human powered sand mixer mechanism? 6

[tbartczak]

Hello All,

I'm looking for some tips on how to design and construct a human operated sand mixing system that can be operated by a variety of different users (ie. minimum input power).

The mechanism is meant to be part of an experimental off-grid toilet system. We hope to capture the solid and liquid streams in sand, mix thoroughly and then proceed to treat the mixture afterwards. being able to convey the mixture at the same time is a definite plus.

What is the most efficient way to accomplish this goal? What kind of mechanism can tolerate wet sand and still require reasonably low effort? We have been thinking about modifying equipment such as continuous sand mixers from the sand casting industry, but I wonder: is there an easier way?

Operation would be intermittent, and we are looking for a feedrate of approximately 2 - 5 kg / min when in operation

what we have looked at previously:

http://www.ofml.net/spartanII.html

Thanks very much,

Tomek

 

[SnTMan]

How about an old fashoned meat grinder?

http://www.google.com/search?q=meat...a=X&ei=2UDSULSKMsmw0AG13IGoBg&ved=0CAcQ_AUoAQ

Regards,

Mike

 

[Compositepro]

And what does the sand do except increase weight and volume and prevent the possibility of pumping?

 

[dhengr]

Half the idea of efficient waste treatment is to minimize the weight and volume of the waste stream. What on earth do you think the sand adds to your system, except a heavy component which must be removed during treatment? What you’ve looked at so far, certainly doesn’t look ‘off-grid’ to me. A septic tank and drain field or settling tank and lagoon are about as ‘off-grid’ as you can get, and they use the sand, in place, as a filtering and biological reaction medium.

 

[racookpe1978]

It appears to me that you've got two reasonable choices: Best one would depend on your back 9the user's back and shoulder) and how you intend to "dump" or distrcbute the mixed residue when done.

Easiest mixer for varying amounts of product is a long trough - to mix 2 125 bags of concrete for example, my dad used a 16 - 18 inch wide open-topped wooden (plywood) box about four feet long, with each end sloped slightly rather than being square-ended. We'd mix the concrete bags with pea gravel and sand by hoes.

You'd have the problem of shoveling out the mix: lifting it back up into a wheelbarrow, perhaps by a shovel. Neither would be pleasant repeated for many hundred pounds of mix. Especially when the mix is wet, and needs be re-spread back out after being dumped from the wheelbarrow.

Alt is a man-driven concrete-type tipped (or inclined) barrel mixer - probably driven by a hand (shoulder and back!) crank and gear and pinion system. More expensive obviously, but it could be motor-driven too. The mix would be higher (and needs to be lifted up and filled into the mixed) but then it could be dumped back out into the wheelbarrow without liting it again.

 

[tbartczak]

Hi Mike,

I have actually tried a meat grinder. Unfortunately, wet sand clogs it up and greatly increases effort almost immediately. Beyond that it doesn't appear to be a very good mixer.

 

[tbartczak]

Hi CompositePro,

The sand is used for odor control, preliminary filtration and to help prelim separation of the solid and liquid streams. it is then used upstream in the onsite disinfection process. unfortunately, at this point, I cannot go into detail about how that happens.

So yes, ideally, avoid sand but that is not an option at this point, unless another aggregate is chosen that is lighter, less abrasive and has similar locally available to sand, then sand it is.

I'm open to ideas. . .

 

[dvd]

something with carbon in it to absorb odors, such as chopped grass or hay, sawdust, or maybe ground charcoal.

screw conveyor or an inclined (declined) drum with internal flights

 

[berkshire]

Have you looked at a ribbon type screw conveyor?
B.E.

"A free people ought not only be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
-George Washington, President of the United States----

 

[tbartczak]

Hi B.E.

Yes, I have looked at them, and think they show promise. Further to that, I have found that the ribbon blender is quite interesting too (although it does not convey as well). The ribbon blender I found (see link) has both clockwise and anti-clockwise ribbons, which really help a homogenous mixture to form quickly.

http://www.google.com/imgres?imgurl...FbSUKTrGMTErQHWhIGoCg&ved=0CGIQ9QEwAw&dur=288

Thanks,

Tomek

 

[geesamand]

The challenge is balancing keeping the overall mixing torque low (meaning you won't easily be able to turn over the whole mass at once) against preventing dead spots. The balance will depend on how much mechanical advantage you can build into the system (reducer drive?) and how large/heavy your media pile will be.

Without making the whole system overly complicated, I would look at a smaller mixing impeller that self-clears and mixes a small part of the pile while also traversing through the entire pile leaving no part untouched. That sounds complicated but the right clever design could make it possible.

On a related note, take a full analysis of what "bad" things will end up in there. Jamming due to unexpected materials should be expected. There should be a reasonable way to manage this problem without the operator having to take a "hands-on" approach.

 

[racookpe1978]

An Archimedes-style enclosed screw-drive would be very prone to jamming that way. Very hard to clean as well, compared to a more-open open cone-shaped drum mixer

Maybe an open drum, inclined to raise the mix up to allow dumping into the hypothetical wheelbarrow, but the screw be only half-the diameter of the drum?

 

[berkshire]

tbartczak,
I am a little unclear as to how far you want to convey the mixture.
I am presuming ( very Dangerous I know.) that you are using a dry composting type system.
Do you just want to mix, or would you like to use the mixing system to convey to a remote dump site?
If you are conveying over some distance, a single direction ribbon conveyor will thoroughly mix your contents if the input is constant.
B.E.

"A free people ought not only be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
-George Washington, President of the United States----

 

[tbartczak]

Hi Berkshire,

Yes, please let me specify. the conveyance will only be happening to the next stage of the process. We are still speaking conceptually at this point, but I would be surprised if it was more than 1.0m, and I imagine could be as little as 200mm

T.B.

 

[dgallup]

How about a cat? Mine seem to mix excrement and sand pretty well.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[berkshire]

tbartczak (Mechanical)
Would this kind of mixer work for you?

http://www.newdawnengineering.com/website/brickandtile/mixer/

"A free people ought not only be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
-George Washington, President of the United States----

 

[tbartczak]

Thanks berkshire

a very interesting idea. I think this is the most feasible mechanism I have come across thus far. I would probably alter the implementation to use a hand crank instead (and gear it up as necessary) but I think that it could definitely work. Much appreciated.

Sincerely,

T.B.

 

[racookpe1978]

From berkshire's link:

With a robust 140 litre drum, this solid machine can mix a full wheelbarrow (65 litres) of concrete at a time. Mixing is fast and complete as the 21 chain "fingers" do their work.

Early prototype Concrete Mixer (shown right). This model has been replaced by one with 5 handles to increase ergonomic efficiency but the basic layout remains the same. The hand operated Concrete Mixer can properly mix 65 (wet) Litres of concrete in about 45 seconds. It takes less than half the total energy of shovel-mixing, does it in half the time and with only half the variation in cured strength (Univ. of Witwatersrand tests).

Saving effort and speeding up the job is what Appropriate Technology is all about. This mixer has all ball bearing mounts, a 2.5mm thick steel drum and is portable enough to carry to the job site with two men.

Mixing is done with 21 chains rather than the usual 3 paddles.​

"

That's the idea I had in mind above - Too bad they copied my idea and built my invention before I could patent and sell it! 8<)

I wonder how these 21 "chain fingers" work?

 

[berkshire]

Mr Cook,
They are pieces of chain tack welded or bolted to the drum at one end, on the downside they lay flat against the drum, on the upside,they are pulled up through the mixture.
B.E.

"A free people ought not only be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
-George Washington, President of the United States----

 

[Artisi]

The space age mixer is certainly clever, although the turning handles sticking out into space look like an accident waiting to happen and the extended frame / feet protruding into the work area at the front are probably a nuisance when loading the sand, gravel and cement. The chains inside the drum sound as though they could be very effective for mixing.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)