Blog post - Pneumatic Motor

Air motor

Pneumatic motor – the ideal drive for industrial processes

(Blog post, November)

DEPRAG ensures the selection of the correct pneumatic motor design for any application

Stepless speed regulation due to alteration in the amount of air or operating pressure

Winding drives can be found in many production processes: they wind continuous materials before or after their handling on spirals, rolls, reels or balls. The spectrum of material to be wound ranges from base paper of up to 10 metres wide or thin film with a thickness of 6 μm, to carbon fibre threads with low elasticity and high durability against tearing. Every material to be wound places different requirements on the winding drive due to their specific features in terms of surface, hardness, tensile strength, cross-section profile or thickness. Reams of paper with a roll diameter of around two metres for example are wound at a high speed of up to 2000 m/min. Films are a sensitive material which must be wound or unwound very precisely. The winding of metals on the other hand means that large masses are in play which influence the winding process. Pneumatic motors are safe and robust drive systems providing a drive solution for winding processes.

A pneumatic vane motor consists of a rotor which turns inside an offset chamber in the rotor cylinder. The vanes in the rotor are pressed against the wall of the rotor by centrifugal force creating working chambers. Inside these chambers the sealed compressed air expands and pressure energy in changed into kinetic energy and the rotor turns.

A pneumatic motor (or mini pneumatic motor) is characterised by the fact that the speed automatically adapts as the load changes. The pneumatic motor runs idle when fully loaded. When a lower load is applied and a lower torque on the pneumatic motor spindle then the working speed is close to idle speed. The working speed is reduced as soon as the torque increases. At 50 percent of the idle speed the (mini) pneumatic motor reaches maximum power. "This is also the optimal working range of the pneumatic motor. In the range between 40-50% of the idle speed the pneumatic motor is particularly energy efficient. A criterion to which we particularly pay attention during motor design", explains DEPRAG Product Manager for Airmotors Dagmar Dübbelde.

The pneumatic motor can be loaded until standstill

Additionally in comparison to an electric motor, the pneumatic motor can be loaded until standstill without problems. After reducing the load it will run again immediately. In a characteristic curve an additional advantage in comparison to electric motors becomes clear: Whilst electric motors have their maximum power consumption at maximum torque (stalling torque), the energy requirement (air consumption) of pneumatic motors sinks with increased torque. Pneumatic air is also an unproblematic energy source. There are no hazards due to electric cables or other electric connections and short circuits are not an issue.

DEPRAG SCHULZ GMBH u. CO. KG from Amberg, Germany has established itself as a proficient partner in the branch of mini pneumatic motors and tools and provides pneumatic drives such as pneumatic vane motors, turbines and tooth gear motors for every conceivable application. The robust and efficient pneumatic motors are adapted by the company to every application in regards to the required torque and working speed and can also be customised for winding drives.

Pneumatic vane motors designed for maximum torque

Two factors are decisive for pneumatic motor design: the required winding speed and the maximum torque. To calculate the maximum torque, the largest possible roll diameter is taken i.e. the size when the roll is fully wound. The winding speed should also be determined when fully wound. When the roll is carrying less material, the roll diameter will be smaller and the pneumatic motor will automatically wind the material more quickly, the working speed adjusts correspondingly to the load (the lower torque). If the pneumatic motor rotates too quickly then the speed can be steplessly adjusted by altering the air supply, the operating pressure or a combination of the two.

Regulation of the speed using the air supply

By regulating the air supply the speed can be simply and flexibly reduced. There are two options depending on the application situation: throttling supply air or exhaust air. By throttling the exhaust air, the speed of the pneumatic motor is reduced without noticeably reducing the power or the torque of the pneumatic motor. A throttle valve keeps the exhaust air back and creates so-called backpressure or counter pressure – the speed is reduced.

If on the other hand you want to reduce the speed of the pneumatic motor and also the power or the torque, then a throttling of the supply air would be recommended. Another specification for winding applications could be to keep the continuous material taut. In this case the pneumatic air must be present at all times to keep it taut. In order to reduce the air consumption the motor’s supply air is throttled and operated with reduced operating pressure. It is designed to be energy efficient corresponding to the requirement.

Speed regulation through operating pressure

As well as regulating the air supply the speed can also be adjusted using operating pressure. The technical data of DEPRAG pneumatic drives is based on an operating pressure of 6 bar. Every DEPRAG pneumatic motor can be operated between 4 and 6.3 bar as required in order to adjust the speed and torque. A reduction of operating pressure always makes sense if the pneumatic motor used for the winding material (e.g. paper) is too powerful. For example it could be the case that the pneumatic motor is so powerful that the paper may tear during winding. By throttling the supply air the pneumatic motor power can be reduced to prevent tearing. By reducing operating pressure by 1 bar torque is reduced by 17%. If the pneumatic motor is operated at 4 bar, the torque is reduced by 33%.

A mini pneumatic motor operated at 4 bar can still be too strong in a winding application e.g. for empty running rolls. In order to utilise the torque range of the air motor further DEPRAG offers the option of equipping the pneumatic motor with spring loaded vanes, so-called forced started vanes. Using these vanes with torsion spring it is possible to run this pneumatic motor with an operating pressure of less than 1 bar. Product Manager Dagmar Dübbelde explains, "When you start a pneumatic motor the vanes must be pressed outwards by centrifugal force to create working chambers. This takes a fraction of a second. Using forced start vanes, i.e. vanes which are already pushed against the wall of the rotor cylinder using torsion spring, then the working chambers are already created. The power control range of the pneumatic motor (from 0 watt to maximum power) can be almost fully exploited – ideal conditions for a winding drive".

The pneumatic motor offers several advantages for a winding drive application. The power density of the pneumatic motor is very high. Additionally the pneumatic motor requires only two thirds of the size and a third of the mass of a comparable electric motor.

Pneumatic Motor: Food industry compliant and explosion-proof

For use in the food industry e.g. in packaging machines, pneumatic motors must withstand cleaning agents and steam. The pneumatic motors of the DEPRAG ADVANCED LINE range have external parts made from stainless steel and are sealed so they do not need to be housed in special casings. The seal of the air motor is so good that it can even be used underwater. DEPRAG pneumatic motors can be used grease-free, i.e. with un-lubricated air supply. For the greasing of the planetary gears DEPRAG uses food industry conform USDA-H1 grease.

The pneumatic air motors of the BASIC line and the ADVANCED line are also ATEX conform i.e. permissible for use in potentially explosive environments. The workings of the pneumatic motor mean that it is predestined for use in critical surroundings as the decompression of the air cools any frictional heat created. Therefore the air motor is cool when loaded and overheating and the ignition of gases is impossible. The internal overpressure also prevents the infiltration of harmful dirt and dust.

Pneumatic motors can additionally be steam sterilised when fitted with suitable vanes – an advantage in medical technology applications. These robust drives are ideal for use in conditions where heat, vibration and dust are an issue.

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