Sorting By Weight? Creative Solutions?

I have what I think is an interesting problem, but I feel that it has probably been solved somewhere else out there. Maybe the problem hasn't been solved exactly like I am describing it,
but I'm sure some similar ideas exist. But I have looked and talked to a lot of people about this and so far I haven't been able to find a solution. I'm really hopeful that someone out there will be able to help. So on with the problem...
I am running a process that is filtering out garbage & gravel pieces. (2 inches & smaller). These pieces are falling down into a pile after they are screened out. (Dropping probably 15 feet). I need to be able to sort the two types of material before or after they have fallen down into the pile. (Before/while they are falling would be the most ideal solution).
95% of the garbage is very light when compared to the weight of the rocks that are passing through. So if I could automatically sort the product into two piles based on weight, I would be very happy to manually remove any heavy garbage that snuck in. The reason why I can't sort it all manually to begin with is because of the amount of material that is being screened out. We will create a pile of 2-4 tones each day of this garbage & gravel mixture.
The problem can really be summed up by saying that I would like to sort items by weight and prefer to incorporate the energy of them falling 15 feet in someway. Due to the volume of product that we are doing, the solution would have to be something that is easy to maintain and not too complex to do. (The quicker and easier the better).
But does anyone have any ideas or related suggestions? I'd love to hear from you!
Thanks,
Tim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@hotmail.com wrote:

In flour mills, currents of air are used to sort flour particles by size and mass density. While your gravel/garbage is falling, you could use some sort of blower to push the lighter garbage out of the waste stream into a collection chute.
If you need to be very energy efficient, you could have a device which rotates to face ambient winds, and adjusts the flow rate in response to the strength of the wind, so no blower would be needed.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@hotmail.com wrote:

Air separates density, rollers and shakers separate shapes. This gives you an idea how it all works http://www.zanin-italia.com/en/prodotti/pulitori-separatori/PSS.html
In your case if you slide it off an incline on to two conveners going away from the direction of the fall and against the direction of the fall you can have an adjustable splitter to drop the light stuff on the belt going back to the way the stuff was fed and the heavy stuff the way it came off the incline. The stream needs to be spread thin and even and launched with a substantial velocity in direction parallel to the ground so the greater sectional density of the heavy material carries it further than the lower sectional density stuff.
Your problem is easy. The hard one is separating black pepper and from rat turds and other things the same size with similar shape and density that have to be clean up really well.
Gordon Couger Stillwater, OK www.couger.com/gcouger
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 22 Jun 2005 02:11:35 -0500, Gordon Couger

This problem was looked at many years ago by the Warren Spring Laboratory in Stevenage, UK. A pilot plant was built in Doncaster, Yorkshire, I believe. Google doesn't seem to know about it.
--
Terry Harper
URL: http://www.terry.harper.btinternet.com /
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.