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PYRO5.TXT - Casings and General Construction, Part 2
This is part of a series of files on pyrotechnics and explosives. It's serious
stuff, and can be really dangerous if you don't treat it seriously. For you
kids out there who watch too many cartoons, remember that if a part of your
body gets blown away in the REAL world, it STAYS blown away. If you can't
treat this stuff with respect, don't screw around with it.
Each file will start with a set of safety rules. Don't skip over them. Read
'em and MEMORIZE 'em!! At the beginning, there will be a set of general rules
that always apply. Then there will be some things that you HAVE TO KNOW about
the materials you will be using and making this time. Read it thoroughly
before starting anything.
Pyrotechnic preparations and explosives are, by their very nature, unstable,
and subject to ignition by explosion or heat, shock, or friction. A clear
understanding of their dangerous properties and due care in the handling of
ingredients or finished products is necessary if accidents are to be avoided.
Always observe all possible precautions, particularly the following:
1. Mix only small batches at one time. This means a few grams, or at
most, an ounce or so. Don't go for big mixes -- they only make for
bigger accidents. The power of an explosive cubes itself with
every ounce. (9 Ounces is 729 times as powerful as one ounce.)
2. When weighing chemicals, use a clean piece of paper on the scale
pan for each item. Then discard the used paper into a bucket of
water before weighing the next ingredient.
3. Be a safe worker. Dispose of any chemicals spilled on the
workbench or equipment between weighings. Don't keep open
containers of chemicals on your table, since accidental spillage
or mixing may occur. When finished with a container, close it, and
replace it on the storage shelf. Use only clean equipment.
4. Where chemicals are to be ground, grind them separately, NEVER
TOGETHER. Thoroughly wash and clean equipment before grinding
another ingredient.
5. Mixing of batches should be done outdoors, away from flammable
structures, such as buildings, barns, garages, etc. Mixes should
also be made in NON METALLIC containers to avoid sparks. Glass
also should not be used since it will shatter in case of an
accident. Handy small containers can be made by cutting off the
top of a plastic bottle three or four inches from the bottom. Some
mixes may most conveniently be made by placing the ingredients in
a plastic bottle and rolling around until the mixture is uniform.
In all cases, point the open end of the container away from
yourself. Never hold your body or face over the container. Any
stirring should be done with a wooden paddle or stick to avoid
sparks or static.
Powdered or ground materials may also be mixed by placing them on
a large sheet of paper on a flat surface and then rolling them
across the sheet by lifting the sides and corners one at a time.
6. Never ram or tamp mixes into paper or cardboard tubes. Pour the
material in and gently tap or shake the tube to settle the
contents down.
7. Store ingredients and finished mixes where they will not be a fire
hazard away from heat and flame. Finished preparations may be
stored in plastic bottles which will not shatter in case of an
accident. Since many of the ingredients and mixes are poisonous,
they should be stored out of reach of children or pets, preferably
locked away.
8. Be sure threads of screw top containers and caps are thoroughly
cleaned. This applies also to containers with stoppers of rubber
or cork and to all other types of closures. Traces of mixture
caught between the container and closure may be ignited by the
friction of opening or closing the container. Throughout any
procedure, WORK WITH CLEAN CONDITIONS.
9. ALWAYS WEAR A FACE SHIELD OR AT LEAST SHATTERPROOF SAFETY GLASSES.
Any careful worker does when handling dangerous materials. Be sure
lenses and frames are not flammable.
10. Always wear a dust respirator when handling chemicals in dust
form. These small particles gather in your lungs and stay there.
They may cause serious illnesses later on in life.
11. Always wear gloves when working with chemicals.
12. Always wear a waterproof lab apron.
13. If you must work indoors, have a good ventilation system.
14. Never smoke anywhere near where you are working.
15. Make sure there are NO open flames present, and NO MOTORS (they
produce sparks inside.) No hot water heaters, furnaces, or pilot
lights in stoves!! Sparks have been known to very readily explode
dust floating in the air.
16. ALWAYS work with someone. Two heads are better than one.
17. Have a source of water READILY available. (Fire extinguisher,
hose, etc.)
18. Never, under any circumstances, use any metal to load chemicals or
put chemicals in. Fireworks with metal casings are worse to handle
than a live hand grenade. Never use any metal container or can.
This includes the very dangerous CO2 cartridges. Many people have
been KILLED because of flying fragments from metal casings. Again,
please do not use metal in any circumstance.
19. Always be thoroughly familiar with the chemicals you are using.
Some information will be included in each file, but look for
whatever extra information you can. Materials that were once
thought to be safe can later be found out to be dangerous stuff.
20. Wash your hands and face thoroughly after using chemicals. Don't
forget to wash your EARS AND YOUR NOSE.
21. If any device you've built fails to work, leave it alone. After a
half hour or so, you may try to bury it, but never try to unload
or reuse any dud.
22. If dust particles start to form in the air, stop what you are
doing and leave until it settles.
23. Read the entire file before trying to do anything.
24. NEVER strike any mixture containing Chlorates, Nitrates,
Perchlorates, Permanganates, Bichromates, or powdered metals don't
drop them, or even handle them roughly.
These rules may all look like a lot of silly nonsense, but let's look at one
example. When the move "The Wizard of OZ" was made, the actress who played the
good witch was severely burned when one of the exploding special effects got
out of hand. The actress who played the bad witch got really messed up by the
green coloring used on her face, and the original actor who played the Tin Man
got his lungs destroyed by the aluminum dust used to color his face. The actor
we know of as the tin man was actually a replacement. The point is, these
chemicals were being used under the direction of people a lot more knowlegable
of chemicals than you are, and terrible accidents still happened. Don't take
this stuff lightly.
***********************************
We'll only be using a few chemicals this time. Here's the list:
Potassium Perchlorate KClO
4
A poisonous oxidizer, usually white but sometimes a slightly pink powder. Much
more stable than its Chlorate brother, it can often be substituted for it to
make a mixture safer.
Sulfur S
A yellow element that acts as a reducing agent. It burns at 250 degrees,
giving off choking fumes. Purchase the yellow, finely powdered form only.
Other forms are useless without a lot of extra and otherwise unecessary effort
to powder it.
Aluminum Powder Al
An element added for brilliance and to speed up the burning rate of a mixture.
A silvery powder, it often contains small amounts of finer dust that can be
hazardous if stirred up in the air and inhaled. Not nearly as dangerous or as
flammable as when in dust form, but still best to use with some caution.
Sodium Salicylate HOC H COONa
6 4
A white powder that functions as a reducing agent. Not nearly as effective as
other more common reducing agents, so used only when it gives a special
advantage, as in whistles.
Last time, we were discussing construction techniques for some small salutes.
If you followed the directions carefully, you should have made some reasonably
large noises. These little training salutes looked about the same size as an
M-80 or a Silver Salute, but were nowhere nearly as powerful. This was
intentional. Since these things are thoroughly nasty, we started small, though
tried to keep it from becoming obvious. The larger the volume of space inside
the tube, the more powder we can put in, and the more powerful it will be.
Our training salutes had a 7/16" Inside Diameter, was 1 1/4" long, and had
1/4" end caps that take up space that then can't hold powder. The volume of a
cylinder is V = Pi * R * R * L. R is one half of the inside diameter or 7/32".
L is the tube length, minus the size of the two end caps, or 3/4". Pi is about
3.14. This gives us a volume of .113 square inches.
A Silver salute has an Inside Diameter of 1/2", and an M-80 has an inside
diameter of 9/16". Each of these has a length of 1 1/2", and uses only about a
1/8" end cap, because it used the rock-hard (and shrapnel producing)
pyrotechnic cement we learned of last time, instead of the safer paper plugs
we used. Applying the same formula, the silver salute encloses a volume of
.245 square inches, or more than twice the volume of the training salute. The
M-80 encloses a volume of .310 square inches, which is nearly three times that
of the training salute. When we consider that explosive goes up roughly with
the cube of the amount of explosive, we see that small changes in the
dimensions of a salute can bring a huge change in its power. Of course, if you
read the safety rules printed at the beginning of every one of these files,
you will have figured that out for yourself. If you want to make larger
salutes, and I just know you will, it would be a good idea to not use the
pyrotechnic cement, and just make the casing a bit longer so that the paper
end plugs can be used. You can do what you want, but if you perforate your
eyeballs with splinters of pyrotechnic cement, you'll miss out on reading part
6 of this series, and that would really be a pity.
Cherry Bombs
Cherry bombs have been known to be terribly dangerous, largely because they
tended to be coated with the pyrotechnic cement, often stretched out with
cheaper sawdust. These have blinded a great many people. Their reputation has
been further smeared by street punks who dip cherry bombs in glue, then in
BB's, and let them dry into little anti-personnel grenades for hurling into
rival street gangs. The sheer stupidity of such an action can't be adequately
expressed. We'll talk about a safer way to make and use these items.
Cherry bombs start with two small paper cups, one of which fits inside of the
other, to make a crude ball. The smaller ball gets a hole poked in it, and the
fuse inserted and glued in place. The smaller cup is then filled about halfway
with flash powder, the salute powder mentioned last time works nicely, and the
larger cup is glued in place. In the old days, the ball was then held by the
fuse and dipped in the pyrotechnic cement, and set aside to harden. Instead,
without letting the glue on the two cups dry, cover the entire ball with
several layers of glue-soaked paper strips. Make the strips of brown kraft
paper (supermarket paper bags will do) about 2 inches long and a quarter of an
inch wide. These have to be pressed with your fingers onto the outside of the
cups. The entire thing should end up covered with four or more layers of the
paper strips. It's best to put on all the layers at once. If by any chance
the thing should go off while you're making it, the soggy paper will just
split open, and you'll get burned. But once you let some of the layers dry,
you have a potentialy explosive device and could be damaged severely if it
went off.
Making the little paper cups is an interesting exercise in ingenuity. Since
dealers in pyrotechnic materials will sell these cups for less than ten cents
a set, (for smoke bombs only, of course!!) they're hardly worth the effort to
make yourself. But if your funds are limited, or you just enjoy doing it
yourself, we'll look at a couple of ways to do it.
A piece of soaking-wet brown kraft paper can be formed over a round bulge or
into a rounded impression. If two or three such sheets are formed over or
stuffed into such a shape, with a layer of glue between each, they'll dry into
nice cup shapes. Controlling the shapes of the cups can be tricky, but the
outside cup must be able to fit snugly over the inside one. If it's too small,
it won't fit at all, and if it's too big, it will be hard to glue to its mate.
If you think about it, you don't have to control both the inside and outside
dimensions of each cup. The outside of the small cup has to match the inside
of the large cup. A round pin-shaped form will give good control over the
INSIDE diameter, so a round pin should be used to form the OUTSIDE cups. A cup
shaped indentation allows control over the OUTSIDE diameter, so it should be
used to form the INSIDE cup. The outside diameter of the pin should match the
inside diameter of the indentation.
Matching the two parts is easy if you have access to a machine shop. With a
lathe and some decent measuring tools, you can cut the indentation out of a
block of metal and turn the round head over a piece of metal bar stock.
Machinable plastic will work fine too, but it's just not as nice, and stinks
when you machine it. Iron or steel will rust, changing the carefully machined
dimensions and anyway, they're too much of a hassle to cut. Avoid them. Wood
of any kind will warp, swell, and otherwise deform itself. It won't work.
Aluminum won't rust and is easy to machine. This is best if your machining
experience is limited. Brass is really NICE, though. Being able to machine
your own parts is also nice if you plan to make a dozen or so of each part so
that you can make more than one set of cups at the same time.
Okay, so what do you do if you don't have access to a machine shop? Well, a
little walk through a hardware store will give you the right materials, and
you can even make multiple sets of matched pins and cups, even if they are
really hokey looking. The indentations can be found in the plumbing section,
under plastic pipe. Get the end caps, either in the 1/2 or 3/4 inch size. Note
that the size of pipe is the inside diameter of the pipe, not the outside, so
a 1/2 inch end cap will make decent sized cups. The 3/4 inch cap will make
really hefty sized ones.
There's a little problem with these end caps. Their insides are more
cylindrical than they are cup shaped, and the cups they make won't be
hemispherical. The bottom edges can be filled in a bit with some epoxy glue.
Start with a little, so it doesn't run. When it hardens, add another layer.
Keep adding layers until the inside is rounded.
The pin portion can be hammered from a piece of copper pipe about 3 inches or
so long. If you got a 1/2 inch pipe cap, get a piece of 1/2 inch pipe. Clamp a
1/2 inch steel bar into a vise, slide the pipe down over it. The bar should
leave enough empty pipe above it so that you can hammer the copper into a
curved top. If you can get a ball bearing that will fit into the pipe, so much
the better. Hammer the pipe gently, turning it around the bar as you hammer
it. Don't try to form the pipe too fast, or you'll crack the pipe, and you'll
have to cut the end off and start over. Since it's possible to knock fragments
loose, you should wear safety glasses while you do this. Hammer inward, rather
than downward, as much as you can. The downward hammering will smoosh the
copper downward and outward, causing the outside diameter to increase. We
don't want this. You don't have to hammer the pipe until the top is completely
closed. You can leave a hole about 1/4 inch wide and it won't hurt anything.
Practice this out with 1/2 inch pipe. It's much harder to form 3/4 inch pipe
without cracking it, but it can be done. Once you've got the end formed
properly, the pipe will have expanded enough that it will no longer fit into
the pipe cap. Take the bar out of the vise, set it and the pipe flat on an
anvil, or the anvil-end of the vise, and roll it while hammering it. Keep
checking the fit of the pipe into the cap until it fits easily.
Congratulations! You've just made a forming pin.
Now to make some cherry bomb cups. Cut out three 3 inch squares of kraft paper
and soak them in water. Form one tightly over the forming pin and drop a glob
of white glue over the top. Put the second wet sheet on top, smear it all
around to cover the one side with glue, and form it tightly over the first.
Repeat this with another drop of glue and the third sheet. Now, take some
heavy cord and wrap it around the paper to hold it in place. Set it aside to
dry overnight. If you were careful enough not to get any glue on the outside,
you should be able to unwrap the string when its dry. Then, trim the cup with
a small pair of scissors. You now have one completed outside cup.
The inside cup is a little trickier. Here, you also start with three soaking
wet sheets of kraft paper. Stuff the first into the indentation. Wipe some
glue over one side of the second wet sheet and stuff it in on top of the
first. Then do the same glue-and-stuff caper with the third sheet. Press all
three sheets in tightly again, and set it overnight to dry. When dry, trim
this cup as well. Exactly how much to trim will be obvious when you have one
of each. The two cups should fit together snugly to form a crude ball.
Smash paper over Stuff paper into
the forming pin the forming cup \
/ \
/ ________ _____ _____ <--
---> / \ \ / | <-- fuse
/ ____ \ ____ \_/ ____ |
/ / \ \ | | | | _|_
| | | | | | / | \ <-- inner cup
| | | \___/ | | | |
| | | | ||..|..|| <-- outer cup
| | |_______________| | ..|.. |
\_____/ powder is inside
Outer Cup Fixture Inner Cup Fixture Assembled Cups
If all of this seems an awful lot of work, remember, I did say that it was
easier and worthwhile to buy the ready made cups. But all of this does work,
so if you want to increase your experience in pyrotechnic fabrications, give
it a try. To tell the truth, there's nothing that these cherry bombs can do
that a tube salute cannot, and with lots less work. But cherry bombs seem to
have some mystique that give them everlasting popularity.
Oriental Salutes
There's another way to make very effective salutes, one that's totally
different from the standard tube salute we see in The States. The cost of the
materials is lower than what we've discussed, but they take a lot of time.
This makes them the choice in poor countries, where labor is cheap. Since
salutes are banned in the United States, these oriental items aren't imported.
The usual salutes are the quickly made tube type that are made in clandestine
factories right here in the good ol' U S of A, and most people have never seen
these hard little pear-shaped oddities.
Unlike tube salutes, which must have mostly empty space and use a supercharged
flash powder, these items are packed solid and contain low grade flash powder
and ordinary gunpowder. Here is a crude cross section.
----
/----\- Oriental Salute
//++++\-\-
//+ -- +\\-\- +++ = flash powder
||++/**\-\\\\\\ *** = gunpowder
||++|================== === = fuse
|| +\**/-////// Paper is represented by all of the following:
\\+ -- +//-/- // -- || \\
\\++++/-/-
\----/-
----
As you can see (??) the salute is made of a central ball of gunpowder
surrounded by an outer shell of flash powder. The gunpowder is enclosed in a
tissue shell to keep it from mixing with the flash powder. The fuse is coated
heavily with paper so that it will burn through the layer of flash powder
***WITHOUT*** igniting it. The fuse only ignites the gunpowder in the center.
This produces a burst of hot gas that quickly ignites all the flash powder.
While the American salutes rely on extra fine aluminum dust and a
considerable air space inside the salute to get the powder to flash all at
once, the oriental device uses a gunpowder ball, almost like a primer, to
rapidly ignite the flash powder that uses much coarser powdered aluminum.
While this takes effort to make, it can be used by those who don't have
access to aluminum dust, but can file down an aluminum block with a fine
file.
Start with a 3 inch length of green fuse. Last time we discussed the higher
degree of side spit produced by red fuse, and that has a greater chance of
igniting the flash powder on its way to igniting the gunpowder. This gives a
salute with less reliability. Use green fuse if you have it.
Place a pinch of FFFF grain plack powder in the center of a 3/4" square of
tissue paper. Use wrapping tissue, as opposed to the flimsier facial tissue.
Dip the fuse into the powder and fold the tissue up into a ball at the end of
the fuse. Twist the tissue ends and apply a little glue to attatch it to the
fuse. When dry, wrap 2 or 3 layers of masking tape around the fuse where it
meets the ball. This will shield the flash powder from the burning fuse. Now
that we've attatched a tiny ball on the fuse, we'll do it again with a larger
one. The dimensions can vary as we have some choice as to how large a bang we
want to make. Lets start with a tissue square about 4 inches square. Into
this we dump about 3 grams of flash powder made of
Potassium Perchlorate - 4 parts
Sulfir - 1 part
Bright Aluminum Powder - 1 part
The bright aluminum powder is much easier to find in chemical supply catalogs
and can also be made by filing an aluminum block with a fine file. There's no
need for aluminum dust here. Fold the tissue up around the gunpowder ball,
bringing the corners of the tissue up onto the fuse, wrapping it around the
fuse and securing it with a drop of glue. You should now have a ball of flash
powder with a tiny gunpowder ball inside, to which the fuse extends. This
ball has to be wrapped with two or three layers of dry newspaper strips,
about 1/2 inch wide. Wrap them around the bottom and attatch them to the
fuse with a twist and a drop of glue.
The dry paper is to keep the flash powder dry when we wrap it all with
similar strips of kraft paper soaked in paste. Once again, wrap it around the
bottom and twist it around the fuse. The paper should really be dripping wet
with paste. While attatching the dry paper is tricky, doing it with the wet
stuff is downright frustrating, until you've had some practice. It would be a
good idea to try this first with tissue, sand, and wire until you get the
technique down. You'll probably want to attatch 3 to 5 layers of the glue
soaked paper. If you choose to use a larger tissue square and more
flashpowder, you'll get better results by adding additional layers.
If you want to get decorative, you can get colored model airplane tissue from
a good sized hobby shop. Wrap this on as a final layer. The layers of paper
wrapped around the fuse will change the shape of the salute from a cherry to
more like a pear. This is to be expected. Leave the finished salute in a dry,
warm (not hot!) place for a couple of days. After drying, if made properly,
the casing will be hard and sound like a piece of wood when knocked on a hard
surface.
Whistles
These little curiosities are fun to make, but tend to be tricky. Unless
they're made just right they'll just make a lot of fire and smoke. The
chemicals must be very well mixed, the tube has to have the proper
dimensions, and even the smoothness of the inside of the tube will make a
difference.
Sound is simply the result of rapid back and forth changes in air pressure.
Burning pyrotechnic mixtures certainly create pressure. If we can produce a
device whose burning rate changes rapidly, it will produce sound. The trick
is not only to get it to change, but to change at speeds that will produce
tones that we can hear. If a mixture burns deep down inside a tube, and the
gas can't escape as fast as it's produced, the pressure inside will increase.
If the mixture's burning rate is very sensitive to the pressure it's under,
we might have the makings of a whistle composition. Since we might not expect
that such properties are common, we won't be surprised if we need some rather
unusual chemicals to make whistles.
It turns out that many aromatic compounds (molecules with benzene rings in
them, for you chemistry nuts) will work. Unfortunately, many such compounds
are liquid at room temperature, and even the solids tend to evaporate. Many
that do work have other problems.
If you have access to some of the outdated pyrotechnic texts, you'll see
whistle mixtures that use Potassium Picrate. This stuff is extremely sensitive
to shock and should never be used. The fact that it has to be homemade from
the even more sensitive Picric Acid is thoroughly scary.
Even the old texts mention the danger of Picrate whistles, and suggest a
"safer" composition of Potassium Chlorate and Gallic Acid. Last time we
discussed how a Chlorate can ignite spontaneously in the presence of an acid,
and we won't use this either. We won't even mention the proper proportions
needed, though we will say that old texts seem to have gotten copied from
other old texts and somewhere along the line, someone accidentally reversed
the proportions. As a result, many, but not all of the old texts have the
proportions swapped. It's just as well. Fewer people will have gotten hurt
from this mixture if they tried it, it didn't whistle, and they gave up
making it.
The modern whistle formulation consists of
Potassium Perchlorate - 7 parts
Sodium Salicylate - 3 parts
This is far safer than any of the other formulations, and happens to be
cheaper, too. For once, everything worked out in our favor!
Whistles need some special care. While some variation is allowed, it's
suggested that you follow these instructions to the letter. There are so many
different little things that can be done wrong that it can be hard to find the
problem if you're not familiar with what's required. It's best to exactly
follow a set of instructions that work, and once you've got that down you can
make small changes, one at a time.
The inside of the tube should be as smooth as possible. In fact, commercial
whistle tubes are often made of plastic to get the smoothness. In the orient,
they use bamboo tubes, which work best. But even if we lack a consistent
bamboo supply, and don't have some special plastic that resists softening
while containing a flaming mass of chemicals, we can still make do with
carefully rolled paper tubes. Shopping bag kraft paper tends to be fairly
rough. See if you can find a supply of kraft paper on a roll. Commercial rolls
come 3 or 4 feet long and quite thick. It's often used for wrapping packages
and the like. You won't want to buy it by the roll, but you may be able to
find a business that uses it for wrapping that may be talked into selling you
a dozen or so feet of it. If you can get some, roll it carefully, and try to
keep it from getting any bends that would mar its surface. Alternately, some
stores use paper bags made of a very thin, very smooth kraft paper. These
aren't supermarket-style bags, though. Check various clothing stores and
others that use the type of bag that opens by bulging out at the middle,
rather than unfolding into a box shape. If the paper has been bleached and
dyed pink or blue, the whistle won't mind.
Papermaking machines operate by pressing a slush of wood pulp between two
surfaces. One is a felt-like material, and the other is a fine wire mesh. The
difference between the surfaces gives paper two different surface finishes
from side to side. Sometimes this is more obvious than others. On some kraft
paper, one side will be smoother. If so, just keep the smoother side pointed
to the inside surface of the tube. Since you want smoothness, wrap the paper
around a 1/2 inch diameter metal or plastic rod, rather than a wooden dowel.
Don't glue it yet. Wrap at least 4 or 5 layers around the rod and then twist
the rod so that the paper is wound as tightly as possible. Now, set it on a
flat smooth surface and unroll it as far as you can go without letting the end
on the inside come unravelled. Apply a line of glue along the juncture where
the flat portion of the paper meets the rolled part, and start rolling it up
again, pressing the roll into the flat surface.
Keep adding glue where it becomes thin and keep rolling. Make sure that none
of the glue runs out the ends of the roll, or it will make it difficult or
impossible to remove the tube. If your supply of the smooth paper is small,
stop after applying 4 or 5 layers and build it up the rest of the way with the
cruder grade of kraft paper. The tube should be rolled until the wall is at
least 1/8 inch thick. If you're just learning, it would be better to roll it
up to 1/4 inch thick. The reasons will become clear later.
When the tube is rolled to the proper thickness, cut off the ends that don't
have sufficient glue, remove it from the rod, and let it dry thoroughly. The
paper should have been of sufficient size that when the scrap ends are cut
off, the tube is 4 or 5 inches long.
We haven't discussed chemical mixing much yet, except for the motorized
milling for gunpowder, and that's a special case. Many pyrotechnic mixtures
have to be thoroughly mixed to work well, and it's not possible to tell the
difference by looking at the mixed powder. In his book "Pyrotechnics", George
Weingart discusses the use of fine screens for mixing chemicals. This isn't
talking about window screens; they just won't do. Many metal dealers offer
metal meshes that almost might be considered coarse metal cloth. Finely
powdered chemicals can be mixed by slowly swirling them in a soft plastic
container and then repeatedly pressing them through these mesh screens. These
screens can mix the chemicals exceptionally well.
One thing Weingart mentions is that one should avoid letting their fingernails
strike the screen, as that can create a spark and cause a fire or explosion.
While it seems amazing that anyone would want to push flammable or explosive
chemicals through a screen with their bare hands, it does bring up another
concern. While we avoid metal tools wherever possible, there might be a
circumstance where a metal tool might accidentally fall on a screen, causing a
spark. In these modern times, it's possible to get brass mesh screens, and
brass doesn't spark when it's struck.
Now, back to mixing chemicals. Powder each ingredient separately until it
resembles flour or confectioner's sugar. Combine the ingredients in a soft
plastic container and swirl it slowly to crudely mix them. Then press them at
least 5 or 6 times through a 100 mesh screen. Brass is the material of choice,
for reasons already mentioned. Once mixed, it's time to load the tube.
There's a problem when loading the tube. We've made all sorts of efforts to
keep the inside of the tube smooth, and now we're going to go dumping in
chemicals and scraping it with a ramrod. We can't eliminate this problem, but
we can minimize it. We know that we need a long empty space in front of the
whistle tube. It's possible to fill the front end of the tube with a dowel and
load it from the back end. This will at least keep one end clean.
Get a block of wood and drill a 1/2 inch hole into it. The hole needs to be at
a good, right angle, so drill the hole with a drill press, not a hand drill.
Glue a 1/2 inch dowel pin into the hole so that it sticks out about one and a
half inches. With the glue dried and the dowel extending squarely from the
block, you can slide a whistle tube down on the dowel and proceed to load the
tube.
The block and tube is loaded from behind a heavy barrier, to protect you from
an explosion, in case the whistle explodes while loading. This is not a
frivolous extra. While an explosion of this material is unlikely, you can
never completely trust chemical mixtures. Every now and then, you can get
surprised, and the trick is to make sure that the surprises aren't harmful. A
good barrier is made from two pieces of steel plate welded or bolted firmly
together at right angles. This is another tool that the pyrotechnic
practitioner uses a great deal. The steel barrier is attatched firmly to a
workbench in such a way that you will stand inside the "V" area that it makes.
|
| /<--- Edge of workbench
You |/
stand |
here /|
/ |
/ |
_________|<--- Steel Barrier
/
/ O <-- Casing being loaded
The barrier should be made such that another plate can be attatched
horizontally on top. We won't need it for these tiny whistles, but it's
important for some larger casings that get loaded by ramming, like skyrockets.
The horizontal plate will have a hole through which you load the fuel and
insert the rammer. These whistles are small enough that you can position
yourself where the "V" portion alone can protect you. But don't try to load
the casing without it. Remember, if you're standing at a workbench, the casing
being loaded will be mere inches from your balls. If that won't persuade you
to be careful, nothing will, and maybe the removal of your "stupid genes" from
the gene pool will be a benefit to humanity.
You'll want to wear a heavy face shield and protective gloves while ramming.
Ear protection, the things that look like large earphones, aren't a bad idea,
either. As a ramrod, you'll want another 1/2 inch dowel, 1 foot long, but this
one should be sanded a bit so that it fits loosely down the tube. This will
keep the smooth insides from getting rubbed and scraped as you load the
whistle composition. Load the composition, moistened just slightly with
alcohol, about 1/2 teaspoon at a time, and ram it by hand. The safety rules
that come with these files caution you from ramming any mixture. This is good
general advice and it should be followed. However, there are a few cases where
it can be gotten around. The mixtures must be moistened and relatively
insensitive to shock. They must also be loaded from behind the aforementioned
barrier, so that even if anything does go wrong, you'll just end up with
ringing ears and a desire to go out and get yourself sloshed. Now that we've
discussed the barrier and the rules of ramming, we can ammend our safety rule,
but only very slightly.
Don't hit the rammer with anything and don't ram it really hard. While you ram
the casing, you should be standing back so that you can't actually see it,
your view blocked by the barrier. The only part of you that will be exposed to
a possible explosion will be your heavily gloved hands, and they'll be at the
end of a foot long dowel. If you don't ram straight into the tube, or you ram
too hard, the tube will be cocked sideways, and the whistle will probably be
ruined. Since you won't be looking directly at it, this will take some
practice. For this reason, you might want to make your first whistle casings
twice as thick, so that they will be a bit more forgiving of your errors as
you learn. If you're going to make a lot of these, you might consider
building a wooden fixture that will guide the rammer straight into the tube.
Note that if there is an explosion, the dowel may be fired from the tube like
a bullet from a gun, so hold it in such a way that it will not be driven into
your hand. Also, make sure that it's not "aimed" at anything that you don't
want trashed.
Guiding in the ramrod will be nearly impossible for the last inch or so, so
stop there. Cut a 1/2 inch plug off of a 1/2 inch dowel and slide it down the
tube until it rests gently against the powder. Then drip a bit of glue into
the tube, turning it so that it glues the casing to the dowel all the way
around, and set it aside to dry. Don't set it on its side. Keep it pointing
straight up so that the glue doesn't run. Now, to get the proper performance
out of this thing, the alcohol must dry completely. This means setting it
aside for a week or two before proceeding further.
Now we have to hook a fuse onto this thing. It's easier said than done. Once
again, we'll want to use green fuse instead of red, because of its reduced
side spit. Since side spit will gunk up the smooth inside surface of the tube
with residue, green fuse will be more likely to produce a working whistle. The
need for an open tube keeps us from having any good solid surface to attatch
the fuse to, and so if we had somehow imbedded it in the powder, any wiggling
of the fuse would have broken up the nicely packed powder. Any pressing of the
fuse into the powder can cause cracks and keep the whistle from working. There
are two ways of attatching a fuse. Neither is very good.
The easy way, which might be best for beginners, is to bend a length of fuse
over double, and stick one end in the tube, contacting the powder, and the
other end outside the tube, held in place with a ring of tape wrapped around
the tube and the fuse. The advantages are that its easy to do, and any
external bumping on the fuse will be absorbed by the tape, and little shock
will be transmitted into the powder, where it might shake some loose. The
disadvantages are, it burns in direct contact with the inside surface of the
tube, roughing up the surface, once it burns past the tape, the fuse is no
longer held against the powder, but can fall loose. On top of this, the end is
open to the air, so all sorts of crud can settle inside if it sits around for
a while. Glue a thin paper cover over the hole if you use this method.
The second method is to glue a single layer tube of wrapping paper over the
tube that extends about an inch and a half beyond the open mouth of the tube.
When this is dry, insert a length of green fuse that's just long enough to
reach the top of this new paper tube. The fuse should touch the powder at the
line where it meets the wall of the casing. Bunch the wrapping paper tube up
against the fuse, and apply a little glue where the paper touches the fuse.
Now, pulling the paper foreward, twist it as tightly as is practical around
the fuse without causing it to move and rub against the powder, and slip a
lose knot of string over the twist and pull it tight. Apply a dab of glue on
the string and let it dry. By pulling the paper foreward before attatching it
tightly to the fuse, you cause it to pull the fuse inward against the powder.
Even when the fuse burns through the paper, some tension will be retained.
This gives a greater chance that the whistle will be ignited. It also covers
over the open mouth of the tube and only touches the inside surface of the
tube at the point where it touches off the powder. The disadvantages are that
it takes longer to make, and that any bump into the fuse will cause it to
crumble the powder. This second method is preferable if you are careful in
handling your whistles. Since you presumably have complete control of your
whistles from workbench to firing, you can store and move them with the needed
care.
As has been said, the powder has to burn from inside a tube to make an audible
sound. As the powder burns deeper inside, the length of the open tube
effectively increases. This increased length changes the speed with which the
burning chemicals oscillate (it slows them down) causing the frequency to to
start out high pitched gradually dropping down to a very low frequency. This
is the reason for the distinctive sound of whistles and the reason you never
hear one going in the other direction. It also sets a limit on how long a
whistle can be, since they will tend to be uninteresting if they drop below
the range of human hearing.
Whistling Rockets
The strict requirements on making a working whistle and the need for an open
tube would seem to make it impossible to put it in a rocket engine and get a
whistle. Yet whistling rockets are available. The larger skyrockets tend to
have a whistle tube attatched to the outside of the rocket, and both the
engine and whistle get ignited simultaneously by a branch in the fuse. The
tiny whistling rockets use a clever way of getting a rocket-like action out of
an open tube.
/\
/ \
/----\
|****|
|****|<---Whistle tube with
|****| nose cone and fins
|****|
/|===\|\
/ |===\| \
/ |===\| \
/ |===\| \
|____|===\|____|
===\
===\\
Solid plug--> === \\ <--Fuse
attatched to === \
support base ===
=============
If we were to stuff a loose plug down the whistle tube with a hole just large
enough to admit the fuse, then when the whistle composition ignited, the
pressure would would fire the plug from the tube like cork is forced from a
champagne bottle. If we take a whistle tube with only a limited amount of
composition in it, attatch a nosecone and fins, and stuff a stationary plug up
the whistle tube, then when the composition is ignited, the whistle tube would
blow itself up off the plug into the air. The reason for the limited amount of
whistle composition is for weight considerations. Only the initial burst of
gas will fire the whistle tube into the air, and any extra composition will
just weigh it down. The trick is for it to stay in the air while it's
whistling. A whistling rocket that pops into the air and then lands on the
ground while still whistling will be regarded by spectators as a "dud".
Commercial whistling rockets tend to use plastic tubes, and use inside
diameters only 1/4 to 3/8 inch. There's usually only about a 1/4 inch depth of
fuel inside.
Some of the tiny whistling rockets end with a report. Since a regular
firecracker would add too much weight, the usual report is made by adding a
chemical that detonates, exploding without a casing. If the nosecone end of
the whistle tube has a small hole in it before its loaded, then a small amount
of whistle composition will be visible through it. A small wad of Lead Azide
can be placed into this hole so that it will be ignited and explode when the
whistle composition is just burning out. The Lead Azide can be kept from
crumbling off by hiding it under the nosecone. Preparation of Lead Azide is
described in part 2 of this series.
Stay tuned for part 6, where we'll talk more about fireworks that require
special construction. Have fun but keep it safe!
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