Chapter 9: Conveying & Material Handling | P&Q University Handbook

Efficient material handling is essential to productivity and profitability at pits and quarries.

Conveyor systems, which automate the movement of crushed stone, sand and gravel, link crushers, screens and stockpiles in virtually every aggregate operation. Whether transporting raw materials from the quarry to the processing plant or transferring crushed stone to a stockpile, conveyors offer advantages over manual or vehicle-based transport.

Conveyors provide continuous material flow, minimize interruptions and can eliminate production bottlenecks. 

They are also more cost-effective versus rolling stock methods of material handling, reducing the need for trucks and heavy equipment while lowering fuel and maintenance costs.

Importantly, conveyors enhance workplace safety by eliminating the need for workers to manually move heavy materials, reducing the likelihood of accidents. Conveyor systems are also more environmentally friendly than truck transport, producing fewer emissions and less dust.

Here’s an overview of the major conveyor options producers need to consider.

Fixed vs. Portable Conveyors

The decision between a fixed conveyor and a portable one hinges on the mobility needs of the operation. 

Fixed conveyors are built for permanent or semi-permanent installation, typically at stationary plants where material flow is consistent and the layout is unlikely to change. These systems are anchored in place and often support high capacities. They’re built for long-term durability and efficiency.

Portable conveyors, on the other hand, are designed for flexibility. They’re used in temporary or mobile crushing and screening spreads, and they can be relocated as needed. While portable conveyors may not offer the same structural robustness or capacity as fixed conveyors, their ease of setup, takedown and transport makes them ideal for contractors or sites that frequently shift locations.

Wheel-mounted portable and track-mounted mobile conveyor systems join portable and mobile processing plants to provide flexibility for short-term, seasonal or remote aggregate sites. 

They integrate seamlessly with portable or mobile crushers, screens and washing plants to complete a processing circuit without the need for permanent structures. They also can be used to extend stockpile reach, as well as loading trucks, railcars and ships.

More common in the U.S. than track-mounted conveyors, wheel-mounted portable conveyors are typically used in operations with relatively stable terrain and modest relocation needs. They are towed into place using trucks or loaders and supported by tires or skids.

Common portable conveyor types include portable radial stackers, low-profile telescoping radial stackers, self-contained stackers (with diesel-over-hydraulic power), portable transfer conveyors and truck unloading systems.p

Beyond traditional aggregates, both portable and mobile conveyors are often used in construction and demolition recycling operations, where materials such as recycled concrete and asphalt are processed on-site. Their ability to move between tight spaces and adapt quickly to changing volumes make them well-suited for urban recycling yards. 

They can also be used in portable concrete and asphalt batch plants, feeding hoppers or silos directly for improved productivity and reduced loader cycles.

The frame style of a conveyor is also important, impacting both its structural performance and appropriate use. 

Truss frame conveyors are constructed with a steel lattice structure, offering high strength-to-weight ratios. This design is often chosen for longer conveyors, where added structural support is necessary, such as overland systems or stackers spanning wide gaps or elevations.

In contrast, channel frame conveyors use a formed steel or rolled channel design, making them better suited for shorter runs or portable units. Channel frames are simpler and more compact – and this is beneficial when space is limited or when frequent transport is required. However, they typically cannot span as far as truss systems without additional support.

Engineering & Safety

Bulk conveyor systems are foundational to aggregate operations. And while indispensable, these systems pose inherent risks and maintenance challenges. 

Ensuring safety, maximizing efficiency and extending the service life of components are interrelated objectives that must be addressed systematically. 

A comprehensive safety audit is a first step to identify operational hazards. Evaluate guarding around pinch points, functionality and accessibility of emergency stop systems, compliance with lockout/tagout (LOTO) procedures and the presence of safe walkways for personnel crossing conveyor paths. Findings should be documented and prioritized to guide corrective actions.

Safety should be built into conveyor design from the start. Systems should incorporate modular components for easier servicing, continuous emergency shutoff pull cords and enclosed return rolls to eliminate pinch hazards. 

Preventive maintenance plays a critical role in hazard prevention. Regular inspections of belts, pulleys, bearings and idlers can identify wear before it escalates. Thermal imaging and vibration analysis are valuable diagnostic tools for spotting overheating or misalignment. 

Also, housekeeping around loading zones and conveyor structures helps to eliminate slip and trip hazards, as well as and reduce fire risks from buildup. Maintenance records are essential for tracking issues and identifying recurring problems.

Training and operator engagement are equally important. Personnel must be trained on system-specific procedures – including hazard recognition, LOTO and emergency response. Routine drills and reinforcement of safe behaviors foster a workplace culture where safety is a shared value.

Controlling dust, spillage and carryback is necessary to maintain safe and efficient operation. Proper chute design, belt cleaning systems, sealed skirtboards and a regular cleaning schedule mitigate these issues.

In inclined belt conveyor applications, managing the risk of rollback is essential to maintaining a safe and efficient operation. Anti-runback systems are engineered specifically to address this concern by preventing the uncontrolled reversal of the conveyor belt and material flow – especially in the event of a belt failure or unplanned stop.

Modern anti-runback systems can be integrated directly into the conveyor rollers. These systems rely on a precision mechanism involving cams, cylinders and centrifugal force to allow forward rotation while instantly locking the roller if reverse movement is detected. This “one-way” functionality ensures that if the belt loses tension or breaks, it cannot run backward, avoiding potential hazards to personnel and damage to structural components.

Used most often on the inclined sections of conveyors, anti-runback rollers enhance safety by eliminating the risk of sudden backsliding. This prevents catastrophic material spillage, protects take-up systems and pulleys, and reduces the likelihood of costly unplanned downtime. Importantly, this protection is automatic and passive requiring no external power or manual activation.

Industries such as aggregates can significantly benefit from this type of safety solution. Incorporating anti-runback roller systems is not just a preventive measure; it’s a best practice for responsible, efficient and safe conveyor operation.

High-quality components improve both safety and reliability by reducing failure points, minimizing downtime and limiting exposure during maintenance. 

Safety is not static; it requires ongoing evaluation. Establishing a safety team or assigning shift-based champions helps track near misses, review incidents and share learnings across the operation.

Improving conveyor efficiency

Ultimately, system efficiency is driven by both design and operation. Design decisions made early on impact serviceability and long-term reliability. Modular components, inspection access points and self-cleaning or enclosed designs reduce material buildup and allow easier maintenance, contributing to reduced downtime.

Preventive maintenance is central to system performance. Inspections should focus on wear-prone items and be supplemented with condition monitoring tools such as thermal imaging and vibration analysis. Maintenance logs help to identify patterns, allowing for data-informed improvements and more efficient scheduling of repairs.

Certain upgrades provide significant efficiency gains. Low-drag idlers reduce energy use, while ceramic or replaceable lagging on pulleys minimizes slippage and wear. Modern impact beds and skirtboard systems improve material control, and belt tracking systems prevent misalignment. Magnetic separators protect downstream equipment by removing ferrous debris.

Technology further supports operational efficiency. Sensors monitoring speed, alignment and temperature, coupled with supervisory control and data acquisition systems and automated lubrication allow for predictive rather than reactive maintenance. Even simple alignment sensors can prevent costly belt or component damage.

Efficient material flow begins with proper load zone design, centered material discharge and dust suppression. Paired with a robust housekeeping plan, these steps maintain clean operations and prevent disruptions.

Efficiency must also be cultural. Operators should be empowered to analyze root causes of delays and contribute to continuous improvement. Sharing performance metrics and conducting post-event evaluations reinforce accountability and collective ownership of system performance.

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