Batch 2017-batch-02

We're nearly out of Quickburst igniters, they haven't been great at lighting erythritol grains anyway, and they're kind of expensive... So we decided to experiment with making igniters, and the first ones we decided to try are "epoxy fire" using a formula from Scott Berfield.

For our first attempt, we made up a 10g batch with the following formula:

  • 68% KNO3, 6.80g, hand ground with mortar and pestle to fine grain size
  • 7% magnesium powder, 0.70g
  • 1% air float charcoal, 0.10g
  • 24% West Systems 105+205 epoxy, 2.40g
    • 2.01g 105 resin
    • 0.39g 205 hardener

Two folded papers were used to weigh out the KNO3 in one, and a mixture of the magnesium powder and charcoal in another. The epoxy was mixed in a small disposable plastic cup with a popsicle stick, then the magnesium and charcoal were poured in and mixed until complete wetted. Then the KNO3 was added and mixed until everything became a homogenous mix. It was a dry-ish, crumbly consistency, but packed into lumps easily.

We used Chinese made e-matches with 2m leads, and used plastic drinking straws about 1/4" in diameter cut into 1" lengths. The procedure was to slide the ematch through the straw, pack material into the straw from the "back" end until it was mostly full, then pull the ematch lead until the match head was just at the forward end of the straw, then pack more material in the front end of the straw until the match head was just covered. Using nitrile-gloved fingers, it was then easy to mash on both ends simultaneously to make sure we had good packing with minimal voids, leaving both ends flush with the straw.

The matches were left to cure overnight, and then the straws were carefully sliced lengthwise with a razor blade and peeled off, revealing what looked like very solid cylindrical igniters. They look a lot like the Quickburst ones.

These igniters were made on 17 May 2017.

Results

They didn't work. The basic problem is that the pyrogen on the Chinese e-matches is aggressive enough that they blow the end of the epoxy fire cylinder apart without igniting the rest of the igniter. Next time we'll try with home-made bridge wires on shooter wire.

Observations

A 10g batch was just enough to make up 6 igniters, and the pot life seemed a little tight. Next time, it seems like trying a 15g batch with the slower 206 hardener might be a good plan?