EXPERT INSIGHT INTO

A past example of an apron feeder. The design and manufacture spans more than 120 years.

AN EXPERT INSIGHT INTO APRON FEEDER EVOLUTION

Apron feeders transport large, lumpy, abrasive and heavy materials under severe impact conditions. Metso product specialist Thomas Thomas draws upon his experience to share some insights into apron feeders, and their applications within the minerals processing industry.

Apron feeders are robust machines that are designed for long-term use in a diversified range of industrial applications,” Thomas Thomas, who is Metso’s business development manager, based in Perth, said. “Their primary function is to extract or feed material short distances at a controlled rate of speed, which prevents choking of material that feeds crushers and other equipment. Apron feeders are also commonly used to reclaim material at a uniform rate from hoppers, vaults, bins, and stockpiles.”

Apron feeder design has evolved over time to meet changing industry requirements and challenges. With 37 years in the mining industry himself, including 24 years at Metso, Thomas said that Metso has 150 years of engineering know-how, including 125 years of experience in apron feeder design and manufacture.

“Throughout this time, we have built a global install base of over 2000 feeders,” he said. “I would say in the past 20 to 25 years, the design has seen a quantum shift. The apron feeder has become so reliable and user-friendly that it generally needs very little maintenance and is now widely available to suit most applications.”

Thomas said that machine design characteristics have evolved over time, and many improvements have been introduced to reduce the need for routine servicing. “Apron

Thomas Thomas is Metso’s product specialist in apron feeder technology.

feeders were traditionally designed with many components that required constant lubrication and maintenance,” he said. “Cast and forged apron feeder chains are an example of this. Traditional chain designs that required regular lubrication have given way to sealed and lubricated (SALT) units, which do not require any lubrication throughout the life of the unit. SALT designs for other components such as rollers and tractor-type tail wheels have also been incorporated in Metso apron feeders. These design improvements ultimately make things easier for operators by increasing machine reliability and therefore reduce the need for day to day maintenance.” IMPROVING OPERATOR SAFETY Machine designs have also evolved to improve operator safety. One such example, Thomas said, is the apron feeder pan, which is also referred to as a “flight” (see Figure 1). “Pans are high impact, abrasion-resistant wear parts responsible for extracting material and discharging it from the feeder,” Thomas explained. “These components need to be stopped and secured during periods of routine maintenance. As you can imagine, if the pans move while workers are on the machine, it’s like having a rug pulled from under you – it poses a significant risk to worker safety. We have developed a locking mechanism for Metso feeders to address this issue. When the locking mechanism is engaged, a pin made from high tensile steel secures the chain and prevents it from moving in any direction. To further improve safety, a limit switch or proximity sensor is incorporated to indicate pin disengagement via an audio or visual alarm.”

Thomas said that one of the main challenges for the extractive industry in the current operating environment with respect to apron feeders is the increased pressure to reduce capital expenditure costs. “Producers are faced with a tough choice, and sometimes opt for a cheaper machine that is satisfactory for current operating parameters but does not have the capability to reach future production targets. In my

Figure 1. Pans (or flights) are one of the features of a modern apron feeder.

opinion, it’s better to opt for a design that is future proofed, rather than purchasing the cheapest machine available. This allows greater flexibility in the long-term, and you will avoid the need to replace or retrofit a larger machine into the existing footprint, which can be a costly exercise.”

SERVICING THE FEEDER To maximise the availability and reliability of an apron feeder, Thomas recommended ongoing maintenance. “This type of machine doesn’t require a huge amount of maintenance,” he said. “Apron feeders are generally very reliable and will just keep working. Having said that, monthly checks are a good idea to make sure the bolts aren’t loose on the pans. It is also good practice to maintain the correct chain tension. This requires a brief inspection but guarantees smooth operation and longer component life. “It is common for operators to overlook simple tasks like checking the clearance between the pans and skirts. An apron feeder can suffer premature wear if the recommended clearance between these components exceeds 13mm. Larger clearances also increase the risk of bigger lumps of raw materials getting wedged into the gap. In some cases, this may cause the machine to stall but it is also possible for a machine to fail catastrophically at its

Figure 2. A jack trolley eliminates the need to lift heavy rollers manually when servicing the machine.

weakest point. I have seen this first hand, and it presents a major threat, not only to equipment but also to worker safety.”

To that end, Metso has incorporated an innovation into its apron feeders – a jack trolley (see Figure 2) – that eliminates the need to lift heavy rollers manually when servicing the machine. Rollers traditionally sit beneath the apron feeder pans and chains. Changing them out can be difficult due to their weight – and even smaller rollers can be too heavy for manual lifting.

“To address this concern, we have developed a tool that makes the job safer and easier,” Thomas said. “It has been designed to allow operators to remove and replace rollers without the need for lifting equipment. This is much safer and eliminates a lot of the manual work that was previously required.”

Thomas has predicted an exciting future for the apron feeder, “with many technological improvements on the horizon. Personally, I believe smart technology will provide operators with the capability to optimise their feeders with production requirements in real time, to accurately forecast maintenance requirements and avoid unplanned downtime. “Replacing apron feeder components can be a costly process, which is often a result of the machine’s location in a plant. Access can be difficult which makes servicing components an extensive exercise for many operators. There is certainly an opportunity to design feeders in such a way to synchronise the life of key componentry and the associated change-outs. By changing out key componentry at the same time, total maintenance costs can be drastically reduced over the life of the machine.” •