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An alternative ball mill - tumble tryer, er dryer.


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#1 ChrisPer

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Posted 14 March 2021 - 08:15 PM

When I decided I wanted to make my own BP, I was inspired by Skylighter's article on making high-powered black powder. I wanted to make hotter powder than the commercial product we could have once got here, but now even that is unobtanium. I wanted it to be like Swiss 3Fg.

 

Ball milling is obviously needed to make good corned product. I started pulling together kit, watching youTube and building tools. (Have you seen Clickspring's channel? Oh wow.)

 

I hunted for a rock tumbler but even secondhand ones were very hard to find. We dont have Harbor Freight here, and the local vendors retail price is way too much.

 

Verge collections of large rubbish are a big thing here. We go sharking, cruising the piles for garden furniture and toys for grandchildren. From an earlier one I had slabs of steel 19mm and 25mm thick for a Skylighter-style hydraulic press! Hmm, what has drive shafts and motor I could loot for a tumbler?  Oooooh, a tumble dryer would also have a giant pulley for reduction!

 

So I thought a moment more and said why build another frame and motor mount? Just mount the white-pipe tumbler barrel inside the dryer tumbler. It took a while to think that out. MDF profiles bolted against the three ribs in the dryer drum now make up a spider to hold the barrel in the centre.  I used high density foam scraps from an Ikea kids play mat to cushion the barrel in position.

 

I bought 150mm (6") sewer pipe and inspection caps and build two drums. Ribs inside.  

 

Sandbags for safety? I stacked up bags of pool salt. Same price as sacks of plasterers sand, dont have to fill, and can use in the pool later. After seeing a youTube of someone letting off small explosive charges in a dryer, I found a 3' square aluminum expanded mesh for confining door explosions. 

 

A chunk of the same mesh as a bucket screen is now ready to screen media balls from product when emptying the mill barrel.

 

My first runs revealed a lot of problems. 

 

A cargo strap to hold it in axially didn't work; the strap tended to fall off around the roundness of the barrel lid even with duct tape trying to retain it. Yesterday I set bolts through the MDF profiles as lugs to run cord lashing around.  I will add hooks and rubber strap next.

 

The 150mm full-diameter inspection caps leaked potentially explosive dust in to the dryer. Strip, vacuum out. Duct tape wrap of  lid to confine dust to barrel.

 

The dryer timer went up to 120 mins. I hated not being able to set it running for more than two hours when the experience of others shows more is needed, 4-6 hours. 

 

The dryer stops and reverses direction every minute. By my calculation this drops about 5 seconds or 8% of milling time in the toilet. Instructables.com has a couple dryer motor salvage articles, and its clearly possible to wire it differently.

 

I stripped the dryer and traced out the wiring, trying to understand all the switching. Having found everything I expected (and a lot I didn't expect -clever guys these appliance makers), I sketched an original circuit diagram for the machine, and thought out what I wanted. Now it has:

Door safety switch and broken belt detector as per original;

Three position switch (was hot, cool, warm) now does 'off', clockwise, anti-clockwise. Re-labelled appropriately.

Time switch and auto-reverse are completely out of the circuit; knob removed from fascia.

All thermal cut-outs for overheating are out;

Heating circuit and element completely removed. (the element is a 400mm dia ring - I wonder if it could be useful? Would it be tungsten, or nichrome?)

And for a few $ I got a 24hr time switch for the wall socket, which lets me set start and stop times for the run, at a distance from the machine. For single-ingredient milling it could be left unattended to start and end.

 

Now we are cooking! 


Edited by ChrisPer, 15 March 2021 - 12:11 AM.

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#2 SeaMonkey

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Posted 14 March 2021 - 11:43 PM

Great story!  Goes to show what some determination and ingenuity are capable of!


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#3 ChrisPer

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Posted 15 March 2021 - 01:09 AM

Thanks!

 

 

For those interested:

On this Simpson dryer the pulleys at the back had nothing to do with the drum. They run an extractor fan which is like the old blower for a forge - just radial vanes pulling air in past the heater element and through the drum, to exhaust at the top rear. 

The drum drive belt is only 1/2" wide rubber, grooved, and wraps directly around the middle of the drum.

There is no ball or roller bearing setup for the drum; instead, the front and back  of the drum have a 1/2" axial length cylinder formed around the opening and around the mesh of the closed end, about 200mm dia at the closed end, running in formed sheet metal rings, with a strong fabric tape between the drum and frame to separate the metal from rubbing.

 

The barrels I made are 150mmx150mm long sewer pipe, from the guidelines in the ball milling post, intended to mill 500g/1lb of powder at once.  Balls are .690 cast, and I plan to make a cylinder instead of ball and re-cast in wheel-weights or some other harder lead alloy.  The screw caps seem like a good idea but since I have to tape them I might as well have gone to end caps both ends and saved a lot of time modifying the fitting to make it short enough.

 

If I find a suitable pot system I would like to go to 8" diameter.



#4 ChrisPer

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Posted 25 March 2021 - 06:39 PM

Pro tip1: If you replace the fan belt, it gives a lovely draft of air through the dryer drum, around the tumbler barrel, which might help cool the bearings and motor.

 

Pro tip 2: If the tumbler barrel leaks, that fan will evenly distribute a half-pound of meal across every horizontal surface in the workshop despite the best efforts of the sandbags and mesh to keep trouble enclosed.  :blush:


Edited by ChrisPer, 25 March 2021 - 09:57 PM.


#5 Richtee

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Posted 26 March 2021 - 09:46 AM

 

Pro tip 2: If the tumbler barrel leaks, that fan will evenly distribute a half-pound of meal across every horizontal surface in the workshop despite the best efforts of the sandbags and mesh to keep trouble enclosed.  :blush:

Heh... 

 

Pretty cool contraption there, tho! Well met!


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#6 ChrisPer

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Posted 05 April 2021 - 06:56 PM

Pro tip 2: If the tumbler barrel leaks, that fan will evenly distribute a half-pound of meal across every horizontal surface in the workshop despite the best efforts of the sandbags and mesh to keep trouble enclosed.  :blush:

 

My mistake. The whole pound of meal was vented. The balls in the tumbler barrel were pretty much whistle-clean.

 

I have done 8 hours of vacuuming and moving stuff to remove the dust.  

 

Then I opened up the tumble dryer, and I found that the tumbler barrel was still retained in the spider frame by its new lashing system.

 

But the lid was completely unscrewed, despite the duct tape I put around it to seal. Obviously it was not clean enough when I taped it shut and maybe not tightened down, but I didn't think that should happen!  <_<

 

My assessment of the cause: the tumbler barrel itself was loose in the mounting frame, and only the lid  was supported by the foam packing. So the tumbler barrel was relatively free, and it just unwound from the lid under the large weight, and rotating hammering, of the ball media charge. 

 

SO, I stripped and cleaned the  dryer inside and out, and weighed a new charge.

 

The barrel is cleaned outside with turps to let the grey tape stick, and a careful double taping applied. 

 

I will add some wedges to immobilise the tumbler barrel in the frame. Also, I will make the next barrel with two 6" end caps on the barrel instead of a screwed inspection cover lid.

 

Meanwhile, the previous batch pucks have been snipped up, ground in the ceramic burr coffee grinder and sieved. 

 

The batch yielded about 70% 3F, 20% 4F,   -  and 10% fines to add to the next batch of pucks.

 

Density up to 1.77 in pucks, and reached almost 90% of commercial powder density in the volumetric measure - ie I set an adjustable measure to 100gn marking, and the charge thrown weighed 88gn.

And my open-air burn test gave a very fast BOOF!  

 

This is REALLY good!  :D 


Edited by ChrisPer, 05 April 2021 - 08:49 PM.





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