View Full Version : Can shredding

04-23-2004, 12:12 AM
I would like some ideas on a problem that I have. Any suggestions will be appreciated. Between my beer drinking and others soda pop drinking there are a lot of cans available for my metal casting habits. I don't like crushing cans because the size and shapes are so varied. I've been thinking of making a can shredder that I can set up on my lathe. My current consept is a tube that leads to a drum on the lathe that has carbide bits that shread the cans in short order. The drum design must not load up with the gummy aluminum and the shreaded aluminum should go out of a shoot into a bag or a can. The best design would allow for a big hopper that would take a trash can full of alumimun cans and the lathe would just grind them into shreds.
A lubricant may be necessary to keep the edges from loading up.

Any Ideas?



04-23-2004, 12:48 AM

04-23-2004, 06:57 AM
Here local they use a hammer mill at one yard and a converted limb shredder at another,both big monsters.I would bet a common lawn mower with a modified blade would do the trick,it would make a little noise though.

Another alternative would be a briquett spike in a press,basically a male spike and a female cone mounted in an over grown can smasher,you keep pushing one down on top of another until 20 cans take up the size of one and it still gets rid of the mositure in the can.Just a thought.

04-23-2004, 10:11 AM
Spence: Several years ago,friend and i discussed same problem. The residue in the cans is reason enough to not use the lathe. We discussed shredders, even a furnace that would come on, melt the cans weekly (idea rejected but not for moisture problems), finally he built a machine holding two rubber tired automobile wheels,running tread to tread. a loading chute fed the cans, tires flattened them. Garbage can caught them.

It worked, tire pressures were less than 30 psi but did take some adjustments. The machine was too big for the shop ( can volume did not justify the storage room). Modifications were more fun after a few cans of beer and contemplation of the problem- For example: When tilted back to 45 degrees launch angle, direct drive from a 1/2 hp motor, you can feed one can at a time and put cans in a collection can (Garbage can) on the far side of the shop. Trick is to put the collection can where the cans are going, rather than adjusting the launch machine. (sort of like shooting at a barn and painting a bullseye around the hole)

ANy way, two tire, tread to tread, belt drive (direct drive lacks torque to handle multiple cans) and rain coat (the partial cans spray considerable distance).

Friend died, this machine was one of our notable failures to solve all the worlds problems. Old steel beer cans were better- man could develop a grip by crushing them.

04-23-2004, 02:47 PM
I woouldn't do it on a lathe, but a gang of old carbide-tipped dado blades on a common shaft should do a pretty good job. Use the ones with a small number of teeth which normally go between the finer-cutting blades to clear the middle of the dado. Have heavy stationary fingers between the blades, but not too close. Run the blades so they are coming up as they hit the can so the uncut portion will fall back to be hit again.

Hope that's not too much of a "whacko" idea. http://bbs.homeshopmachinist.net//biggrin.gif


[This message has been edited by winchman (edited 04-23-2004).]

Excitable Boy
04-24-2004, 02:38 AM
Docsteve, the images are priceless. I can see some buddies and I building a machine like that sometime in the past if we'd had the raw materials. Great Story, thanks.


Pursue Excellence and the rest will follow.

[This message has been edited by Excitable Boy (edited 04-24-2004).]

[This message has been edited by Excitable Boy (edited 04-24-2004).]

04-26-2004, 09:09 AM
I'm sure you guys know all about the danger of water and melting scrap. I just think it is ironic that the aluminum die cast company were I work we are not allowed to bring in aluminum cans for lunch. All the soda machines dispence cups. This is because wet or potentially wet scrap is kept sepparate and run through a drier first. If something wet is in the regularly dry scrap from the die cast machines it could cause an explosion of molten aluminum at the melting furnace. The weight of all the rest of the scrap would push the soda can down under the 1250 degree molten aluminum. As soon as the heat gets to the moisture much aluminum leaves the furnace.

I used to operate a die cast machine before automatic ladles were used. You have to be sure anything you stick into the aluminum is dry or it would blow up in your face.

Sometimes if I was bored I would wring out my soaking wet gloves over the molten aluminum. The water balls up and sometimes dances. It stays about one eighth inch above the aluminum as though floating.

Super Dave

04-26-2004, 11:20 PM
Good point,when I run my furnace I have a basket on top where I can place about 60 lbs of mixed scrap(cans,screen door ex,cast aluminum etc)it allows the use of waste exhuast heat to both dry out and pre-heat the next batch before it hits the pot.Saves on fuel and time,pre-heating in this manner cutts the melt time nearly in half.

04-28-2004, 09:23 PM
We had the same problem with molten lead and zinc tanks at a place I worked. However the moisture wasn't the only problem. Water boils off at 212, so anything that held water would be too cold to put in the molten metal. All tools must be warmed (and dry) before going into the tank. Nothing like a lead bathe if you got in a hurry.
David from jax

04-30-2004, 11:03 AM
I have been TOLD,several times/several places, that plumbers stick a wet finger into molten lead or solder, that it just sizzles and you get finger out quickly there is NO sensation of heat nor damage done.

Never tried it my self, never saw it tried, ain't gonna try it, don't suggest ANYONE try it. Don't need no safety lectures, seems to me that a speck of dross, too cold a pot etc could make things go wrong.

Anyone actually know if it works?

04-30-2004, 04:08 PM
Hey Docsteve66,
I don't know about a wet finger in molten lead (and I'm not about to try it) but I
was present when a plumber was adding some
old lead pipe to his pot that had some water in it.
When they got him to the emergency room
the doctors lifted his eye lids and pryed
out lead that conformed perfectly to his
He didn't lose his sight but had several bad weeks.


05-01-2004, 07:40 PM
Few years ago, I was using a "hot glue gun". Must have been some water in there, somewhere. The glue kind of backfired, sprayed hot glue all over face and one ear. Looked like a 'coon for a while, skin peeled above and below the glasses. No scars now, quite painful for a few moments. I would have thought (had I thought at all) that any water would have evaporated as the glue was fed into the chamber. Wife peeled a "mask" from the face and glasses (there were holes in the mask). We forget the large aomunts of heat (as opposed to temerature) that accompany a change from liquid to solid or gas to liguid. Really cooks like a crock pot as it cools.

05-03-2004, 09:14 AM
I don't think I'd stick my finger (or anything else http://bbs.homeshopmachinist.net//biggrin.gif) into a pot of molten metal. But I have held a boiling pan of water in the palm of my hand (several times), and there's no heat felt on the bottom of the pan. (As long as the boiling continues!)

Oops, forgot to add: Use a cast iron pan if you decide to try this.

[This message has been edited by lynnl (edited 05-03-2004).]

05-03-2004, 12:24 PM
"...there's no heat felt on the bottom of the pan. (As long as the boiling continues!)"

I'm suspicious about that, and I'm not about to try it. The only reason the water would continue to boil is that heat is being transfered from the pot to the water. If there's enough heat available to raise the temperature of the water above the boiling point, there's certainly enough there to burn your hand. The transfer of heat isn't upward only; it goes toward anything at a lower temperature.

My guess is that the time it takes for you to start FEELING the heat is about the same as the time it takes for the bottom of the pot to drop below the temperature required to boil water. It's not unusual to get a burn injury even though you moved away from the hot object before you felt any pain.


05-03-2004, 01:15 PM
i poured molten lead over my fingers once skin came right off them - nice burns
- and had to do a dance for a while.
wouldnt stick my finger in any lead.

a story i heard -around here there was a person who discovered that he could pick up portugese men of war ie the nasty jellyfish with a float on it -he had thick calloused hands- worked fine until one day he had a pee after............

05-03-2004, 04:00 PM
Roger, I won't attempt to explain all the physics involved. ('cause I don't remember) But (with a heavy cast pot) the bottom is at room temp while it's vigorously boiling ...a matter of 5 - 10 seconds or more. As the boiling subsides you'll feel the bottom start to warm up, slowly at first then more rapidly. But not so quickly that you can't set it down without being burned. It doesn't get uncomfortable til the bubbles have almost totally stopped.

You can safely test it by simply bringing a finger up close, then closer and closer til contact is made. You'll have time to back it away if it's too hot.

It doesn't work that way tho with a thin aluminum or SS pot or pan. I think because the entire pan (sides, etc) just don't retain enough heat to sustain the boiling process when removed from the heat source. I haven't tried it with any kind of ceramic container. Seems like that should work too.

05-04-2004, 11:10 AM
This one I HAVE done. Most here have done too, but for anyone who has not:

You can boil water on a sheet of paper, over an open flame. Seems the heat of flame is transfered to the water fast enough to keep the paper cool. the paper above the water must NOT be touched by the flame.

Had a smart ass young engineer, one of the others showed him the stunt. He repeated the stunt for a bet in one of the shops. They all had seen it done before, but the young fellow was fresh meat.. The old fellows bet was that he could not do it- Acted just as though they had never sen it done.. The older guys gave him a Dixie cup to demonstrate his expertise with. Course the lower rim caught fire, let the water leak out, put the fire out. the water never boiled. Young fellow learned to think a little more from that and more things he jumped into.

Gonna check out the wet finger in lead thing next time i get a chance. Affix (firmly so it can be pushed into the lead) a wet weiner on a LONG stick and dunk it. I bet on it being exciting. Damn fool stunt for anyone to try!

05-06-2004, 12:34 AM
most of the metal is in the pulltab - take them off and return the emptys for refund. The bad thing about the cansis the urethane coatings inside and out and the food let over - better off with crappy old auto transmissions

05-13-2004, 01:23 AM
Hi Thrud,

So good to hear from you. I hope you are enjoing the summer and getting out between hospital visits and not eating too much of your sisters meatloaf.

I'm getting pretty familiar with aluminum and I like using cans because it is a resource that I have and it is neat to make something useful out of them. The problem with cans is that the aluminum is to gassy and too soft or is to pure unalloyed aluminum (once the 50% slag is removed.) I like melting down castings whenever I come across them and they still contain residual degassing compounds and some useful alloying metals, so is better for castings where those properties are important. Still it is nice to have the raw materials on hand for whatever castings you want to do.

I think that the problem of can shredding or crushing is common enough to be a good project for a consumer product. Some of my ideas for a shredder would result in a noisy appliance. Another Idea I had was a setup of cone shaped rollers that would roll the cans into a solid extrusion material.

One day I would like to be involved in manufacturing a product of my own. Nothing else offers the ability to scale up income/production like that. Of course software has that beat because it scales up with a manufacturing cost increase and material cost increase of nearly zero. Bill Gates had the right vision at the right time.

05-13-2004, 08:59 PM
I read a post on this very board long time ago that someone was working in a foundry or taking a tour of one, don't remember the specifics. But someone took put a paper cup (the pleated kind that hangs on the water dispenser) of water and placed it on a red hot slab of steel. The water proceeded to boil, until it was all boiled away, at which point the cup went up in flames. Sounds cool, I'll try it if I ever get the chance.

06-07-2004, 05:47 PM

Dave Opincarne
06-10-2004, 09:23 PM

I've seen the fingers in the lead demonstrated on a kids science show years ago. I think it was Ira Phlato (sp?) of NPR's Science Friday that did it too. The paper cup trick sounds neet but the foundy forman would kill me and then I'd lose my job. No moisture in the foundry. Except for the water cooling coils in the bottom of the furnace, lots of automatic shut down sensors there, but it still scares me to think about it.


J Tiers
06-11-2004, 12:21 PM
<font face="Verdana, Arial" size="2">Originally posted by docsteve66:
You can boil water on a sheet of paper, over an open flame. Seems the heat of flame is transfered to the water fast enough to keep the paper cool. the paper above the water must NOT be touched by the flame.


BTW, some Indians (Amerind) used close-woven grass bags (too flexible to call them baskets) to cook in over the fire. Worked like the paper cup, I assume. I find the very close tight weave of the basket/bags to be more amazing than the boiling of the water, though.

06-13-2004, 04:16 PM
Dave Opincarne: I have an old "Audels " book on welding with a discussion of thermite.
Seems (according to audels) that college boys used to do exactly what you suggest- excepting it was on street car rails- a dab of thermite, ignite and the trolley was welded to the track by the time the car was ready to move on.

Dave Opincarne
06-13-2004, 07:19 PM
A famous MIT gag (hack) not an original idea on my part.

06-15-2004, 07:04 PM
Dave: I would have bet a beer that my cite of Audel's was correct. I just checked my newest version (1967) and the story was not there.

Pretty long time ago we did some thermite welding and no one had real experience, so we used the Audels book as a guide and succeeded. I THINK the book we had then had the story but it may have been just one of the things some one said. I personaly doubt (now that I have checked) that it would work the way I claimed to have read it. We used a mold and tried several test runs before we got a good weld- I suspect the thermite would not heat the iron to welding temp with out the mold.

Good story, lets the imagination run free, but I think I passed on some bum dope- even if the original book did have the story. Sorry Bud

Dave Opincarne
06-15-2004, 11:45 PM
Steve -

I seem to remember coming across it in some sort of collection of early MIT pre-digital age hacks. Another one I remember was someone wrote a program to "walk a tape drive" The program got the tape reels running back and forth fast enough to get the drive to walk across the floor like an out of balance washing machine. Remember the giant black balloon emblazoned with 'MIT' coming out of the 50 yard line during a Harvard game about 20 years ago?


06-16-2004, 10:02 AM
Pretty hard to top the UBC engineers. I think hanging a VW from the Golden Gate Bridge without getting caught is pretty good.


Dave Opincarne
06-16-2004, 08:42 PM
ROFLMAO! Especialy how long it took them to figure out what to do. Can't imagine it happening today though. Does anybody know what happened to the radical and extream hobbies page?

06-21-2004, 08:05 AM
How about a hopper feed to allow cans thru one at a time, rollers to flatten them & meshing slotted rollers (like a big paper shredder) to cut 'em up?
Sounds like a plan,