Swede Posted July 15, 2009 Posted July 15, 2009 (edited) Those who know me, know that I love making tools and tooling. A few days ago, I made an impact sensitivity rig to test compositions using the traditional falling weight test. Yesterday and today, I decided to whip up a fairly simple BP burn timer using off the shelf components I had on hand. Prior to this, the speed of a particular BP batch was visual - "Wow, that's fast!" - or counting frames in a video. A lot of guys launch objects like tennis balls to test BP, and time the trajectory, which is probably as good a method as you can do, as you are measuring real-life performance. But I've always thought a channel of BP, with a good timer, would be cool. A couple of years ago, I helped my daughter with a science fair project, and we made use of a Red Lion Control timer, model CUB7T0. This is a very simple timer that turns ON with a complete circuit between 2 terminals, and turns OFF when the circuit is broken. Best of all, it measures down to the 1/1000th of a second. The basis of the device is a length of aluminum "L" mounted on a board. Two brackets to hold the channel were milled out of additional aluminum. http://www.5bears.com/firew/bpspd01.jpg To complete/break the circuit to activate the timer, I initially thought an ultra-fine copper wire could be burned through by the BP flame, but tests showed this to be impractical. I then decided to use a pair of SPDT micro switches set up to pivot, with fine cotton thread holding the switches closed. When the cotton burns through, the release of the first switch completes the circuit, and the burn-though of switch #2 halts the timing. http://www.5bears.com/firew/bpspd03.jpg I mounted the timer on the board using simple strips of velcro. The entire pine board got a couple of coats of nitrocellulose lacquer, the wood finish of choice for the pyro! http://www.5bears.com/firew/bpspd02.jpg This timer was not expensive... I'm thinking it was about twenty bucks. If you need a super-precise (and inexpensive) timer/counter, this is a good one. For the first test, I used a decent riced lift powder. I filled the channel to a visually pleasing state, nothing excessive, but a good, consistent trail that I knew would burn fine. I weighed the BP, and it was about 4.2 grams, so I reduced it to 4.0 grams, and that will be the amount of BP to use for all future tests to maintain consistency between runs. Mass (I think) is better than volume, because pressed BP will be significantly less volume-wise, yet the amount of gas products (and power) should be similar. Outside, I rigged the device and attempted to video the test, but the video tanked. The rig did not, and everything worked perfectly. The powder train burned in 0.459 seconds, with the cotton threads and micro-switches doing what they are supposed to do. I am going to ignore the time that is consumed by the switches because mechanically, they should cancel out if they perform equally. In other words, if the first switch takes 0.005 seconds to activate the timer, and the flame front is 0.005 seconds past the thread, when the flame hits the STOP thread, it'll be another 0.005 seconds before the timer halts, thus cancelling each other. The resultant time should equal the burn. There will always be minor variations in how the powder is laid, but I'm guessing further tests should show good consistency. http://www.5bears.com/firew/bpspd05.jpg The whole thing is a "relative" setup, meaning the measurements have meaning only for me; I'll be able to compare batch "A" vs batch "B" if I run them identically. I'll be able to compare different charcoals, added binders, pressing, granulation, all sorts of things. It's also pretty fun to run it, and of course a good whiff of BP smoke is very motivating, always a good thing. It would also be a good setup for a BP speed contest at a meet or similar. Edited July 15, 2009 by Swede
andyboy Posted July 16, 2009 Posted July 16, 2009 I've always wanted one of these since I saw something similar on Dan Williams page but there would have to be multiple tests on the same batch since the flame jumps from time to time. Good job as always, I love to see the attention you put into everything you do.
Swede Posted July 16, 2009 Author Posted July 16, 2009 Thanks Andyboy, I agree that three separate runs with the same BP, averaged, should produce a good number. It was a quick and dirty project on a day that would otherwise be wasted. I don't know how useful it would be, beyond a curiosity. I guess if one was really deep into BP speed, then it'd be useful. Maybe it'll give someone ideas.
andyboy Posted July 16, 2009 Posted July 16, 2009 Now, just hook it up to a mortar and use it to measure the speed a shell exits at, shouldn't be to complicated.
dagabu Posted July 21, 2009 Posted July 21, 2009 Thanks Andyboy, I agree that three separate runs with the same BP, averaged, should produce a good number. It was a quick and dirty project on a day that would otherwise be wasted. I don't know how useful it would be, beyond a curiosity. I guess if one was really deep into BP speed, then it'd be useful. Maybe it'll give someone ideas. Have you tried quick match yet?
Swede Posted July 22, 2009 Author Posted July 22, 2009 Have you tried quick match yet? No, but the machine should work fine for both BM and QM. With quick match being so fast, the disparity between the switch actuations might be a factor. If switch "A" takes 0.013 seconds, and switch "B" takes 0.019 seconds, that error would definitely impact a QM test. I'll give it a try. Should be interesting.
Recommended Posts