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How to double engine output while reducing air consumption

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article image The simple structure of air motor and pneumatic tools means they are more or less immune to dirt and humidity.
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Motor size and power. RPM and continuous operation. For years, these engineers have had to compromise between these factors when choosing motors, but pneumatically driven turbines would allow the best of both worlds.

The automatic processes used to manufacture today’s modern materials place heavy demands on the driving motor. Engineers would be remiss to dismiss out of hand the potential gains to be made by choosing pneumatic motors with their excellent power-weight ratio.

According to Dr Rolf Pfeiffer, managing director of DEPRAG, air tools have been a success story in the mining and manufacturing industries since the 19th century.

In hazardous areas, where a single spark could be catastrophic, pneumatic equipment was, and continues to be the preferred choice.

“Wherever there is a risk of explosion - for example in the bulk materials handling systems as used in the chemicals industry - the air motor will come into its own,” Dr Pfeiffer said. “The other side of the coin is that air motors can also be sterilised and are therefore used within the medical technology industry.”

The simple structure of air motor and pneumatic tools means they are more or less immune to dirt and humidity, according to Dagmar Dübbelde, DEPRAG air motors product manager. They can be operated until full load down to standstill without damage.

“The most significant advantage is that for the required drive output they are a third to a fifth lighter and are more compact than their electric counterparts,” Dübbelde said.

However, with the majority of compressed air today generated using electrical means, inefficient use of air can be an issue, especially with the common vane motor, which does not effective utilise the volume expansion properties of compressed air.

According to Dübbelde, issues to do with a motor’s power efficiency need to take into account all the factors associated with the unit and the application.

“You cannot make a direct comparison between air motors and electric motors. Ultimately it is the application that is the deciding factor in the choice of drive,” he said.

In an example packaging application, the required speed is 450rpm, but during the extended period where the packing tape is being sealed, the torque is 25Nm at reduced speed.

Since electric motors cannot withstand overload for extended period due to overheating, the motor for the application would need to be designed for torque under load, requiring 1170W output.

With the air motor’s torque characteristics and the way it deals with increased temperature, a smaller air motor can be used in the application – one with a nominal torque of 15Nm and a nominal speed of 275rpm, requiring power output of 430W.

Additionally, turbines are an alternative to the vane motor. Being fluid dynamics machines, turbines use the volume expansion properties of compressed air much more efficiently than vane motors do, resulting in them requiring just a third of the amount of compressed air. When fitted with a centrifugal governor, air consumption can be reduced by a further 50 percent.

The power-weight ratio (kilowatts/kilograms) is also unrivalled, just half the size of the vane motor.

“Turbines are particularly suited to robot-controlled applications or where space is at a premium, for example inside the fuselage of an aircraft, but they are also used in high quality manual machinery,” said Dr Pfeiffer.

This means lighting machining tools and grinders which still deliver a edge in power.

While turbines do not need oil and there are no wear parts, they are best suited for continuous operation in stationary applications, such as grinding, milling, deburring or drilling metals and wood.

They are also ideal for use where there is very little mounting space available.

DEPRAG SCHULZ is able to produce turbine drives in power range between 500W to 50,000W, and has the software and design infrastructure in place to develop turbines according to customer requirements.

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