Name: Insensitive Bridgeless E-match
Source: Alan Yates
| percent | parts | component |
|---|---|---|
| 64.00% | 16 | Potassium Nitrate |
| 12.00% | 3 | Lampblack (conductive) |
| 12.00% | 3 | Magnesium (-60 mesh, flake) |
| 4.00% | 1 | Aluminium (-40 mesh, granular) |
| 4.00% | 1 | Aluminium (16 um, bright flake) |
| 4.00% | 1 | Sulfur |
Using 1 part to 1 gram makes a good quantity which can be kept in a small (~75 ml) polypropylene jar ready for dipping hundreds if not thousands of match heads.
Screen together the Sulfur and Potassium Nitrate using at least a 60 mesh screen. Alternatively, ball mill them for a few minutes along with the lampblack if you wish.
Measure out the Lampblack, it will be at least 6 heaped teaspoons of volume. Add sufficient Acetone to make the lampblack into a thin paste, this will make it much less messy to work with than attempting to screen it together with the Sulfur and Potassium Nitrate.
Add the Magnesium and Aluminium to the Lampblack paste, then mix in three to four teaspoons of syrupy NC lacquer and mix well. Mix in the Sulfur and Potassium Nitrate, add more Acetone as required to produce a suitable consistency paste.
Cat-5 solid core cable makes an excellent e-match head. Cut about 600 mm of the cable and remove the four pairs from the outer sheath. Separate the 4 pairs and twist them tight at one end. Tie a knot in the opposite end about 3 inches from the end, bare about an 3/4 of an inch and twist them together (safety shunt). Bare 10 mm of the other end and twist the insulated part together so there is about 0.5-1 mm gap between the bare conductors. The end is ready to dip.
Depending on the consistency of your composition paste it may take 2-3 dips to produce a good 2-3 mm in diameter blob of coating. There is no need to dry it between coats, a brief delay and some gentle blowing between dips seems to do the trick, it will skin-over and hold another coat. Be careful not to make the blob too big, it will just take longer to ignite than it needs to (larger heat capacity).
Once completely dry the match will measure around 3.5 Ohms and ignite from a 9 Volt battery in around 1 second. It will not cook off from 50 mA continuously. No where near as sensitive as a nichrome bridged match or my sensitive bridgeless pyrogen. I consider this lower sensitivity a safety feature. These e-matches are high-current igniters, designed for mains or capacitive discharge ignition systems, but a beefy conventional system will fire them with no significant delay.
Conductive Lampblack may be hard to find. Ethyne (Acetylene) Black is the best if available, it is extremely conductive, but often contains traces of acetic acid which is no problem with this composition but it might be with the sensitive version.
If you don't have access to Magnesium or fine Aluminium flake any fine metal powder will do. Zinc dust works well, as does fine spherical Aluminium if you have nothing else. The metal is basically there to produce sparks and a higher burning temperature. Some Titanium makes an excellent spark generator for igniting stubborn compositions.