The separation occurs by a phenomena called Fluidization.
Wikipedia -Fluidization (or fluidisation) is a process similar to liquefaction whereby a granular material is converted from a static solid-like state to a dynamic fluid-like state. This process occurs when a fluid (liquid or gas) is passed up through the granular material.
When a gas flow is introduced through the bottom of a bed of solid particles, it will move upwards through the bed via the empty spaces between the particles. At low gas velocities, aerodynamic drag on each particle is also low, and thus the bed remains in a fixed state. Increasing the velocity, the aerodynamic drag forces will begin to counteract the gravitational forces, causing the bed to expand in volume as the particles move away from each other. Further increasing the velocity, it will reach a critical value at which the upward drag forces will exactly equal the downward gravitational forces, causing the particles to become suspended within the fluid. At this critical value, the bed is said to be fluidized and will exhibit fluidic behavior. By further increasing gas velocity, the bulk density of the bed will continue to decrease, and its fluidization becomes more violent, until the particles no longer form a bed and are “conveyed” upwards by the gas flow.
When fluidized, a bed of solid particles will behave as a fluid, like a liquid or gas. Like water in a bucket: the bed will conform to the volume of the chamber, its surface remaining perpendicular to gravity; objects with a lower density than the bed density will float on its surface, bobbing up and down if pushed downwards, while objects with a higher density sink to the bottom of the bed. The fluidic behavior allows the particles to be transported like a fluid, channeled through pipes, not requiring mechanical transport (e.g. conveyor belt).
Once lights (plastic or aluminum) are hovering over the table, fluidization, they slide down the slope of the table because they no longer have friction to hold them to the table. The heavies (in this case copper) stay in contact with the table. They vibration bounces them up the ramp. It is an easy concept in theory but it defies logic. Think of the lights as snow on a mountain. An avalanche happens when friction is lost and the solid turns to a liquid state as gravity pulls it down the hill.
I am sorry if I put everyone to sleep. Times are tuff in my slow little start up and it has been very stressful. This forum is a place I like to read and occasionally joke around. I like to laugh and don't mean to be short or rude. I have spent years studying this process and building machines to do a certain task.
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