jamesp
Cave Dweller
Member since October 2012
Posts: 36,154
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Post by jamesp on Nov 30, 2019 8:53:31 GMT -5
Hot rod coarse grind rotaries:
These 7 pound capacity barrels are rolling 1 to 1.5 inch rocks plus a single 1.5 to 2 pound big rock added at 60 rpm. They are often run at 80 rpm without bruising due to small diameter and slurry if no big rock is added. They do not have a tall fall being small in diameter which allows safer higher speeds. Large diameter barrels present problems at higher speeds due to the taller fall ratio with typical 1 to 2 inch rocks. 1/2 X mass X velocity X velocity = impact force. The ratio of rock size to inside barrel dimeter is small which allows proportionately much high speeds without high velocity impacts. The SiC 30 breakdown rate to SiC 500/1000 tumbling 1 to 2 inch Mohs 7 rocks is well under 48 hours with slurry which equates to fast grind rates. To avoid clean outs every 2 days some slurry is poured off and water added to thin and a 1/2 dose of SiC 30 added. Best to do 48 hour servicing.
Video camera has a hypersensitive microphone. The sound of an efficient safe grind is bang on.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,154
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Post by jamesp on Dec 13, 2019 7:57:16 GMT -5
For the people that may want to speed coarse grind. But having to add some coarse grit and thinning slurry every day or two.
This ball mill illustration was used to estimate the fastest speed a 6 inch I.D. rock tumbling barrel should rotate.
Even at the subcritical speed of 85 rpm some impacts are starting to occur however a tacky slurry would reduce this impact behavior.
Conclusion for safe speed was 60 to 80 rpm with slurry.
6 inch inside diameter ball mill, without slurry, 3/8" steel balls:
subcritical speed = 85 rpm - just beginning minor impacts critical speed = 113 rpm - moderate impacts super critical speed = more than 113 rpm - total destruction
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Post by RocksInNJ on Dec 13, 2019 8:06:54 GMT -5
Great video!
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,154
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Post by jamesp on Dec 13, 2019 8:29:02 GMT -5
Well it's not an exact comparison of a rock tumbler RocksInNJ but it tells a bit about the mysterious behavior within a barrel. What was surprising is that the damage occurs at the upper right center at critical speed and lower left center at super critical speed. In both situations the impacts are rock on rock and not rock on barrel. Just looking at the pros and cons of speeding up the coarse grind. This stuff excites me(yes a pervert). Consider one fast 12 pound tumbler that can shape more rocks than three slow 12 pound tumblers using about the same power. Granted, it would need to be built more rugged, make more noise and require more attention.
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Post by RocksInNJ on Dec 13, 2019 9:08:50 GMT -5
Granted, it would need to be built more rugged, make more noise and require more attention. Sounds like a few women I know lol.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,154
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Post by jamesp on Dec 13, 2019 9:11:37 GMT -5
Granted, it would need to be built more rugged, make more noise and require more attention. Sounds like a few women I know lol. Got no solutions for that issue RocksInNJ lol. celibacy perhaps...
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