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  #271  
Old 08-27-2013, 11:34 AM
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Ez2cDave Ez2cDave is offline
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Quote:
Originally Posted by Jerry Irvine
I have seen instructions on the internet on how to make Thermalite wick/fuse clone from scratch. CXA Canada used to make it.

Jerry



NOTE : The original article contained pics and illustrations . . . This FORUM does not allow ATTACHED or EMBEDDED images . . . If anyone wants a copy, E-MAIL me @ Ez2cDave@aol.com

Thermalite Equivalent Fuse
__________________________________________________ _______________________

The word "thermalite" has come to be widely used in the pyrotechnics community as a generic term referring to a specific kind of fuse or ignitercord. The commercial version burns very hot and is therefore useful for initiating hard to ignite compositions. One very common usage is as an igniter in amateur composite rocket motors. The fuse comes with external wrappings of nichrome wire which can be used to perform electrical ignition. Sources for thermalite are increasingly hard to come by and purchasing it by mail will usually require permits and licenses. Thus, the need for producing a suitable home-made equivalent has never been greater. The method presented here represents my own adaptation of the method described in a publication entitled "Homemade Imitation Thermalite Ignitercord" by Firefox Enterprises, Inc. This project illustrates the production of only one of the many varieties proposed in the Firefox publication and does not begin to offer the full wealth of information contained therein. Various combinations of binders and chemicals can be used to produce burn rates ranging from 5 seconds per inch to slightly more than one second per inch. Since my most common use of thermalite is for cross-matching time fuse, I chose to illustrate the fastest burning and easiest to ignite variety.

WARNING!! This project uses chlorates and finely powdered magnesium. The dry composition is very sensitive and must be handled with proper care. This procedure should only be attempted by those whose knowledge and experience will minimize the risks of handling these materials.
________________________________________


There are a few pieces of minor tooling that enhance the process of making thermalite, but they are very simple to make. First, a pedestal to hold the batter cup is nice because it frees up the hand that normally would have to hold it. This one can be clamped to the edge of a work bench so that the batter cup is held out over the floor. It is made of pieces of 1 x 4, one of which has a round hole in it for the cup.

Here, I have made a drying rack by using hot glue to fasten 18 clothes pins to another piece of 1 x 4. This is hung from the ceiling of my shop so that fairly long lengths of fuse may be suspended from it if desired.

A binder for the fuse composition is made by mixing the following: (parts by weight)

• vinyl resin................................. 47 parts
• nitrocellulose lacquer(10%)....... 25 parts
• dibutyl phthalate(plasticizer)..... 10 parts
• acetone.................................... 18 parts

The vinyl resin and plasticizer are available from Firefox. Thirteen bucks will buy enough of both to make more fuse than most people will use in a lifetime. You can mix up a lot of the binder at once and store it in a jar for whenever it's needed.

Now the dry composition is prepared. This is where a good deal of caution and proper handling becomes imperative. The list of chemical ingredients is:

• potassium perchlorate................. 37 parts
• potassium chlorate...................... 30 parts
• charcoal, air float........................ 10 parts
• magnesium, 200-325 mesh........ 15 parts
• red iron oxide, ferric..................... 5 parts
• aluminum, -325 mesh, flake.......... 3 parts
• sodium bicarbonate(additional)..... 1 part

The magnesium should have been treated with potassium dichromate or coated with linseed oil prior to using it in this composition. This will make it less likely to react with any water present in the acetone. Another alternative is to use molecular sieves to dry your acetone. The potassium perchlorate, potassium chlorate and iron oxide are screened together first. Make sure a screen which has never been used with sulfur is chosen for the screening. In a separate mixing cup, the remainder of the dry ingredients are weighed and stirred together. Finally, the two compounds are mixed together using a gentle method called the diaper method, shown in this picture. The two piles are placed on a large piece of paper, such as newspaper, and mixed by picking up alternating corners to gently roll the powders over each other until thoroughly mixed.

Prior to mixing the binder with the dry powder, the core wires should be prepared. For a typical batch, I cut 18 lengths of 26 gauge copper wire to a length of 19 inches. The wire is then "roughed" by pulling it through my pinched fingertips which are holding a piece of folded sandpaper. This gives the wire surface enough texture to allow the batter to stick to it. Now, 25 grams of dry mix and 17 grams of binder are placed in a 5 ounce paper cup and stirred to make a batter about as thick a pancake batter. The cup is placed in the "batter pedestal" and a small hole is poked in the bottom. The batter should be thick enough that none will drip out of this hole. This "first dip" is accomplished by pushing the wire up through the hole until about an inch of it protrudes from the top surface of the batter. A tissue is used to clean the batter from the top 1/2 inch of the wire. Then the wire is grabbed from the top and slowly pulled the remainder of the way through the batter. After the first dip, the batter diameter will be quite small at about 1/16 of an inch. The wire is then clipped into the drying rack and the procedure is repeated for the remainder of the wires. They will be ready for the second dip in a few hours.

The second dip is identical to the first, except that the hole in the batter cup may need to be widened slightly to allow the thickened first dip wires to go through. The batter can be slightly thicker for the second dip so that the coating will be thicker also. Pulling speed will also affect the finished thickness somewhat. Very slow pull speed allows some of the batter to drain off, yielding a thinner coating. Both of these factors can be varied to adjust the final diameter between the range of 1/8 inch to 3/16 inches. It may be necessary to add a few drops of acetone and stir the batter occasionally because this solvent evaporates so quickly. Again, the dipped wires are clipped to the drying rack until they are completely dry. This will take about 6 to 8 hours.

When completely dry, I cut the finished igniter cord into 6 inch lengths so they can be easily stored. The finished product is firm, but flexible. It is very durable because the composition will not flake off easily when the cord is bent. This stuff is quite water proof and burns with a pleasing and loud hiss. I have found a plethora of uses for this marvelous improvisation for thermalite. Among them are:

• It can be used as a substitute for visco in most cases, although the slower speed variety is better for this purpose. At 3 cents a foot for materials cost, it's less expensive, too.
• It is a very good replacement for black match when used for cross-matching.
• I use a small length of it in the nozzle of fountains when I want to ignite many at once with sticky match. The same concept is used to ignite girandola drivers and most other forms of black powder rockets.
• Whenever I use sticky match to replace quick match for mine and shell leaders, I put a piece of the thermalite at the end of the match to assure ignition of the lift powder.
• I haven't tried this yet, but I think there is a good possibility that short lengths of this cord could be used to make go-getter inserts in a shell. A few wraps of masking tape with a little bit of one end left exposed, would create very energetic little rockets. Even unwrapped lengths will fly all over when lit if they are not attached to something.

I'll close this project page with a few comments about the Firefox booklet. If you are seriously contemplating this project, I highly recommend that you purchase the booklet. It contains two different dry formulations and two binder solutions. It will tell you how to make this thermalite equivalent in a variety of ways to achieve a wide range of burning speeds. I have not included all this information in my project description because Firefox deserves to benefit from their development efforts and publication of this material.

________________________________________
Comments and suggestions from visitor feedback:
• From: Terry McCreary (terry.mccreary@murraystate.edu)
To: dwilliams@wecreate4u.net

Just visited your web page. Re: The preparation of imitation thermalite: I've always preferred to prepare the liquid mix, then add the metal(s) and mix til wetted, then other solids, and finally the KClO4 and KClO3s. In this fashion, much of the solid-to-solid friction encountered when mixing solids is avoided; the liquid mixture appears to act as a phlegmatizing agent (love that word!)




Last edited by Ez2cDave : 08-27-2013 at 12:16 PM.
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  #272  
Old 08-27-2013, 11:50 AM
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Ez2cDave Ez2cDave is offline
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Quote:
Originally Posted by STRMan
I wonder how deep the core was and what diameter is was?


Even 3 years later . . . a GOOD QUESTION !

Check out the PIC . . .

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  #273  
Old 08-27-2013, 11:54 AM
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Ez2cDave Ez2cDave is offline
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AND . . .

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  #274  
Old 08-27-2013, 02:03 PM
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Doug Sams Doug Sams is offline
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Quote:
Originally Posted by Ez2cDave
Even 3 years later . . . a GOOD QUESTION !
Here are some pics, from earlier in the thread - much earlier - which include annotations of the core depths and a close-up from which the diameters might be culled.

http://www.oldrocketforum.com/showp...39&postcount=27

Doug

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  #275  
Old 05-29-2017, 01:04 AM
Rick M Rick M is offline
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Quote:
Originally Posted by blackshire
Sugar rockets aren't quite as hazardous to make as black powder motors, and they lend themselves to core-burner grains. (It's really a necessity with sugar motors due to the propellant's lower specific impulse.)


Someone donated some B14-0 motors to me (he heard that I give Estes motors away to kids at rocket events) and thought I'd do some researching on them.

My understanding is that black powder has an Isp of 80 and the sugar motors I make 125-140 depending on what pressure I run them.

Here's one of the last sugar motors I tested:
https://www.youtube.com/watch?v=eeOVhQKnTfg&t=0s
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  #276  
Old 05-29-2017, 01:27 AM
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Quote:
Originally Posted by Rick M
Someone donated some B14-0 motors to me (he heard that I give Estes motors away to kids at rocket events) and thought I'd do some researching on them.

My understanding is that black powder has an Isp of 80 and the sugar motors I make 125-140 depending on what pressure I run them.

Here's one of the last sugar motors I tested:
https://www.youtube.com/watch?v=eeOVhQKnTfg&t=0s
Hermann Oberth would be so proud! (It also reminds me of the Aerojet 260" diameter solid motor tests.) The Kegeldüse ("cone") liquid propellant rocket engine that he static fired in that position was probably only a fraction as powerful as yours. Do all of your sugar motors build up thrust slowly like that? (I imagine it could have been the grain configuration instead, as the little "Five Cent Sugar Rockets" seem to zip up and away rapidly.) B14s were prized for their quick, "kick-in-the-pants" liftoffs. If you can duplicate--or exceed--their performance with a sugar propellant, probably a lot of people would happily "roll their own" sugar B14s if you sold a "How-To" pamphlet with the 'recipe.'
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  #277  
Old 05-29-2017, 08:46 AM
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Quote:
Originally Posted by Doug Sams
I have seen some later B14's that looked more like B8's - they didn't begin to have the larger cores seen on the earlier B14's. It wasn't clear to me if this was due to worn out drills, substitution (ie, selling B8's as B14's before finally getting new cert's and name changes), or mislabelling.

(I posted a pic of the various B14 and B8 nozzles somewhere, but danged if I can find it now...) [Edit: It was on my old website, but I need to upload it to my new one.]

Doug

.


Doug,

I realize this is from several years ago . . .

Are these the pics you were referring to ?

Dave F.
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  #278  
Old 05-29-2017, 12:42 PM
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Quote:
Originally Posted by Ez2cDave
Doug,

I realize this is from several years ago . . .

Are these the pics you were referring to ?

Dave F.
Yes, the two on the left are mine.

Doug

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  #279  
Old 05-29-2017, 12:48 PM
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Ez2cDave Ez2cDave is offline
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Quote:
Originally Posted by Doug Sams
Yes, the two on the left are mine.

Doug

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Thanks, Doug !

Dave F.
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  #280  
Old 05-29-2017, 05:44 PM
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Jerry Irvine Jerry Irvine is offline
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B14's didn't have a rapid start time only a high initial thrust. If you look at the trust curve it is similar to an F100 (symmetrical bell) but with a trail off similar to a C5. That's why GH likes C5's and B14's. He would like A10's if the trail off wasn't so friggin long.
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