Pyrogen for rocket igniters?

[Phil]

If I dissolve pong balls in acetone then add 100 mesh screen mixed BP to it, will that give me a useful pyrogen to coat my igniter blanks with or is it a waste of time?

[Arthur]

Ping pong balls may or may not be NC -likely not these days. A Plain bridgewire will not fire most simple mixes.

[Phil]

I've found some ping pong balls that I feel like contain NC. They burn pretty violently. I actually got my wireless ignition module I made and my blanks to go along with it dialed in. My igniters get VERY hot, require a lot of current and take a second to heat up (Using a 12v UPS battery), I was just interested in finding a way to make them more reliable since I'm currently taping visco fuses to them and as glowing hot as my blanks get I feel like if I don't have them taped perfectly it could lead to a lot of duds. I've made a small batch of this pyrogen nonetheless. If it doesn't work out are there alternatives for dipping igniters in that can be readily made?

Edited May 13, 2021 by Phil

[SharkWhisperer]

I've found some ping pong balls that I feel like contain NC. They burn pretty violently. I actually got my wireless ignition module I made and my blanks to go along with it dialed in. My igniters get VERY hot, require a lot of current and take a second to heat up (Using a 12v UPS battery), I was just interested in finding a way to make them more reliable since I'm currently taping visco fuses to them and as glowing hot as my blanks get I feel like if I don't have them taped perfectly it could lead to a lot of duds. I've made a small batch of this pyrogen nonetheless. If it doesn't work out are there alternatives for dipping igniters in that can be readily made?

BP added to your NC lacquer dip will make a world of difference. Are you firing visco alone or using these as rocket motor igniters (different flame needs). If firing visco fuses alone, you've got to burn through that plastic coating. A plain wire can get red-hot and fire much, but it'll fire off pyrogen before needing to get that hot and improve energy transfer/fuse ignition. The Talons and knockoffs are like clothspins that push a thin nichrome filament across your fuse to maintain contact. I hate them and they always take a second to ignite. Unsure of your power delivery and nichrome traits (amps delivered, battery internal resistance, shooting or igniter wire type/dimensions, or nichrome length/thickness/specific alloy), so can't comment on that. But if you're getting red-hot nichrome, you will get improved visco ignition if your dip is BP-enhanced, for sure (provided your BP is good quality). +100 mesh might be suboptimal--you want a hot localized flame for fuse ignition (and hot sparky flame transfer for rocket motor ignition). So you want a hot regulated burn speed--not flash speeds. For my BP enhanced rocket igniters (that work just fine for mortars, etc, for direct ignition (or fuse ignition), I typically use BP around 20-40 mesh. I usually add some metal to increase heat. For BP ignition, I might only add Al at 5-10%. For sparky hot rocket motor igniters, I typically use -60 MgAl, which also burn very hot but tosses more sparks than Al alone does. If adding more than 10% metals, you might need to adjust your oxidizer--often I'll add potassium perchlorate to the mix in a stoichiometric ratio, or a slightly fuel-rich mixture (depending on the mesh-size of my metals). Very fine metals are going to get closer and closer to approaching flash speeds. Larger mesh sizes will give a still-hot but longer burning pyrogen. Adjust burn rate by adjusting comp size or by adjusting fuel/oxidizer rate (or oxidizer selection). My goal is to get a sustained but immediately igniting pyrogen and not to create flash on a wire, which will burn super hot, probably ignite BP in mortars etc with zero trouble, but: 1) might burn too fast for reliable burn-through of the visco outer coating, and 2) might be too fast burning and pop, thus damaging my rocket motor fuel grains (if used to fire rockets), or blow itself away from the visco before igniting it. You can also do two other enhancements easily to light visco with your nichrome: 1) wrap the whole connection in non-conductive electrical tape--contains the heat while allowing current to flow through your nichrome while preventing the visco from getting pushed away, or 2) Using an eyedropper or small paintbrush to add a dollup of BP/NC slurry/dip at the junction where your nichrome meets visco. Nicking the visco with a razor blade (or splitting the end if that's your ignition point) will allow direct flame access to your visco bp core. Primary consideration is not damaging or shorting your nichrome segment. You should be able to modify your power delivery so that nichrome heats near instantly, and pyrogen even faster (before nichrome gets red-hot). If mimicking the cheap Chicom wireless units (single or double cue) and using a thin-enough nichrome, a 9-volt battery should give instant igniter firing. The NC in these binders/lacquers are flammable but in my opinion contribute little by themselves to energy transfer, but they allow the pyrogen within to fire reliably. Your celluloid PP balls are probably not ideal but are workable because they are flammable NC, but just not as nitrated as the NC in smokeless powder (probably on the order of 10-11% nitration in PP celluloid vs 13.5% in smokeless NC. Proper NC PP balls will burn with a vigorous orangey flame, with little smoke production and will leave little ash behind.

[Phil]

I added several teaspoons of my 100 mesh screen mixed BP to my NC lacquer dip. I let it dry for a few hours then when testing it didn't want to light off at all, checking the resistance with a ohmmeter it seems the wire burned out without igniting any of the bp lacquer. Like the lacquer coating smothered the ignition. I took a torch directly to my igniter and it burned top to bottom smoothly like a fuse. That was with three coats applied though, if I apply one thin coat the flame doesn't want to propagate all the way through in one go. I'd like to fire visco alone. I can quicken the time it takes my blanks to heat up by using less dense coils of nichrome around the wrap, but the reason I've settled with a 1 second time is because I haven't been able to successfully make a pyrogen so I wanted the wire to stay hot for longer before burning out to increase my chances of ignition with a bare wire. I don't have mg/al but I do have airfloat dark aluminum.

This is what my igniters look like for reference.

[SharkWhisperer]

I added several teaspoons of my 100 mesh screen mixed BP to my NC lacquer dip. I let it dry for a few hours then when testing it didn't want to light off at all, checking the resistance with a ohmmeter it seems the wire burned out without igniting any of the bp lacquer. Like the lacquer coating smothered the ignition. I took a torch directly to my igniter and it burned top to bottom smoothly like a fuse. That was with three coats applied though, if I apply one thin coat the flame doesn't want to propagate all the way through in one go. I'd like to fire visco alone. I can quicken the time it takes my blanks to heat up by using less dense coils of nichrome around the wrap, but the reason I've settled with a 1 second time is because I haven't been able to successfully make a pyrogen so I wanted the wire to stay hot for longer before burning out to increase my chances of ignition with a bare wire. I don't have mg/al but I do have airfloat dark aluminum.

 

This is what my igniters look like for reference.

That looks like a looooong piece of nichrome; no wonder it takes a second to heat up. If your BP is decent and your lacquer is quenching your flame, then it's probably crummy lacquer. Or crummy BP. How does your BP burn alone in a small pile? Should go "poof" essentially instantly, without leaving more than a few char marks on paper (no burn through, and should burn faster than you can start counting). If hand-ignited, and the coated igniter only burned like a fuse, that just doesn't sound right. A thick stripe of your BP/lacquer slurry painted on paper, dried and ignited, should burn pretty aggressively and reasonably quickly. I can see an NC-only coating burn like that--unconfined NC, even from smokeless, doesn't burn all that quickly (guncotton will because of the massive surface area showing). Pyro Al can heat things up a little if added to BP alone, but I'd start at +5% (of BP mass) and go up from there in small increments until you hit a sweet spot. I question your BP quality--seems the most likely issue. With a thick lacquer and enough pyrogen, a single dip should suffice.

[Phil]

That looks like a looooong piece of nichrome; no wonder it takes a second to heat up. If your BP is decent and your lacquer is quenching your flame, then it's probably crummy lacquer. Or crummy BP. How does your BP burn alone in a small pile? Should go "poof" essentially instantly, without leaving more than a few char marks on paper (no burn through, and should burn faster than you can start counting). If hand-ignited, and the coated igniter only burned like a fuse, that just doesn't sound right. A thick stripe of your BP/lacquer slurry painted on paper, dried and ignited, should burn pretty aggressively and reasonably quickly. I can see an NC-only coating burn like that--unconfined NC, even from smokeless, doesn't burn all that quickly (guncotton will because of the massive surface area showing). Pyro Al can heat things up a little if added to BP alone, but I'd start at +5% (of BP mass) and go up from there in small increments until you hit a sweet spot. I question your BP quality--seems the most likely issue. With a thick lacquer and enough pyrogen, a single dip should suffice.

My BP is using commercial hardwood airfloat, it doesn't burn super quickly in an open pile but it does burn at a steady rate. Instead of a WOOOSH it's more like a wooOOOOOssshh. I wouldn't doubt the lacquer being crummy. I think I'll try the thing you suggested by cutting the fuse, using a single DIP and trying a small bit of aluminum. I tried a single dip earlier and it ignited unlike before with multiple coats but it was rather weak and unsatisfying.

Edited May 14, 2021 by Phil

[SharkWhisperer]

My BP is using commercial hardwood airfloat, it doesn't burn super quickly in an open pile but it does burn at a steady rate. Instead of a WOOOSH it's more like a wooOOOOOssshh. I wouldn't doubt the lacquer being crummy. I think I'll try the thing you suggested by cutting the fuse, using a single DIP and trying a small bit of aluminum. I tried a single dip earlier and it ignited unlike before with multiple coats but it was rather weak and unsatisfying.

Commercial airfloat, oh my. Not really a fan. No matter where in the world you are, you can easily find the wood to make better charcoal and faster powder. Even a cheap untreated 2x4" piece of lumber from HD etc (are you US based or elsewhere?) can make reasonably decent BP. Definitely faster than most hardwoods junk charcoal sold as airfloat. The commercial airfloat I have gets use in fountains and primes, and in my opinion is good for pretty much nothing else. Others might disagree. I hope this wasn't a Skylighter or FWC BP kit...those suck (the charcoal does, the other ingredients are fine). Are you milling your BP or just screen mixing?

 

You can get more BP onto your wire by diluting your lacquer with acetone a bit to thin it, but more BP means less NC binder. The balance might become more important with your ingredients. Hot BP might make a world of difference, even in a mediocre binder/NC lacquer... Maybe post a pic of your BP-coated igniter. Also test your igniter resistance before firing. Kinda useful to know. It's going to vary by nichrome length/number of turns, but you want to standardize your wire handling/cutting procedures for consistent results.

[Phil]

I have a bag of eastern red cedar pet bedding but I've never gotten around to building a TLUD to convert it to charcoal yet. I here it makes very hot charcoal. I am based in the US. I'm screen mixing the BP. The kno3 I think was sold as 325 mesh or something really fine, Majority of it readily passes the screen. Of course I dump the few leftover table salt sized granules back into a separate container so they don't end up in my BP. The way I'm currently making the blanks is with a nichrome wire wrapped at about 1 or 1.5mm spacing up until it reaches the other conductor. With the length of nichrome and pieces of wire I use and the wrapping I'm consistently getting 6.5-7.5 ohms. 36 gauge nichrome 80, I think the wire is solid 22 awg. I like using the heatshrink to help hold the two pieces together. How long do these typically take to dry all the way through? Could letting them dry overnight help any?

Edited May 14, 2021 by Phil

[Phil]

I made a smaller igniter with a smaller bridgewire gap and less wraps and measured it at 2.2 ohms instead of 7.5 ohms. Heats up instantly. I was a bit skeptical if it would stay hot long enough before burning out to light my crappy lacquer.

 

Did as you suggested and I cut lengthwise the bottom of a piece of fuse exposing the core, dipped it in some of my lacquer and "glued" it to the middle of the bridge wire. After letting it cure for a few minutes secured it with masking tape and this was the result. This was before it was fully dried too. I like it. If I can get five of these to go in a row I think I'll be satisfied.

Edited May 14, 2021 by Phil

[SharkWhisperer]

I made a smaller igniter with a smaller bridgewire gap and less wraps and measured it at 2.2 ohms instead of 7.5 ohms. Heats up instantly. I was a bit skeptical if it would stay hot long enough before burning out to light my crappy lacquer.

 

Did as you suggested and I cut lengthwise the bottom of a piece of fuse exposing the core, dipped it in some of my lacquer and "glued" it to the middle of the bridge wire. After letting it cure for a few minutes secured it with masking tape and this was the result. This was before it was fully dried too. I like it. If I can get five of these to go in a row I think I'll be satisfied.

Looking good. 7.5 ohms is A LOT of resistance. My entire circuit with 50 feet shooting wire, internal battery resistance, and igniter is less than that. The ERC bedding will give noticeably better results than crummy hardwood airfloat and you don't need a TLUD. Just stuff a paint can with it ($5 at HD for new one if you don't have a clean empty one), seal it tight, poke a single hole in the lid with a nail or drill, and torch it over a firepit, gas or charcoal grill, etc, rotating/flipping occasionally, until the flammable gasses stop coming out the hole. If you flip it upside down, it'll sound like a jet engine while burning off, and you get the bonus of using that energy to help heat your container. Once it stops off-gassing (maybe 30 min to an hour) I cover the hole and can with a wet scrap towel to: 1) block off the gas exchange so you don't get oxygen into the hot charcoal which can cause white ash formation, and 2) drop the can temperature faster. Don't open it until it's cool. You should have a can of nice black charcoal with only a few if any white edges. With the pre-chipped stuff, it's a simple matter to get it into dust. A coffee grinder will do it quickly but messily.

 

Strongly suggest you get yourself a cheapo HF ball mill/rock polisher (2 barrel) for milling individual comps and/or your BP. Though hard non-sparking grinding media is best, like lead balls (antimony hardened or not) or stainless steel, they are an investment. For single-chem milling, you can use lighter/cheaper glass marbles from the dollar store, but they'll take longer than lead to do the job. Some worry about milling BP with glass marbles, and I don't recommend it, though I can say I've milled probably 50+ jars long ago without issue. Important that you use single-color, transparent glass marbles, because the swirly patterned ones are likely to contain metallic pigments that might be more susceptible to sparking. Better would be to eventually acquire some decent heavy grinding media. Screen mixing efficiency is unclear because I don't know what mesh screen you're using or how many passes you're making. Milled -325 mesh KNO₃ is ok, but not if you have visible granules in it--that's definitely not 325 mesh. That too, can be additionally milled or ground in a coffee grinder, too, and should be as fine as possible. Sulfur is rarely an issue if coming from a reputable source. Charcoal can absorb a very large percentage of water from the air and still feel perfectly dry. Straight out of the retort/paint can (I use a 6-gallon lock-lid bucket from Ace hardware) fresh charcoal will have little-to-no water and can be used immediately. If you store your charcoal in a sealed container with some desiccant packets, you can keep it water free. That said, if you stored charcoal is questionable, simply spread it out on an oven sheet and bake any water out of it in a kitchen oven at 250-300F for an hour or so, and then use it or store it airtight (with desiccant; I use recyclable color-indicating silica beads). IF you have a gas oven, keep in mind that gas burning creates its own water, thus complicating your efforts. In that case, cook it at 300F for a bit, with the door cracked to let new water out, turn oven off and open/close door to let out most/all of new water, and then close it back up to cook off residual water using residual heat. Electric stoves don't have this issue, obviously. Simples!

 

Anyways, you're on your way, and it's some simple adjustments to get your BP quality turned up several notches.

 

 

Edited to clarify temps in Fahrenheit, so our Euro pals don't burn up the kitchen, tsk tsk.

Edited May 14, 2021 by SharkWhisperer

[SharkWhisperer]

I have a bag of eastern red cedar pet bedding but I've never gotten around to building a TLUD to convert it to charcoal yet. I here it makes very hot charcoal. I am based in the US. I'm screen mixing the BP. The kno3 I think was sold as 325 mesh or something really fine, Majority of it readily passes the screen. Of course I dump the few leftover table salt sized granules back into a separate container so they don't end up in my BP. The way I'm currently making the blanks is with a nichrome wire wrapped at about 1 or 1.5mm spacing up until it reaches the other conductor. With the length of nichrome and pieces of wire I use and the wrapping I'm consistently getting 6.5-7.5 ohms. IMG_0009.jpg IMG_0010.jpg 36 gauge nichrome 80, I think the wire is solid 22 awg. I like using the heatshrink to help hold the two pieces together. How long do these typically take to dry all the way through? Could letting them dry overnight help any?

If you can't smell acetone/solvent anymore than they are dry enough for use.

[WSM]

More than three decades ago, my first pyrogen was potassium nitrate and magnesium powder suspended in collodion. It worked great but if stored for very long wouldn't work anymore (they were inert six months after they were made).

 

The better pyrogen was based on H-3 (potassium chlorate and charcoal), which worked well and stored well also. Fine metal powder added improved the effect. My favorite was -400 mesh titanium sponge, if you can even find it anymore.

 

Some exotic Goldschmidt reactions (thermite-type mixtures) make for very hot components of excellent pyrogens, especially for difficult to ignite composite rocket grains.

 

An important detail is making sure there are no bubbles in the pyrogen slurry, which might leave a small gap over the bridge wire and result in a misfire failure. Making sure the slurry is in intimate contact with the bridge wire, plus being fully dry is key to getting consistent reliability and good results.

 

(can you tell I've had a little experience with this?!)

 

Good luck and be safe!

 

WSM

Edited May 16, 2021 by WSM

[Mumbles]

I came to mention what WSM brought up. BP based slurries on ematches are often not stable long term. The degradation is probably more on the order of months than hours. The nitrate in BP tends to slowly degrade the nichrome wire over time. This would probably be accelerated by humid conditions or wet acetone used to make the match slurry.

 

A common fix is to use a non-BP first coat, and a BP second dip. This protects the bridgewire, and provides some of the extra sparks, flame, burn time, and general lack of incompatibilities that makes BP ideal.

[SharkWhisperer]

I thumbs-upped Mumbles' comment but it doesn't show... anyways,

 

KNO₃ (and many other oxidizers and otherwise reactive chems) can degrade nichrome (and copper, and cheap copper-clad Al) wiring. That said, I've never had lifespan issues with BP-coated igniters. Or obvious erosion. I've made BP- (usually with MgAl) dipped igniters that have been 100% at least 2 years later (probably longer). KNO₃ can be "corrosive" (given the right scenario--i.e., moisture...), of course. And Nickel/Chromium behaves differently from pure Cu. Perc doesn't seem to erode nichrome as fast as nitrate does, at least anecdotally in my observation... Chlorate even less. Remember that's anecdotal and not evidence. Others' observations are welcome.

 

My last BP-coated igniters have never gone inert, over a long time. Perhaps using larger pyrogen particles (e.g., 20 mesh) minimizes KNO₃-to-metal contact/corrosion with local metallic components and reduce wire damage. 2-year-old fire-wires still light up motors with a fury. And it's easy to make new ones if they they don't work 100% to your liking. Just start fresh. Takes 30 min to build a whole bunch of igniters. 5 min more to mix/dip them, and 5 min to store... Easy & Affordable. A whole hour all-in, whoa!. Simples.

 

Not a big fan of "double-dipping". Leaves an extra physical layer that tends to shatter with an unnecessary "pop" (more so the more concentrated your polymer/NC concentration is) that might disrupt propellant grain integrity instead of just burning super hot. My BP motor/fireworking (not APCP) standby is thick/hot NC in dry acetone, carrying 10-20 mesh BP (hot charcoal: willow, ERC, paulownia etc) granules and perhaps 5% metal--Al is fine though I prefer MgAl--sparkier. Never Mg alone. You're not aiming for FP speeds, but a hot, reasonably quick, sustained burn. A single thin/light dip works for anything BP-based. For APCP, a similar comp is supplemented with catalyst (iron or copper oxide) and a different MgAl/Ti metal mix to ensure hot sparks, and perhaps a small sulfur component to lower ignition temperature. If I lean too far away from desired oxidizer/fuel ratios by adding a lot of metal, I'd consider spiking the mix with a small quantity of perc. This reliably fires the F/G-sized APCP motors I use. Many use boron/KNO₃ to light APCP, which will give a hot burn but boron can be expensive, difficult sometimes to source, and fumes are toxic. Or you can ditch the BP and devise a perc & metal based pyrogen, with or without charcoal. Modifying oxidizer content and fuel granule size will get you the hot burn you're looking for. I generally avoid using H3 (KClO₃ and charcoal only), though some igniter dip kits are just H3, because I prefer to avoid chlorates when possible, metals burn hotter than charcoal faster, and charcoal quality can vary more than metals from batch-to-batch. It's all personal preferences, so long as it's reasonably safe and gets the job done.

 

Delayed ignition (anything but instantaneous) when firing off a battery is generally is due to not ramming enough amps of electrical current through the bridgewire (if equipped) to instantly fire a hot pyrogen coating, and your device/rocket. Usually an easy fix.

 

Good to know your battery's internal resistance. And total resistance of your shooting wire. Both ways? And resistance of your igniter. All-fire or all-safe current? Not tough stuff but super useful. Practice caution. Eyes and hands are reasonably tough, but not all that tough... Glasses and gloves are your friends.

Edited May 19, 2021 by SharkWhisperer