A clean conveyor belt is a safer conveyor belt

Martin Engineering’s seasoned process engineer, Dan Marshall, shares expert advice about mitigating spillage and dust in the conveyor belt discharge zone.

In the harsh and demanding environment of mining there are no guarantees, and completely cleaning a conveyor belt can be a tough challenge. Spillage, carryback, chute clogging and fugitive dust emissions block walkways, foul rolling components, cause unscheduled downtime and worsen air quality, but they don’t have to. Manufacturers of innovative equipment continually work to enhance workplace safety and production efficiency by minimising these issues wherever possible.

After installing modern belt cleaning technology, operators notice that the amount of material entering the transfer chute increases significantly, instead of just piling around the discharge area. This greater volume can cause blockages in the transfer chute, leading to downtime for clearing clogs. However, engineers can take a comprehensive approach and design an efficient discharge transfer point with co-ordinated components. This strategy aims to extend equipment life between scheduled shutdowns, enhance safety by reducing maintenance needs, and address the root causes of inefficiency.

 

Signs of inefficiency at a discharge zone

The discharge zone begins at the last troughed idler before the conveyor belt flattens and meets the head pulley. Cargo falls from the conveyor into a transfer “drop” chute, which can lead to various destinations including another conveyor, a storage silo or pile or a transport vehicle. The primary cleaner is installed after the discharge stream to remove any material that may have adhered due to the cargo’s weight or properties such as moisture, cohesion or heat. A secondary cleaner removes dust and fines from divots and cracks in the belt. Material cleaned by the secondary cleaner is typically directed onto a sloped surface connected to the transfer chute.

Obvious signs of discharge inefficiency include spillage, carryback, chute clogging and dust. Each of these alone can cause a workplace safety violation, but together they lead to unscheduled downtime and higher operating costs.

From an operational perspective, three of the costliest issues are workplace injuries, belt damage from friction, and the replacement of fouled equipment.

 

Spillage and safety

Primary cleaners or “scrapers” can fail in several ways, causing adhered coarse aggregate and caked fines to pass by the blade and spill around the discharge area. This fugitive material can build up quickly and encapsulate the belt, fouling rolling components and causing the belt to ride on top of the course pile, leading to serious belt damage and increased belt temperatures from friction.

Fugitive material spills onto walkways, blocking access for maintenance and creating a trip and fall hazard. When coarse grit fouls rollers, it causes them to freeze, leading to friction and high- heat damage to the vulnerable return side of the belt, reducing the equipment’s lifespan. To prevent belt fires and dust explosions, seized idlers and rollers should be maintained and replaced immediately, making clear access to the system essential.

Cleaning up spills can be expensive, distract staff from other important tasks, and pose a workplace safety risk if workers are cleaning around a moving belt. What might seem like a simple job at first, such as shovelling spill material back into the cargo stream or into bins, demands more effort over time as the problem gets worse. Using machinery like front loaders or industrial vacuums to clear material can accidentally cause contact with the stringer or supports, which could lead to belt mistracking.

Mistracking can be a major cause of spillage, not just along the belt path but also at the discharge point. The blade is centred on the head pulley, but if the belt isn’t, adhered material can cause spillage.

Recommendation: Install a belt tracker at a distance of 3 to 4 times the width of the belt before the head pulley as the trough angle flattens, to ensure the belt hits the centre of the head pulley.

Over- or under-tensioning and/or extending blade changes for too long can lead to spillage. Over-tensioning causes quick wear on the belt/splice and reduces blade lifespan. Under- tensioning allows material to pass without being properly removed. Ignoring primary cleaners for too long can result in pull-through, where the belt’s force causes the blade to face the opposite direction and, in some cases, break off.

Recommendation: Enter into a service agreement with the blade manufacturer to regularly monitor, tension and replace the blades as needed. Consider installing a modern assembly that allows workers to slide units from the stringer for quick and easy one-person blade changes. There is also the option of innovative cleaner technology with four times the lifespan of the standard primary blade and no tensioning required for the life of the blade.

Reducing carryback

Anything that sticks to the return side of the belt and moves with it is considered carryback, which can cause serious damage to a system. Not only is it a major source of fugitive dust and fines, but it also easily migrates into return rollers and takeup pulleys, fouling the bearings, drives and the face of the roller. The grit grinds down roller bearings and leads to excessive friction heat, causing them to become mis-shapen and seize.

Like spillage, carryback can migrate to the underside of the belt that doesn’t carry material. These chunks travel all the way to the tail pulley. The intense pressure between the pulley and the belt causes the hard, sharp mass to damage the vulnerable side of the belt and the pulley face, repeatedly cycling and causing more damage. Along with decreasing the belt’s lifespan, dust and fines can get into these blemishes and contaminate the pulley face.

When a roller or pulley face becomes fouled, it is covered with abrasive grit that can wear down and damage the belting over time. In some cases, fouling causes slippage, which can disrupt the smooth operation of the belt and lead to mistracking.

Recommendation: If there is sufficient space, install secondary and tertiary cleaners to guarantee the belt is thoroughly clean on the return. To enhance safety, consider units that allow a single worker to pull them away from the stringer for quicker external servicing.

Consider placing a diagonal or V-shaped plow underneath the loading zone just before the tail pulley, which rides on the underside of the belt and removes any loose material. For more effective cleaning and to lessen friction damage, opt for a plow with torsion arms instead of one held in place by chains. Install belt trackers or crown rollers along the upper and lower belt paths to maintain proper alignment.

 

Safely addressing bulk handling clogs

A clogged transfer chute or hopper is one of the most dangerous situations in bulk handling. Untrained and uncertified personnel should never enter a clogged chute or bin under any circumstances. A sudden discharge can be deadly, as an unknown void can engulf and crush a worker. Material adhered vertically to the sides can loosen and cause a sheet of debris to fall on someone inside the vessel.

Buildup points in chutes include:

• Rockboxes – shelves, even if they’re sloped, can experience buildup.
• Exit gates or doors – since these help control flow, they are also prone to clogging.
• Sloped points – located under the secondary cleaner, chute grades, or at choke points.
• Metal surface grain – the metal grain of chute plating should align with the flow of cargo.
• Exposed surfaces – surfaces where moisture can gather and lead to buildup.
• Damaged surfaces – surfaces with scratches, dents, creases or divots.

Faulty methods for dealing with buildup include hitting the sides of the hopper with a mallet or poking at the obstruction from below to loosen it. In some operations, clogs are so common that specific spots for pounding are marked, and mallets are kept nearby for convenience. However, this is dangerous because it weakens the structural integrity of the vessel or chute, risking buckling. The ripple damage caused by pounding makes it easier for material to accumulate, reducing the time between clogs and increasing unscheduled downtime. Poking from below is even more hazardous, as a sudden discharge can send tons of material rushing out, risking injury to anyone nearby and damaging equipment below.

Recommendation: Air cannons strategically installed around the chute have nozzles aimed in the direction of the material flow. Powerful bursts of air are distributed across the surface inside the vessel, dislodging material and preventing buildup. The air cannons are supported by vibration units that ensure gates and narrow spouts on hoppers and chutes maintain proper flow before bridging begins. In many cases, vibration alone can manage most dry material flow, but changes in humidity that increase the stickiness of cargo and chute surfaces, along with fluctuations in production volumes, are much better handled by air cannons.

 

Discharge dust

Emissions at the discharge zone can be found billowing out of the chute against the direction of the cargo stream or exiting the sides and bottom as it loosens from the belt’s return side. Dust has become a highly regulated workplace and environmental concern which can lead to stiff fines and potential forced downtime if high volumes of respirable crystalline silica (RCS) is detected. RCS is found in nearly every substance pulled from the earth, but is prevalent in limestone, coal clay, etc. Regulators measure fugitive particulate matter (PM) at the size of <10 microns mass (μm) in volumes of >50 micrograms (μg) per cubic meter (m3) over an eight-hour time weighted average (TWA). This is the volume an d size determined to cause serious chronic lung issues in workers, and it doesn’t just apply to RCS, it is any PM.

Dust emissions returning from the chute can result from uncontrolled airflow at the exit point. The emissions can also be caused by hitting rock boxes designed to slow the flow of material or by an unobstructed impact that causes turbulence.

Dust from carryback can permeate the area and spread emissions along the entire length of the belt return. If the belt reaches into a tower or is exposed to the outdoors, this causes dust to be carried long distances by air currents into nearby communities, leading to potential violations. Studies have shown that dust can be controlled through adequate cleaning at the discharge using Levels 1–3. Level one is a primary cleaner, level two a secondary cleaner and level three a tertiary cleaner.

Recommendation: Reconfiguring the chute’s exit into a sloping scoop allows material to be slowed and loaded onto the next belt in a controlled, centred way with less turbulence. Air cannons installed along the chute are aimed with the material stream and can help direct airflow.

Conclusion

Modern bulk handling industries are evolving and expanding daily.

The demand for raw and processed materials for construction and manufacturing continues to rise. Increased production can alter throughput volumes and belt speeds, which directly impact spillage, carryback, clogging and dust.

Retroactively installing equipment that enhances both safety and efficiency should be a priority for any operator. Although the initial capital investment might be slightly higher, the return on investment (ROI) and benefits are not limited to fewer injuries but also include reduced labour costs for maintenance, fewer equipment replacements, improved compliance and an overall lower cost of operation.

Dan Marshall, process engineer, Martin Engineering.

Introducing Daniel Marshall: Marshall received his Bachelor of Science degree in Mechanical Engineering from Northern Arizona University. With nearly 20 years at Martin Engineering, Marshall has been instrumental in the development and promotion of multiple belt conveyor products. He is widely known for his work in dust suppression and considered a leading expert in this area. Marshall has published over two dozen articles covering various topics for the belt conveyor industry; presented at many conferences and is sought after for his expertise and advice. He was also one of the principal authors of Martin’s FOUNDATIONS™, The Practical Resource for Cleaner, Safer, and More Productive Dust & Material Control, Fourth Edition. For more information, contact info@martin-eng.com or visit www.martin-eng.com.

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