Anyone Know Why Metals Spark?

M

me2

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I've seen many claims on youtube that any sparking of the edge is causing damage to the heat treatment. My own experience sharpening with a belt sander does not support this. RichardJ's experience with paper wheels on his knives doesn't appear to support it either.

So what causes blades to spark? I'm not just talking about grinding. When you hit sword edge to edge they will spark as well. I've sparked many a machete when accidentally hitting a rock, and when throwing rocks at some old metal framed TV trays, the rocks would spark when they hit the frames. (I was using a sling, not by hand throwing.) I am refering to blades since this is a knife forum. Also, I know that some metals don't spark, like the copper based alloys used for non-sparking tools in hazardous environments.
 
If you get iron hot enough in an oxygen atmosphere it will burn.
Apply a spark to steel wool in a pure oxygen atmosphere and it will burn with a flame. That is what happened in the Apollo 1 disaster.

IIRC sparks are small pieces of iron knocked of the blade. The friction of the impact gets them hot enough that they burn in the air.

Affect the heat treat? no way.
 
the oxidation reaction of copper is not exothermic enough to produce flame.
 
Not really related but one time I was shooting bow&arrow and hit a piece of farm equipment and it sparked the tip and the arrow still hit the target. Not exactly a good way to shoot but cooler than hell :thumbup:
 
Generally speaking, the spark is caused by a very small piece of the steel being chipped off. Now this tiny piece has a larger surface area to mass ratio. The tiny piece begins to rust/oxidize fast and give off heat. It gets so hot it begins to glow red. That is your spark. It's usally not the stone that sparks, but the iron alloy which begins with iron plus carbon to increase hardness.

If you would like a more formal explination, with a little more of the science behind it, you may go here -

www.survivaltopics.com/survival/flint-and-steel-what-causes-the-sparks/
 
Google told me these folks said it's a pyrophoric action of iron being exposed to steel. That might also explain why 5160 produces a cuter shower of sparks than 154CM.

edited to add: I type slow. What saw45 said!
 
knarfeng said:
IIRC sparks are small pieces of iron knocked of the blade. The friction of the impact gets them hot enough that they burn in the air.

Affect the heat treat? no way.
Click to expand...

Well, it's a matter of degree. When grinding on a piece of steel, the sparks will fly from the first instant, but that doesn't mean the whole piece is hot...yet.

Keep a water bucket nearby, and dip your work often. If it's too hot to hold in your bare hands, it's too hot.

Keep in mind that thin metal heats much, much faster, so you will need to cool it continuously. Like when working on the cutting edge.

Definitely none of your work should change colors.
 
it makes me laugh when guys say the paper wheels ruin the edge. there is no possible way for the edge to heat up enough just working up a small burr. however it is possible after numerous passes and with enough pressure either on a belt sander or on the abrasive wheel to get a blade hot enough to turn colors and cause any damage. someone would have to be pretty illinformed about sharpening to do something like this and probably shouldnt be using power sharpening equipment. i posted a message about a few myths or false claims i read or heard over the years. http://sites.google.com/site/richardjsknives/using-the-paper-wheels
 
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Thanks people. I guessed it was something along the lines of the small bits burning all by themselves, since it doesn,t take a grinder to make sparks. That pesky oxide layer gets in the way of all sorts of cool stuff. This is the same reason that there is a lot of caution applied to any dust of aluminum or titanium, though these need a spark to start the reaction, like a cigarette or match. I know that grinding can cause problems with heat build up, but just the presence of sparks doesn't mean it has. I have also noticed that only my carbon steel blades regularly when being sharpened, though the stainless ones will do it too if I'm not careful.
 
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