kskid
Cave Dweller
Member since July 2014
Posts: 98
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Post by kskid on Sept 16, 2018 23:32:05 GMT -5
I typically rough roll several large stones with assorted smalls and 36 SiC in my QT6 for 2 weeks at a time. The barrel has been in constant use for three or four years. I've replaced the lid gasket once due to wearing through at the center post.
I recently noticed that the bottom of the barrel seemed to get progressively more concave between cleanouts. I figured it had probably been that way all along & I just never noticed. The other day I noticed that the bottom had sucked in so far that it trapped one of the large stones against the lid, causing a bump near the center of the concave barrel bottom. I know it's never been that concave before.
I know 36 is hard on the barrel, so my first thought was that it's worn the bottom thin making it weaker and easier to deform, but then I wonder how in the world is enough vacuum being created to suck the bottom inward? The tumbler is in a consistently air conditioned shop, I continually remove and add a random selection of found rocks from the same location, I use the same amount of grit and water in each batch, and the rate/amount of deformity is fairly consistent across batches. I can't imagine air is being forced out of the barrel, as there's no indication of leakage around the lid seal. I'm stumped.
Has anyone had similar experience? Any ideas to explain it? Thanks!
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Post by aDave on Sept 17, 2018 1:26:19 GMT -5
Are you filling with warm/hot water? I can see cooling of the water causing a potential vacuum within the barrel. Otherwise, I'm at a loss. I've not experienced what you have.
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Post by pauls on Sept 17, 2018 3:37:31 GMT -5
Sorry I have no idea what causes it but I know my barrels always pull a negative pressure, no leakage around my lid I have a thick rubber gasket that sucks in and never leaks, always tumbling agate, pet wood. I presume it's some strange chemistry happening. Steel barrels, (propane cylinders) Silicon Carbide Rain water. Agate (silicon dioxide) Thats all that's in there to react
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Post by aDave on Sept 17, 2018 11:32:47 GMT -5
I have been thinking about this overnight, and I'm left wondering if it somehow has to deal with the way the lid is secured as the knurled knob is tightened. When you tighten the knob, the screw post of the lid is pulled upward, as this causes the flat lid and gasket to form a compression fit against the outer lid. It may not be clear the way I wrote it, but since you have your barrels, see if that makes any sense. Notice after you put the outer lid on, there is a bit of a gap between the flat and outer lid. Tighten yours up, and see if it causes your barrel to concave at the bottom. Again, as with me mentioning filling with warm water, I'm just taking wild guesses, as I've really got no idea.
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NRG
fully equipped rock polisher
Member since February 2018
Posts: 1,687
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Post by NRG on Sept 18, 2018 22:37:35 GMT -5
The iron propane tank is rusting with the oxygen in the barrel. The iron oxide takes up far less space than the oxygen gas did before. Leaving you a vacuum.
Voilá
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Post by aDave on Sept 18, 2018 22:43:38 GMT -5
The iron propane tank is rusting with the oxygen in the barrel. The iron oxide takes up far less space than the oxygen gas did before. Leaving you a vacuum. Voilá This is a QT6 barrel which is rubber.
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NRG
fully equipped rock polisher
Member since February 2018
Posts: 1,687
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Post by NRG on Sept 18, 2018 22:50:33 GMT -5
The iron propane tank is rusting with the oxygen in the barrel. The iron oxide takes up far less space than the oxygen gas did before. Leaving you a vacuum. Voilá This is a QT6 barrel which is rubber. Not pauls barrel. Sorry, I thought he was OP. Edit:OP is prolly due to change in temp from the time the barrel was sealed to when it was opened.
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Post by aDave on Sept 19, 2018 12:09:03 GMT -5
Edit:OP is prolly due to change in temp from the time the barrel was sealed to when it was opened. So much for overthinking it. You probably nailed it. Occam's razor.
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Post by pauls on Sept 20, 2018 0:28:12 GMT -5
Thanks NRG, Rust. That was my original thought too. Nice to have it confirmed.
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Post by gmitch067 on Sept 20, 2018 9:33:18 GMT -5
kskidI do not know why... but I have been experiencing the same... I have been running one 12 lb, two 6 lb, and two 3 lb Lortone barrels near continuous for the last year and a half and I am noting that the bottoms seem to be sucking inward more and more (I check the tumbles 3-4 times daily and make it a point to feel the bottoms to see if there is any gas build-up). This year, where I live in Northern California, has not been as hot as last year... but there seems to be more concave feeling to the barrels (now... than there was 6 months ago). I use only 80 grit (or 60-90 grit) in the 3 lb. barrels, and 45-70 grit in the 12 lb. and 6 lb. barrels. The 12 lb. barrel seems to suck it in more than the 6 lb. barrels. I have not noticed as much concavity when progressing to finer grit stages... it is mostly happening in the coarse grit stage. I have a rubber gasket that covers the metal lid of one of my 6 lb barrels that keeps popping off (I will be replacing it soon)... Because of the lid problems, I double check seating and really crank down on the top screw. As I place the barrel(s) back into the tumbler I have noticed that there is no concavity. It is only after a day of tumbling that I have noted it sucks inward again.
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Fossilman
Cave Dweller
Member since January 2009
Posts: 20,709
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Post by Fossilman on Sept 21, 2018 9:11:51 GMT -5
Occasionally mine do the same, but I take no notice to it...Its when the barrels swell up and push out, than you have a problem..
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kskid
Cave Dweller
Member since July 2014
Posts: 98
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Post by kskid on Sept 21, 2018 22:21:08 GMT -5
Thanks to all for the good suggestions and comments! Water is nearly room temp... I'm inclined to believe that you called it, aDave. I do screw the top down pretty tight when I close up the barrel. I could see where the bottom might be stiff enough to resist initially, but would gradually pull in to relieve the deformed metal lid (and more so with wear). Next time, I'll leave it as loose as I dare & report the results. Just when I thought I'd overcome impatience between cleanouts, I'll be pacing again to see what happens to the barrel with the knob a bit less tight. I'll report back in a couple of weeks!
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kskid
Cave Dweller
Member since July 2014
Posts: 98
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Post by kskid on Oct 11, 2018 23:07:35 GMT -5
Well, it doesn't seem to have anything to do with how tight the lid is screwed down. I left it as loose as I dare on the last run and the bottom of the barrel sucked in just the same. Time to adopt the fossilman philosophy - pay it no mind & be glad it's not pushing out.
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