Machinedesign 1852 Deprag 0 0

Air motors give papermaking a lift

Nov. 5, 2008
Germany's paper industry is the largest in Europe, and with revenues of approximately 14.9 billion euro, it is fourth worldwide behind the U.S., China, and Japan.

Germany's paper industry is the largest in Europe, and with revenues of approximately 14.9 billion euro, it is fourth worldwide behind the U.S., China, and Japan. Thousands of different paper types are manufactured at over 180 locations, with more than 44,000 employees working to produce 23.2 million tons per year. The use of sophisticated papermaking machinery incorporating sturdy motors helps keep the paper mills rolling.

The papermaking process itself has changed very little since 105 AD, when it was first recorded. Basically, fibers are moistened in water and then scooped out with a sieve; this paper web is then pressed and dried. Today, gigantic paper machines are used to turn the pulp into paper. This poses an enormous challenge for machine builders, as individual components must withstand extreme pressures as well as harsh chemicals. The caustic liquid that eventually becomes paper must be "stirred" again and again, requiring an especially durable motor.

One such motor that has proven strong enough for the paper industry is a stainless steel air vane motor. Deprag Schulz GmbH, Amberg, Germany, is a manufacturer of these specialized motors that must resist water, acid, and heat. Stainless steel housing is standard and all motors used in the paper industry are totally sealed, keeping dirt and dust out. The drive spindle is also made of non-corrosive stainless steel and is resistant to aggressive chemicals. In particular, it has a highly durable radial shaft seal.

Besides papermaking, air motors are used in many applications. They work on a simple principle: Air created by the compressor causes the motor shaft to rotate. In the vane motor, the rotor starts to turn in the eccentric cylinder. The vanes held in the rotor slits are pushed to the edge of the cylinder wall by centrifugal force, creating working chambers for the expanding air. The expansion of compressed supply air then changes into kinetic energy, thereby generating rotational movement.

Depending on the design, air motors require only a fifth of the weight of a standard electric motor or a third of the size. What’s more, their performance is almost constant over wide speed ranges. Performance is adjusted by altering operational pressure; simply throttling air quantity smoothly controls speed. An air motor can be loaded until standstill without problems or damage: When load is reduced, it restarts immediately and successively as many times as required, even at high duty cycles. Finally, air decompression cools friction heat, preventing overheating; no possibility of short circuit is another advantage over electric drives.

For more information, visit Deprag Schulz GmbH.

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