Most bulk material handlers have probably run into it at some point: Production is rolling along, and goals are being achieved. All the while, some of the product is traveling past the drop-off point, returning along the underside of the conveyor belt, and building up on return rollers, bend pulleys, and snub pulleys.
At first, the carryback might be minimal enough not to impede progress. Other factors such as material type and conveyor-belt condition may also influence how slowly or quickly carryback begins to interfere.
Regardless, all carryback will eventually need to deposit itself, usually on the ground. This creates safety hazards, fugitive dust, and housekeeping issues. As much as 3% of the total bulk material load further can be lost due to carryback, spillage, and dust. If left unmanaged, carryback will also wear down equipment and compromise belt tracking.
Preventing Conveyor Carryback with Belt Scrapers
An industrial conveyor belt in both theory and practice will likely never be 100% carryback-free, but carryback doesn’t have to be a recurring operational drawback. Installing a belt cleaning system is an effective way to minimize it. By setting cleaning goals for their facilities and implementing the proper components, operators can achieve:
- more profitability from less downtime, clean-up, and maintenance caused by spills
- greater retention of material
- more-enduring conveyor equipment
- fewer problems with fugitive dust
The right conveyor-cleaning technology will involve a primary belt scraper with an abrasion-resistant polyurethane blade that removes excess material from the conveyor belt. The primary cleaner is designed to scrape 60% to 70% of the carryback material, usually by removing larger pieces.
While the primary cleaner can be placed anywhere on the conveyor’s return run as long as the belt is supported, the aim is to return the carryback cleaned from the belt to the material flow. For this reason, most scrapers are installed inside the head chute with the head pulley as the primary cleaning position.
The right primary cleaner also will be made to suit belt sizes and speeds for any industry or application. It should be able to be retrofitted to other cleaner brands as well.
The optimal primary belt scraper includes a self-contained tensioner that adjusts with the blade as it wears in order to maintain consistent pressure and cleaning. This adjustability is important. Too much pressure on the conveyor belt can force the blade away from it and leave a gap, which can result in hydroplaning.
In addition, as the polyurethane wears, the blade’s surface area increases, reducing the blade-to-belt pressure and making it less efficient. A primary cleaner with a self-contained tensioner helps to avoid all of these issues, which in turn helps reduce labor hours.
If the conveyor scraper has a wave profile, it can provide varying attack angles that reduce blade-edge bull-nosing. Changing the blade should also be safe, easy, and quick by removing one blade pin, pulling out the worn blade, sliding in the new blade, and replacing the pin.
The belt cleaning system design further should account for sufficient space for proper belt scraper installation, which will help ensure the belt cleaner’s performance and longevity.
What Is the Importance of Secondary Belt Cleaners?
While the primary conveyor scraper can remove up to 70% of carryback, operators will typically aim for an even greater reduction.
Secondary belt cleaners continue where primary belt scrapers leave off by clearing material that remains on the belt beyond the head pulley. Located right behind the head pulley and anywhere else they are needed on the belt line, secondary belt cleaners are especially adept at removing fines. They can also be of particular importance at facilities that handle sticky bulk material or operate in a humid climate.
Secondary belt cleaners are often used with a pre-cleaner for the greatest results. When combined with primary cleaners, they can, in some cases, increase cleaning efficiency up to more than 90%. If the bulk material is particularly dry and fine, a secondary belt cleaner can even be used as a stand-alone conveyor belt cleaning solution.
A well-designed secondary belt cleaner will include:
- a one-piece rubber blade with tungsten carbide tips plus flaps that make carryback slide away from the blade
- a blade holder that keeps the center of the scraper on the belt, making it notably useful for cupped or worn conveyor belts
- blade ends that push down for even pressure across the blade, which also arcs into the center as it wears to maintain blade-to-belt contact
- the ability to pivot and bend around a central pivot, allowing it to conform to worn, uneven belts
- a Rosta joint tensioner to absorb severe impacts
- a low-profile modular design for desired performance even in confined-space chutes
- threaded rods for easily moving the belt cleaner up to the belt or down for maintenance
A complete conveyor belt cleaning system might also include spray bars alongside secondary cleaners in the mission to eliminate carryback. Certain bulk materials, including water, can help to further break down or collect remaining carryback in a form that is easily cleared from the conveyor belt.
For particularly challenging applications, operators can incorporate a customized wash box, a fully enclosed system that integrates both belt scrapers and spray bars. The spray bars flush material off the bottom pan and out of the drain portal. This essentially provides operators with both a cleaner conveyor belt and a wastewater management system.
Other Ways to Keep the Conveyor Belt Clean
Every operation’s challenges with carryback are potentially unique, and they can require a plan of attack that applies specialty solutions in addition to the main cleaning components.
One such component is a motorized brush cleaner to prevent fines and residue from getting trapped in recessed areas that blade-type cleaners cannot reach, such as on grooved, ribbed, and chevron conveyor belts. A motorized brush cleaner activates only when the belt is moving, and the motor turns the brush opposite the belt direction for optimal cleaning. A cleaner bar also makes the assembly self-cleaning.
Other specialty components might include plow (plough) cleaners such as V-plows and diagonal plows for clearing material that gets pinched between the conveyor belt and the return pulley, which can cause the belt to break.
Importance of Belt Cleaner Maintenance
Clearly, belt cleaning systems are important, but many can often be installed and then forgotten. One survey indicated that about 25% of all conveyor belts have a cleaning system; of that amount, only 25% are correctly maintained. Without proper maintenance, even well-designed and -installed belt cleaners will add to rather than subtract from operational problems.
As discussed, belt cleaners should have adequate space for safe installation and access, as well as work platforms that allow for ergonomic inspection and service. These factors encourage the likelihood of more-frequent belt cleaning system maintenance.
Benetech: Your Ally in Bulk Material Handling
Benetech supports greater production and safety by controlling carryback with a belt cleaning system developed for your facility. In addition to designing and installing your system, we can help train personnel in proper system maintenance. To discover more about our capabilities for your operation, contact us at (630) 844-1300 to speak with a specialist.