Essential considerations in belt conveyor design
With an unprecedented demand for raw minerals, belt conveyors are more critical to the mining industry than ever before; from transporting material over rough terrain, to delivering product to loadout and every stop in between, belt conveyors keep minerals moving from mine to market.
Troughed belt conveyors serve as the basis of all handling systems, thanks to their flexibility, opportunity for customization, and the many settings in which they can be applied. However, the harsh operating conditions, heightened risks, increasingly high-value products, and often remote locales associated with the mining industry mean that standard conveyor designs are insufficient. For a safe, reliable, and efficient conveyor system, producers must take several factors into consideration during the design stages to achieve a successful result.
Priority 1: Safe operation
Depending on the site location, different bodies may oversee safety regulations, but maximizing safety is always a top priority. By utilizing conveyors, facility managers are already improving safety by reducing the need for manual transport, but the inclusion or reinforcement of a few additional components can further bolster site safety.
Guarding – Guarding is essential to any operation, no matter the industry, protecting workers from moving parts and pinch points. The heavy loads and high torque associated with mining conveyors makes guarding even more important in these settings. For these reasons, many producers choose to go beyond the minimum requirements for guarding, incorporating additional guarding where appropriate and ensuring guarding is made of heavy-duty materials that can withstand any potential impact.
Additional protection such as the use of closed-end housing bearings or idler guards that act as a catch basket (to protect employees from a falling idler in the event of a failure) can also be incorporated.
Emergency shut-offs – Emergency pull-cord switches should be included at regular intervals along the length of the conveyor and should include a pull-cord which runs the entire length of the conveyor.
Training – Comprehensive employee training on both operation and maintenance is critical to minimizing risks, as well as eliminating unnecessary human-
Maintenance – Conveyor systems must be regularly inspected and maintained per the OEM’s recommendations. Early identification of issues typically allows them to be addressed before they can escalate into a major safety hazard. Regular inspection and maintenance are also imperative to maximizing equipment service life and efficiency.
Fugitive dust control – Fugitive dust (or other material) control measures are necessary to mitigate the many hazards associated with dust. A buildup of fugitive material is often the cause of trips, slips, and falls, as well as failed components and even premature equipment failure.
For these reasons, skirtboards are often added at loading points to prevent fugitive material from escaping. Dust pick-off points can also be incorporated, allowing fugitive dust to be captured.
Priority 2: Reliability
A stalled operation can quickly incur extensive costs in lost productivity (not to mention maintenance costs). Further, remote mine sites can often mean weeks of waiting on a repair or replacement component, making reliability a top priority.
Conveyor reliability is dependent upon a number of factors. Most notably the following:
Build quality – Mine-duty conveyors require heavy-duty components and rugged materials of construction. This might also include the use of special cover compounds, galvanization, or other treatments to protect structural components from the elements and fugitive material.
Wear liners such as UHMW, Tivar, or abrasion-resistant steel are also often incorporated.
Material characteristics such as bulk density, moisture content, particle size distribution, corrosivity, abrasiveness, and more must all be factored into the design and selection of components.
Maintenance – Even the most well-designed conveyor cannot remain reliable without proper maintenance. Pre-emptively replacing worn components not only helps to prevent unexpected downtime, but it also contributes to a safe working environment. Keeping a comprehensive inventory of spare parts also helps to minimize unnecessary downtime.
In the above photo of a conveyor head section, for example, the guarding is protecting workers from high-speed sheaves and V-belts. These should be regularly inspected and replaced as needed to avoid a failure. The head pulley cleaners, pictured in orange, also require inspection for wear, as well as regular adjustment for proper tension. A replacement blade should always be kept on site. The gear reducer, shown below the motor, also has routine maintenance requirements, including regular oil changes.
Automation – An advanced automation and controls system can be a major help, not only in making start-ups and shutdowns more seamless and reducing wear on motors, but also in identifying potential issues such as a worn bearing.
Redundancy – In cases where unexpected downtime simply is not an option, building redundancy into the system with capital spares may be a fitting option.
Similarly, redundant control systems can be used to ensure that the conveyor can be safely stopped or controlled in the event of a control systems failure.
Priority 3: Efficiency
As technologies advance and we strive to maximize available resources, the importance of efficiency continues to grow, with even slight inefficiencies becoming less and less tolerable. An efficient conveyor maximizes throughput, minimizes downtime, increasing profitability.
To optimize a conveyor system for efficiency, engineers must carefully balance several factors in the initial design.
Belt speed – Belt speed must be configured according to operational priorities; it might be tempting to maximize belt speed, but this can increase wear and tear on components, while also requiring more energy to operate. Too slow, however, and belt speed can limit throughput.
The optimal belt speed depends on the specific requirements of the mining operation, including the type of material being transported, the distance and elevation of the conveyor, and the capacity of the conveyor system.
Belt width – Likewise, belt width is also a balancing act. A wider belt can increase throughput by allowing more material to be transported at once, but a narrower belt can be more efficient for transporting smaller amounts of material. In either setting, it is important to ensure that the width of the belt is compatible with the rest of the conveyor system, including the size of the rollers and other components.
Idler size and spacing – Idlers, typically CEMA D or CEMA E, should be spaced to minimize conveyor belt sag without incorporating an excessive number of idlers. Idlers should also be sized to minimize friction between the belt and rollers to reduce unnecessary wear and tear.
Pulleys – Pulleys should be designated as heavy-duty, with mine-duty or engineered class offering more rugged options.
Loading – Loading also plays an important role in the efficiency of a conveyor system. The loading area should be designed to evenly distribute material on the center of the belt. The incorporation of a belt feeder, which meters material onto the belt from a bin or hopper is often essential in this setting.
The design of the loading area must also consider the velocity at which material will hit the belt and the size of the material. Additional components such as an impact bed may be necessary to minimize belt wear.
Drive assembly – The drive assembly is another important consideration in the overall efficiency of a conveyor. Depending on whether the system will be started with a full load, fluid couplings or a soft-start package may be necessary to reduce stress on the motor and avoid unnecessary energy costs.
Variable frequency drives (VPFs) are also often essential in the mining industry, allowing operators to promote a smoother start-up and shutdown of the system, again minimizing energy requirements and stress on the motor.
As moving minerals from mine to market as efficiently as possible becomes increasingly important, mineral producers are continuing to rely on belt conveyors to keep their operations running smoothly.
The unique challenges associated with handling minerals and ores, however, demand a tailored solution beyond the standard. Mine-duty conveyors must prioritize safety, reliability, and efficiency, with several options available to meet these demands in each category. CMJ
Dan Baxter is material handling sales engineer at FEECO International.