Protective Pulleys - by RULMECA

Posted in: , on 3. Oct. 2011 - 21:09

Protective Pulleys

Mike Gawinski, Rulmeca Corporation USA

(First published by World Cement - Bulk Materials Handling Review, August 2011)

Introduced in Germany and Denmark in 1953, Rulmeca Motorized Pulley belt conveyor drives made their debut in North America in the 1980s at major ship loading terminals and surface mines [1]. Stone quarries, foundries, iron ore mines, and recycling facilities took advantage of the product's compact size and reliability in the 1990s. Then, in the early part of the 21st century, steel mills, cement plants, power plants, and coal preparation plants began installing Motorized Pulleys to replace old exposed drive systems in North America as well as in Europe [2].

Motorized Pulleys that enclose all drive components within an oil-filled and hermetically-sealed pulley shell (Fig. 1), such as provided by Rulmeca, significantly increase system reliability, lower maintenance expense, improve personnel safety, save space, and reduce power consumption.


Fig. 1:

A Motorized Pulley seals motor and gearbox

within oil-filled pulley shell

The hermetic seal and oil bath are frequently cited as the key features to improving reliability when comparing Motorized Pulleys with exposed drive systems in harsh environments where abrasive dust (e.g. high silica content) or corrosive materials (e.g. salt) are present. However, the product’s compactness is also mentioned, especially where personnel access is restricted.

Note that Motorized Pulleys are lighter than exposed drive systems because exposed systems require motors and gearboxes to be protected within separate cast iron or steel enclosures. Internally-powered pulleys enclose their motor and gearbox within the pulley shell, eliminating redundant parts (Fig. 2). Furthermore, the internal drivetrain acts like a deep beam, resisting deflection in a light weight package and eliminating the need for a heavy "through shaft."


Fig. 2:

An exposed drive system requires extensive guarding

to protect motor, gearbox, and personnel

Motorized Pulley Usage at Buzzi Unicem USA plants

In January 2009, Buzzi Unicem USA requested that JBM Incorporated utilize Rulmeca Motorized Pulleys in a new raw material receiving hopper project at the company’s Pryor plant in Oklahoma. Axel Hernoe, German-born maintenance manager of the Pryor plant, said, “I was well acquainted with Motorized Pulleys because of my good experience with them in the German mining industry in the 1960s, but I was unaware that the technology was available in the United States until late 2008. Our material’s high silica content can sometimes cause maintenance problems. Since Rulmeca supports product sales and service from their facility in Wilmington, NC, I decided we should give Motorized Pulleys a try.”

The project included two model 320M 7.5 HP units to drive raw material hopper collector conveyors at a belt speed of 384 fpm, six hoppers, structure, and feeders; designed, fabricated, and installed by JBM Incorporated of Knoxville, TN.

The Pryor project was completed within a month of the installation of a new grizzly screen bypass conveyor, which also incorporated a model 320M Motorized Pulley (10 HP with 300 fpm belt speed), at Buzzi Unicem USA’s Stockertown, PA plant, more than 1,000 miles from Oklahoma.

Having served Buzzi Unicem USA for 18 years, JBM Incorporated was soon awarded two more conveyor projects. Each project included the design, fabrication, and installation of a new synthetic gypsum receiving system. The first was installed at Buzzi’s Greencastle, IN plant in October 2009 and the other was installed at the company’s Festus, MO plant in June 2010. Based on previous successful projects Motorized Pulleys were recommended to and accepted by Buzzi Unicem USA for use in the two projects. The Motorized Pulleys “made all aspects of the project simpler and faster, especially because there are no external components to support and guard,” noted JBM design engineer Mike Lane. “Internally powered conveyor drives simplified the entire process,” he added.

The Greencastle project included the use of 3 model 220H Motorized Pulleys, each at 1 HP with a belt speed of 38 fpm, as hopper feeder drives (Fig. 3). Each feeder belt conveyor loads a drag chain conveyor which snakes the synthetic gypsum through the existing structure into the primary product flow.


Fig. 3:

Three Motorized Pulleys drive feeder conveyors in the

new "syn gyp" receiving system at Greencastle, Indiana

With a similar scope to the Greencastle project, the Festus system included the use of 5 model 220H, identical to those used at Greencastle. This was a strategic decision to use common components in the two projects so that spare parts can be shared among plants, if necessary.

More Motorized Pulleys at Pryor, OK

Having watched the performance of the new 7.5 HP Motorized Pulleys for 8 months, Pryor plant personnel decided to solve additional operational problems with Rulmeca Motorized Pulleys, starting with the replacement of a 75 HP exposed drive system on 550 ft long tunnel reclaim conveyor #1 in 2009.


Fig. 4:

The reclaim conveyor #1 at the Pryor plant

elevates material 138 feet

Electrical supervisor, DeWayne Wagnon, said, “Our reclaim tunnel conveyor is fed by six belt feeders and has a concave vertical curve, elevating material from beneath the storage pile 138’ up to the transfer tower (Fig. 4). It had been causing us production delays for years. If we overloaded the conveyor and tripped the breaker under load, we’d have to shovel material off the belt to restart it. On the other hand, when we started the conveyor with an empty belt, it bounced up at least 4 feet, damaging the belt and our feeder support structure (Fig. 5).”


Fig. 5:

The concave vertical curve with 75 HP head drive “bounced up”

when starting with empty belt, damaging tunnel feeder supports

Rulmeca engineers suggested replacing the 75 HP head drive with two model 630H Motorized Pulleys, each at 50 HP, in the head and tail positions. Converting to a dual drive system would not only offer more power but would offer 360 degrees of belt wrap instead of 180 degrees. Calculations showed that slack side tension could be reduced by 2,000 lbs, extending belt life significantly. Furthermore, instead of replacing the 30” wide 3 ply belt with a 4 ply belt, as originally planned, the dual drive system enabled the plant to continue using the 3 ply belt, even with 33% more drive power.

One of the most significant benefits of the head and tail drive configuration is the complete elimination of belt bounce. Now, the belt remains snugly within the troughing idlers throughout the concave curve, even when started empty. This is because effective belt tension is spread evenly between the head and tail pulleys.

Plant personnel were also surprised at how quickly the two 50 HP Motorized Pulleys were installed (Fig. 6). Weighing just 1,850 lbs/each, the 24” diameter Motorized Pulleys were installed in one shift. Since all components are internal, it was not necessary to spend time aligning motors, gearboxes, couplings, and pulleys.


Fig. 6:

Two 1,850 lb Motorized Pulleys

were installed in one shift

In head and tail position, Motorized Pulleys are controlled and synchronized through the use of two flux vector VFDs. Controlling the motors in this manner insures load-sharing and provides protective features such as overcurrent protection, ramp up and ramp down in addition to offering the possibility of changing belt speed should that be necessary.

The Pryor plant retrofitted several other conveyor drives in 2010, all of which were driven by flux vector VFDs. High Rock Weigh Feeder conveyor drives for Raw Mills #1 and #2 were each converted to a model 400H (16” diameter) Motorized Pulley at 5.5 HP with a 48 fpm belt speed to drive the 30” wide x 8’ long feeder conveyors in the spring and summer (Fig. 7). The #3 Finish Mill Limestone Feeder was converted in the fall, using a model 320H (13” diameter) Motorized Pulley at 1.5 HP and 24 fpm, to drive the 30” wide x 11’ 3” conveyor.


Fig. 7:

The High Rock Weigh Feeder has 30” wide belt with 4” sidewalls

and is driven by 16” diameter 5.5 HP Motorized Pulley at 0.8 to 80 fpm

Since amp draw and Motorized Pulley temperature were carefully monitored during commissioning, these feeders are capable of moving a wide range of material throughput (from less than 1 tph to more than 100 tph.) VFDs automatically vary the power supply frequency from 1 Hz to 100 Hz. Since Motorized Pulleys cool their motors by transferring heat through the pulley shell into the conveyor belt, is was essential to verify that adequate cooling was available through the wide frequency spectrum.


The Buzzi Unicem USA experience is typical. Many international major bulk materials handling facilities have first “tested” a Rulmeca Motorized Pulley on a secondary conveyor to verify the product’s reliability and maintenance characteristics and then installed the drive on problematic primary conveyors.

Since Motorized Pulley technology was developed in Germany and Denmark in the 1950s, European plant personnel, in general, are acquainted with the drive’s benefits. However, a growing number of companies are adopting the technology in the Americas, Asia, Africa, and elsewhere. They will learn, as others have known for decades, that Motorized Pulleys offer an optimal alternative to exposed conveyor drive systems, especially in harsh operating conditions.

When properly applied, Motorized Pulleys can increase conveyor “up time”, reduce electrical power consumption, improve plant safety, save space, and lower maintenance expense.


[1.] Michael J. Gawinski, Wolfgang Gresch, Motorized Pulleys Solve Harsh Environmental Problems at North American Ship Loading Terminals, Proceedings of Bulk Europe 2006 Conference, Barcelona, Spain, October 2006

[2.] Steve Pringle, Mick Barry, Mike Gawinski, Motorized Pulley Solves Dirt Conveyor Problem at UK Coal Colliery, 23rd Annual International Coal Preparation & Aggregate Processing Exhibition & Conference, Lexington, KY, May 2006

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