Astec Australia’s advanced screening

Astec Australia’s advanced screening

Astec Australia’s Adam Gordon highlights the benefits of high-frequency screening for glass recycling.

Equipment supplier Astec Australia’s passion for innovation has seen it position itself at the forefront of offering advanced technologies for materials recovery facilities and recyclers. 

Adam Gordon, National Account Manager – Aggregate and Mining has been outlining the productivity benefits of high-frequency screening for glass recycling over conventional screens.

Astec’s various plants offers waste operators the ability to remove deleterious materials such as straws and labels through screening processed waste glass back into sand for reuse at significantly higher tonnages than what is currently available. 

“Most conventional screens will only screen efficiently down to a four-millimetre particle, but as soon as the plasticity or moisture content increases, those screens become grossly inefficient and your tonnage drops,” Adam explains.

These high-frequency plants were brought to Australia in November 2016 to demonstrate their ability to screen very fine and difficult material. 

“The demonstrations showed they could handle far more throughput compared to a conventional screen and keep running, whereas a conventional screen had to stop every two hours to unblock it.

“With the mass of particles being smaller, in order get separation of the particles for a smaller sized fraction you need that high frequency to separate them above the surface tension between the particles,” Adam explains.

The operating principles of high-frequency screening works on the basic processes of stratification – as larger size particles rise to the top of the vibrating material bed and smaller sized particles sift through voids to the bottom. It also works on the probability of separation as particles that reach apertures are rejected if larger than the opening or passed through if smaller.

To maximise fines efficiency, Adam says it’s important that the right amount of frequency is induced to the bed of material causing stratification to take place. The angle should also match or pass the angle of repose of the material being screened, according to Adam.

He says the screening action can be adjusted to suit the material, with up to seven different exciters per deck that can be fine-tuned for speed and stroke to suit the mass directly above. 

Adam says that many believe that in order to give the material the opportunity to pass through the opening, one must decrease the screen angle, but this is not true.

“By decreasing the angle, an excessive bed of material will build up on the screen, thus preventing stratification from occurring. 

“With stratification and separation in mind, it becomes obvious that to more efficiently screen your product, one must increase the angle of the screen.”

Individually adjustable hydraulic motors enable revolutions per minute (RPM) and stroke adjustments, thus allowing stratification to take place. 

Adam explains that conversely, there is only one stroke and RPM in conventional screens. 

Some models available include the Tracked Astec FT2618VM High Frequency Screen, which is driven by 11 variable speed hydraulic vibrators running at up to 4200 RPM.

Overall, Adam is buoyed by the results and encourages operators to see the evidence for themselves.