Luckily, there is a lot to choose from in screening equipment – many more choices and brand names then ever before. “So, which one is the best, the most universal, the most economical and the simplest to operate for what I am doing?” you may ask. This is a rather lengthy subject to discuss depending upon what type of producer you are classified as.
Are you a portable contractor looking to classify varying materials? A custom producer with clients expecting you to offer a diversified output due to the multiple products they offer to the concrete and asphalt markets? Or are you a major output production facility looking for maximum output of one to two size-ranges of material for the high demand purposes of mining minerals or precious metals? Then there’s all the specialty guys – whether it be decorative landscape material with multiple sizes and colors of product to those out along a river’s edge doing placer-type gold mining.
At either end of the spectrum there are many ways and styles of getting the material sized or separated into specific needs that sometimes require more energy due to a horizontally operating machine opposed to the less energy-intensive incline, allowing the physics of gravity to play an extremely important part in the equation, which is actually free-form energy without cost. Some screening requires longer retention time over the media, mainly due to the presence of Mother Nature’s naturally-occurring binding agents such as ground moisture and clay seams. These can cause structural contamination if not addressed, therefore requiring machines be designed longer and flatter in operation in order to allow added vibration and time as the material crosses the media, creating maximum opportunity to shake and separate through attrition. These are all details that begin the process of choosing a best fit or applicable machine for individual processing needs. Below is a quick list of types of screening machines available and a brief descriptive and highlight of each.
Track-mounted screens are becoming more popular every day, from traditional incline screens to rotary trommel screens. These remote-controlled, self-contained screens are highly adaptive and portable. They are universal, especially when docked next to their crushing counterparts, which can also be situated on track-type undercarriages. These machines usually come equipped with fold-out stockpiling conveyors and even conveyors that will recirculate oversized product back into the crusher until it is eventually sized down to fit through specific classification media. Other benefits include quick set up times and smaller footprints required for operating. Some downsides are rather high dollar investment and lower productivity than traditional stationary screens. These machines are often rental tools¬ – if renting versus purchasing can reduce initial dollar investment allowing the contractor better job-specific bidding opportunities.
Portable rubber tire-mounted screens have dominated certain mid-range production markets for years and have always been extremely dominant in the resale market, keeping these types of screens extremely popular, if not the most popular, today. These screens are typically flat or horizontal in configuration and reach lengths of 24 feet. Inclines have also been popular, but require the plant to be lifted into position – an extra step. They also require a longer feed conveyor to reach the elevated height. So the incline version (although being the first ones on the market) has stayed the course (being structurally fixed) to become some of the best production-based machines on the market requiring less horsepower and machined parts, making them extremely efficient and long-lasting.
Another long-lived screen has been the trommel screen, which is a great design for aggregates to organics and everything in between. Being rotary drum-designed machines and positioned on a declined foundation, they use both gravity and scrubbing along with some intermittent lift elements to break down and classify conglomerated materials. Depending on their length and diameter along with decline they can be highly productive but typically the trommel of today is best suited for topsoil and organic-based producers.
Lastly, and similar to this category of screening, is the static wind fall screen – simply a screen positioned anywhere from 40 to 60 degrees on a declined slope. You dump directly onto it with a bucket loader or excavator and it uses only gravity for a single pass. The material being processed separates onto a clean coarse and falls through a mixed size of fines, usually size-specific for whatever the project requires. These screens are often very low productivity and are used as a “safety” to keep oversized material from getting into something that was just dug out.
This was just a brief overview of one of the most specific parts of an aggregate producer’s world. It takes a lot of information and product gradation specifications in order to determine the very best type of screening machine and associated media suited for your predetermined budget.
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Tim Holmberg / 2915 Idea Ave. / Aberdeen, SD 57401