World’s first ATEX-approved pneumatic brake motor

Assembly Technologies Pty Ltd
Sunday, 18 May, 2008

Explosion prevention is a hot issue within the field of systems engineering. Friction, overheating or sparks could lead to disaster in potentially explosive environments. Brake motors are essential in stopping loads in case of power failure or danger of injury, but the solutions for hazardous (explosion risk) areas are very limited and expensive.

Engineers at Deprag in Germany have developed an entire system with exposed parts made out of stainless steel, consisting of motor, brake assembly and gears. It corresponds with ATEX standards and was specially developed as a drive for vat drainage equipment from Beer-Fördertechnik.

Beer-Fördertechnik is a renowned manufacturer of custom-made system components for bulk goods technology. Based in Bad König, Germany, the company has been involved with batching, conveying and transportation since 1976. They had been searching for a drive-solution using an integrated brake assembly to optimise the safety of their vat drainage equipment that is 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/L) and ignition energy of less than 20 mJ.

Wilfried Beer, managing partner of Beer Fördertechnik, speaks enthusiastically of the immense advantages of this new type of brake motor. “By using this complete system for my vat drainage equipment, I can save myself enormous additional construction and manufacturing expenses because the brakes, which provide the safety for my mechanism, are already integrated.”

The application of the air motor with integrated brake involves the tilting of a vat using the power of the air motor to begin a tilting and draining procedure. At the highest point, the dead centre, the motor switches off and the brakes are applied, holding the current position. The integrated brake, which acts as a holding brake, comprises three brake disks, a pressure spring and a piston. They are controlled separately using an airline. When the control line has a pressure of over 5 bar, the brake is released. If the pressure drops below 5 bar, it is engaged.

Here is where the ATEX compliance is important. A normal brake has a grey area, where if the control line pressure is close to the compression force of the spring the brake can slip, which would cause dangerous levels of heat thereby elevating the risk of explosion in a hazardous area. To produce a motor, which could be authorised for use in potentially explosive environments, DEPRAG engineers had to think outside the box. Gerd Zinn, manager of the Serial Machine Development Department, said: “By implementing a safety valve, we have minimised 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. The brakes are then forced together fully and the motor is blocked.

Product manager Dagmar Hierl is pleased, stating that “with this entirely new type of drive system we have been successful in launching an attractive complete system on the market according to ATEX guideline 94/9/EG corresponding with: EX II 2GD c IIC T5 (95°). We are further expanding our leading role as a provider of air motors for all technology markets.”

Because of the way they are constructed, air motors are ideally suitable for use in potentially explosive environments. The principle is simple — the air pressure, which is created by a compressor, starts the motor rotation. The rotor of the vane motor, 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, the compression energy changes to kinetic energy and the rotary motion is created.

There is also an additional advantage, in that the expanded air cools down and in fact becomes cold around the motor. Therefore, using an air motor in potentially explosive areas vastly reduces the risk of gases sparking under high temperatures.

Further advantages of this new type of complete system are explained by Hierl: “A compact planetary gear is needed for a brake air motor, so that the required torque and necessary motor speed can be defined to fit the client’s wishes.”

Individual client requests often lead to innovative developments such as the ATEX conforming brake motor. The holding brakes developed for Beer-Fördertechnik are suitable for a braking frequency of up to 600 braking operations per hour.

Assembly Technologies Pty Ltd

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