August 2019

Expert insights into apron feeder evolution

  • By Thomas Thomas, Bulk Material Handling Product Specialist, Metso

Apron feeders are used to transport large, lumpy, abrasive and heavy ores under severe impact conditions – including wet, sticky or frozen operations. Recent design innovations have made these machines longer lasting and safer for operators. 

Apron feeders are robust machines that are designed for long-term use in a diversified range of industrial applications. 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 address common problems that operators face. In the last 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. 

Changes in design over the past 20 to 25 years

Machine design characteristics have evolved over time, and many improvements have been introduced to reduce the need for routine servicing. Apron feeders were traditionally designed with many components that required constant lubrication and maintenance. Cast and forged apron feeder chains are examples 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 unit life. SALT designs for other components such as rollers and tractor-type tail wheels have also been incorporated. These design improvements ultimately make things easier for operators by increasing machine reliability, and therefore reduce the need for day-to-day maintenance. 

Machine designs have also evolved to improve operator safety. One such example relates to apron feeder pans, which are also referred to as flights. Pans are high impact, abrasion-resistant wear parts responsible for extracting material and discharging it from the feeder. 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 – a significant risk to worker safety. In response to this, we have developed a locking mechanism for Metso feeders that 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. 

Apron feeders and challenges in the current operating environment

One of the big challenges for the industry is 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 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.

Apron feeders are used to extract or feed large, lumpy, abrasive and heavy ores under severe impact conditions. 

Maximising availability and reliability

Apron feeders are generally very reliable and will just keep working, without needing a huge amount of maintenance. Having said that, monthly checks are always 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 only requires a brief inspection but is important to guarantee 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 13 mm. Larger clearances also increase the risk of bigger lumps of hard ore getting wedged into the gap. In some cases, this may cause the machine to stall; however, it is also possible for a machine to fail catastrophically at its weakest point. I have seen this first hand, and it presents a major threat, not only to equipment but also to worker safety. 

Recent safety innovations

An innovation that has been incorporated into Metso apron feeders eliminates the need to lift heavy rollers manually when servicing the machine. Rollers sit underneath the apron feeder pans and chains. Changing them out is difficult due to their weight – even smaller rollers are too heavy for manual lifting. To address this concern, we developed a tool that helps make the job safer and easier. The tool 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.

Apron feeder technology has come a long way, as this vintage machine shows. 

Apron feeder technology and the future

The future is very exciting for apron feeders, with many technological improvements on the horizon. Personally, I believe smart technology will provide operators the capability to optimise their feeders with production requirements in real time. This technology will also provide operators with the ability 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 changeouts. By changing out key componentry at the same time, total maintenance costs can be drastically reduced over the life of the machine. 

About Metso

Metso is a world-leading industrial company offering equipment and services for the sustainable processing and flow of natural resources in the mining, aggregates, recycling and process industries. With our unique knowledge and innovative solutions, we help our customers improve their operational efficiency, reduce risks and increase profitability. Metso is listed on the Nasdaq Helsinki in Finland and had sales of about EUR 2.7 billion in 2017. Metso employs over 12 000 people in more than 50 countries. Visit metso.com.

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