Cojo0331 Posted December 8 Posted December 8 We are looking into the use of copper thermite to create igniters capable of burning at higher temperatures than standard commercial igniters. To initiate the reaction, we are using nichrome wire attached to the ends of our copper wires. However, we are uncertain about the best binder to use with the thermite to effectively mold it around the copper/nichrome wire assembly. Do you have any recommendations for a binder or alternative methods to develop exceptionally high-temperature igniters?
cmjlab Posted December 9 Posted December 9 Nitrocellulose lacquer has worked for me. There are also "designer" lacquer mixtures with NC and a butyral? additive to provide a bit of flexibility, etc. but just NC has worked great for me, as is. Followed by a couple additional dips in plain NC lacquer once 1st (and 2nd if used) fire layers are on. The additional dips build up a protective coating that helps protect the pyrogen a bit, but also acts as a bit of containment (in my opinion) resulting in a bit louder pop when fired. Chuck
cmjlab Posted December 9 Posted December 9 Oh I should add - I've never "moulded" it around the bridgewire though. I suppose that would work, but would take an awfully long time to make any real number of igniters. I've always created a thick slurry (close to the consistency of pancake batter) of copper / mg or copper / Al thermite with NC lacquer. The consistency was thick enough to only need one dip, but thin enough that it would still smooth out into the typical ematch looking head, then once dry (usually by the time you have dipped a hundred ematches or so) then go back and dip them in the NC lacquer of thinner consistency. 1
cmjlab Posted December 9 Posted December 9 Do you live in the U.S.? If you do, you may eventually come to the same conclusion I did..... it's easier to buy cheap Chinese ematch off ebay. (Not to discourage you from making them, it was and js fun to make them). Here's an example of the chinese ebay ones: Ebay Firework Igniters (30" Leads) The Cons: It's hard to find ones longer than 36" max. Not Regulated - So i wouldnt trust there claimed safe ohms inputs for systems that test continuity, etc. They aren't a thermite, so they won't burn as hot, or sling molten metal for hard to ignite comps (of course theres ways around that). The Pros: Cheap, Easy, Reliable (so far). I've used a few hundred now and not a single one has failed. I have several hundred mire as well, in case ebay or the USG puts an end to it. Done with my ematch rant now, I promise! I just like to share what I've learned, knowing that if you are anything like me - you want to learn for yourself. 🙂
Arthur Posted December 10 Posted December 10 You should also realise that thermite is notoriously difficult to ignite, it will NOT ignite from an igniter or visco. Getting a suitable prime sequence is essential.
cmjlab Posted December 11 Posted December 11 In my experience copper thermite will light quite easily if the metal particle is small enough, and is improved greatly when using Mg flake (Ive used -325 Flake Mg with success and shared video of it here on APC at some point, for a different purpose though). However, a more sensitive first fire will slightly improve ignition time (by fractions of a second). It also increases burn / accidental ignition risk. Even Al thermite lights pretty easily if you use German Dark Al. If someone has a different experience I'd love to hear about it.
Arthur Posted December 11 Posted December 11 Remember that the primary function of an igniter is to prevent ignition 'til commanded.
Cojo0331 Posted December 11 Author Posted December 11 What ratio are you mixing the thermite to NC? I have read too much NC will create a thermal sink, so I don't want to do that.
cmjlab Posted December 11 Posted December 11 I've never read about NC lacquer creating a thermal heatsink. I'd like to read about it if you recall the source. The sensitivity of the Copper / Magnesium thermite was more important than the slurry consistency, in my experience. The slurry holds the thermite in suspension until the bridgewire heats up. The theory I've read and liked is that the nichrome bridgewire is partially vaporized and melted, creating enough internal heat to ignite the thermite with a pop. (** If you've never made copper thermite, especially with fine metals such as flake magnesium or dark aluminum, I'd recommend you make a sub gram quantity to observe safely. It acts almost like flash, and has a lower ignition temperature than normal thermite**) I didn't use a set ratio. I just added NC slowly to a small batch of Copper / Magnesium thermite, until the consistency was around the consistency of cold molasses or honey. When your match head is dipped it should retain a small bulb on the end, and smooth out while hanging. If it's too thin, just dip a second time. With the right consistency, they will resemble commercial ematch size and shape.
Crazy Swede Posted December 12 Posted December 12 15 hours ago, Cojo0331 said: What ratio are you mixing the thermite to NC? I have read too much NC will create a thermal sink, so I don't want to do that. To traditional compositions for electric matches, a NC lacquer based on two different nitration grades was used to achieve a nice and thick solution. The total amount of NC was 4 % in the lacquer and buthyl acetate was used as solvent. In the formula (lead dioxide, zirconium etc), about 25-30 weight percent of the lacquer was used to achieve the right consistency for dipping.
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