17 replies to this topic

[StarScream]

Hey Guys

I’d like to share a sobering experience I had today. I hope that this information will help make all of us just a little bit safer, and maybe even help prevent a disaster for someone someday.

I was grinding up large chunks of lump charcoal today, which I always do before milling it to airfloat for BP, rockets, star formulas, etc. I used to use a small electric coffee grinder for this, but found it to be too tedious because of the small amount that can be ground at a time, and the blades in them don’t seem to last very long against hard lump charcoal either. Today I took out my brand new meat grinder that I bought specifically for grinding charcoal, and WOW what an improvement. It filled a large coffee can in about 10 minutes. It used to take at least an hour or two to process this amount with the old, wimpy little coffee grinder. I was rather impressed!

I was just about to load up my milling jar and start milling it all down to airfloat, when I decided to do something that really woke me up. I grabbed a rare earth super magnet that was sitting close by and ran it through the coffee can of freshly ground up lump charcoal, and sure enough… metal particles! They must have come from inside the meat grinder.

This stopped me dead in my tracks. Fully paranoid now, I cleaned the magnet and ran it through another container of charcoal that had been ground up in my electric coffee grinder months earlier… metal particles again! I’m guessing these particles were likely from the blade wearing down. Makes me shudder to think that I have milled many batches of BP using this charcoal contaminated with ferrous metal particles.

Needless to say, I will never again use charcoal for live BP milling that has not been thoroughly checked and cleaned up with a magnet first.

Get out those magnets boys and go fishing. Never know what you’ll catch!

Stay Safe

[digger]

Certainly sounds a little sobering.

I have to say though, I have now started making my own charcoal and I never use a coffee grinder for anything. I simply give the charcoal a slight crush and chuck it in the mill and 1 hr later it is air float.

Just to add to your bits of metal experience. I found iron fillings in one batch of KNO3 that I had bought, I always dissolve and filter a bit out of the batch to determine the insoluble impurities.

[Pretty green flames]

Some good info there StarScream. Made me rethink my method of grinding down charcoal.

Though you may want to check if the metal was present before the milling/crushing process, get a plastic hammer and smash a couple pieces of charcoal and then run a magnet through it. The metal may have gotten into the charcoal during the manufacture process and not during the milling operation.

[rocket]

I’ve heard about this problem before. The problem was from what the charcoal was cooked in. As the metal tin oxidized flakes of oxide/metal where braking off and being processed into the charcoal as it was ground.

[Bonny]

I'll check any charcoal I have around...although I think I've already processed and used it all. When I cook it, I always throw away all the small bits left in the bottom that may contain metal flaked off the tin, and only keep the large pcs. I do use a meat grinder so I will be checking any new batches for sure.

[MDH]

This is why I always damp or wet mill.

[StarScream]

Some good info there StarScream. Made me rethink my method of grinding down charcoal.

Though you may want to check if the metal was present before the milling/crushing process, get a plastic hammer and smash a couple pieces of charcoal and then run a magnet through it. The metal may have gotten into the charcoal during the manufacture process and not during the milling operation.

Metal in commercially produced charcoal is a definite possibility. The wood they use has been known to contain staples, nails, bullets, wire and more.

I’m 99% sure my metal contamination came from my coffee grinder and meat grinder, because I ground a batch of homemade willow with the meat grinder the day before I ground the commercial lump with it, and both charcoals had traces of metal in them. The amount of metal is small, but it’s there nonetheless. Any amount of ferrous (sparking) metal in a batch of ballmilling BP makes me cringe. Even pounding fountains and rockets by hand with traces of a sparking metal in the charcoal makes me a bit nervous.

This is why I always damp or wet mill.

Yuck. Doesn't that just create a big clumpy mess inside the milling jar?

[MDH]

No... I Have my ways.

[knackers]

This is why I always damp or wet mill.

have you previously tested your charcoal for metal particles ? and found some ?

i cook my own charcoal, but wrap it up in a few wraps off news paper and gently but firmly persuade it with a hammer to break it up then mill it,,, there is a small waste, about 1/4 of a gram out off 200grams, then throw the paper away and no mess, mill dry with no mess, seems easier than grinding it with grinders ( coffee or meat ), have never thought of testing for metal, but have now and found none,

Edit...... come to think of it, my cooker is stainless so it won`t be magnetic... (and won`t flake )...... all these meat grinders,, must be plated cast steel, iron ?
if you have ever primarily used them for meat, you must also have been eating it !! stainless is the way to go !

if your magnet touches the charcoal it will pick it up, ( anything will ) try blowing your magnet, if it hangs on its magnetic if not it may be static,

Edited by phill 63, 19 September 2008 - 09:48 AM.

[YT2095]

you`ll find that it will be Fe3O4 and not elemental iron itself, Fe3O4 is created in a reducing atmosphere (such that charcoal provides), don`t forget that the wood itself will contain iron as the plant itself uses it as an essential trace element!
Fe2O3 (rust) is easily converted to the Fe3O4 (Magnetite) by heating with charcoal.

[pyromaniac303]

So if the iron is not elemental, will it still retain its sparking properties or is it safer? I also have seen iron oxides being used to speed up the burn rate of rcandy propellants, would the same effect apply to BP?

Some good info so far, I have recently been using a cast iron meat grinder and never thought to check for metal particles.

[Bonny]

i cook my own charcoal, but wrap it up in a few wraps off news paper and gently but firmly persuade it with a hammer to break it up then mill it,,, there is a small waste, about 1/4 of a gram out off 200grams, then throw the paper away and no mess, mill dry with no mess, seems easier than grinding it with grinders ( coffee or meat ), have never thought of testing for metal, but have now and found none,

I used to grind my charcoal in a similar fashion, except I would put it into a paper bag and then hammer. The meat grinder works very well and is has very little mess. Just put aplastic bag over the end and secure with an elastic band.

[seymour]

While much of the flakes that come off old and oxidized drums is indeed Fe2O3 or Fe3O4, I have had flakes fall off which had silver shiny patches, were nice and bendy and were certainly not free from Iron or steel at all! While its good to discuss this in detail, the stakes are too high (you ball mill blowing up) to be casual about it, or assume that the flakes falling into your charcoal "are just ferrous oxides, nothing else".

Please, once your ferrous charcoal barrel/pot/tin whatever you use starts to rust dangerously, (or preferably before this point!) get a new one!!!!!!!

If only copper was cheaper... it would be ideal.

[Pretty green flames]

One thing, I think many of you are forgetting that nowadays most metal containers (paint cans for example) that pyros use for cooking charcoal are lacquered inside and outside, didn't it come to you that the shiny flaky stuff may just be carbonised lacquer. I'm not saying that the flakes are 100% not metal but it seems unlikely to me that metal would just flake off.

[seymour]

The drum that I had that dropped flakes containing metal had been kept exposed to the elements for a long period of time. Obviously if you keep your charcoal tins in good health, they should last safely. Unfortunately I don't have room inside for my old 200L tin, and I had to recycle it for other uses.