3/23/2014 Balancing machine - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Balancing_machine 1/3

Balancing machineFrom Wikipedia, the free encyclopedia

A balancing machine is a measuring tool used for balancing rotating machine parts such as rotors for electricmotors, fans, turbines, disc brakes, disc drives, propellers and pumps. The machine usually consists of two rigidpedestals, with suspension and bearings on top supporting a mounting platform. The unit under test is bolted to theplatform and is rotated either with a belt-, air-, or end-drive. As the part is rotated, the vibration in the suspension isdetected with sensors and that information is used to determine the amount of unbalance in the part. Along withphase information, the machine can determine how much and where to add weights to balance the part.

Contents

1 Hard-bearing vs. soft-bearing

2 How it works

3 Other balancing machine types

4 See also5 Further reading

6 External links

Hard-bearing vs. soft-bearing

There are two main types of balancing machines, hard-bearing and soft-bearing. The difference between them,however, is in the suspension and not the bearings.

In a hard-bearing machine, balancing is done at a frequency lower than the resonance frequency of the suspension.In a soft-bearing machine, balancing is done at a frequency higher than the resonance frequency of the suspension.Both types of machines have various advantages and disadvantages. A hard-bearing machine is generally moreversatile and can handle pieces with greatly varying weights, because hard-bearing machines are measuringcentrifugal effects and require only a one-time calibration. Only five geometric dimensions need to be fed into themeasuring unit and the machine is ready for use. Therefore, it works very well for low- and middle-size volumeproduction and in repair workshops.

A soft-bearing machine is not so versatile with respect to amount of rotor weight to be balanced. The preparationof a soft-bearing machine for individual rotor types is more time consuming, because it needs to be calibrated fordifferent part types. It is very suitable for high-production volume and high-precision balancing tasks.

Hard- and soft-bearing machines can be automated to remove weight automatically, such as by drilling or milling,but hard-bearing machines are more robust and reliable. Both machine principles can be integrated into aproduction line and loaded by a robot arm or gantry, requiring very little human control.

How it works

3/23/2014 Balancing machine - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Balancing_machine 2/3

With the rotating part resting on the bearings, a vibration sensor is attached to the suspension. In most soft-bearingmachines, a velocity sensor is used. This sensor works by moving a magnet in relation to a fixed coil that generatesvoltage proportional to the velocity of the vibration. Accelerometers, which measure acceleration of the vibration,can also be used.

A photocell (sometimes called a phaser), proximity sensor, or encoder is used to determine the rotational speed, aswell as the relative phase of the rotating part. This phase information is then used to filter the vibration information todetermine the amount of movement, or force, in one rotation of the part. Also, the time difference between thephase and the vibration peak gives the angle at which the unbalance exists. Amount of unbalance and angle ofunbalance give an unbalance vector.

Calibration is performed by adding a known weight at a known angle. In a soft-bearing machine, trial weights mustbe added in correction planes for each part. This is because the location of the correction planes along therotational axis is unknown, and therefore it is unknown how much a given amount of weight will affect the balance.By using trial weights, you are adding a known weight at a known angle and getting the unbalance vector caused byit.

Other balancing machine types

Historically any balancing necessary for slower operating machinery would be done simply by rotating thecomponent between centres and slackening the centres slightly until vibrations became apparent as the heavy sideof the component flew out in a greater circle where its obvious eccentricity could be seen and marked with chalk. asmall piece of plasticine or putty would be applied to the side opposite the chalk and the test repeated until the

component semed to run with acceptable smoothness.[citation needed]

Static balancing machines differ from hard- and soft-bearing machines in that the part is not rotated to take ameasurement. Rather than resting on its bearings, the part rests vertically on its geometric center. Once at rest, anymovement by the part away from its geometric center is detected by two perpendicular sensors beneath the tableand returned as unbalance. Static balancers are often used to balance parts with a diameter much larger than theirlength, such as fans. The advantages of using a static balancer are speed and price. However a static balancer canonly correct in one plane, so its accuracy is limited.

A blade balancing machine attempts to balance a part in assembly, so minimal correction is required later on.Blade balancers are used on parts such as fans, propellers, and turbines. On a blade balancer, each blade to beassembled is weighed and its weight entered into a balancing software package. The software then sorts the bladesand attempts to find the blade arrangement with the least amount of unbalance.

Portable balancing machines are used to balance parts that cannot be taken apart and put on a balancingmachine, usually parts that are currently in operation such as turbines, pumps, and motors. Portable balancers comewith displacement sensors, such as accelerometers, and a photocell, which are then mounted to the pedestals orenclosure of the running part. Based on the vibrations detected, they calculate the part's unbalance. Many timesthese devices contain a spectrum analyzer so the part condition can be monitored without the use of a photocell andnon-rotational vibration can be analyzed.

See also

Carl Schenck, German businessman

3/23/2014 Balancing machine - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Balancing_machine 3/3

Gordon E. Hines, inventor of hard-bearing balancing machines and other balancing technologies

Rotordynamics, applied mechanics of rotating structuresTire balance

Further reading

Adolf Lingener: Auswuchten. Theorie und Praxis. Verlag Technik, Berlin und München 1992, ISBN 3-341-00927-2

Hatto Schneider: Auswuchttechnik. 6. Auflage. Springer, Berlin u. a. 2003, ISBN 3-540-00596-XSchenck Trebel Corporation (1990), Fundamentals of balancing (3rd ed.), Schenck Trebel Corporation.

External links

Basic frequently answered questions about balancing machines (http://www.precibalance.com/gfaq.pdf)Detecting and correcting unbalance in toolholders for high-speed machining (http://www.hofmann-

global.com/en/documents/ToolholderBalancing.pdf)

Retrieved from "http://en.wikipedia.org/w/index.php?title=Balancing_machine&oldid=588522196"Categories: Measuring instruments

This page was last modified on 31 December 2013 at 13:34.Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply.

By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.