Pneumatic motors ideal for winding processes, says manufacturer

24th April 2015

  

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Pneumatic motors, which are characterised by the fact that the speed of the motor automatically adapts as the load changes, are safe and robust drive systems that offer several advantages for a winding drive application, says German pneumatic equipment manufacturer Deprag.

This is because the power density of the motor is very high and the air motor requires only two-thirds of the size and a third of the mass of a comparable electric motor.

Winding drives roll continuous materials, before or after handling, on spirals, rolls, reels or balls. Further, the spectrum of materials that can be wound range from base paper of up to 10 m wide to thin film with a thickness of 6 μm. Carbon fibre threads with low elasticity and high durability against tearing can also be wound.

Deprag notes that each type of material to be wound has different requirements for the winding drive, owing to its specific features in terms of surface, hardness, tensile strength, cross-section profiles and/or thickness.

Further, while reams of paper with a roll diameter of around 2 m are wound at a high speed of up to 2 000 m a minute, film is a more sensitive material and must be wound or unwound very precisely. The winding of metals, on the other hand, means that large masses are at play, which impacts on the winding process.

Deprag explains that pneumatic motors run idle when fully loaded and, when a lower load is applied, with a lower torque on the motor spindle, then the working speed is close to idle speed. The working speed is therefore reduced as soon as the torque increases and, at 50% of the idle speed, the pneumatic motor reaches maximum power.

“This is the optimal working range of the pneumatic motor as, at between 40% and 50% of the idle speed, a pneumatic motor is particularly energy efficient – a criterion to which we pay particular attention when designing a motor,” explains Deprag airmotors product manager Dagmar Dübbelde.

Compared with an electric motor, a pneumatic motor can be loaded until standstill without a problem and, after reducing the load, the motor will immediately run again.

Further, electric motors have a maximum power consumption at a maximum torque which, when reached, stalls the torque, whereas the energy requirement or air consumption of pneumatic motors drops with increased torque.

Pneumatic air is also an unproblematic energy source. There are no safety hazards as there are no electric cables or other electric connections; short circuits are also not an issue.

Maximum Torque
Dübbelde highlights two decisive factors that affect motor design: the required winding speed and the maximum torque. To calculate the maximum torque, the largest possible roll diameter is taken, which is the size of the roll when it is fully wound. The winding speed should also be determined when fully wound.

When the roll carries less material, the roll diameter will be smaller and the motor will automatically wind the material more quickly, as the working speed adjusts correspondingly to the load, or the lower torque. If the motor rotates too quickly, then the speed can easily be adjusted by altering the air supply, the operating pressure, or a combination of the two.

Speed Regulation Using Air Supply
By regulating the air supply, the speed can be simply and flexibly reduced. There are two options of air supply regulation, depending on the application situation, namely throttling supply air or exhaust air.

By throttling the exhaust air, the speed of the 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 back pressure or counterpressure, thereby reducing the motor’s speed.

However, if the user wishes to reduce the speed of the air motor as well as the power or the torque, then throttling the supply air would be recommended.

Another specification for winding applications could be to keep the continuous material taut. In such a case, the pneumatic air must be present at all times to keep it taut. To reduce the air consumption, the motor’s supply air is throttled and operated with reduced operating pressure. The motor is therefore designed to be energy efficient in accordance with the user’s requirements.

Speed Regulation Through Operating Pressure
In addition to regulating the air supply, the speed of a pneumatic drive can also be adjusted by manipulating operating pressure. Further, while the technical data of Deprag pneumatic drives is based on an operating pressure of 6 bar, every Deprag pneumatic motor can operate between 4 bar and 6.3 bar, as required to adjust the speed and torque.

A reduction of operating pressure makes sense if the motor being used to wind materials like paper is too powerful. For example, a motor could be so powerful that paper may tear during winding.

By throttling the air supply, the motor power can be reduced to prevent tearing. By reducing operating pressure by 1 bar, torque is reduced by 17%. Therefore, if a pneumatic motor is operating at 4 bar, the torque is reduced by 33%.

However, a pneumatic motor operating at 4 bar can still be too strong in a winding application, in the case of empty running rolls, for example. Therefore, to use the torque range of the air motor further, Deprag offers the option of equipping the motor with spring-loaded vanes, also known as force-start vanes. Using these vanes with a torsion spring, it is possible to run a motor at an operating pressure of less than 1 bar.

Dübbelde explains: “When you start a pneumatic motor, the vanes must be pressed outwards by centrifugal force to create working chambers, which takes a fraction of a second. Using force- start vanes – vanes that are already pushed against the wall of the rotor cylinder using a torsion spring – the working chambers are already created and the power control range of the motor can be almost fully exploited, creating ideal conditions for a winding drive”.

Edited by Samantha Herbst
Creamer Media Deputy Editor

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