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GeorgePapa
12-22-2009, 07:17 PM
Have read the following and considering the contents strange (though had to cosider the source as very serious indeed) am asking if you know anything about it.

George.

Aviation Electronics
Technician - Basic
NAVEDTRA 14028

• Jun 1991: Original edition released.
• Mar 2003: Minor revision released.

NEVER use the grinding wheel on
nonferrous metals. When used with this
type of material, the grinding wheel could,
in effect, explode.. This could result in a
serious injury to or death of personnel.

Published by
NAVAL EDUCATION AND TRAINING
PROFESSIONAL DEVELOPMENT
AND TECHNOLOGY CENTER

Page 7-10

MaxxLagg
12-22-2009, 07:29 PM
Well, they CAN load up to the point where they can blow up on you. The trick is to dress the wheel often to avoid loading it up. I've ground non-ferrous material numerous times over the years with standard grinding wheel with no problems other than excessive heat build-up. Dress the wheel often,use coolant, and oh, did I say? Dress the wheel often.

PTSideshow
12-22-2009, 07:29 PM
I don't know if they explode, they do become unbalanced and have a catastrophic failure while rotating at high speeds. The use of ferrous grinding wheels for non ferrous materials is a non brainer as the become clogged and destroy themselves sooner or later. The aluminum becomes wedged in between the openings of the grit et all
more than most would want to know (http://www.georgiagrindingwheel.com/grindingwheels_basics.htm#faq1)

shawnspeed
12-22-2009, 07:41 PM
When I was in high school in the '80s , we had a individual try to shortcut on a foundry project by finishing a aluminum part on the grinder , when the teacher stepped out for a moment,( we were told to file the part to finish it)Just as the teacher returned, the wheel let go , missing the student and knocked a big chunk out of the cinderblock wall... needles to say that was a new saftey talk at the beginning of every simester.....

Black_Moons
12-22-2009, 07:54 PM
Intresting, I have heard of this before..
And iv also seen my (usally more intelligent) brothers grinder completely and utterly loaded with aluminum.. and another time with wood... you could hardly SEE the wheel anymore it was so badly loaded.. I think he blamed the wood on his wife, but I think the aluminum was him -_-;
I even GAVE him a diamond wheel dresser.. and asked him every time I saw him for 4 months if he had used it... Never did get a 'yes' -_-;
Hes a 'professional' welder too.. And has allready had a 4.5" angle grinder wheel blow up in his face when he was new on a job.. (Don't trust your coworkers NOT to put a 10,000rpm wheel on a 20,000rpm high speed sander to give to the new guy!)

Also heard of aluminum dust + corroded iron dust (iron oxide) + grinder sparks = thermite going KABOOM.

Jack772
12-22-2009, 08:19 PM
I saw a wheel on a toolpost grinder let go. It took big chunks out of a wooden door.

KiddZimaHater
12-22-2009, 08:52 PM
I've ground aluminum plate on a surface grinder.
I used WD-40 for lube, and dressed the wheel after every 3rd pass across the part.
No problems.

mechanicalmagic
12-22-2009, 09:01 PM
Yes, you can grind Aluminum with the PROPER wheel. Anybody seen Blanchard ground Aluminum tooling plate?
Norton wheel:
http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200332113_200332113

But they are hard to find.

john hobdeclipe
12-22-2009, 09:25 PM
I'd want to know more about what kind of wheel they are talking about. What abrasive? What bond?

Norton says to use their black silicon carbide wheels on Aluminum.


I saw a wheel on a toolpost grinder let go. It took big chunks out of a wooden door.

I saw a toolpost grinder wheel explode, and part of it took out a window behind the lathe, part of it bounced off the lathe carriage and went up and took out a flourescent light, and part of the wheel hit my friend just below the belt and knocked him onto his a$$. Of course, we didn't report the injury...he was working on a home project for me at the time.

SilveradoHauler
12-22-2009, 10:40 PM
One of the best things I put in the shop was a big belt grinder.

Safe for aluminum.

Takes the strange grinding projects away from the well dressed conventional grinding wheels on the bench grinders, and reduces the grinding wheel dressing!

Belts run pretty clean, and I use a big rubber belt cleaner when they get a little clogged from aluminum.

oldtiffie
12-23-2009, 01:54 AM
I'd want to know more about what kind of wheel they are talking about. What abrasive? What bond?

Norton says to use their black silicon carbide wheels on Aluminum. ,................................................

.

Yep that's so. Same does/goes for pretty well most non-ferrous stuff that needs to be ground.

Same applies to TC tips/inserts too if you don't have a diamond or cubic boron wheel or the Norton "Hard" ("blue") wheel as silicon carbide wheels will do it at a pinch.

The most likely cause is abuse such as when a wheel will not "ring" properly.

Clogging (-up) and poor balance and poor dressing don't help much either.

There is far too much "urban myth" and "boogie-man" stuff about as regards grinding wheels.

More faults can be traced back to the operator than to the machine or the wheel.

Evan
12-23-2009, 03:02 AM
There is a lot of "it depends" in this question. In particular it depends on what sort of aluminum you want to grind. Aluminum and it's alloys go all the way from 6000 psi to over 100,000 psi in ultimate yield strength and from soft-as-warm-butter-dent-it-with-your-teeth to harder than mild steel.

Pure dead soft electrical aluminum will clog up any wheel faster than a Big Mac clogs your arteries. 7075 T-6 grinds more like steel and the swarf can make tiny needles. If you do need to grind aluminum on a regular wheel touch the wheel with a wax stick first. It will help to prevent loading. Don't use oil though. While it won't hurt a vitrified wheel it can cause failure of some resin bonded wheels depending on the resin type.

As far as making a wheel explode just because it was touched with aluminum, no.


Also heard of aluminum dust + corroded iron dust (iron oxide) + grinder sparks = thermite going KABOOM.


While the apocryphal Thermite Reaction does exist it is a lot harder to make it happen in practice than some urban legends would have you believe. I tested this particular "almost myth" and there is no way I could get any sort of response from aluminum dust from my belt sander mixed with oxidised steel from the wheel grinder. It made no difference what ratio I used or how hot I made it. No thermite, none. To make thermite you need aluminum powder and FeO3. FeO3 is Hematite while the result of burning iron in air makes a combination of unburned iron, FeO and FeO2 fume. There isn't enough oxygen in the dust from grinding iron to promote a thermite reaction.

dp
12-23-2009, 03:08 AM
I thought the hazard increased if the iron rusted. That is, rusted iron powder intermingled with ally powder could produce a hell fire inferno that you can't put out. I haven't looked at the chemical makeup - just one of the things you hear in the rumor mill.

I know that in my yoot I could energize a number of exotic combustibles with various powdered metals - copper being a rather colorful one. The chemlab at BHS had some fun stuff :)

Evan
12-23-2009, 07:57 AM
One of the biggest problems is the aluminum. It's flammable even in air but only if enough surface area is exposed. I tried that experiment too. I collected a large bag of aluminum fines from my belt sander and tried tossing handfuls in a bonfire. It barely even sparkled just slightly. Mostly nothing at all happened, the powder wan't fine enough.

IF you could make it fine enough AND the iron fines had formed FeO3 from exposure to water after grinding THEN you might be able to produce a thermite reaction.

What I have seen happen is fine iron powder catch fire in a very controlled manner. It glows red hot and the combustion is slow and stable, very easy to douse with some water. This is about the same as you will have if you light a wad of fine steel wool with a match.

JoeFin
12-23-2009, 08:04 AM
What makes everyone beleive they are discussing Surface Grinding Wheels or even Bench Grinding wheels in this article ?

Being the advisory was directed to "Aviation Electronics Technician" I would have thought they were discussing 4.5" peanut grinder cut off wheels

Evan
12-23-2009, 08:16 AM
4.5 inch cutoff wheels are unlikely to cause "death". Yes, it is possible, but unlikely. Also, why would an aviation electronics tech be more likely to be using a cutoff wheel? As an aviation tech I was constantly resharpening drill bits on the ever present bench grinder.

Black_Moons
12-23-2009, 08:34 AM
As I have mentioned in a previous post. my brother took a 4.5" wheel explodeing at over 13,000 rpm to the face (Note those wheels are only rated for 11,000~ rpm or so, And the wheel was mounted by some fool to a 20,000rpm high sped sander).. Surived with a few dozen stichs.
While Im not saying these wheels are 'safe' to explode, Id put them rather low on the lethality scale.. the 7" or 9" disks are a little scary however.

sconisbee
12-23-2009, 12:03 PM
...... the 7" or 9" disks are a little scary however.

I'll second that, i've had a 9" cut off let go on me when in use cutting steel tube, fortunately i was wearing the right face shield as it significantly reduced the speed of the shrapnel... however even with the right shield on a piece did pierce the face shield and i have a scar running down from my eye to just above my lip to remind me, still got the shield too, just as a reminder to wear the right gear....had i not been wearing it..well i would guess i would have lost the eye at a minimum......

Not entirely relevant to the topic tho...

whitis
12-23-2009, 12:21 PM
Yes, the wheels can "explode" mechanically rather than chemicallly. Aluminum gums up the wheels. Then it stops grinding because it is gummed up and you push harder to compensate which makes more heat. The expansion of the aluminum forces the grains of the wheel apart cracking the adhesive. Centrifugal force does the rest. If you dress the wheel before the cracks start, the wheel is still usable. Of course, dressing itself can stress the wheel. There are wheels that are specifically made for aluminum - different adhesive.

Grinding ferrous metal and aluminum on the same machine (grinder or sander) without cleaning can cause thermite explosions. Here is an accident report:
http://www.hanford.gov/rl/?page=542&parent=506
This accident involved the aluminum from a small handful of pop rivet heads.

You grind some steel. The iron oxidizes due to heat and/or is allowed to sit and rust. You grind some aluminum. Vibration or air currents (vacuum system) cause the dusts to mix forming thermite. Then you grind some steel and the sparks ignite.

Aluminum dust can also cause fire and explosions in dust collection systems. The Lemmerz plant is one example.
http://www.csb.gov/investigations/detail.aspx?SID=33

Combustable dust explosions (not just metal dust) have resulted in a number of accidents:


Since 1980, there have been at least 350 such explosions in the U.S., killing 133 people and injuring hundreds more.

http://www.cbsnews.com/stories/2008/06/05/60minutes/main4157170.shtml

Aluminum dust is not always easily ignitable, and, therefore, the hazard of dust explosions is often ignored.
http://www.meridianeng.com/TEE%20Reference%20Data%20Sheet%20for%20Aluminum.pd f

Water can absorb some of the heat the reaction needs to maintain itself but it can also cause explosive hydrogen gas to form. Aluminum can also form an exothermic reaction with water.
http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/aluminum_powder/working_alu.html

Most grinding wheel accidents seem to be of the getting your hand caught in moving machinery variety, followed by disintegrating grinding wheels (which can happen whether or not you grind aluminum):
http://www.osha.gov/SLTC/machineguarding/grinder_accidents.html
However, all the fatal accidents listed involved disintegrating wheels and most of the disintegrating wheel accidents that made the list were fatal.

But considering how careless people often are, these accidents don't seem to happen all that often.

A couple anecdotal reports:


It happened to an old boss of mine. It blew up around his arm, missing it luckily, 1 piece went through the roof another went through two pieces of drywall and embedded itself into a refrigerator. (Wheel disintegrating while grindging aluminum)



I have seen two instances of aluminum explosion. One in a vacuum being used to collect aluminum dust, the other, a grinding station where steel stag from an adjoining grinding station ignited the stream. Grinding stations must be dedicated to aluminum only. Combining station use with other metals can cause explosion.

http://www.mmsonline.com/dp/forums/forum_results.cfm?t_id=5433&f_id=112&pub=MMS

Whether or not you are grinding aluminum, you should keep your torso and head out of the plane of rotation.

toolmaker76
12-23-2009, 09:08 PM
I have seen many wheel explosions over the years. Most of the time it is either work not well secured, or grinder rpm is in excess of wheel rating. One of the first things I was taught was to be aware were not to be when grinding, especially when you start the wheel.

With aluminum, the solution was to coat the wheel with wax, redress and rewax frequently.

Here's wishing everyone a Merry Christmas!

Evan
12-23-2009, 10:16 PM
Yes, the wheels can "explode" mechanically rather than chemicallly. Aluminum gums up the wheels. Then it stops grinding because it is gummed up and you push harder to compensate which makes more heat. The expansion of the aluminum forces the grains of the wheel apart cracking the adhesive. Centrifugal force does the rest. If you dress the wheel before the cracks start, the wheel is still usable. Of course, dressing itself can stress the wheel. There are wheels that are specifically made for aluminum - different adhesive.



Wheel grit isn't held together with adhesives. There are two main types of grit wheels (excluding superabrasives). One is resin bonded in which the grit is mixed in a composite matrix of high temperature plastic and sometime fibre. The other is a vitrified wheel in which the grains are melted together.

A resin bonded wheel is a composite structure and may also be reinforced with fabrics such as is the case with most cutoff wheels. The structure doesn't rely on the abrasive being glued together by the resin. The resin (and fabric) IS the structure that produces the mechanical integrity of the wheel and the grit is along for the ride.

The resin doesn't crack because of expanding aluminum. The aluminum is only on the very surface of the wheel and makes no difference to the mechanical integrity of the wheel. The type of wheel you are speaking of is rarely resin bonded anyway. Virtually all bench grinding wheels are vitrified construction. Vitrified wheels break because of mistreatment causing cracks from shock, faulty construction, gross imbalance or over speeding. Aluminum won't cause a vitrified wheel to crack just because it is loading the surface.

Evan
12-23-2009, 10:29 PM
Grinding ferrous metal and aluminum on the same machine (grinder or sander) without cleaning can cause thermite explosions. Here is an accident report:
http://www.hanford.gov/rl/?page=542&parent=506
This accident involved the aluminum from a small handful of pop rivet heads.


That report is highly suspect. It's been floating around online for years. There isn't enough aluminum in a dozen pop rivet heads to cause the reported effect. Also, thermite doesn't explode, it burns. In order to burn it must be heated to extremely high temperature and it also must stay in a dense mass for the reaction to proceed. I have used thermite in the past and am quite familiar with it's pyrotechnic properties. An offhand random mixture of improperly constituted ingredients is very unlikely to ignite, let alone cause an explosion. I have tried exactly that using the exact same materials as reported with absolutely no result.

Also, the "report" is entirely anecdotal and has inconsistencies as well. The man was reported as using a belt sander but the problem is later attributed to a grinding wheel.



Recommended actions:
The victim recommended that the manufacturer of the grinding wheel should include a very strong warning about the dangers posed by grinding steel after having ground aluminum. That warning should include precautions to thoroughly clean the grinding machine of all aluminum dust before grinding iron or steel.