Turning Archive

HAZARD with CBN wheels

John K Jordan
New to me.

I keep some magnets under the front and behind my CBN wheels to try to contain some of the fine steel dust until I can hook the grinders up to the dust collector. Today some steel dust ignited and started burning and glowing red hot. It was "smouldering", the heat moving through the steel fluff. Unnoticed it might have caused a shop fire.

I have one powerful magnet just to the side of the front of a 600 grit wheel on a bench grinder that has collected a bunch of fine powder since the last time I cleaned it, probably 3/4" of steel fuzz.

This morning I was sharpening some scrapers to get them ready for a demo next week. As usual, I had dribbled some Trend diamond honing liquid on the wheel before sharpening. The sharpening was not aggressive and I don't remember seeing sparks while sharpening.

I suddenly noticed smoke from the magnet and some spots of orange-red glow deep inside the glob of powdered steel. My first thought was to grab it and carry it outside - a mistake since the increased air flow from walking made it burn faster and hotter. So I carried it back and dunked the magnet in some cooling water to put it out.

Now I'm sure every teenage science nerd knows how easy it is to ignite fine steel wool. In fact, sprinkle a bit of fine aluminum or silver powder into the steel wool first and you will have thermite, capable of welding railroad tracks or at least dropping gobs of molten steel on the floor. But I never imagined the minimal sparks from a 600 grit CBN wheel setting the steel dust on fire!

I had been sharpening for 1/2 hour or so so I have no idea if the dust was just then ignited or if it had been smouldering for a while.

In my case I have all the grinders on a stainless steel table which may have minimized the damage if I hadn't noticed. I suspect the heat could burn into and possibly ignite a wooden table.

Action items for me:
- inform others (check)
- inspect the area carefully after each sharpening session (check)
- keep the steel dust from accumulating cleaning up every day
- experiment with the Trend diamond honing fluid and steel dust/wool and see if it if flammable and if it might contribute to the problem
- experiment with igniting steel powder stuck to a magnet to see if it might smoulder unnoticed for an extended time
- get the dust collector with spark arrestor screens hooked up to the grinders



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