Explosion prevention is a “hot topic” within systems engineering, since friction, overheating, or sparks can quickly lead to disaster in potentially explosive environments. Deprag Schulz GmbH, a manufacturer of air motors headquartered in Amberg, Germany, recently solved an explosion-prevention challenge with an innovative drive system. The company's engineers developed a complete stainless steel solution consisting of a motor, brake assembly, and planetary gears. The new system corresponds with ATEX standards (European Union regulations for explosive environments) and is used as a drive for vat drainage equipment from Beer-Fördertechnik, a manufacturer of custom components for bulk goods technology also based in Germany. The company had been searching for a drive solution with an integrated brake assembly to optimize the safety of its vat drainage equipment, primarily used in the chemicals industry. The equipment provides vat drainage of toxic powder materials with grains smaller than 100 µm, a bulk weight of 0.86 kg/liter, and ignition energy of less than 20 MJ.

Deprag engineers developed an air motor holding-and-brake drive system that practically guarantees explosion prevention. It also ensures dust-free drainage of toxic products from the vat draining equipment with a loading volume of up to 200 kg. The new system works as follows: A vat is moved using power from the air motor to begin a tilting and draining procedure. At the highest point, the dead center, the motor switches off and brakes are applied, holding the current position. The integrated brake, which acts as a holding brake, is comprised of three brake disks, a pressure spring, and a piston, all controlled separately using an air line. When the pressure in the control line is over 3 bar and the spring load is less than the compression force, stress is taken off the brake disks and the motor can turn. If the pressure in the control line is below 3 bar and the spring load is greater than the compression force, brake disks are forced together and the motor is blocked.

To produce the explosion-proof motor, Deprag's engineers had to get creative. If an air pressure of more than 3 bar remained in the lines that control the brakes, then the brake disks might constantly rub against each other and cause excessive temperature increases. This would elevate the risk factor in potentially explosive areas. A safety valve is used to minimize this risk. The valve turns the air feed off automatically when the pressure falls under 5 bar, causing the pressure applied to the brake to become zero. Brakes are then forced together fully and the motor is blocked.

Because of their unique construction, air motors are well suited for use in potentially explosive environments. The principle is simple: The air pressure, which is created by a compressor, starts the motor rotation. Vane motors function in this way: The rotor, which revolves in an eccentrically set cylinder, is set in motion. There are vanes in its slots, which are pushed outwards against the cylinder wall through centrifugal force. Working chambers are created for the expanding air pressure. Through the expansion of this restricted supply air, compression energy changes to kinetic energy and rotary motion is created. An additional advantage is that the expanded air cools — and becomes cold — around the motor, greatly reducing the risk of gases sparking under high temperatures.

The holding brakes developed for Beer-Fördertechnik are suitable for a braking frequency of up to 600 braking operations per hour and are available in various torque ranges in the 1.2 kW stainless steel motor program from Deprag. For more information, visit www.depragusa.com.