by Jon M. Casey
Recyclers will at times find a need for a screen plant or trommel to help sort materials of all kinds. Whether it is wood waste, topsoil, RAP, old concrete or a myriad of other materials, the decision to acquire a screener can be daunting, especially if the producer is looking for a portable unit. Not only is the screen configuration and the material it is made of important, but the means of transporting it from site to site and the ability to move it once it is on the job, are but a few of the considerations the screen buyer faces. Most WHEN readers already have faced these challenges.
This article is designed to provide a brief overview of a few of the portable screen plants that are available on the market today. It is not intended to be an endorsement of any particular brand, but it is presented here to provide a pictorial glance at several manufacturers’ products as they were demonstrated in recent months. Many of these units were demonstrated at Compost 2016 in Jacksonville, FL this past January. Others were spotted elsewhere.
Trommels are designed to screen material into two fractions, and occasionally into three if the unit is equipment with a side discharge conveyor like the Vermeer TR620 for example. In a conventional configuration, material is fed into the infeed hopper of the trommel where it enters an inclined, rotating screen tube, where larger material stays within the tube, while smaller material falls through and is conveyed to a product discharge stockpile. The oversized material continues and it is discharged at the rear of the drum. In the case of Vermeer’s TR620 unit, an optional front fines conveyor allows for the use of an additional screen that permits the creation of a third product emerging from the front end of the unit. The remaining material is screened along the length of the trommel in the conventional way. This optional conveyor can be mounted on either side of the unit for easier loading.
Other trommels shown in this article include the McCloskey 512, the Peterson Pacific Terra Select T7, Doppstadt’s DZ750, the Edge Innovate TRM 516, McCloskey’s 628RE, Neuenhauser’s 6020, the Revolver RT508, and Terex’s TTS 620. While this list is by no means exhaustive, it demonstrates the variety of manufacturers who have done the R&D necessary to produce portable trommels. All but one of the units shown here are wheel mounted. Wheels allow the unit to be moved from site to site by using an over the road tractor.
Several manufacturers offer tracked options, which includes the self-propelled capability. For example, the McCloskey 512 is a self-propelled tracked unit, which can be moved from place to place onsite without hitching it to a tractor. Moving from job site to job site would require a lowboy trailer, however. Other manufacturers offer some form of track mounted trommel configuration, depending on the customer’s needs. Production rates vary depending on the size of the trommel, with that decision coming from the end-user at the time of purchase.
Trommel screens can vary in opening size and internal drum configurations to meet customer needs. Specialty drums may contain knife blades for opening plastic or paper bags of composted yard waste. Screen opening sizes and shapes can help recyclers sort material of two or three sizes, depending on the equipment brand.
High frequency vibratory portable screens
Unlike the aforementioned trommel screens that process material moving it through a rotating drum configuration on a linear basis, a portable, high frequency vibratory screen unit, moves material across one or more slanted fixed screens that sift the material into two or more fractions before being discharged onto conveyors that stockpile the screened material nearby. Like the trommels, vibratory screens are used in a number of applications including mixed C&D, wood waste, recycled asphalt and concrete, soil blends and compost, to name a few. Screen media used in these machines can vary in a number of ways.
Some manufacturers offer a punch screen, 3-D design while others are a woven mesh of steel stranding or other steel formulations. Innovative screen materials like the rubberized Flip-Flow screen from SPALECK, features screwless mounted screen mats on the lower deck, an unusual design. This “flapping” counter flow process helps insure less screen blinding and higher production rates of difficult materials. Polymer screen inserts are available for vibratory screens as well. These include products like those offered by Polydeck Screens.
Another style of screen plant is the Star Screen model, like the Komptech MultiStar XL3 or the Neuenhauser Superscreener 3F. The actual design of the star screen process can vary depending on the manufacturer and on the material that the customer desires to separate. A star screen, or star bed, is a system comprised of a number of parallel rotating shafts, perpendicular to the flow of the material. These shafts are spaced closely together and the “stars” that make up “fingers” that move and sort the material are intermeshed, in an alternating or zigzag pattern. As the shafts rotate in the same direction as the material flow, the star “fingers” not only move the material onward, bouncing it along the star bed, but they also move material of a desired size, through the spaces between the stars, down to a conveyance that transports the screened material to a stockpile. This kind of screen plan is useful when screening dissimilar sized and/or wet material such as composted mulch or mulch containing rocks or other larger items.
When it comes to the final decision making process, aftermarket maintenance and service is critical. Downtime is expensive in a number of ways. Not only is finding the right screener for the job an important part of the screen purchase, but also having the reliable parts and service system in place after the sale is important as well. As it is with most everything we buy, the best results come from purchasing the product from a reliable source that has an established network of sales and service facilities within reasonable time and distance from the customer. Waiting for parts or service is expensive. When the time comes to do the shopping, a trip to an event like Compost 2016, hosted by the U.S. Composting Council or other large recycling events where a live demonstration is taking place is well worth the investment.