The Beat of a Different Drum Motor

The drum motor has all drive components—electric motor, gear reducer, bearings—housed inside the drum, providing a safer, more sanitary design, and is capable of communicating with central plant control or other plant equipment.

VDG (Van Der Graaf) drum motors are manufactured to power belt conveyors for a wide array of industries, including food processing. In 1985, Alexander Kanaris, president of VDG, established a drum motor manufacturing facility in Brampton, Canada. In 2009, an expanded manufacturing facility was opened in Michigan. Today, over 200,000 sq ft of manufacturing space in the U.S. and Canada employs automated robotic production equipment to produce drum motors. All of the components used in VDG drum motors are manufactured in-house, using American materials and labor.

Implementing sanitation processes to battle bacteria has become increasingly challenging in food manufacturing. The VDG sanitary series SSV drum motor features an all-316 stainless-steel construction and IP69K sealing that can withstand washdown pressure up to 3,000 psi. The enclosed drum motor design has no external moving parts compared to conventional exposed conveyor drives, eliminating areas for bacterial harborage and reducing washdown time and water consumption, while increasing sanitation, efficiency, and worker safety. It also eliminates the maintenance required on external components of a conventional conveyor drive, such as the motor, gear reducer, sprockets, and chain. 

Kanaris has become one of North America’s leading experts on drum motor technology and shares his expertise with ProFood World.

PFW: What are the most important benefits and functions of drum motor technology?

Kanaris: Drum motor belt drive design entered the conveyor drive industry in the early 1950s as a unique drive for belt conveyor applications. Drum motor belt drive design is different from a conventional conveyor drive in that the drum motor has all drive components—electric motor, gear reducer, bearings—housed inside the drum. Without exposed drive components and with no other drive parts rotating outside the conveyor frame, it presents a unique belt drive design. The drum motor also maximizes space utilization and worker safety, as components, such as external electric motor, gear reducer, bearings, chain, and chain guards, all traditionally mounted outside the conveyor frame, are not needed. Those components can be hazardous to staff required to work near conventional conveyor drives and render the conveyor line susceptible to bacterial contamination.

Most standard conventional conveyor drives use a 90-degree gear reducer mounted directly on the drive shaft or use sprockets and chain to drive the head conveyor drive drum. Using a 90-degree gear reducer, especially a worm gear reducer, impedes the efficiency of the drive, resulting in mechanical losses.

PFW: How can drum motor technology improve plant floor efficiency and sanitation?

Kanaris: Due to its self-contained design, the VDG drum motor is space-optimized, allowing more floor or overhead space for conveyor systems, and improves safety since there are no external drive components that can pose hazards. In addition, the VDG sanitary series SSV drum motor allows the belt profile to be machined directly onto the 316 stainless-steel drum, eliminating the need for plastic sprockets that can contribute to foreign material contamination and removing areas prone to bacterial harborage. This sprocketless SSV drum motor is a unique and attractive alternative to a conventional drive for food processing applications by eliminating gaps and crevices where food by-products can accumulate, increasing sanitation, and reducing the amount of time and water required for washdown. 

Drum motors are both spatially and mechanically more efficient than conventional conveyor drives as well. Compared to the 90-degree arrangement of most conventional drives, in a drum motor, the electric motor is connected in-line with the gear reducer, resulting in a 20 to 40% increase in mechanical efficiency, depending on the type of gear reducer it is compared with. This leads to lower energy consumption without any sacrifice in torque or performance. The streamlined design of the drum motor also eliminates the need for chains and sprockets, promoting workplace safety and taking up a much smaller footprint than conventional conveyor drives, which require all components that rotate the drive drum to be mounted externally. Lastly, the amount of time required to install a drum motor into the conveyor frame is significantly less than the time required to install an external conveyor drive.

PWF: How are drum motors maintained?

Kanaris: All VDG drum motors are designed for 80,000 hours of continuous operation before scheduled maintenance is required, drastically reducing the amount of maintenance-related downtime a plant has to account for. An oil change is the only required maintenance.

PFW: Please describe drum motor design in detail.

Kanaris: A drum motor is a cylinder with two square shafts on either side and an electrical connection box protruding on one side of the drum motor that houses the electrical connections. The shafts are square and do not rotate. They are fixed and mounted on the conveyor frame, eliminating the need for pillow block bearings. The electric motor that is housed inside the cylinder (drive drum) is an AC squirrel cage design motor. The stator does not rotate, therefore, there is no need for rotating brushes or slip rings delivering power to the stator windings.

The rotor shaft is the input pinion driving either a two- or three-stage gear reducer. The last stage of the gear reducer is driving a gear ring that is bolted directly to the end-flange, and the end-flange is bolted directly to the rotating drive drum. All internal components, motor, gears, and bearings are working in an oil bath. The drum motor is hermetically sealed and filled one-third with oil. The oil inside the drum motor is used as a lubricant and also provides cooling. When the drum motor is running, the oil transfers the heat generated from the electric motor and gear reducer to the rotating drum and dissipates it to the conveyor belt. As the temperature inside the drum motor rises, the internal pressure can rise up to 1 atm [atmosphere] or 14.6 psi. Because of the internal pressure, it is necessary for the drum motor to be hermetically sealed to prevent oil leakage. 

PFW: What is the range of drum motor belt speed, horsepower (hp), and drum diameter? 

Kanaris: Depending on the manufacturer, drum motors are available in different drum diameters, belt speeds, and horsepower. The diameter of the drum motor is dictated by the required horsepower and belt speed. Since all mechanical and electrical components must fit inside the cylinder, the drum motor rating is geometrically restricted. In order to achieve the required belt speed, drum motors offer a range of fixed gear ratios. When a different belt speed is required, it can be accomplished by changing the ratio of the gear reducer or by using a frequency inverter. The SSV sanitary drum motor is available in diameters from 3.1 to 8.5 in., with a horsepower range from 0.25 to 7.5 hp. The total range of all VDG drum motor designs is from 3.1 to 42-in. diameter, and hp range from 0.25 to 500 hp.

The SSV Sanitary Series drum motor is designed for sanitary food production and is installed at major vegetable processing facilities. Image courtesy of VDG.The SSV Sanitary Series drum motor is designed for sanitary food production and is installed at major vegetable processing facilities. Image courtesy of VDG.

PFW: What is the history of drum motor use in North America?

Kanaris: Drum motors represent approximately 7% of the overall conveyor drive applications in North America. With all the benefits they offer, it would be reasonable to ask why they have low market penetration. When drum motors first appeared on the market, the overall selection of belt speeds, horsepower, drum diameters, and drum lengths were very limited, with belt speed selection being the larger issue. For these reasons, the majority of conveyor drives using chains and sprockets to power the head roller were more popular.

Changing belt speeds on conventional drives can be achieved by simply changing the drive sprockets, resulting in different drive ratios. Changing the belt speed of the drum motor requires removing the drum motor from the conveyor frame and changing the gear ratio of the gear reducer. This problem has been largely eliminated with the introduction of variable-frequency inverters.

Adjusting the belt speed with a frequency inverter contributed to a relatively small increase in market penetration of the drum motor. Market study indicated that conveyor manufacturers and end users implement the drum motor only when there are space constraints. Market feedback also showed issues with oil leakage and premature bearing, gear, and electric motor failure. These issues had to be addressed in order to increase drum motor market share.

PFW: How has VDG changed drum motor design practices?

Kanaris: Most drum motor manufacturers are producing drum motors as a sideline to other industrial products they manufacture or supply. Combined with low market penetration, these companies have little incentive to allocate funds and resources into research and development to improve the design and thus to increase market share.

In 2010, VDG began a two-year study of testing and analysis, which revealed that lack of heat dissipation was a major issue impacting overall product reliability. The basic principle of electric motor design is the method of cooling. The majority of electric motors used as conveyor drives are fan-cooled, which is a very effective method, albeit not ideal for sanitary applications due to bacterial movement in the air.

Since all drive components of the drum motor are housed internally, fan cooling is not possible. Instead, the drum motor uses oil to transmit the heat from the electric motor to the drum shell and dissipates it to the belt.

Cooling of the drum motor through oil submersion is not as effective as fan cooling a standard conveyor motor. Operating conditions can negatively impact the heat transfer from the motor to the belt. If, for example, an application requires the drum motor to have rubber lagging for belt traction, the rubber lagging will resist heat from exiting the drum motor. Stainless-steel drum motors for sanitary and food processing applications are particularly sensitive to temperature elevations because stainless steel has poor heat transfer properties. Without sufficient heat dissipation, oil temperature rises, and the oil viscosity decreases and may not provide adequate lubrication, resulting in premature mechanical component failure. In addition, the elevated oil temperature increases the internal pressure, which can affect the sealing system of the drum motor. This creates the potential for oil leaks. In 2012, as a result of this study, VDG developed a new generation of drum motor design.

In a drum motor, the electric motor is connected in-line with the gear reducer, resulting in a 20 to 40% increase in mechanical efficiency. The design also eliminates the need for chains and sprockets, promoting workplace safety, taking up less space than conventional conveyor drives. Image courtesy of VDG.In a drum motor, the electric motor is connected in-line with the gear reducer, resulting in a 20 to 40% increase in mechanical efficiency. The design also eliminates the need for chains and sprockets, promoting workplace safety, taking up less space than conventional conveyor drives. Image courtesy of VDG.

PFW: How does drum motor technology help food and beverage manufacturers improve sustainability?

Kanaris: In the past, all of the issues mentioned above were mainly an inconvenience to end users but not a major detriment at the time, since belt conveyor engineers over-designed and were liberal in selecting motor hp. More often, the specified hp of a drive would have been twice or more the required hp needed to drive the belt conveyor. Due to this over-design, conveyor drives, including drum motors, were not subjected to continuous full load conditions.

Today, energy conservation is more important than ever. Conveyor equipment needs to operate longer hours, at full load, and close to the rated drive performance. In an electromechanical device, such as a drum motor, there are two sources generating heat: the electric motor and the gearbox. The gear reducer accounts for about 15% of the heat generation, while the majority of the heat is produced by the electric motor. The electric motor also has two sources of heat generation: the current density of the stator winding and the magnetic density of the laminated core. By increasing these densities, the temperature generated by the electric motor will increase, and by reducing them, the temperature will decrease. However, reducing the current and magnetic densities in the electric motor to achieve lower temperature will also reduce the amount of work the motor will produce, resulting in a reduction of torque and horsepower. Therefore, the standard method of calculating electric motor windings is no longer valid and cannot be used to design the electric motor for drum motor applications.

The research I mentioned earlier resulted in a mandate for a new motor design that generates less heat inside the drum motor. This new design includes using a new method of calculating the electric motor windings combined with different lamination sizes and materials with different metallurgic composition, and it has substantially reduced the drum motor temperature. Today’s new drum motor design offers an unmatched option for powering belt conveyors. VDG’s ongoing investment into R&D and in-house design has resulted in an innovative drum motor that fulfills all the critical needs of a sanitary food processing plant, while contributing to a more efficient use of energy, water, and space. Simultaneously, we have developed a new intelligent drum motor design, capable of communicating with central plant control or other plant equipment with data feedback for a more efficient production throughput.

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