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, operators need to separate the dirt from the stone and size the recycled concrete 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 operator can tell you how important quality screeners are to a business, but what's right for one operator 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 small, highly customized design modifications to the overall type and size. With new technologies and development of advanced screen media, operators 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. The first step in the process is to consider whether the company's production has been maxed out or will continue to grow.
Size it Up
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 and the number of end size products, an operator 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 sales for a year 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), eight hours per day, the operation will require a machine capable of screening around 600 tons per hour (tph).
This rate is key to the success of a business. In the previous example, a screener that processes 300 tph limits profits and caps the company's growth potential. On the other hand, a machine with a potential output of 900 tph likely will come with extra expenses but no added value.
Another thing 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 keep in mind 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 operator needs smaller, specced materials. 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, operators 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 ft. (3.6 m) wide with an option to upgrade to a 14-ft. (4.2 m) wide hopper. Very few manufacturers offer a 14-ft.-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 two 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-ft. hopper, but a 14-ft. 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 two 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
Operators 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 perfect solution for preventing larger materials from traveling into the hopper and through the screener. This hinged grid catches larger materials, and operators 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 ideal for heavy-duty, dirty, wet and sticky applications. 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 operators 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-ft. hoppers would not be used to the full potential, as the livehead measures 12 ft., leaving 2 ft. (.6 m) of the hopper unusable.
Apron Feeder vs. Belt Feeder
From the hopper, material is fed onto a standard belt feeder. The standard belt feeder is perfect for sand and gravel operations. It is cost efficient and will hold up well in numerous applications. However, for operators 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. Because of its durability, the apron feeder can handle nearly anything an operator throws at it, and that makes the entire machine much more versatile.
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 operators 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's 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 are ideal for reclamation, landfill jobs or any other type of screening where clogging, blinding or breakage may be an issue. Finger decks can easily 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 contractors work for — large piles of neatly sorted, valuable product that is ready for selling, using or building.
As you might imagine, these 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 holds. This additional tonnage with height is the reason why stockpiling height is so important. A stockpile consisting of a typical rock mixture might hold approximately 228 tons (207 t) if the pile is 8 ft. (2.4 m) high with a top width of 2 ft. and a base width of 16 ft. (4.8 m). By increasing the height of the pile by only 9 in. (23 cm), the total weight of the stockpile will increase 29-percent, to approximately 295 tons (267 t). Higher stockpiling capabilities serve as a time saver, as operators can run for longer periods without having to move material. This is why screener conveyors with the potential to stack even 8 to 10 in. (20 to 25 cm) higher can make a significant difference in an operation.
Conveyors take quite a beating. Conveyors commonly incorporate rollers, which are hot spots for damage and reduce wear life when large materials are being processed. Rollers commonly 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 like large rock, metal or large pieces of wood. 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 in. (122 cm) wide. The industry offers belts up to 63 in. (160 cm) 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 operators 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.
Operators are guaranteed to 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 exceptional customer service. Some companies offer the convenience of 24-hour online parts look up and ordering with live service support that's responsive and able to help you keep your operation on track. Along those same lines, every manufacturer should be capable of providing a one-year, 1,000-hour warranty. If not, let it serve as a warning.
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.