Film canister Shell For Mortars or Rockets
Film canister Shell
For Mortars or Rockets
This is a rough and by no means full description of the making of a
simple,
quick but yet interesting piece of fireworks.
I first heard about it in 1994, when I
visited ************** in
****************. As far as I know , this is his invention, but I
those empty film
cannisters as well. My experience with the film
cannister shells is not over yet, and nor have
I tried all of my ideas
when it comes to payload/construction. What I will tell you now is
can only wish you a
safe and enjoyable expansion of your fireworks
items. Have fun!!
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As with almost
every fireworks item, people have their favorite
materials and methods. My favorite film
cannister is the black HDPE
type of cannister, the type that KODAK films arrives in. What I
think
is the most important part is the lid. It should , in my opinion, be
of the type
that "squeezes" the rim of the cannister between one inner
and one outer part of the
lid. Here in ********, these lids are
black.
There are also one type of gray lid
that might work, but it gets
rather soft when hot glue is applied, and I have had some trouble
when
I tried to put it on without paying attention to the soft rim.
I have also
tried a few FUJI type cannisters. They are transparent, and
their lids is more like a plug
that does not overlap with the rim from
the outside. When gluing these lids with hot glue, you
get a weak
seal, causing a bad break.
As in all other types of shells, uniform
strength is important. But
carefully designing a shell using a powerful break in a flashbag
is
often a successful way of eliminating the effect of a weak joint. So
don’t loose hope
if you are stuck with hundreds of FUJI type
cannisters. They might work perfect with the
appropriate design of the
shell.
The fuse used in these shells is perhaps
the biggest difference
from the ordinary shells. A conventional time fuse might work
perfect, but it is not neccesary, and the work of cutting and priming
these fuses is a waist
of good pyro time. But still the fuse has to be
reliable and easy to make. Visco could perhaps
be used, but it is not
so easy to get here.
So to avoid these problems, the film
cannister shell uses a special
tube of black match. Instead of cotton, acryl string is used. I
got my
acryl in a knitting store, and if you can choose between several
types, pick the
thickest. Then black match is made the usual way,
being sure to squeeze all the air out of the
fuse, to avoid any air
holes through the fuse. Dusting the finished fuse with BP is not
neccesary.
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When he makes Teflon fuses, he uses a binder made from 8.5 grams of
animal glue per 100 ml. of
water. He also reports that household
gelatin theoreticaly is the same, only more refined. He
has used it as
a substitute when he didn’t have anything else. You have to use hot
water
to dissolv it. It makes a pretty good and stabile suspention of BP.
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When the black match is dry,
it can be cut into pieces of about 2-2.5
cm. Then the middle part of the fuse is wrapped with
Teflon tape, also
known as PTFE tape. The length of the wrapping determines the timing
of the shell, and has to be adjusted to the burning speed of the black
match. 1.5-2 cm is a
good starting point. Just be sure there is at
least 2-3 mm of match on each end that is not
wrapped in tape, or else
a dud is on its way! The Teflon tape is soft and gives a tight
seal
around the match, so that no flame can spread along the surface of the
fuse. Two or
three layers of tape is sufficient. One roll of tape can
make a lot of fuses, and the tape is
easy to stretch and tear. With a
little practice, it only takes a few seconds to make a fuse.
Of course, if you make a lousy black match, the fuse is not as good as
it
could and should be. But as far as ******* ******** has experienced,
it is at least as good as
you could expect commercial time fuse to
be. He has fired several hundreds of these shells,
without any of them
flower potting or failing to ignited. That should speak for itself.
Depending on the diameter of your fuse, the quickest and easiest thing
to do is
to get some kind of punching device to punch a hole in the
lid of the cannister. But as the
lid is soft, anything that can make a
hole is usable. However, punching gives the best hole.
Then the fuse is simply just glued into the hole using hot glue,
applying glue to both
sides of the lid.
Well, this is where every pyro has to use his own
imagination. Colored
stars, tailed stars, strobes, anything will do. Now you have a way to
stars not having to
wait for the 3" shells to dry. Just remember,
small shells require small stars (usually).
You are on your own
here. Just let the imagination flow free and undisturbed !
If
you attempt to use flash, go ahead! The shell has space for 30+
grams of flash, but you might
want to sacrifice some of it for some
layers of craft paper on the inside walls. The film
cannister is
not strong enough to get the full potential out of the
flash. Depending on
your flash however, it is a quick way to get a
salute in a hurry (don’t make them if you are
in a hurry!), and added
titanium or zirconium makes the shell noteworthy.
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In his opinion, if you
use 70:30 KP flash, reinforcement of the cannister
is not neccesary. If you use nitrate based
flash, you should however
do something to add strength.
In addition he has experimented
with flash cannisters using masking
tape in stead of hot glue, not because he believe there is
big danger
if you use hot glue, but because of the consequences if anything goes
wrong.
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As in all other types of shells, the burst makes the difference
between a lousy shell
and a good shell (not the whole truth, but a lot
of it!) And as we all have a different
favorite burst, often depending
on the type of stars, size and effect wanted, I will not tell
you that
I have found the best solution, cause I haven’t! I will tell you what
works for
me.
Due to the small size of the shell, and the relatively weak walls, a
powerful burst is neccesary if you want a good spread. And I did, so I
used flash burst. What
flash to use, is your own choice. I have tried
both perclorate flash using Dark German Al, and
a milder nitrate based
flash using a slower Al. They will both work if the correct amount
of
flash is used.
I guess that whistle mix is possible to use as well, and if a
milder
burst is wanted, H3 or BP might give the desired effect. What I do
know is that
by using a powerful break, the weak joint by the lid is
of no consearn. Using a softer burst
especially together with the FUJI
type of film cannister on the other hand, causes the lid to
pop open
not rupturing the cannister, creating an effect not unlike the
commercial
rocket heading does. This can be desirable, especially if
no loud noises should be made. The
more powerful burst also creates a
good bang (YEAH!). So depending on your intentions, you
have almost
all the possibilities also found in the larger shells. The film
cannister is
not suited for large inserts though!
Just as with traditional shells,
you have different ways of arranging
the burst and the stars. The far quickest method is to
just fill the
cannister almost full of stars, dump in a weighed or measured amount
of
burst (I use about 1 gram of flash), and let the flash be loose
among the stars. What I have
experienced is a rather weak pop and not
a good spreading of the stars. Using FUJI
cannisters,the several stars
often came down unignited when the lid popped off. More flash,
quicker
flash and better priming of the stars might solve the problem. I
still have to
improve this method.
The other method that I have used with best results is also a bit
more
laborous. In order to get better spread of the stars, I make a small
flashbag that
keeps the flash centered in the cannister. If I remember
correctly, the diameter of the
flashbag was about 6-7 mm, so that one
gram of flash could fit into the bag. The flashbag I
used was about 1
cm shorter than the length of the cannister, so that I got one layer
of
stars on the bottom of the cannister. I filled the flashbag with
flash, and glued it onto the
lid , making sure to keep it straight
until the hot glue was cold.
In the mean
time the cannister was filled with one layer of stars on
the bottom. Then a sort of
"canulle" was prepared, a paper cylinder
slightly wider and shorter than the
flashbag consisting of two layers
of paper was held in the middle of the film cannister, while
the stars
was filled around it. Leaving a little space for the lid on top, not
filling
too many stars in the cannister, the cannister in now ready to
the final assembly.
glue. You want the
glue to touch both the outside and the inside of
the cannister rim. Be aware of the
theoretical danger with hot glue
and stars with low ignition temperature. In practice, the
glue cools
down a bit before you are able to put the lid on, and it should be
safe. I
also wipe away all loose flash or BP that is stuck on the rim
or other surfaces that get in
touch with the hot glue, as well as
dumping the flash into the shell before I add the stars.
The stars are
likely to have a lower ignition point than most flash types, but the
stars
are easier to keep out of contact with the glue.
Please tell me if there are any
examples of accidents caused
by hot glue.
Assuming that you have a centered
paper canulle of the proper
diameter, putting the flashbag into the hole should be simple.
Note
that the canulle is not removed, and that it will act as a
reinforcement of the
flashbag.To get reproducible results, flashbag
and canulle has to be standardized.
make sure that the lid gets into the correct
position, and that no air
bubbles penetrates from the outside to the inside of the shell. Due
to
the hot glue, the air trapped inside the shell and between the lid and
the rim will
often cause bubbles to form. If you want to be sure no pin
holes are present, just add some
glue outside along the lid when the
shell has cooled. With some practice, this is not
neccesary. If you
have the gray type of lid, you will have to keep some pressure on it
until it has cooled. Be aware, that the lid often gets a bit too hot
to touch with your bare
fingers. If all steps went as they should, you
now have a film cannister shell!
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He does not fill the
"edge" of the lid with glue before he puts the
lid on the cannister. He puts on the
lid and applies glue to the
outside of the shell only. This is partly because he wants to
avoid
any contact between the hot glue and the content of the shell, but
also because he
believe the glue might destroy the already almost
airtight construction of the lid. This also
gives less trouble with
bubbles forming.
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One note about the
flashbag. Using flash as burst, you will often
discover that the limits between success and
failure are small. I have
used 1 gram of perclorate flash in the flashbag, but that was at
the
edge of what my stars could take. Adding only a few turns of paper to
the flashbag
OR the canulle, the stars were blown blind. If you do not
have an accurate scale, you can get
problems with the consistency of
your shells. A milder flash might help a lot. Only careful
tuning of
the burst will give the best results. Remember that BP based stars
probably
can take even more powerful bursts than I have used.
In order to launch
the shell, you must have a mortar or a
rocket. Since I haven’t put any of these on a rocket
(yet!), I will
only cover the more common and traditional way to launch a shell. What
you have to get is a tube of paper, steel or preferably HDPE. If I do
not remember wrong, the
film canister is about 36-37 mm OD. I have
used mortars with 36mm ID, but I had to cut excess
glue off all my
shells to keep them small enough to fit into the tube. So save time,
get
a larger tube. Now I’m using used 40 mm candle tubes, cut to 25 cm
length. The tubes are glued
onto a wooden plate using the marvelous
hot glue. Ignition is not by the quick match method
used with larger
shells, but through a small hole at the side of the mortar. I insert a
piece of black match, pour 5 grams of fff sporting grade BP into the
mortar, add the shell
with fuse end down, and the shell is ready to be
launched!
Here is a
picture of me matching several film cannister shell
mortars. You also see some crossette fans
and one of the 6" shell we
fired that evening.
The shells are also easy to
fit onto a rocket. The rocket at the
bottom is carrying a film cannister shell.
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Now, this
is as far as I can get you. The rest is for you to find
out. A few thoughts and ideas not yet
tried by me is:
Attaching comets to give rising tails. Just be sure the comet does
not
burn through the cannister. Some protection might be needed. Making a
large Roman
candle filled with these should draw some attention!
Filling a larger(5")
cylinder shell with film cannister shells to get
shell of shells. If precision timing is
required, use time fuse or
make the Teflon type as accurate as you can.
Making
multi break shells (with bottom shot, or rather top shot). The
Teflon trick allows short
delays. Longer mortars and heavier lift
might be needed.
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He has
successfully used glued on glitter and charcoal compositions as
rising tails to the shells,
and they work perfect glued onto the
opposite side of the fuse. He have had no problems caused
by the
comets burning through the cannister, but as an insurance, you might
wrap the
comet with some wrapping tape.
He also suggests making parachute shells from a
two-cannister
arrangement, one cannister holding the flare and the other holding the
parachute.
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I hope you enjoy
learning about the film cannister shells. They are
certainly worth more attention and
publicity. Maybe we will see
"Best film cannister shell" as a part of the
competition at the PGI
convention. Who knows? It is all up to us!
Typed by
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