It might look like a standard scalper on initial inspection but thanks to new product innovations in multi-frequency technology, it is now possible to make even a simple twin-deck screen a multi-purpose performer. Damian Christie reports.
In recent years, Astec Australia has made important strides in the Australian quarrying and mining markets in the promotion of high and multi-frequency product innovations in fixed, modular and tracked screening plant.
According to the company, this has been in response to increasing interest from producers globally in the use of high frequency screening technology across a variety of applications.
Certainly as part of stationary plant, higher frequency screens have been able to generally process wetter, stickier materials more efficiently and separate particles from about 25mm down to as low as 425µm.
The challenge for various OEMs of mobile screening plant technology has been the ability to incorporate them onto tracked and portable units.
Astec has in recent years produced three track-mounted options for various aggregates applications:
- The FT2618VM which has successfully worked in train with the company’s other mobile units, such as the FT2650 tracked jaw crusher and the FT300 tracked cone crusher, as an end of chain screen for specific manufactured sand profiles.
- The GT205 two-deck multi-frequency tracked plant, which is equipped with a high frequency screen on the bottom deck to allow more efficient product cuts, while maintaining a conventional top deck for top size overs. This screen can process virgin and recycled aggregates alike (eg recycled glass, gypsum, topsoil) and even waste materials for low grade roadbase specifications.
- The GT165MF, which, like the GT205, incorporates a conventional screen on the top deck for larger raw feed and a multi-frequency screen on the bottom deck for scalping. This design is an extension of Astec’s standard GT165DF unit.
There are three GT205MF units operating in Australian quarries: two in Victoria and one in Tasmania. The first of these, delivered in January 2018, has successfully processed a variety of materials: glass, plasterboard, gypsum, topsoil, crusher dust and manufactured sand.
The first GT165MF arrived at Astec’s Melbourne premises in September and, at time of writing, was being prepped for imminent sale and delivery.
Patrick Reaver, product development manager and inside sales manager for Astec Mobile Screens in the US, was a presenter at the IQA’s annual conference in Geelong in October.
He discussed the merits of high frequency and multi-frequency screens and, in discussion with Quarry, cited the GT165MF as a great example of how they can add value to fine materials.
“The GT165 multi-frequency is based on the same platform as the standard GT165, a robust machine built for heavy-duty applications, but with the addition of the high frequency vibrators on the bottom deck that allows us to screen in some of those very tough conditions,” he explained.
“So with the benefits of the scalper on top, you can do flexible things with large rock, while on the bottom you get into those tougher 20mm and below applications, where it’s a finer or high moisture application. You can utilise the high frequency vibrators down there, and really screen better in those tough applications.”
Reaver said the GT165MF retains, with the exception of the multi-frequency technology, the essential platform of the standard GT165DF.
The 35-tonne unit features a twin-deck 5m x 1.5m (16’ x 5’) screenbox, with a maximum feed size of 610mm, and is powered by a 129kW Caterpillar Tier 3 diesel engine.
The standard top deck features a lower speed adjustable amplitude of about 950 revolutions per minute (rpm), an increased stroke rate of 6mm to almost 10mm, and hydraulic controls for variable angle operation.
The multi-frequency bottom deck has six independently controlled exciters that can each apply an additional frequency to the screen media of up to 4200 rpm.
This contributes to increased stratification and higher separation, with sizing down to as low as 400µm.
The GT165MF is also equipped with an 8m3 heaped capacity hopper with impact bed and 1400mm belt feeder plus four product conveyors – overs, underscreen, bottom deck overs and fines, with hydraulic variable speeds and hydraulic discharge height adjustments of three to four metres.
These features are echoed in the GT165DF but Reaver said that where the GT165MF distinguishes itself is in the multi-frequency technology on the bottom deck which promotes more flexibility for the producer.
“You can screen just as you would with the standard GT165, and then on top of that, you can screen in tougher conditions where bottom decks are your largest bottleneck. The bottom deck is always going to be your bottleneck because the material is too fine, too wet.
“However, with the GT165MF in those applications, we can keep screening. You can run it with it on as a multi-frequency, or you can turn it off and run it as a standard GT165. You have that ability to switch back and forth, with the basic push of a lever.”
Adam Gordon, Astec Australia’s national account manager for aggregates and mining, told Quarry that on a traditional twin-deck scalper, 600mm rock may be screened on the top deck and 20mm on the bottom.
However, the different masses of material require different forces to achieve the most efficient screening outcomes.
“By having the multi-frequency vibrators at the bottom, that have six adjustable settings, you can finetune them for that load over that section of the screen media, independent of the screenbox that is taking care of that bigger material,” he said.
“So you have a lot more throughput, efficiency and accuracy with that multi-frequency bottom deck.”
Reaver added the versatility of the GT165MF means it can perform in applications ranging from finer and wetter materials to heavy scalping to low grade base to a material as tough as recycled asphalt (rap), in which the end specifications could be 14mm at the top and 4.75mm at the bottom.
The GT165MF can act as a standalone unit because the feeder hopper allows for the unit to work with a loader or an excavator.
“The three product conveyors all have plenty of height for ample stockpiling where you can either use a loader or you can transfer that onto other conveyors.”
In a train, he said, “our tracked crushers feed right into it. We have a wing on the back that drops right down, and then likewise, the discharge conveyors have enough stockpiling that we can also feed into a secondary or tertiary crusher, or one of our tracked crushers as well.
“So, with the extended overs conveyor, you can, for example, drop the overs conveyor down to catch both overs products, put the extended conveyor on and you’ll still have the height to feed into your other tracked units.”
Reaver stated that the GT165MF is designed to work more with other Astec types or brands than with other makes of mobile crushers and screens.
“We make sure all the Astec products work together well. We provide tracked crushers, tracked screens, all products that we know are going to work together well. When it comes to other brands, we don’t necessarily check across those.
“If you look at our GT165 as a whole, we have a really tall stockpile height, so I would say we’re going to feed into other crushers just as well or better than anybody else, but more often than not, we make sure they are working with our own family.”
While the GT165DF is specifically offered as a tracked unit, the GT165MF is offered in the North American market in three configurations: a standalone stationary plant, on a trailer chassis and as a mobile tracked unit.
Australia to date has only received the tracked mobile units but the Astec Australia team indicated the stationary and trailer product lines were not out of the question, provided the latter complied with Australian road standards.
One of the challenges they’ve experienced with the more mature Prosizer closed circuit crushing plant in the past has been compliance across all states and territories.
The company’s new Prosizer 2514MF, for example, has had to be developed to comply first and foremost with Victorian road regulations, which are firmer than the other jurisdictions.
Nonetheless, based on the success of the GT205 two-deck multi-frequency screen, and the popularity of the GT165DF, Reaver is optimistic that, whatever its configuration, the Australian market will embrace the GT165MF.
Many of the same options available to the standard machine – eg punchplate and grizzly bars on the top deck, wireless track remote, heavy-duty hydraulic grizzly for the hopper, and standard steel screencloths for both decks – can also complement the multi-frequency GT165 – as if the multi-frequency technology isn’t already enough of a potential “game changer”.
“We have a lot of options available on the GT165, from auto-greasers to chute wings, drop-down kits to accept over products, or extended conveyors,” Reaver said.
“That’s why people like that direct feed-style screen so much because you can do so many things. The GT165 is already a ‘jack of all trades’ versatile screen as it is, and the multi-frequency takes it to the next level. We view the multi-frequency as an option on our standard 165 as much as anything but it’s really a product all on its own.”
A multi-frequency GT165MF screen – the first to be received in Australia – arrived at Astec’s Melbourne sales yard in September.