Advantages of automation

Engineered to operate at high speeds and over considerable distances, conveyors are generally designed with electrical power only at essential locations such as the head pulley, without secondary access for sensors, lights, accessories or other devices.

Running auxiliary power can be complicated and costly, requiring transformers, conduits, junction boxes and oversized cables to accommodate the inevitable voltage drop over long runs.

That was the challenge at Illinois Cement Co. in LaSalle, Illinois, specifically on the outdoor conveyor between the limestone crusher located at the quarry hopper loading point and the stackout conveyor. Operators needed a power solution that was easy to install and maintain, yet provided enough current to drive an automated dust suppression system, a pneumatic belt cleaner tensioner and the air cannon equipment being implemented there.

The goal was to curb fugitive dust and spillage, increasing cargo flow efficiency and minimizing labor costs for cleaning and maintenance.

“Running a line from the breaker was more of an investment than we wanted to make without knowing how successful the material control efforts would be,” says Brian Brandner, maintenance planner at Illinois Cement. “When Martin Engineering technicians proposed that they use their roll generator to power the new equipment, we were skeptical because we’d never seen anything like it.”

The long ride

Coming from a quarry six miles away, trucks haul about 18 metrics tons of raw limestone per load and drop it into a hopper leading to the crusher, which reduces the rock to 4-in. minus.

The crusher deposits aggregate onto the 164-ft. No. 153 conveyor that transfers it to No. 107-1, which is fitted with a baghouse dust collection system at the transfer point. It is the longest outdoor conveyor system on the site, running 600 ft. and discharging either onto a stackout conveyor or the 250-ft. belt leading directly into the plant, based upon immediate production needs. The No. 107-1 conveyor is a 30 in.-wide mechanically spliced belt with a 35-degree trough that travels at 400 ft. per minute (fpm), conveying nearly 300 short tph of limestone.

The belt is protected from the weather by a corrugated pipe dome leading from the loading zone along the entire length of the belt, with the exception of the discharge zone at the head pulley.

The LaSalle, Illinois, area experiences four distinct seasons, including freezing winters and hot and dry summers, with rain in between. This means cargo arriving from the quarry can be either wet or dry and dusty. The changing conditions present challenges throughout the entire conveying system.

“After it’s crushed, dry limestone increases the potential for fugitive dust during several months of the year, so we already have a highly efficient dust collection system in place,” Brandner says. “The issue is that the filter cartridges plug quickly, due to the moisture, and they are costly to maintain and replace.”

Different weather conditions also trigger carious types of carryback, and cleanup was labor intensive. Dry fines adhered due to cargo pressure and dislodged from the return side of the belt, leading to accumulation around the discharge zone. In humid conditions, wet carryback would adhere to the surface and lodge in cracks on the belt, allowing it to travel and spill material along the entire conveyor path as fas as the tail pulley.

“The primary cleaner blades we had in place wore quickly, causing spillage that required us to take personnel from other areas to clean the buildup,” Brandner says. “We were out there cleaning or adjusting the tension to minimize spillage a few times a week. Cleaning would intensify, depending on the material being conveyed or the weather conditions during operation. When it got really cold, we wouldn’t have as many issues with dust or carryback, but the frost accumulation required us to keep the belt running at all times, which lowered the blade life and caused undue wear on the belt.”

Automating localized power generation

Having had a positive relationship with Martin Engineering for several years, managers at Illinois Cement invited a team to examine the issues on the No. 107-1 conveyor and offer solutions. Performing a walk-the-belt procedure, which assesses every aspect of the system from performance to safety, technicians offered a two-phase plan.

Phase one involved placing a “smart” dust suppression system at the transfer point between the No. 153 and No. 107-1 conveyors. Phase two included an automated, pneumatically-tensioned belt cleaner and air cannon system at No. 107-1’s discharge zone. The Martin Roll Gen system powers both components.

“It’s designed to be a self-contained mini power station that’s retrofitted onto existing idler support structures, so the generator can be employed on virtually any steel roller,” says Andrew Timmerman, product development engineer at Martin Engineering. “As conveyors move toward more sustainable and autonomous ‘smart systems,’ the Roll Gen eliminates the power accessibility obstacles to employing sensors, cleaners and dust control systems such as we installed for Illinois Cement.”

The unit employs a magnetic coupling that attaches a “drive dog” to the end of an existing roller, matching the outside diameter of the generator to that of the idler.

Rotated by the movement of the belt, the drive dog engages the generator through the outer housing’s machined drive tabs. The magnetic attachment ensures that electrical or mechanical overload does not force the roll to stop. Instead, the magnets disengage from the roll face. By placing the generator outside the material path, the Roll Gen avoids the damaging effects of heavy loads and fugitive material.

Addressing dust

To manage the dust, technicians installed a Martin surfactant dust system at the transfer point between No. 153 and No. 170-1 to deliver a chemically-enhanced water spray as a topical treatment for material at the point of emission. Triggered by a sensor as soon as the load enters the transfer point, the system supports dust mitigation measures already in place to minimize the labor needed for maintenance and replacement of the dust collector cartridges.

Powered by the Roll Gen, the automated control panel features a manual shutdown on its face, as well as a material sensor that can be adjusted to fine-tune the system’s sensitivity and duration of spray. The pump box houses the water intake hose, dosing pump and booster pump.

To maximize the effectiveness of the surfactant additive, specialized nozzles evenly distribute the engineered spray, delivering full coverage and shutting off when material is no longer present.

“All of the components are industrial-rated to ensure they can withstand long operational periods in punishing environments,” Timmerman says. “An automated system defeats its purpose if it frequently needs maintenance, so the control panel carries a NEMA (National Electrical Manufacturers Association) 4 rating to protect the inner workings from the outside elements.”

Cleaning the belt

Close to the midpoint of the system, conveyor No. 107-1 begins a gradual 20-ft. rise and discharges into the transfer chute leading either to the stackout conveyor feeding the storage area or the main conveyor entering the plant.

At that transfer point, technicians installed a Martin QC1 primary cleaner XHD tensioned with an automated blade system (ABS).

Built for demanding applications in varying environments like those found at Illinois Cement, the QC1 XHD can withstand temperatures from minus 30 degrees to 300 degrees. Handling belt speeds of up to 1,200 fpm, the blade design maintains a tight edge against the belt while passing smoothly over the mechanical splice to deliver reliable cleaning across all stages of the blade’s life.

Connected to a 24-volt DC air compressor and a control panel powered by the Roll Gen, the ABS pneumatic tensioner delivers precise monitoring and tensioning to reduce the labor typically required to maintain optimum blade pressure through manual adjustment. Equipped with sensors to confirm when the belt is running empty, the system automatically backs the blade away, minimizing unnecessary wear to both the belt and cleaner.

Upon detection of an empty belt, the system is set to run for one full belt rotation, equating to about three minutes, to clean the surface thoroughly before pulling away. The result is a consistently correct blade tension with reduced power demand on startup, all managed without operator intervention.

“The new cleaner has been a game changer when it comes to the amount of maintenance, equipment wear and manpower for cleanup,” Brandner says. “The blade’s no longer just scraping an empty belt, which has extended the blade’s operational life and been a lot easier on the belt face and splice.”

After the systems were implemented, operators reported a 75 to 80 percent reduction in carryback.

“Decreased spillage means less cleanup, but it also had another outcome,” Timmerman says.

Transfer chute flow

While monitoring the results of the installation, Martin Engineering technicians observed that the decreased spillage resulted in a proportional increase in fines discharged down the transfer chute.

Exposed to the outside environment, the chute began to form significant buildup along the sides, at the diverter gate and on the internal shelf meant to slow the flow of material. The technicians had a solution to this unexpected result and, to mitigate the buildup, installed a Martin Hurricane air cannon.

A straight pipe assembly, fed by the plant’s existing compressed air system, attaches the 70-liter tank to the chute wall. Firing a blast of air at up to 120 psi from a pressurized tank through a 12-in. fan jet nozzle, the air stream is shot at a downward angle of about 225 degrees across the surface of the shelf and down the wall. With an effective area of up to 22.6 sq. ft., the air blast mitigates material buildup and promotes cargo flow.

The air cannon’s valve requires a positive signal from the solenoid in the form of an air pulse to trigger discharge to eliminate the risk of unintentional firing due to drops in pressure. Engineered to fire only when the belt is running and loaded, the system eliminates wasted air from firing when there’s no cargo on the belt or when the conveyor is idle. The control panel is powered by the same Roll Gen as the ABS, while also giving operators the ability to fire the cannon from ground level.

“When there’s cargo flowing, the cannon fires about every 10 minutes, which keeps fines from clinging to the walls and promotes proper flow,” Brandner says. “If the material is extra wet and building up faster than usual, we can just go over and fire it manually at any time.”

Results

After several months of operation, with some minor adjustments, the automated equipment has exceeded performance expectations. This includes the effectiveness of the Roll Gen units, which have delivered consistent power to the necessary systems.

“We’ve been closely monitoring performance and found little to no degradation in energy output so far,” Timmerman says. “Neither unit has required maintenance, and wear on the equipment has been minimal. By avoiding the high costs of installation and maintenance of conventional power transmission equipment, we estimate the units will pay for themselves long before their service life ends.”

The use of multiple technologies working in tandem to control material flow and prevent fugitive particles dramatically improved the efficiency of the material handling system. The modifications have helped Illinois Cement reduce labor and equipment expenses, considerably cutting the manpower needed to clean spillage along the conveyor path. The result is a cleaner, safer and more productive operation.

“The entire project has been a success, particularly in how many man-hours we save in maintenance and upkeep,” Brandner says. “The tensioning system does a great job, and the Roll Gen puts out enough power that we’re considering adding an automated secondary cleaner and a vibrating dribble chute to capture even more carryback.”

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Information for this article courtesy of Martin Engineering.