendix relating to the dangers and correct usage of cadmium bearing alloys.
Standard disclaimers apply here, folks. I'm just repeating what the book
says.

There is another AG9 alloy manufatured by THESSCO Ltd in the UK that goes
by the memorable trade name of MX20N; it does not say it contains cadmium but
at the same time does not say that it doesn't (if you see what I mean). The
remarks for that alloy are 'Nickel Bearing for brazing carbides'. I suspect
that it does contain cadmium because the same manufacturers M19MN alloy (which
is an AG18 alloy) has the remark 'Nickel-manganese bearing. Cadmium free,
for carbides'

The conclusions I drew from all of this were...

* Yes you can do it
* Life is much easier if you know what the composition of your stainless is
* Talk to your local supplier and see what they have to offer; you should
probably use a special purpose alloy to do it.

Personally I would be very tempted to make the parts for the item in question
and 'shop around' my local welding shops for someone who 'knows' stainless.
The application you cite sounds like the joints will need to be good and hardy;
you may save a lot of time and effort by 'contracting' it out.

Tim
--
Tim Kirby --------- Cray Research Inc., Eagan, MN, USA ----------- t...@cray.com
Disclaimer: I disclaim, therefore I am. Be warned ...
-------------------------------------------------------------------------------
When all else fails, Immortality may always be assured by spectacular error(JKG)

The good news, BernzOmatic makes an alloy that works:
Model NS-3 nickel silver flux(?) coated rod, color of rod
blue, 85,000psi, 1250-1750 F working temp. (It is expensive).

Warning -- some alloys of ss will develope fractures at brazing
tems, but the filler usually fills well. You'll have to judge
for your self on structure if it happens.

+------------------------------------------------------------------------+
| pete...@headcheese.daa.uc.edu In real life: John M. Peterson |
| |
| College of Design Architecture Art & Planning |
| University of Cincinnati 45221-0016 513-556-1207 |
+------------------------------------------------------------------------+

Take whatever RPM you estimated and divide it by the number of balls in
the race. If there were 8 balls, a speed of 875 revolutions per second
(52,000 RPM ) is believable, though doubtful.

But you're not dealing with an airfoil here. This is a simple case of
impingement and the air velocity must be sufficiently higher than the
ball bearing speed to deliver sufficient impingement force to balance
the frictional and aerodynamic losses.

That said, a race speed much faster than the air velocity is possible simply
because the balls and cage travel at a fraction of the velocity of the
outer race.

Not quite, oh Compressor Breath. It's a ball, not a cylinder. The
tangental speed at the point of strongest air contact has to be less
than the air speed. Other points on the ball can travel faster - just
like the surface velocity of your tire is far greater than the surface
velocity on your axle.

The farthest part of the ball from the axis of spin is travelling
at 1250 MPH. However, the axis of spin is travelling at 0 MPH - it's
standing still and pivoting in place. So if the majority of the air
passes tangentially at a point somewhere between the axis and the
equator, the equator of the ball could easily be moving several times
faster than the airflow.

In addition, any air around the ball would be pushed along
tangentally, which would make it move away from the ball. This means
the ball is spinning in a partial vacuum, with the highest vacuum at
the equator where the surface is moving the fastest.

Now it gets really funky: since the air is being pushed away from
the equator far more than the axis, the air coming from the source
would have less influence on the equator than on points closer to the
axis. Therefore, the influence of a single stream of air aimed at the
equator would be directed mostly on two points somewhere between the
equator and the axis - just for giggles, we'll call them the tropic of
cancer and the tropic of capricorn.

So there it is - a single airstream directed at the equator affects
the ball mostly at the tropic circles (or would that be the arctic and
antarctic circles?) and the speed is multipled at the equator. Q.E.D.

But then, I'm just theoretizing. Feel free to flame me if I don't
know what I'm talking about.

I can't see that the the latter is important...a boat can move 20 miles/hour with
a 10 MPH wind and have zero velocity component in the direction of the wind...it's
STILL going faster than the wind!

sorry, the space between the ball and the cone *was* the venturi! Also, the design
used had an air plenum behind the cone, and the air actually entered through tangential
holes in order to produce a "whirlwind" of air circulating around the axis of the
cone (at least that was the theory).

JK

Very fine instrument bearings do achieve rpms around 60,000
(1000 rps). However, it's unlikely that a randomly selected
bearing could reach even this rpm driven by hand assembled
or held air drive.

Gary

Note that he said "the ball", not the "ball bearing assembly". This
is a single 1" diameter ball, floating on a spinning flow of air at a point
only part way out the radius, so the equitorial velocity could easily be
greater than the air-speed at the point of application.

[ ... ]

Well, yes this would be the case if it were a ball-bearing assembly
(outer race, cage & balls, and inner race), but as stated above it appears
to be a single ball. However this is analogous to the application of air at
a location part-way out the radius (as in my paragraph above), except that
there is only a linear increase in speed, not the "geared-up" speed of
driving the ball cage (as in a planetary gear system.)

--
Email: <dnic...@d-and-d.com> | ...!uunet!ceilidh!dnichols
<dnic...@ceilidh.beartrack.com>
Donald Nichols (DoN.) | Voice (Days): (703) 704-2280 (Eves): (703) 938-4564
--- Black Holes are where God is dividing by zero ---

I can't remember the final speed but it was 100's of krpm, measured with
a strobe light. As a guide to the final speed, the article strongly
recommended strong shields around the cone, as it tended to explode
after a while! If you consider the stress required to burst a solid
lump of steel, 0.5" dia....

And don't ask me to look up the article - my model engineering club has
ME magazines back to the turn of the century and they appeared every two
weeks - and yes, that is a lot of magazines!

David Jenkins

Whether you're rich, or whether you're poor, on the whole
it's better to be rich. (Max Miller)