Discussion:
brass media
(too old to reply)
Jonathan Battat
2003-10-31 02:59:20 UTC
Permalink
before i start milling bp, i just wanna double check that brass is good for
media (in terms of non-sparking and safety) I know it should be, but double
checking never hurts.

Also i have some balls, but I need more and they are rather expensive. I'd
like to buy .5" or smaller brass rod and chop it up into short lengths to
supplement the balls. Would it be better to use lengths that would be about
the same as the diameter of the rod, medium ones (maybe about 2") or long
ones that are just about the length of the jar? Maybe it doesn't even make
a difference because rods are so inefficient compared to balls? Any
comments?

thanks for any help
jonathan
Richard J Kinch
2003-11-01 06:19:16 UTC
Permalink
Any comments?
Why not lead? Cheaper, more effective, easy to cast and cut yourself.
scabsbuychinese
2003-11-04 08:20:34 UTC
Permalink
Post by Richard J Kinch
Any comments?
Why not lead? Cheaper, more effective, easy to cast and cut yourself.
Because brass is a much better alternative to lead. The only reason
lead is so popular is because almost everyone who uses it does so only
because they know someone else that uses it. So, they just do whatever
they do without thinking on their own what a better alternative would
be. As far as it being cheaper, maybe so if you don't do much milling.
If you do a lot of milling, brass lasts longer. Lead more effective?
It sure isn't by much!! Have you even used brass?
And it may be easy to cast your own lead, but chopping up brass bar
and rounding off the ends is worth the work more by a longshot,
because it doesn't contaminate your powder like lead. Ceramic media
whatever kind you get, sparking or not, is a good non contaminating
alternative to milling individual chemicals. There are more reasons
not to use lead, than there are to use it.

Kolin
Joe 123
2003-11-05 16:11:57 UTC
Permalink
I have been using lead for almost 1yr now and Im begining to not like it.
My BP always comes out grey and the mill is very heavy with lead. I
recently tried using 302SS 3/8" balls. I can put more media in my mill and
my BP comes out black instead of grey. Its my understanding that the 300
series stainless are non-sparking. So far so good. I paid about 6 cents
per ball and I have about 1000 of them in a 1.5 gal jar. So as far as
price goes lead is a bit cheaper but not by much.
Post by scabsbuychinese
Post by Richard J Kinch
Any comments?
Why not lead? Cheaper, more effective, easy to cast and cut yourself.
Because brass is a much better alternative to lead. The only reason
lead is so popular is because almost everyone who uses it does so only
because they know someone else that uses it. So, they just do whatever
they do without thinking on their own what a better alternative would
be. As far as it being cheaper, maybe so if you don't do much milling.
If you do a lot of milling, brass lasts longer. Lead more effective?
It sure isn't by much!! Have you even used brass?
And it may be easy to cast your own lead, but chopping up brass bar
and rounding off the ends is worth the work more by a longshot,
because it doesn't contaminate your powder like lead. Ceramic media
whatever kind you get, sparking or not, is a good non contaminating
alternative to milling individual chemicals. There are more reasons
not to use lead, than there are to use it.
Kolin
Alan Yates
2003-11-06 03:04:20 UTC
Permalink
I doubt it is the lead making your BP grey, mine comes out grey when I use
certian charcoals, with some photographic printing charcoal (mixed
hardwoods) or lampblack it comes out jet black, with pine charcoal, balsa,
or whatever the local BBQ charcoal is it comes out grey.

I mostly use the common BBQ charcoal (not brickettes) as it is the cheapest
and it works just fine (I got several kg free at the local supermarket
because it wouldn't scan at the register). I've tried burning it off to
assess the ash content, I do not believe it is a high ash content making it
grey.

It darkens once you add moisture and granulate or press. Perhaps it is more
a function of how the potassium nitrate is incorporated. As I don't have
access to an electron microscope I can't really study the difference, but I
would really like to try some day.
Post by Joe 123
I have been using lead for almost 1yr now and Im begining to not like it.
My BP always comes out grey and the mill is very heavy with lead. I
recently tried using 302SS 3/8" balls. I can put more media in my mill and
my BP comes out black instead of grey. Its my understanding that the 300
series stainless are non-sparking. So far so good. I paid about 6 cents
per ball and I have about 1000 of them in a 1.5 gal jar. So as far as
price goes lead is a bit cheaper but not by much.
Post by scabsbuychinese
Post by Richard J Kinch
Any comments?
Why not lead? Cheaper, more effective, easy to cast and cut yourself.
Because brass is a much better alternative to lead. The only reason
lead is so popular is because almost everyone who uses it does so only
because they know someone else that uses it. So, they just do whatever
they do without thinking on their own what a better alternative would
be. As far as it being cheaper, maybe so if you don't do much milling.
If you do a lot of milling, brass lasts longer. Lead more effective?
It sure isn't by much!! Have you even used brass?
And it may be easy to cast your own lead, but chopping up brass bar
and rounding off the ends is worth the work more by a longshot,
because it doesn't contaminate your powder like lead. Ceramic media
whatever kind you get, sparking or not, is a good non contaminating
alternative to milling individual chemicals. There are more reasons
not to use lead, than there are to use it.
Kolin
--
Alan Yates
http://www.vk2zay.net/
The Moon is Waxing Gibbous (92% of Full)
Richard J Kinch
2003-11-06 22:24:53 UTC
Permalink
Post by Joe 123
Its my understanding that the 300
series stainless are non-sparking.
Just what science underlies such an understanding?

A typical 3xx stainless alloy is "18-8" (such as tableware), which means 18
percent chromium, 8 percent nickel, with nearly all of the balance of 74
percent being iron.

Grab an old 18-8 spoon, and rub it on a high-speed grinding wheel. It will
generate plenty of sparks. Not nearly as much as tool steel or mild steel,
but still enough that you would never call it "non-sparking".

Lead is superior to stainless as a BP milling media in every respect.
Toxicity is a non-issue in the concentrations involved. Do you think
abraded chromium and nickel from stainless are less toxic than lead?
Joe 123
2003-11-07 01:57:29 UTC
Permalink
My understanding is that 3xx series stainless is softer, corrosion
resistant, and ~30% less dense (Pb). I think corrosion of the media has a
lot to do with sparking, speaking of iron. Corrosion creates pitting and
jagged areas on the ball. These areas have high friction, like in a
collision, especially if two corroded areas meet. Thats why 3xx SS is
safer. 3xx SS wont corrode (at least it hasent in the 2 months Ive used it
~4 batches of BP) Not getting your media wet also helps it to last longer.
I can put 30% more media in my mill verses Pb.


Your grinder theory works for copper, nickle, brass, ceramincs etc. I dont
remember grinding Pb but I bet it would spark. Having shot a few bullets at
the range I notice sparks from all lead bullet on concrete back wall?

I could care less about contaimination but lead is more likely to
contaiminat chemicals from one batch to the next. corroded chrome steel
will turn everything reddish brown.

I will agree that lead is hands down safer. My opinion is 3xx SS is an
alternative for those who understand and have experience in the art. I am
simply stating my opinions.

I think 316SS would be the ideal choice as it is even softer and more
corrosion resistant.

Also, the chaepest way to get SS balls is in the finishing industry. I
thiink they are called "burnishing balls". They are used in balls mills for
polishing and deburring parts. they are not annealed and are basically
"offspec" type stuff.




Joe
Post by Richard J Kinch
Post by Joe 123
Its my understanding that the 300
series stainless are non-sparking.
Just what science underlies such an understanding?
A typical 3xx stainless alloy is "18-8" (such as tableware), which means 18
percent chromium, 8 percent nickel, with nearly all of the balance of 74
percent being iron.
Grab an old 18-8 spoon, and rub it on a high-speed grinding wheel. It will
generate plenty of sparks. Not nearly as much as tool steel or mild steel,
but still enough that you would never call it "non-sparking".
Lead is superior to stainless as a BP milling media in every respect.
Toxicity is a non-issue in the concentrations involved. Do you think
abraded chromium and nickel from stainless are less toxic than lead?
Harry Conover
2003-11-07 08:34:31 UTC
Permalink
Post by Joe 123
My understanding is that 3xx series stainless is softer, corrosion
resistant, and ~30% less dense (Pb). I think corrosion of the media has a
lot to do with sparking, speaking of iron. Corrosion creates pitting and
jagged areas on the ball. These areas have high friction, like in a
collision, especially if two corroded areas meet. Thats why 3xx SS is
safer. 3xx SS wont corrode (at least it hasent in the 2 months Ive used it
~4 batches of BP) Not getting your media wet also helps it to last longer.
I can put 30% more media in my mill verses Pb.
On the downside, SS has nowhere the mass density of lead and so is an
inferior milling media, plus it can spark and hence is unacceptable
for use in explosive environments.

What else needs to be said?

Harry C.
Old Dog
2003-11-09 20:38:26 UTC
Permalink
Post by Joe 123
I could care less about contaimination but lead is more likely to
contaiminat chemicals from one batch to the next. corroded chrome steel
will turn everything reddish brown.
Why would you ever use lead for anything but BP-type mixtures?

-Rich
Harry Conover
2003-11-10 04:39:18 UTC
Permalink
Post by Old Dog
Post by Joe 123
I could care less about contaimination but lead is more likely to
contaiminat chemicals from one batch to the next. corroded chrome steel
will turn everything reddish brown.
Why would you ever use lead for anything but BP-type mixtures?
-Rich
Rich, I'm just taking a wild stab-in-the-dark here, but it would seem
to me that a ball mill is simply a variation on the old concept of a
hammer mill.

If this assumption is correct, the milling media in a ball mill should
have the highest possible mass density while being practical. This
pretty much limits you to elements like lead, gold, and uranium.
Uranium sparks and is much too rare and costly, and gold is even more
costly, hence the selection of hard alloys of lead turns out to be a
cost effective compromise. The surface hardness of the milling media
is another issue, one often neglected.

However, when sparking is not a serious concern, such as the milling
of an oxidizer alone, I see no reason where steel balls could not be
used with only a decrease in milling efficiency (only slightly
extending the milling time).

Harry C.
Old Dog
2003-11-10 05:21:53 UTC
Permalink
Post by Harry Conover
Post by Old Dog
Post by Joe 123
I could care less about contaimination but lead is more likely to
contaiminat chemicals from one batch to the next. corroded chrome steel
will turn everything reddish brown.
Why would you ever use lead for anything but BP-type mixtures?
-Rich
Rich, I'm just taking a wild stab-in-the-dark here, but it would seem
to me that a ball mill is simply a variation on the old concept of a
hammer mill.
If this assumption is correct, the milling media in a ball mill should
have the highest possible mass density while being practical. This
pretty much limits you to elements like lead, gold, and uranium.
Uranium sparks and is much too rare and costly, and gold is even more
costly, hence the selection of hard alloys of lead turns out to be a
cost effective compromise. The surface hardness of the milling media
is another issue, one often neglected.
However, when sparking is not a serious concern, such as the milling
of an oxidizer alone, I see no reason where steel balls could not be
used with only a decrease in milling efficiency (only slightly
extending the milling time).
Harry C.
Harry, maybe you misunderstood my question. I didn't ask why anyone would use
anything but lead for BP, I asked why anyone would use lead for anything other
than BP.

I understand why lead is popular for milling BP - it's efficient and
nonsparking. But why use it for anything else? Ceramic media works fine, and
won't add any lead (or anything else to the milled product if it's quality hard
ceramic media designed and sold for milling.

Sure, steel would work too for some applications, but many types could
eventually be attacked by strong oxidizers. I've heard of using SS for milling
BP, but the thought still makes me more nervous than a little lead residue.

Same with brass - I attended a seminar this weekend where the instructor
complained about the difficulty of keeping a clean finish on brass tooling when
it was used around oxidizers. If you mill with brass, the metal will react with
at least some chemicals, and you will be leaving metal salts in the milled
powder. With many comps it wouldn't make much difference - but copper acts as a
catalyst to many oxidizer/fuel reactions, forms unstable compounds with some
oxidizers, and of course produces color when burned, so could interfere with
color purity.

-Rich
Richard J Kinch
2003-11-10 06:30:43 UTC
Permalink
Post by Old Dog
I understand why lead is popular for milling BP - it's efficient and
nonsparking. But why use it for anything else?
One reason is that you need purchase one less set of media, given that any
slight cross-contaminants are compatible.
Old Dog
2003-11-10 18:31:42 UTC
Permalink
Post by Richard J Kinch
Post by Old Dog
I understand why lead is popular for milling BP - it's efficient and
nonsparking. But why use it for anything else?
One reason is that you need purchase one less set of media, given that any
slight cross-contaminants are compatible.
Sorry, but that doesn't fly at all. You simply cannot prevent
cross-contamination unless you keep both media and mill jars separate for
different types of compounds. I know of no simple way to remove 100% of sulfur
used in a mill jar or with media (without dissolving the jar), so there are
naturally quite a few things you should NEVER mill in the same jar or with the
same media. As we have stressed here time and time again, you simply cannot be
sure that an unknown/untried mixture will not cause problems. The only thing I
would consider milling in my BP jar with my BP media would be a charcoal star
mixture or charcoal intended for subsequent use in BP or glitter/flitter mixes -
and I already have a separate jar for charcoal ONLY, with ceramic media, so I
don't do that either. I also have separate jars (and media) for chlorates, AP,
nitrates *without* sulfur, and resin fuels. I don't mill metals, or I would also
have jars for those.

-Rich
Alan Yates
2003-11-10 07:03:15 UTC
Permalink
I wouldn't mine a set of DU media, would mill pure chemicals nice and
quickly, being around twice as dense a lead. Although it is pyrophoric
and rather soft, I wonder if it can be hardened like lead with antimony?

DU would be dirt cheap if it wasn't for all the political crap
surrounding it, it isn't all that rare and huge stockpiles are just
laying around. I'd glady buy a few hundred kilograms and make a killing
on eBay with DU paper weights. :-)

I was reading about the work done on anti-corrosion coatings for Uranium
and Plutonium for weaponisation during the Manhattan Project last night,
very interesting stuff.

Anyone ever use bismuth media? I have a few pounds of it.

I guess Osmium is too rare and that corrosion problem (which makes a
ridiculously poisonous and reactive, not to mention smelly, oxide) would
rule it out, even if it is wonderfully dense and harder than titanium.
Post by Harry Conover
Post by Old Dog
Post by Joe 123
I could care less about contaimination but lead is more likely to
contaiminat chemicals from one batch to the next. corroded chrome steel
will turn everything reddish brown.
Why would you ever use lead for anything but BP-type mixtures?
-Rich
Rich, I'm just taking a wild stab-in-the-dark here, but it would seem
to me that a ball mill is simply a variation on the old concept of a
hammer mill.
If this assumption is correct, the milling media in a ball mill should
have the highest possible mass density while being practical. This
pretty much limits you to elements like lead, gold, and uranium.
Uranium sparks and is much too rare and costly, and gold is even more
costly, hence the selection of hard alloys of lead turns out to be a
cost effective compromise. The surface hardness of the milling media
is another issue, one often neglected.
However, when sparking is not a serious concern, such as the milling
of an oxidizer alone, I see no reason where steel balls could not be
used with only a decrease in milling efficiency (only slightly
extending the milling time).
Harry C.
--
Alan Yates
http://www.vk2zay.net/
The Moon is Waning Gibbous (99% of Full)
Lloyd E. Sponenburgh
2003-11-10 12:36:45 UTC
Permalink
Richard, most of the 'standard' metalworking texts (and ball media
manufacturers) list 304 SS as 'non-sparking'. One _can_ get a spark from
nearly anything at high enough friction and heat levels. #304 does not
spark under 'normal' impacts with other particles of the same material.

LLoyd
Post by Richard J Kinch
Post by Joe 123
Its my understanding that the 300
series stainless are non-sparking.
Just what science underlies such an understanding?
Richard J Kinch
2003-11-11 06:00:34 UTC
Permalink
Post by Lloyd E. Sponenburgh
Richard, most of the 'standard' metalworking texts (and ball media
manufacturers) list 304 SS as 'non-sparking'. One _can_ get a spark from
nearly anything at high enough friction and heat levels. #304 does not
spark under 'normal' impacts with other particles of the same material.
So Lloyd ... you endorse, say, AISI 304 for milling BP? That was the
application in mind.
Lloyd E. Sponenburgh
2003-11-11 12:39:18 UTC
Permalink
No, Richard, you missed the point. I was not 'endorsing' anything. I said
that commercial makers of the metals list it as non-sparking.

I will use nothing but lead (with all of its warts) to mill any explosive
mixture.

I do use #304 SS balls to mill AP and potassium perchlorate in the absense
of fuels.

LLoyd
Post by Richard J Kinch
Post by Lloyd E. Sponenburgh
Richard, most of the 'standard' metalworking texts (and ball media
manufacturers) list 304 SS as 'non-sparking'. One _can_ get a spark from
nearly anything at high enough friction and heat levels. #304 does not
spark under 'normal' impacts with other particles of the same material.
So Lloyd ... you endorse, say, AISI 304 for milling BP? That was the
application in mind.
Richard J Kinch
2003-11-12 07:22:14 UTC
Permalink
Post by Lloyd E. Sponenburgh
No, Richard, you missed the point. I was not 'endorsing' anything. I
said that commercial makers of the metals list it as non-sparking.
I did get your point.
Post by Lloyd E. Sponenburgh
I will use nothing but lead (with all of its warts) to mill any explosive
mixture.
Sure sounds like an endorsement of something (Pb) to me, one that I would
support.

It is simply my crude experimental observation that austentic species of
stainless have about 40% the "sparking" of high-carbon tool steel or
(shudder) titanium. Maybe the makers you refer to consider this "non-
sparking" (do they use a well-defined test?). Whatever they mean by that,
it isn't relevant to milling media.

Even lead can be pyrophoric, so "sparking" (or not) just isn't a simple
characterization. It only takes one spark out of countless collisions in
your wickedly effective Sponenmill.
Lloyd E. Sponenburgh
2003-11-12 12:32:59 UTC
Permalink
Post by Richard J Kinch
It is simply my crude experimental observation that austentic species of
stainless have about 40% the "sparking" of high-carbon tool steel or
(shudder) titanium. Maybe the makers you refer to consider this "non-
sparking" (do they use a well-defined test?). Whatever they mean by that,
it isn't relevant to milling media.
It _might_ be relevant to milling media. It was a milling media
manufacturer from whom I purchased the 304 balls who lists it as the only
non-sparking medium he sells. He's got a pretty substantial motive to get
that sort of thing right. And, at $14.00 / lb. I've got a pretty
substantial motive to hope he is right.

LLoyd
Richard J Kinch
2003-11-13 06:11:07 UTC
Permalink
Post by Lloyd E. Sponenburgh
It was a milling media
manufacturer from whom I purchased the 304 balls who lists it as the only
non-sparking medium he sells.
Is there a standard for "non-sparking"? Something like, I don't know, a
standardized hammer-drop repeated a zillion times in a flammable-atmosphere
chamber? Or various velocity drops onto black powder?
Lloyd E. Sponenburgh
2003-11-13 12:24:45 UTC
Permalink
Richard,
To be honest, I trusted the manufacturer without reservation, and without
further followup. They've been _very_ leery of selling us milling media
because of its intended use. They more or less coaxed us into buying the
304SS media, saying it was all they were comfortable to sell.

I did an impromptu and ersatz 'test' of the properties by pouring the mass
from one container into another from a height of about two feet (in
near-dark). Everything else I've tested that way lit up like a child's
"spark whizzer". The 304 medium was stone, cold, dark.

LLoyd
Post by Richard J Kinch
Post by Lloyd E. Sponenburgh
It was a milling media
manufacturer from whom I purchased the 304 balls who lists it as the only
non-sparking medium he sells.
Is there a standard for "non-sparking"? Something like, I don't know, a
standardized hammer-drop repeated a zillion times in a
flammable-atmosphere
Post by Richard J Kinch
chamber? Or various velocity drops onto black powder?
Lost Yankee
2003-11-14 17:36:24 UTC
Permalink
Post by Lloyd E. Sponenburgh
Richard,
To be honest, I trusted the manufacturer without reservation, and without
further followup. They've been _very_ leery of selling us milling media
because of its intended use. They more or less coaxed us into buying the
304SS media, saying it was all they were comfortable to sell.
I did an impromptu and ersatz 'test' of the properties by pouring the mass
from one container into another from a height of about two feet (in
near-dark). Everything else I've tested that way lit up like a child's
"spark whizzer". The 304 medium was stone, cold, dark.
LLoyd
Post by Richard J Kinch
Post by Lloyd E. Sponenburgh
It was a milling media
manufacturer from whom I purchased the 304 balls who lists it as the
only
Post by Richard J Kinch
Post by Lloyd E. Sponenburgh
non-sparking medium he sells.
Is there a standard for "non-sparking"? Something like, I don't know, a
standardized hammer-drop repeated a zillion times in a
flammable-atmosphere
Post by Richard J Kinch
chamber? Or various velocity drops onto black powder?
Testing alloys for sparks using a grinding wheel has several
disadvantages for your intended use. As a certified welder of various
alloys I often have to estimate an unknown alloy. The problem arises
from contaminated grinder wheels. What a "Smith" is looking for in
this spark test is color and fracturing of the sparking paricles
mostly to determind types of cast iron, not very valuable in pyro.
Taking a technique from one field of study and using that data in
another field can be ... interesting from a distance.
It is my experience in target shooting that the impact at high
velocity shatters rocks, concerte, causing this material to impact
it's like parts, creating the sparks.
In a simple pryo. world, iron should be avoided. I believe any metal
in a mill will contaminate the mill / media be it lead, brass, even
using several jars, each comp. will have some, be it very small,
amount of the media... so the issue comes down to the level of risk.
In the real world many welders fail to properly judge 300 series SS
after pressing, tooling, cutting, ... because the small amount of
imparted iron from these blades, dies, ... will now show magnetic
atraction, even using a chrome plated putty knife to remove welding
spatter will create rust on the SS after time.
Lloyd's test of pouring like media togather closly simulates the mill
environment, far better than a new grinding wheel made of what? Al
oxides? Resin? Silica?
One other issue with SS is the question of what alloy renains after
years of use? This is another level of risk issue and on a one to ten
scale, I'll have another beer.
If media did not impart material to the jar and comp. your balls would
never wear out. Sorry, I couldn't resist that!
Old Dog
2003-11-14 21:57:38 UTC
Permalink
I don't want to over-simplify, but the issue really comes down to a matter of
degree, doesn't it? While some materials do exhibit piezo effects (think I got
that right), actually generating an electric charge on impact, I believe a much
larger number of materials can be made to spark if there are strong internal
bonds that can be broken by a sharp impact that causes small pieces to detach.
What happens is a simple transfer of a lot of energy to a very small mass that
then releases that excess energy as heat; in the case of flammable materials
there can be secondary effects as the material combines with oxygen in the air.
If enough energy is imparted by the splitting-off process, the particles can
also possess enough energy to undergo further reactions, as in the splitting of
sparks in some ferrous materials.

So there are a very large number of materials that *can* make sparks under the
right conditions. The question is whether they will under conditions of normal
use.

-Rich
Richard J Kinch
2003-11-17 04:27:20 UTC
Permalink
Post by Old Dog
What happens is a simple transfer of a lot of energy to a very small
mass that then releases that excess energy as heat; in the case of
flammable materials there can be secondary effects as the material
combines with oxygen in the air.
This seems a rather overblown characterization of the process, and
confusion of the term "flammable". On a grinding wheel, very tiny
particles are simultaneously rubbed off and heated to free-air ignition
temperature simply by the friction of impact with the grinding wheel. The
smaller the particle, the lower the temperature needed (pyrophoricity).
One would naturally postulate that the same process happens in a hammer-
drop or in a tumbling mill, albeit less energetically. This is why a
grinding-wheel test seems to me to be appropriate for evaluating "sparking"
verus "non-sparking".
Post by Old Dog
If enough energy is imparted by the
splitting-off process, the particles can also possess enough energy to
undergo further reactions, as in the splitting of sparks in some
ferrous materials.
I don't believe that. The terminal sparks occur long after the particle
has left the original event at the grinder wheel. It appears to be more
like a "senko hanabi" or "dragon's egg" effect, where the composition of
the molten mass is changed by the selective combustion, until some
component is used up, at which time a different type of combustion abruptly
occurs.
Old Dog
2003-11-17 05:16:25 UTC
Permalink
Post by Richard J Kinch
Post by Old Dog
What happens is a simple transfer of a lot of energy to a very small
mass that then releases that excess energy as heat; in the case of
flammable materials there can be secondary effects as the material
combines with oxygen in the air.
This seems a rather overblown characterization of the process, and
confusion of the term "flammable". On a grinding wheel, very tiny
particles are simultaneously rubbed off and heated to free-air ignition
temperature simply by the friction of impact with the grinding wheel. The
smaller the particle, the lower the temperature needed (pyrophoricity).
One would naturally postulate that the same process happens in a hammer-
drop or in a tumbling mill, albeit less energetically. This is why a
grinding-wheel test seems to me to be appropriate for evaluating "sparking"
verus "non-sparking".
Flammable - "Easily set on fire" (Webster). Confusion? Are you saying you don't
believe that materials incapable of combination with oxygen (inflammable) can be
heated by impact (or by friction) to a temperature high enough to cause light
emmission? Or that any material that gets hot enough to glow is burning?

Friction = impact? Not in pyrotechnics, at least not according to Shimizu.
Different property - different tests. One comp can be more friction-sensitive
than another comp, and at the same time be less impact-sensitive.
Post by Richard J Kinch
Post by Old Dog
If enough energy is imparted by the
splitting-off process, the particles can also possess enough energy to
undergo further reactions, as in the splitting of sparks in some
ferrous materials.
I don't believe that. The terminal sparks occur long after the particle
has left the original event at the grinder wheel. It appears to be more
like a "senko hanabi" or "dragon's egg" effect, where the composition of
the molten mass is changed by the selective combustion, until some
component is used up, at which time a different type of combustion abruptly
occurs.
In what way is this substantially different from what I just said? Terminal
sparks come from some chemical change in the material that does not occur
without an initial transfer of energy. "A different type of combustion" is not
"undergo[ing] further reactions"? What is it you don't believe?

-Rich
Don Thompson
2003-11-18 02:19:34 UTC
Permalink
Post by Old Dog
Post by Richard J Kinch
Post by Old Dog
What happens is a simple transfer of a lot of energy to a very small
mass that then releases that excess energy as heat; in the case of
flammable materials there can be secondary effects as the material
combines with oxygen in the air.
This seems a rather overblown characterization of the process, and
confusion of the term "flammable". On a grinding wheel, very tiny
particles are simultaneously rubbed off and heated to free-air ignition
temperature simply by the friction of impact with the grinding wheel.
The
Post by Old Dog
Post by Richard J Kinch
smaller the particle, the lower the temperature needed (pyrophoricity).
One would naturally postulate that the same process happens in a hammer-
drop or in a tumbling mill, albeit less energetically. This is why a
grinding-wheel test seems to me to be appropriate for evaluating "sparking"
verus "non-sparking".
Flammable - "Easily set on fire" (Webster). Confusion? Are you saying you don't
believe that materials incapable of combination with oxygen (inflammable) can be
heated by impact (or by friction) to a temperature high enough to cause light
emmission? Or that any material that gets hot enough to glow is burning?
Friction = impact? Not in pyrotechnics,
Nor in Physics.

at least not according to Shimizu.
Post by Old Dog
Different property - different tests. One comp can be more
friction-sensitive
Post by Old Dog
than another comp, and at the same time be less impact-sensitive.
Post by Richard J Kinch
Post by Old Dog
If enough energy is imparted by the
splitting-off process, the particles can also possess enough energy to
undergo further reactions, as in the splitting of sparks in some
ferrous materials.
I don't believe that. The terminal sparks occur long after the particle
has left the original event at the grinder wheel. It appears to be more
like a "senko hanabi" or "dragon's egg" effect, where the composition of
the molten mass is changed by the selective combustion, until some
component is used up, at which time a different type of combustion abruptly
occurs.
In what way is this substantially different from what I just said? Terminal
sparks come from some chemical change in the material that does not occur
without an initial transfer of energy. "A different type of combustion" is not
"undergo[ing] further reactions"? What is it you don't believe?
"terminal sparks" are the result of the particle breaking up while burning.
If it were not for their initial ignition and the subsequent -increase- of
their temperature due to their rapid progress and -increased- exposure to
oxygen [thus the faster reaction] they would not further break up in flight
yeilding "terminal sparks". So. Seems that your initial proposal, that
energy is required to start the ball rolling, can't NOT be believed.
Post by Old Dog
-Rich
--
Don Thompson

Ex ROMAD
Richard J Kinch
2003-11-18 07:55:44 UTC
Permalink
Post by Don Thompson
"terminal sparks" are the result of the particle breaking up while burning.
No, that's just a redundant description. The cause is something else.
Some alloys do this, some don't.
Joe 123
2003-11-18 04:16:06 UTC
Permalink
Just a thought but if we were to purge our jars with nitrogen of someother
inert gas than we could use rusty iron balls for milling BP.

Would not work for flash because the metals them self are so reactive that
when they are milled and a fresh unoxidized surface is created it will react
very quickly with an oxidizer. But BP should be OK. Charcoal is not that
way. If the small fragments produced dont have O2 to react with than maybe

OK im reaching but just a thought. Someone brave can try this one. :)

Joe
Post by Old Dog
Post by Richard J Kinch
Post by Old Dog
What happens is a simple transfer of a lot of energy to a very small
mass that then releases that excess energy as heat; in the case of
flammable materials there can be secondary effects as the material
combines with oxygen in the air.
This seems a rather overblown characterization of the process, and
confusion of the term "flammable". On a grinding wheel, very tiny
particles are simultaneously rubbed off and heated to free-air ignition
temperature simply by the friction of impact with the grinding wheel.
The
Post by Old Dog
Post by Richard J Kinch
smaller the particle, the lower the temperature needed (pyrophoricity).
One would naturally postulate that the same process happens in a hammer-
drop or in a tumbling mill, albeit less energetically. This is why a
grinding-wheel test seems to me to be appropriate for evaluating "sparking"
verus "non-sparking".
Flammable - "Easily set on fire" (Webster). Confusion? Are you saying you don't
believe that materials incapable of combination with oxygen (inflammable) can be
heated by impact (or by friction) to a temperature high enough to cause light
emmission? Or that any material that gets hot enough to glow is burning?
Friction = impact? Not in pyrotechnics, at least not according to Shimizu.
Different property - different tests. One comp can be more
friction-sensitive
Post by Old Dog
than another comp, and at the same time be less impact-sensitive.
Post by Richard J Kinch
Post by Old Dog
If enough energy is imparted by the
splitting-off process, the particles can also possess enough energy to
undergo further reactions, as in the splitting of sparks in some
ferrous materials.
I don't believe that. The terminal sparks occur long after the particle
has left the original event at the grinder wheel. It appears to be more
like a "senko hanabi" or "dragon's egg" effect, where the composition of
the molten mass is changed by the selective combustion, until some
component is used up, at which time a different type of combustion abruptly
occurs.
In what way is this substantially different from what I just said? Terminal
sparks come from some chemical change in the material that does not occur
without an initial transfer of energy. "A different type of combustion" is not
"undergo[ing] further reactions"? What is it you don't believe?
-Rich
Old Dog
2003-11-18 04:42:25 UTC
Permalink
Post by Joe 123
Just a thought but if we were to purge our jars with nitrogen of someother
inert gas than we could use rusty iron balls for milling BP.
What difference would it make? BP isn't dependent on atmospheric oxygen for
anything. Ergo, purging with an inert gas would be nothing but a waste of inert
gas.

-Rich
Don Thompson
2003-11-18 05:36:21 UTC
Permalink
Nope. Black powder contains its own oxygen source. BP should NOT "be OK".
--
Don Thompson

Ex ROMAD
Post by Joe 123
Just a thought but if we were to purge our jars with nitrogen of someother
inert gas than we could use rusty iron balls for milling BP.
Would not work for flash because the metals them self are so reactive that
when they are milled and a fresh unoxidized surface is created it will react
very quickly with an oxidizer. But BP should be OK. Charcoal is not that
way. If the small fragments produced dont have O2 to react with than maybe
OK im reaching but just a thought. Someone brave can try this one. :)
Joe
Post by Old Dog
Post by Richard J Kinch
Post by Old Dog
What happens is a simple transfer of a lot of energy to a very small
mass that then releases that excess energy as heat; in the case of
flammable materials there can be secondary effects as the material
combines with oxygen in the air.
This seems a rather overblown characterization of the process, and
confusion of the term "flammable". On a grinding wheel, very tiny
particles are simultaneously rubbed off and heated to free-air ignition
temperature simply by the friction of impact with the grinding wheel.
The
Post by Old Dog
Post by Richard J Kinch
smaller the particle, the lower the temperature needed
(pyrophoricity).
Post by Joe 123
Post by Old Dog
Post by Richard J Kinch
One would naturally postulate that the same process happens in a hammer-
drop or in a tumbling mill, albeit less energetically. This is why a
grinding-wheel test seems to me to be appropriate for evaluating
"sparking"
Post by Old Dog
Post by Richard J Kinch
verus "non-sparking".
Flammable - "Easily set on fire" (Webster). Confusion? Are you saying
you
Post by Joe 123
don't
Post by Old Dog
believe that materials incapable of combination with oxygen
(inflammable)
Post by Joe 123
can be
Post by Old Dog
heated by impact (or by friction) to a temperature high enough to cause
light
Post by Old Dog
emmission? Or that any material that gets hot enough to glow is burning?
Friction = impact? Not in pyrotechnics, at least not according to Shimizu.
Different property - different tests. One comp can be more
friction-sensitive
Post by Old Dog
than another comp, and at the same time be less impact-sensitive.
Post by Richard J Kinch
Post by Old Dog
If enough energy is imparted by the
splitting-off process, the particles can also possess enough energy to
undergo further reactions, as in the splitting of sparks in some
ferrous materials.
I don't believe that. The terminal sparks occur long after the particle
has left the original event at the grinder wheel. It appears to be more
like a "senko hanabi" or "dragon's egg" effect, where the composition of
the molten mass is changed by the selective combustion, until some
component is used up, at which time a different type of combustion
abruptly
Post by Old Dog
Post by Richard J Kinch
occurs.
In what way is this substantially different from what I just said?
Terminal
Post by Old Dog
sparks come from some chemical change in the material that does not occur
without an initial transfer of energy. "A different type of combustion"
is
Post by Joe 123
not
Post by Old Dog
"undergo[ing] further reactions"? What is it you don't believe?
-Rich
Alan Yates
2003-11-18 06:04:38 UTC
Permalink
It would only be of value when processing something horribably
pyrophoric like Zirconium, and once you removed the blanket gas after
milling the warm metal powder would just about explode in your face.

Obviously no inert atmosphere will save a mixture that can burn in a
vacuum because it has its own oxidiser built in!

I get your point about it perhaps preventing an air-burning metal spark
from starting in the first place, but would you take the risk? Even
worse is that no experiment can prove you didn't just get lucky, some
poor bastard using your technique 10 years from now might be blown up.

I would think piezo and triboelectric effects are just as likely to
ignite a live composition. $deity knows what piezoelectric properties
some random oxide/sulfide/carbonate scale on your rusty media has?
Post by Joe 123
Just a thought but if we were to purge our jars with nitrogen of someother
inert gas than we could use rusty iron balls for milling BP.
Would not work for flash because the metals them self are so reactive that
when they are milled and a fresh unoxidized surface is created it will react
very quickly with an oxidizer. But BP should be OK. Charcoal is not that
way. If the small fragments produced dont have O2 to react with than maybe
OK im reaching but just a thought. Someone brave can try this one. :)
Joe
Post by Old Dog
Post by Richard J Kinch
Post by Old Dog
What happens is a simple transfer of a lot of energy to a very small
mass that then releases that excess energy as heat; in the case of
flammable materials there can be secondary effects as the material
combines with oxygen in the air.
This seems a rather overblown characterization of the process, and
confusion of the term "flammable". On a grinding wheel, very tiny
particles are simultaneously rubbed off and heated to free-air ignition
temperature simply by the friction of impact with the grinding wheel.
The
Post by Old Dog
Post by Richard J Kinch
smaller the particle, the lower the temperature needed (pyrophoricity).
One would naturally postulate that the same process happens in a hammer-
drop or in a tumbling mill, albeit less energetically. This is why a
grinding-wheel test seems to me to be appropriate for evaluating
"sparking"
Post by Old Dog
Post by Richard J Kinch
verus "non-sparking".
Flammable - "Easily set on fire" (Webster). Confusion? Are you saying you
don't
Post by Old Dog
believe that materials incapable of combination with oxygen (inflammable)
can be
Post by Old Dog
heated by impact (or by friction) to a temperature high enough to cause
light
Post by Old Dog
emmission? Or that any material that gets hot enough to glow is burning?
Friction = impact? Not in pyrotechnics, at least not according to Shimizu.
Different property - different tests. One comp can be more
friction-sensitive
Post by Old Dog
than another comp, and at the same time be less impact-sensitive.
Post by Richard J Kinch
Post by Old Dog
If enough energy is imparted by the
splitting-off process, the particles can also possess enough energy to
undergo further reactions, as in the splitting of sparks in some
ferrous materials.
I don't believe that. The terminal sparks occur long after the particle
has left the original event at the grinder wheel. It appears to be more
like a "senko hanabi" or "dragon's egg" effect, where the composition of
the molten mass is changed by the selective combustion, until some
component is used up, at which time a different type of combustion
abruptly
Post by Old Dog
Post by Richard J Kinch
occurs.
In what way is this substantially different from what I just said?
Terminal
Post by Old Dog
sparks come from some chemical change in the material that does not occur
without an initial transfer of energy. "A different type of combustion" is
not
Post by Old Dog
"undergo[ing] further reactions"? What is it you don't believe?
-Rich
--
Alan Yates
http://www.vk2zay.net/
The Moon is Waning Crescent (39% of Full)
Old Dog
2003-11-18 17:28:25 UTC
Permalink
Post by Alan Yates
I get your point about it perhaps preventing an air-burning metal spark
from starting in the first place, but would you take the risk?
I don't. Well-filled and sealed shells contain virtually no oxygen, and they
still work just fine. or you might leave a bit of air space in a salute, or add
something that "fluffs" it, but that is just to give it room to expand to ignite
the maximum amount of contents before bursting the case. Any "trapped" oxygen
has very little if any effect on the results.

If you put a BP or other complete fuel/oxidizer mixture in a mill and add
anything that might initiate a reaction, the presence or absence of a little air
won't mean a thing.

-Rich
Alan Yates
2003-11-19 03:51:35 UTC
Permalink
Post by Old Dog
Post by Alan Yates
I get your point about it perhaps preventing an air-burning metal spark
from starting in the first place, but would you take the risk?
I don't. Well-filled and sealed shells contain virtually no oxygen, and they
still work just fine. or you might leave a bit of air space in a salute, or add
something that "fluffs" it, but that is just to give it room to expand to ignite
the maximum amount of contents before bursting the case. Any "trapped" oxygen
has very little if any effect on the results.
If you put a BP or other complete fuel/oxidizer mixture in a mill and add
anything that might initiate a reaction, the presence or absence of a little air
won't mean a thing.
-Rich
I guess you missed my previous paragraph:

"Obviously no inert atmosphere will save a mixture that can burn in a
vacuum because it has its own oxidiser built in!"

I think you missed Joe's point, even if in practice it doesn't matter is
the super heated particle of metal/scale is burning or just wacking into
some BP at a sufficiently high temp to initiate it.
--
Alan Yates
http://www.vk2zay.net/
The Moon is Waning Crescent (29% of Full)
Lloyd E. Sponenburgh
2003-11-19 12:36:26 UTC
Permalink
Just an aside, Alan --

Black powder does not burn well in a vacuum.

LLoyd
Post by Alan Yates
"Obviously no inert atmosphere will save a mixture that can burn in a
vacuum because it has its own oxidiser built in!"
Alan Yates
2003-11-19 18:54:39 UTC
Permalink
Post by Lloyd E. Sponenburgh
Just an aside, Alan --
Black powder does not burn well in a vacuum.
LLoyd
Indeed, I've read that may common compositions don't work well in a hard
vacuum, they will burn, but not as fast. My guess would be that the
surrounding gas plays an important part in passing the heat around and
limiting the expansive cooling, is this the main cause of the usual
pressure/reaction rate trend?
--
Alan Yates
http://www.vk2zay.net/
The Moon is Waning Crescent (23% of Full)
Richard J Kinch
2003-11-18 07:53:22 UTC
Permalink
Post by Old Dog
Flammable - "Easily set on fire" (Webster).
You evidently harbor opposite meanings for common words, so I can't hope to
correct your other errors.
Post by Old Dog
Friction = impact?
I said "friction of impact". You can't even quote correctly.
Post by Old Dog
In what way is this substantially different from what I just said?
Terminal sparks are characteristic of the alloy, and have nothing to do, as
you incorrectly stated, with how the sparks were first ignited.
Old Dog
2003-11-18 17:53:28 UTC
Permalink
Post by Richard J Kinch
Post by Old Dog
Flammable - "Easily set on fire" (Webster).
You evidently harbor opposite meanings for common words, so I can't hope to
correct your other errors.
You don't like dictionary definitions?
Post by Richard J Kinch
Post by Old Dog
Friction = impact?
I said "friction of impact". You can't even quote correctly.
"Friction of impact" is an oxymoron. "Friction" sensitivity in pyro is
determined by a rotory test - the grinding motion typical of a mortar and
pestle. "Impact" or shock sensitivity is determined by a hammer drop test. They
are two entirely different things. Shimizu uses the examples of certain whistle
mixtures which are sensitive to shock but not friction; and of red thermit,
which is insensitive to impact, but is rather easily ignited by friction.
Post by Richard J Kinch
Post by Old Dog
In what way is this substantially different from what I just said?
Terminal sparks are characteristic of the alloy, and have nothing to do, as
you incorrectly stated, with how the sparks were first ignited.
What I said was that heat can be generated by the impact and consequent breaking
of bonds within the material. That may or may not be sufficient to initiate
oxidation of the material, depending on what it is composed of, but it could
still heat the substance to a temperature high enough to initiate reaction of
comps it subsequently contacts. "Friction" is neither necessary nor appropriate
as an explanation for the effects of impact, and the use of a device which
generates friction as a test of the effects of impact goes against both physical
principle and actual practice.

-Rich
Richard J Kinch
2003-11-19 14:38:05 UTC
Permalink
Post by Old Dog
Post by Richard J Kinch
Post by Old Dog
Flammable - "Easily set on fire" (Webster).
You evidently harbor opposite meanings for common words, so I can't
hope to correct your other errors.
You don't like dictionary definitions?
Your definition is opposite the correct one, your citation is meaningless,
and your latest response is pointless. Vocabulary matters.

Don't bother with the pretentious quoting of Shimizu. He's more of an
alchemist than a physicist.
Post by Old Dog
the use of a device which
generates friction as a test of the effects of impact goes against both
physical principle and actual practice.
The question is whether a material is "sparking" or not, by any means,
including knocking on a cretinous skull. Nobody seems to have a specific
idea of what constitutes "sparking", but given the consequences of getting
it wrong, one can only demand the strictest (most broadly positive) tests
possible, since there is plenty of rubbing and impact action inside a ball
mill.

I defy you to cite a material that is non-sparking on a grinding wheel but
sparking on impact tests, for any prudent specification of "sparking".
Old Dog
2003-11-19 15:43:08 UTC
Permalink
Post by Richard J Kinch
Post by Old Dog
Post by Richard J Kinch
Post by Old Dog
Flammable - "Easily set on fire" (Webster).
You evidently harbor opposite meanings for common words, so I can't
hope to correct your other errors.
You don't like dictionary definitions?
Your definition is opposite the correct one, your citation is meaningless,
and your latest response is pointless. Vocabulary matters.
I guess I'd better throw away the Webster's dictionary.
Post by Richard J Kinch
Don't bother with the pretentious quoting of Shimizu. He's more of an
alchemist than a physicist.
I don't recall Shimizu claiming to be a physicist, or mentioning anything about
elixers or transmutation. Must have missed that chapter. What he did primarily
was relate the actual practices of pyrotechnists in the Far East.
Post by Richard J Kinch
Post by Old Dog
the use of a device which
generates friction as a test of the effects of impact goes against both
physical principle and actual practice.
The question is whether a material is "sparking" or not, by any means,
including knocking on a cretinous skull. Nobody seems to have a specific
idea of what constitutes "sparking", but given the consequences of getting
it wrong, one can only demand the strictest (most broadly positive) tests
possible, since there is plenty of rubbing and impact action inside a ball
mill.
I defy you to cite a material that is non-sparking on a grinding wheel but
sparking on impact tests, for any prudent specification of "sparking".
As I recall, we were concerned with the opposite effect - whether sparking on a
grinding wheel is a reliable indication of the probability of a material
sparking on impact in a mill. Since to the best of my knowledge grinding wheels
are not used to test pyrotechnic materials or media, such a test would have
limited value. It would be rather similar to giving the equivalent of a bathtub
of artificially-sweetened soda to a rat every day and claiming it is dangerous
when the rat develops health problems. Obviously no one can drink a bathtub full
of soda every day; nor would anyone dream of operating a grinding wheel around
mixed pyrotechnic comps. Now, if you were to break up your grinding wheel and
put the bits into your mill with some hard metal media, I predict you might have
problems. I would hesitate to use a mixture of dissimilar very hard media in a
mill, especially corundum with steel.

I have already given examples of materials that ignite easily by friction but
not by impact, and vice versa. That's real world stuff - not theory. You are the
one who said "friction of impact" - I challenge you to cite a reference, since
mine are evidently inadequate in your eyes.

This all begs the question - would you let a physicist loose in your pyro shop?

-Rich
Lloyd E. Sponenburgh
2003-11-19 18:07:28 UTC
Permalink
Post by Old Dog
Obviously no one can drink a bathtub full
of soda every day; nor would anyone dream of operating a grinding wheel around
mixed pyrotechnic comps.
Hmmm.... welllll, see... I _had_ this employee who decided to bring a
grinder, on an extension cord, into a pressing area to fix a tool. That,
with five or six trays (about 60lb) of already-pressed comets on the bench!
He actually started grinding before another employee noticed what he was
about. (actually, it was easy to see the four-foot plume of sparks!) --
"But, but, I was pointing the wheel away from the trays!"

So I guess it's possible that _someone_ might break up a grinding wheel, and
add it to their milling jar.

<<G>>
LLoyd
Joe 123
2003-11-19 19:25:13 UTC
Permalink
Heres my interpretation of "friction of impact":

two rusty balls collide. the impact causes the rusty surface to collapse
creating friction in the material itself. basicly the rust particles create
friction as they are being crushed and as we all know rust is very brittle.
and abrasive.

In a ball mill, balls are rolling around colliding with each other pounding
the heck out of anything that gets inbetween the colliding balls. I would
think that (and im just hypothesising here) to create a spark (under these
conditions) it would be necessary to have a inperfect surface (Which could
be said for any surface). Like a file. Rust is a major inperfection that
will cause much friction and thus heat. In my opinion this is why carbon
steel, chrome steel etc is not good for making BP with. It is almost
impossible to prevent them from rusting. My chrome steel balls rust just by
looking at them!


Lets take two balls of unknown material. Make one ball unmovable (in a
vise) and mount the other one on the head of a drill (whatever it takes).
Turn the drill on and attemp to grind the two balls together. I think we
can all agree that if the balls are rusty then they will spark quikly and
easily. If the balls are completely smooth and uncorroded then you may get
some sparks after a little while (as the surface heats up) but very doubt
full if you get them immediately and will also depend on the material.
BUT then again it only takkes one spark!!!!!


If my drill test is indicative of sparking or not sparking than you will
have a hard time making 3xx SS spark. Throw a little grinding wheel
material in there and thats a diff story. Brass? Maybe the friction
coefficients of metal on metal would be indicative of the ability to spark.
I will look some up and see. If so than steel should be significantly
greater than 3xx SS and lead.

Joe
Post by Old Dog
Post by Richard J Kinch
Post by Old Dog
Post by Richard J Kinch
Post by Old Dog
Flammable - "Easily set on fire" (Webster).
You evidently harbor opposite meanings for common words, so I can't
hope to correct your other errors.
You don't like dictionary definitions?
Your definition is opposite the correct one, your citation is meaningless,
and your latest response is pointless. Vocabulary matters.
I guess I'd better throw away the Webster's dictionary.
Post by Richard J Kinch
Don't bother with the pretentious quoting of Shimizu. He's more of an
alchemist than a physicist.
I don't recall Shimizu claiming to be a physicist, or mentioning anything about
elixers or transmutation. Must have missed that chapter. What he did primarily
was relate the actual practices of pyrotechnists in the Far East.
Post by Richard J Kinch
Post by Old Dog
the use of a device which
generates friction as a test of the effects of impact goes against both
physical principle and actual practice.
The question is whether a material is "sparking" or not, by any means,
including knocking on a cretinous skull. Nobody seems to have a specific
idea of what constitutes "sparking", but given the consequences of getting
it wrong, one can only demand the strictest (most broadly positive) tests
possible, since there is plenty of rubbing and impact action inside a ball
mill.
I defy you to cite a material that is non-sparking on a grinding wheel but
sparking on impact tests, for any prudent specification of "sparking".
As I recall, we were concerned with the opposite effect - whether sparking on a
grinding wheel is a reliable indication of the probability of a material
sparking on impact in a mill. Since to the best of my knowledge grinding wheels
are not used to test pyrotechnic materials or media, such a test would have
limited value. It would be rather similar to giving the equivalent of a bathtub
of artificially-sweetened soda to a rat every day and claiming it is dangerous
when the rat develops health problems. Obviously no one can drink a bathtub full
of soda every day; nor would anyone dream of operating a grinding wheel around
mixed pyrotechnic comps. Now, if you were to break up your grinding wheel and
put the bits into your mill with some hard metal media, I predict you might have
problems. I would hesitate to use a mixture of dissimilar very hard media in a
mill, especially corundum with steel.
I have already given examples of materials that ignite easily by friction but
not by impact, and vice versa. That's real world stuff - not theory. You are the
one who said "friction of impact" - I challenge you to cite a reference, since
mine are evidently inadequate in your eyes.
This all begs the question - would you let a physicist loose in your pyro shop?
-Rich
r***@bestweb.net
2003-11-20 16:37:14 UTC
Permalink
Post by Joe 123
two rusty balls collide. the impact causes the rusty surface to
collapse creating friction in the material itself. basicly the
rust particles create friction as they are being crushed
Interesting!

I've had a tough time defining "friction" to my Principles of Science
students. The definition I've settled on is "a phenomenon wherein something
in contact with something else produces force that counteracts motion of one
relative to the other parallel to the plane in which they touch". I think
that even sort-of covers fluid drag, and would cover the resistance at the
atomic level to deformation as joe123 points out above.

Robert
Richard J Kinch
2003-11-21 05:53:37 UTC
Permalink
Post by Old Dog
I guess I'd better throw away the Webster's dictionary.
That you think "Webster's dictionary" means anything today shows your
ignorance of research and critical thinking. The problem at hand is one of
statistical detection, which in turn requires prequisite knowledge of
theories of sampling and error, which I suspect is as absent as your
etymological perspicacity.

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