Unbalance motor
Unbalance motors are rotary machines with adjustable weights attached to their shaft which, due to the centrifugal forces that occur, generate circular mechanical vibrations during operation.
Drive types
For industrial use, electric motors (mostly three-phase asynchronous machines ) are usually used for the drive. In principle, other rotating machines such as internal combustion , hydraulic or compressed air motors are also suitable .
In combustion engines, the imbalance effect is often achieved by eliminating the counterweights on the crankshaft. However, because of the reciprocating piston movement, the oscillation is then not circular, but elliptical, which, however, can be quite desirable in certain applications.
Vibration amplitude adjustment
The weights mounted on the motor shaft are usually 2-part and often provided with a scale , according to which the weights can be set from 0 to 100% of the maximum unbalance . If the weights are exactly opposite each other, the centrifugal forces cancel each other out (0%), while overlapping results in the maximum imbalance (100%). The vibration amplitude is greatest when the unbalance is greatest.
Vibration frequency
The frequency of the oscillation is determined by the engine speed. The output vibration power increases with increasing frequency. If you want to achieve the same mechanical vibration power with slow-running engines as with fast-running engines, the weights in terms of mass and / or diameter must be increased. If a certain vibration power is required with a limited diameter, this can only be achieved by increasing the engine speed. For example, for relatively slim concrete compactors (so-called vibrating bottles) with an electric drive, converters or converters are used to enable the motors to run faster than the mains frequency of 50 Hz allows.
Special mechanical design
Vibrators are due to the strong mechanical vibrations with larger, more stable and more rigid motor housings, bearing shields provided and fasteners as is common in normal engines of the same size. In addition, much larger plain or roller bearings are installed. Due to the larger motor surface, the resulting heat loss can be dissipated more easily, so that electric unbalance motors usually get by without the fan blades required for normal motors . This makes it possible to mount weights on both shaft ends of the motor.
Synchronous operation
If unbalance motors are used in pairs (for example with vibratory conveyors ), a synchronous speed of both drives is set during operation . This speed is maintained when one of the two motors is switched off. The switched off motor continues to run. This must be taken into account when working on such drives because it is associated with considerable risk of accidents.
application
Unbalance drives are used, for example, for vibratory conveyors, vibrating screens , vibration cleaning devices , vibration compressors , vibrating road rollers , vibrating plates or for massage devices and vibration alarms in cell phones, among other things.
Also silos for bulk materials are often equipped with vibrators to make flowing to the bulk material.