Drum motor
A compact, enclosed drive pulley for conveyor belts, invented in Germany.
Wikipedia / Wikimedia Commons
A drum motor is a single-component drive unit for conveyor belts, consisting of a geared motor sealed inside a steel shell that also serves as the driving pulley. The idea was first documented in 1928, and the first practical drum motor for conveyor belts was developed and patented by the German company Schloemann in the 1930s. The aim was to create a compact, fully enclosed drive that offered higher efficiency and less friction than traditional geared motors.
The basic design uses an electric or hydraulic motor fixed to a stationary shaft. One end of the drum connects the motor's rotor pinion to an in-line helical or planetary gearbox attached to the other stationary shaft. Torque passes from the motor through the gearbox to the drum shell via a coupling or geared rim on the shell or end housing. The in-line transmission, using two or three stages of helical or planetary gears, typically transfers around 90-93% of the motor's output power to the shell, though some configurations may approach 95%. Gears can be made from high-grade steel, sintered metal, or polymers.
Electrical cables or hydraulic hoses connect through one stationary shaft, sealed with compression seals. Shaft and connection seals use materials like NBR, FPM, or carbon. Lubrication is done with oil or grease, which also helps cool the motor; alternatively, motors can be air-cooled. The drum shell is usually made of aluminum, steel, or stainless steel, often crowned to keep the belt centered. Cylindrical shells can be fitted with external sprockets or rotary brushes for special uses. Rubber, PU, or other coatings can be applied to increase friction, and hot-vulcanized or molded lagging can drive plastic or steel modular belts.
The exposed drum shafts do not rotate; they are used to mount the drum motor in the conveyor frame. A single through-shaft design, where the motor and gearbox are fixed with keys or pins, has limited radial load capacity due to bending stress from belt tension, so it's mainly for light-duty conveyors. For heavier loads, two separate shafts are common—one fixed to the motor housing and one to the gearbox housing—which adds strength from the motor and gearbox mass, allowing higher payloads and longer conveyors. One shaft is typically a short stub shaft, while the other varies in length with the belt width. Over certain widths, the shaft can be reinforced to prevent bend
- early patent application
- 1929 (U.S. patent US1876460A filed in 1929, by Schloemann, a German company)
Lore & Background
The drum motor concept was first recorded in 1928, with an early description appearing in a 1932 U.S. patent (filed in 1929) by the Pittsburgh subsidiary of the German engineering company Schloemann. The first practical drum motor for conveyor belts was developed and patented by Schloemann in the 1930s, bringing the concept into practical use for conveyor belt applications. This is a German invention, not a Danish one.
The basic design uses an asynchronous or synchronous electric motor, or hydraulic motor, fixed to a stationary shaft. One end of the drum is coupled through the motor's rotor pinion to an in-line helical or planetary gearbox
Reader's Guide
The drum motor represents a significant advancement in conveyor drive technology by consolidating multiple components—motor, gearbox, and pulley—into a single, sealed unit. This design reduces frictional losses and improves efficiency, with up to 95% of output power transmitted to the drum shell. Its compact, enclosed construction eliminates the need for separate guards, chains, or sprockets, reducing maintenance and downtime.
Today, drum motors are found in airport check-in conveyors, security machines, supermarket check stands, food processing conveyors, weighing equipment, and roller shutter doors. Their hygienic design makes them particularly valuable in food processing, where quick and easy cleaning reduces operating costs. The ability to integrate backstop bearings, electromagnetic brakes, and incremental encoders allows for precise control in inclined conveyors and closed-loop positioning systems.
By requiring fewer parts than conventional drives—often just the drum motor and two fixing brackets—the drum motor lowers inventory costs and simplifies installation. Its weight is evenly distributed within the conveyor frame, and the sealed shell protects internal components from water, dust, chemicals, and other environmental hazards. This reliability and versatility have made the drum motor a standard choice in modern unit handling conveyor technology.
Did You Know?
- The drum motor concept was first recorded in 1928, but the first practical drum motor for conveyor belts was developed and patented by the German company Schloemann in the 1930s, not by a Danish inventor.
- Drum motors typically transmit around 90-93% of output power from the motor to the drum shell.
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