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This side view of a sizer mounted below a coal chute shows the motor and gear reducer arrangement. (Photo: McLanahan)

New online condition monitoring improves performance

By Steve Fiscor, Editor-in-Chief

Sizers work well for reducing raw coal. The smaller size fractions pass through the machine while the rolls compress and crush the larger chunks. Sizers are also able to handle the clay and rock found in raw coal. They also have a low profile and small footprint, which allows them to deliver high capacity crushing in a relatively compact size. Sizers are normally mounted on rails between the chute and the conveyor. Rail-mounting allows the machine to be rolled out for maintenance.

Most sizers consist of a set of rolls with teeth that are connected to electric motors with a set of gear reducers that are mounted directly to the roll shaft. These configurations are familiar to coal operators, which use similar arrangements for conveyor drives. A fluid coupler protects the motor and reducer from shock loads or material hang-up that would transfer excessive forces to the drive components. The crushing rolls rotate at slow speed with high torque. The tooth profile is based on the  material the machine is expected to crush.

The rolls can rotate inward or outward. The shaft on the rolls rotating inward are adjusted hydraulically to maintain a specified gap or size. Outward rotating rolls use adjustable combs to maintain a certain setting to meet specifications. The segments on crushing rolls should be easily replaceable. The combs should be designed in a way that prevents the buildup of clay or other materials.

McLanahan: Designed for Safety and Service

McLanahan has developed a full range of primary, secondary and tertiary sizers to meet the demands of the coal and minerals industries. “Our sizers have been designed and developed based on feedback from our customers to be highly reliable, quick and easy to maintain while also being safe to service,” said Lee Hillyer, director of global sales – mining for McLanahan. “We have a standard range to allow our machines to be of the highest quality, but also cost-effective for our customers with shorter delivery times. The range is standard, but all of our options are configurable on order and allow adjustment during operation to meet the specific requirements.”

While conditions are site specific, Hillyer said coal operators should expect a set of rolls to last anywhere from 12 to 24 months if maintained correctly. “Teeth are typically changed every 12 months,” Hillyer said. “All of our tooth segments have a rapid change out facility, which means a full segment change out can be accomplished within a single 12-hour shift.”

Maintenance is a key element in the design of the McLanahan sizer. Those features include the rapid change-out of segments, breaker shafts and the adjustable breaker bar. The units have motorized tramming wheels to move the machine quickly into position for maintenance. McLanahan also offers real time on-board condition monitoring, which allows the mine’s maintenance group to monitor the machine’s performance.

When he thinks about future improvements for sizers, Hillyer said the mines can expect to see continued improvements in the area of online condition monitoring, which would bring the McLanahan customer service team closer to the maintenance teams on site. “This will better enable everyone to monitor the performance of the machines in real time and allow us to advise our customers quickly before any unplanned downtime can occur,” Hillyer said. “Taking this one step further, we plan to retro fit our existing machines with a condition monitoring package so that our older machines can also take advantage of the latest technology on the market and share the benefits with our customers.

McLanahan produced a slick YouTube video that explains many of these features: www.youtube.com/watch?v=juphQwNCK1g&t=33s

ABON Builds a Big Sizer

ABON sizers are designed and serviced by FLSmidth’s team in Melbourne, Australia. They source the materials, build the machine, and provide the engineering, technical support, and spare parts.

Accepting feed through the top of the crushing chamber, the material is drawn through the toothed rotating shafts, crushing it to the specified size. “These durable and reliable machines deliver high availability and are capable of handling capacities more than 12,000 mt/h, even clay and sticky materials,” Malone said. “The low roll speeds maximize wear life and generate minimum fines, dust, and dynamic loads.”

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FLSmidth delivered a 9,000 mt/h sizer and the mining company that purchased it has ordered five more. (Photo: FLSmidth)

In 2018, a mining project that required a high processing capacity led to the development of the largest ABON Sizer ever built. “It was a huge challenge that needed a huge solution,” Malone said. “The ABON engineers and product team were ready for the challenge.”

Working with the mine’s production, maintenance, and commercial staff throughout 2019, the team created a machine that would achieve the goal, the largest twin-roll sizer they had ever produced. With a weight of more than 270 mt, the ABON 16/400CHDTD-RA Sizer was installed in mid-2021, and it successfully delivered 9,000 mt/h. “The mine was so impressed by its performance, it ordered five more in mid-2020,” Malone said. Since then, these hardworking machines have delivered full production, even when tested by lumps as large as 3- x 2- x 2-m. The mine confirmed the ABON Sizers had delivered robust and reliable operation through at least two cycles of operation of nine to 10 months each, which corresponds to a tooth life of 16 million tons per unit cycle.

MMD Focuses on Tooth Grip Strength

MMD said the additional benefits a sizer brings, such as producing a controlled and well-shaped product with minimal fines while also being compact, energy efficient, and maintenance-friendly, make it an appealing option when it comes to selecting a machine for most material processing operations. MMD said its dedicated in-house technical development team has provided consistent research and development since the sizer’s inception and original patent in 1979. With the experience gained over the years, the company said it has refined and expanded the sizer’s capability to operate successfully in a variety of industries, processing some materials rated at up to 400 megaPascals.

From the sizer teeth design to the drive train, the progress of these specialist heavy-duty sizers has taken many years of careful development and features a range of adaptations to allow them to handle harder rock.

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MMD’s semi-mobile sizer stations require simple pontoon bases rather than costly, heavy-duty foundations. (Photo: MMD)

MMD said it selects tooth designs and materials by prioritizing both durability and functionality. With a focus on ensuring the tooth grip’s strength matches the power required for material processing, we conduct rigorous testing to guarantee optimal performance. The company said its engineers assess various factors such as material composition, surface texture, and mechanical properties to ascertain the machine’s ability to hold and effectively break down the material securely. By adhering to quality standards, MMD said it ensure that its machines not only meet, but exceed expectations in handling diverse materials across various industries.

Another key feature throughout MMD’s range of sizers is the use of in-house designed gearboxes. Using only the highest quality manufacturing processes, materials and components guarantees they can deal with the unique stresses inherent with sizing hard rock.

MMD said its sizers and sizer stations undergo rigorous FEA, DEM and Explicit Dynamics analysis at the design stage. This examination provides data on impact forces, load conditions, fatigue cycles, as well as material flow characteristics, which assist in optimizing the design. This is particularly useful for wet and sticky applications where material hang-ups and blockages could be problematic in features such as hoppers and chute work. MMD said maintenance its sizers is streamlined with swift and effortless shaft replacements, ensuring minimal downtime and smooth operational continuity.

This article was adapted from an article first published in June 2024 E&MJ.