Nessalco Posted November 17, 2016 Posted November 17, 2016 I was given some ceramic milling media, and was milling some granular MgAl down to a very fine grade. It wasn't close, yet - probably about 80 mesh, with some very fine stuff mixed in - started as chips and milled for 6 hours. There was only 8 ounces of material in the mill - just running a test. I had just vented the jars (doing so every hour). My procedure there was to open the jar, let it sit for a couple of minutes to ensure air exchange, recap the jar then place it back on the mill. It's been raining lightly so I take the jars into a closed area, then return them to the mill. While I was placing the final jar back on the mill it slipped from my hands and fell about eight inches onto the mill rollers. WHAM!! A very bright flash, and the jar lid was blown off. The jar jetted flame for a couple of seconds, then subsided. I turned away as quickly as I could, and suffered no injuries. My mill is well bunkered, so everything was pretty well contained. I took a quick look at the jar and cap, and it appears the fire started in very fine powder trapped between the jar and the lid. The lid and some of the media shows sign of fire damage, but only about 1/4 of the MgAl appears to have burned. I'll look more closely in the morning. I don't know if it was the media, or just the fines trapped between the lid and the jar were impact sensitive, or what. I do know I really don't want that to happen again. I was careless, and got lucky. The first won't happen again, and I hope the second holds..... Kevin
Mumbles Posted November 17, 2016 Posted November 17, 2016 We're all glad you're alright other than probably a good fright. Do you think it might have been media on media impact that caused this? I think Lloyd S. or Bob Forward had something like this happen to them after milling Mg or MgAl and pouring the dirty media back into a jar.
Nessalco Posted November 17, 2016 Author Posted November 17, 2016 It could have been the media. This was the first time I had used it. Kevin
NeighborJ Posted November 17, 2016 Posted November 17, 2016 Oh man, that's more than a little sobering. I feel bad for suggesting the process would be safe. Apparently there is something which is more dangerous here than with AL. Now that I think of it, I can recall kileberios talking about adding diesel fuel to the mill to prevent oxidation. If that worked then why not use mineral oil? I just can't understand how it could have happened due to shock.
memo Posted November 17, 2016 Posted November 17, 2016 (edited) glad you are ok,damn sounds like a close call. i have been blade milling in my coffee grinder with no problems , but only 20 or 30 seconds at a time. i would ask Lloyd or august what they think. the only mishap I have had was a melted crucible in the foundry. memo Edited November 17, 2016 by memo
Nessalco Posted November 18, 2016 Author Posted November 18, 2016 Oh man, that's more than a little sobering. I feel bad for suggesting the process would be safe. Apparently there is something which is more dangerous here than with AL. Now that I think of it, I can recall kileberios talking about adding diesel fuel to the mill to prevent oxidation. If that worked then why not use mineral oil? I just can't understand how it could have happened due to shock. No worries, Neighbor. I knew there were risks. Kevin
Col Posted November 18, 2016 Posted November 18, 2016 Its good to hear you are ok. Sounds like there are quite a few factors involved, thankfully luck was on your side
otto Posted November 21, 2016 Posted November 21, 2016 Geez Kevin, I'm glad to hear it was only a "close call". Any chance residual CaCO3 could have contributed anything to this? Makes me a little uneasy now having bought into a pile of Zirc M media (used). I did clean it very, very well before using it not knowing its previous duty. My main intention for it is BP but if there can be impact initiated combustion that's still no good. This is one more re-enforcement for caution and patience at every turn, especially those operations that seem most routine and relatively safe.
Nessalco Posted November 22, 2016 Author Posted November 22, 2016 Otto, I don't think the media had any residual calcium carbonate, but it's possible. I washed it in soapy water, rinsed it three times, then dried it in the oven. I then put some samples back in water to see if anything appeared - it seemed to be clean. I think this was the result of media-to-media impact. The fellow who gave me the media said they buy this type specifically because it is non sparking.
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