Screeners 101: Sifting Through the Facts
by Sean Donaghy
Tips and tricks to select the right mobile screener
You get out what you put in. While this old saying is true with most projects, jobs, or life challenges, it couldn’t be further from the truth in the screening business. In a screening operation, producers need to separate the dirt from the stone and size it into a sellable product. Ultimately, you need to separate the good from the bad to find your profit.
Portable screening plants are a major part of the business for aggregate producers, road builders, and contractors in rock mining, quarry, demolition, and recycling operations. These screeners separate all kinds of valuable materials from waste, so they can be recycled and repurposed for use in a range of applications.
Any producer can tell you how important quality screeners are to a business, but what’s right for one producer may not fit the bill for the next. And, while it seems the only thing separating one mobile screener from another is the color and a logo, there are a multitude of factors to sift through, from overall type and size to small, highly customized design modifications. With new technologies and development of advanced screen media, producers need to do their research and take advantage of the ever-growing options and choices. Selecting the right screener takes time, research, and a clear idea of the goals of the operation.
Size it up
The first step to selecting a screener is to consider whether the company’s production has been maxed out or will continue to grow, because there’s nothing more important than sizing the equipment to match the operation. Understanding the application, materials, and desired production is crucial. With plenty of research and consideration of desired production, size and abrasiveness of material, as well as the number of end size products, a producer can find well-outfitted screeners that align with the goals of the operation.
Keep the company’s goals in mind during the selection process. Calculate projected annual sales and break the number down to tonnages per month. For example, if a company can sell 750,000 tons per year, its screeners need to sort 62,500 tons per month. If the screener is in operation three days per week (approximately 13 days per month), 8 hours per day, the operation will require a machine capable of screening around 600 tons per hour.
This rate is key to the success of a business. In the previous example, a screener that processes 300 tons per hour limits profits and caps the company’s growth potential. On the other hand, a machine with a potential output of 900 tons per hour likely will come with extra expenses but no added value.
Another factor to keep in mind is the end product. The majority of machines are two-deck screeners capable of sorting two sized products and an oversize product. Others feature three deck screens that produce an additional sized product.
Also consider that screen boxes vary in size and design. For example, a few screener/scalpers will be labeled “high energy.” What exactly does it mean, and what is the benefit? A high-energy screen box runs faster and produces a higher stroke than a standard screen box. Many customers notice that the more efficient, lively stroke boosts a machine’s output and produces a cleaner product in comparison to a standard screen box. Be on the lookout for these standout features, and determine what is best for your organization before looking any further into the details.
Scalp or screen
There are two main types of screeners: scalpers and standard screens. Several main differences separate a scalping plant from a standard screening plant. Standard screens have a tipping grid or livehead over the feed hopper to stop large material from going into the hopper. The feeder belt speed can also be adjusted in order to help produce a clean, sized finished product. These screens are at home in a sand and gravel pit, a quarry, and recycled concrete and asphalt jobs, as they often are considered “finishing screens” because they’re capable of producing specific sized end products.
For applications that aren’t all about the specific sizes, there is another option. A scalping screening plant feeds material directly onto a screen as it comes out of the hopper, which eliminates blockages due to oversized, contaminated, and dirty material. The machine is ideal for demolition contractors preprocessing materials like recycled concrete or reclamation applications. Scalping screening plants also are designed to handle much larger, heavier material in larger crushing operations or for producing a gabion stone in a quarry. They are versatile, but aren’t an ideal choice for creating a finished product — especially when the producer needs smaller materials to meet specifications. In fact, scalping screening plants are commonly used to process scrap metals, separate recyclables at old slag dumps, and extract rock from dirt on a construction site. Afterward, producers pull in a standard screen to perform the meticulous work.
While these units have their differences, the style of screener isn’t the only factor one must consider. Plenty of other little factors can make a big difference.
Let’s start where the tough gets going — the hopper. This portion of a screener fluctuates in size and durability. The industry standard hopper is 12 feet wide with an option to upgrade to a 14-foot-wide hopper. Very few manufacturers offer a 14-foot-wide hopper off the bat, but a wider hopper is more important than one might realize.
Obviously, the wider the hopper, the easier it is to feed the machine. Just an extra 2 feet can capture more product and prevent spillage. The size becomes most pertinent when pairing the screener with the loading machine. For example, excavators or equipment with a narrow bucket are ideal for loading a 12-foot hopper, but a 14-foot hopper is wide enough to accommodate a wider bucket. By comparison, a wheel loader bucket can hold approximately twice as much as an excavator bucket. The extra 2 feet of loading space makes a huge difference, so using a wheel loader is a simple way for a company to pick up extra production.
Livehead and tipping grid
Producers can add a livehead or tipping grid to a screener above the hopper. While they perform a similar duty, they are very different. A tipping grid is the appropriate solution for preventing larger materials from traveling into the hopper and through the screener. This hinged grid catches larger materials, and producers can clear them by manually tipping the grid via a remote control. Although this is an affordable option, it can become a chore, particularly in wet or dirty applications where the tipping grid may become plugged frequently.
The other option, a livehead, is essentially a vibrating screen that attaches to the hopper. This piece of equipment is suitable for heavy-duty applications with dirty, wet, and/or sticky material. The unit can be used for two purposes: to scalp dirty material off and eliminate the need for manual cleaning or to size material going into the machine so producers can produce an additional sized product.
Although these units are designed to boost production and create an additional product, they become a hindrance if used in the wrong application. These are built with thick bars that limit the open area, so operations processing finer materials might discover material on the ground that should have been in the hopper. Further, screeners with 14-foot hoppers would not be used to the full potential, as the livehead measures 12 feet, leaving 2 feet of the hopper unusable.
Apron feeder vs. belt feeder
From the hopper, material is fed onto a standard belt feeder. The standard belt feeder works well for sand and gravel operations. It is cost efficient and will hold up well in numerous applications. However, for producers working with metal, large rock, or any abrasive material, a standard belt feeder is likely to tear or break. These more heavy-duty applications require an apron feeder, which is essentially a belt made of metal.
It seems there are just as many types of screen media as there are materials to screen. Most screens feature a typical wire mesh screen media for different sizing applications. However, there are a few heartier options for producers working with abrasive materials.
First, operations working with abrasive materials may want to consider stainless steel as an alternative to regular wire mesh. Although the cost is nearly twice as much, stainless steel offers a higher wear resistance and longer wear life that is worth the extra cost.
Another replacement for the standard screen for certain scalping jobs is bofar bars. Bofar bars, formed of long bars with spaces between, are designed for materials such as recycled concrete that commonly contain a lot of dirt and miscellaneous material. Although bofar bars do a certain amount of sizing, the process doesn’t necessarily end with thoroughly sorted product.
Punch plates are another option. These plates are essentially a piece of sheet metal with spaced holes for heavier applications. Punch plates are better for sizing in comparison to bofar bars and are very durable, customizable, and affordable.
Finally, finger decks work for reclamation, landfill jobs, or any other type of screening where clogging, blinding, or breakage may be an issue. Finger decks can accommodate high-impact loads mixed with recycled waste and debris.
It looks like “just” a pile of rock, but stockpiling is an art. Essentially, this is what producers work for — large piles of neatly sorted, valuable product that is ready for selling, using, or building.
The cone-shaped piles are formed of ton after ton of material, and, the taller the cone, the wider the base, and the more tonnage the entire pile contains. This additional tonnage is the reason why stockpiling height is so important. A stockpile consisting of a typical rock mixture might hold approximately 228 tons if the pile is 8 feet high with a top width of 2 feet and a base width of 16 feet. By increasing the height of the pile by only 9 inches, the total weight of the stockpile will increase 29 percent, to approximately 295 tons. Higher stockpiling capabilities serve as a time saver, as producers can run for longer periods without having to move material. This is why screener conveyors with the potential to stack even 8 to 10 inches higher can make a significant difference in an operation.
Conveyors take quite a beating. Conveyors commonly incorporate rollers, which can be hot spots for damage and reduced wear life when large materials are being processed. Rollers can break under the pressure, and belts become punctured.
As an alternative, some manufacturers offer an impact or sleigh bed conveyor. These conveyors provide more support and are more durable to handle heavy products such as large rock. The impact bed is solid and runs the width of the conveyor to best accommodate the impact of material and prevent belt damage.
Further, most discharge conveyors measure about 48 inches wide. The industry offers belts up to 63 inches wide, which helps prevent clogging. Because the screener is wide and gets funneled down to the conveyor, machines with smaller conveyors create a bottleneck effect. The material begins blinding in the corners, narrowing the opening. This creates productivity and maintenance problems, forcing producers to shut down and clean it out. Look for a machine that has less (or no) restriction as it transitions onto the discharge belt. A free flowing machine with a low drop height is the best option to minimize wear and keep productivity elevated.
Producers can get more bang for their buck when they choose a machine that is taller, bigger, and more rugged. More robust machines often offer features that boost convenience and productivity, such as larger access areas. Double paneled engine compartments allow mechanics more space when performing service on the machine. Dual fuel nozzles provide fueling access from both sides of the machine — a big advantage when working on a smaller site. Some manufacturers build units with access to the engine from both sides, as well. This way, when the unit is parked alongside a wall, fueling and maintenance can still be performed from the opposite side.
Customer support becomes pivotal when parts or repairs are needed. The availability of wear parts and service can make or break an operation’s numbers for any given month. Choose a manufacturer with a good reputation not only for quality equipment and durable components, but also for quality customer service. Some companies offer 24-hour online parts look up and ordering with live service support. Along those same lines, consider the equipment warranty when making a screener selection.
Countdown to the purchase
Purchasing the wrong screener can cause problems, slow production, and result in revenue losses. Taking the time now to sift through the facts and separate the good from the bad will prevent headaches, downtime, and loss of production later.
Sean Donaghy is the national sales manager at Irock. He has more than 20 years of experience in the crushing business and has been with Irock for seven years.