11-18-2018, 11:58 AM
(This post was last modified: 11-18-2018, 12:00 PM by Mark Reich.)
Friction certainly gets metal hot, but I believe sparks are a different thing altogether. Friction produces heat, but heat isn't fire. You can get a bunch of hot steel particles without any sparks, which is common with lower speed grinding and softer steel. When you see a spark it's because a steel particle is actually "on fire", but it burns from reacting to the oxygen in the atmosphere. Yes, more pressure (which is a lot like "more friction") produces more sparks. Perhaps more friction makes the particles hotter, which leads to easier combustion. To be honest I'm not exactly sure what role friction plays, although I can tell you I don't see friction mentioned in relation to sparks. There is something called "oxidation potential" or "reduction potential" that seems germane to the topic, although it gets lost in translation to me.
Check out "Spark Testing" on Wiki. It's one of the most complete guides to different sparks I've seen. It's fun to actually observe the variety of sparks, and learn the subtle differences. An angle grinder is probably the best tool for spark testing because the speed and coarseness of the abrasive produces sparks from merely touching practically anything.
Files are hard, so the particles coming off are very small. Small particles have a lot of surface area (to react with oxygen) compared to their mass, so they immediately burst into flame even at low speed. The softer the steel the larger the particles, and large particles need more speed (perhaps more friction...?) to oxidize fast enough to light up.
The alloying elements of the steel have a lot to do with the sparks too. Chromium doesn't oxidize (rust or burn) very readily compared to iron, which is why stainless steel particles aren't reactive enough to oxidize quickly enough to burst into flame compared to plain carbon steel.
This is a very interesting topic to me, so I'm willing to go out on a limb to throw my 2¢ into the ring. I have no formal training to back any theories I'm mentioning, but I've seen a lot of sparks.
ps- Magnesium fire starters are a lot of fun to me too, Mr. Bud.
Check out "Spark Testing" on Wiki. It's one of the most complete guides to different sparks I've seen. It's fun to actually observe the variety of sparks, and learn the subtle differences. An angle grinder is probably the best tool for spark testing because the speed and coarseness of the abrasive produces sparks from merely touching practically anything.
Files are hard, so the particles coming off are very small. Small particles have a lot of surface area (to react with oxygen) compared to their mass, so they immediately burst into flame even at low speed. The softer the steel the larger the particles, and large particles need more speed (perhaps more friction...?) to oxidize fast enough to light up.
The alloying elements of the steel have a lot to do with the sparks too. Chromium doesn't oxidize (rust or burn) very readily compared to iron, which is why stainless steel particles aren't reactive enough to oxidize quickly enough to burst into flame compared to plain carbon steel.
This is a very interesting topic to me, so I'm willing to go out on a limb to throw my 2¢ into the ring. I have no formal training to back any theories I'm mentioning, but I've seen a lot of sparks.
ps- Magnesium fire starters are a lot of fun to me too, Mr. Bud.