At a glance
Glossary
Our glossary provides you with a quick overview of important balancing technology terms.
This makes it easy for you to keep track of all technical terms and understand the context immediately.
Glossary of balancing technology
Susceptibility to imbalances
Probability of a machine showing a significant change in unbalance within a certain operating time.
Equivalent unbalance for the nth eigenmode
The smallest single unbalance that has the same effect on the nth mode as the actual unbalance distribution in the elastic rotor.
Equalization
Changing the mass distribution of a rotor in such a way that the unbalance or the vibrations caused by it are reduced to permissible values. This is usually achieved by adding, removing or shifting material on the rotor.
Equalization level influence
Change in the unbalance display of one correction plane when the unbalance in the other correction plane changes; usually expressed as a percentage value. The better the plane separation, the lower the influence of the correction plane.
Balancing
Process during which the mass distribution of a rotor is checked and typically corrected so that the residual imbalances, the vibrations of the bearing journals, the bearing forces and/or bearing pedestal vibrations at operating speed or in the operating speed range are within specified limits.
Balancing on reversal
Compensation of the unbalance of auxiliary parts and the unbalance effect due to fit clearance, radial and axial run-out between auxiliary parts and the rotor to be balanced in order to identify the actual rotor unbalance. The rotor is rotated in relation to the auxiliary part in successive measurements.
Balancing quality
Possibility of dividing rigid rotors into classes; product of mass eccentricity and angular velocity at operating speed or path velocity of the center of mass, each in mm/s (see also ISO 21940-11).
Balancing bearing
For example, rolling bearings with reduced clearance to accommodate an engine rotor in a low-speed balancing machine.
Balancing machine
Machine that generates a measured value for the unbalance of a rotor mounted in it, which can be used to correct the mass distribution.
Automatic balancing device
System that automatically compensates for changes in unbalance during operation.
Belt drive
Mechanical drive of a balancing machine consisting of motor, pulleys, drive belt and belt tensioner. The diameters of the motor pulley and the drive diameter of the rotor should not be too similar in order to avoid the occurrence of apparent imbalances.
Limited original imbalance
Limiting the initial imbalance by balancing the individual parts, well-considered design and targeted production and assembly.
Operating balancer
Measuring system for balancing outside a balancing machine in operating condition.
Bending-critical speed
Speed at which maximum deflection of the rotor occurs and this is significantly greater than the movement of the bearing journals.
Bode diagram
When balancing, the course of the magnitude and angle of an oscillation at rotor speed or twice the rotor speed over the speed.
Dynamic imbalance
Condition for which the central main axis of inertia is neither parallel to the shaft axis nor intersects it.
Level separation
Ability of a balancing machine to distribute the unbalance precisely to the correction planes and to minimize the correction plane influence ratio.
Eigenfunction, modal function
Describes the course of an eigenmode as a function of the rotor axial coordinate; function is normalized to a maximum value of one.
Single-plane balancing
Correction of the mass distribution of a rigid rotor in order to reduce the static residual unbalance to certain limit values.
Single-plane balancing machine
Balancing machine that uses gravity or centrifugal force to balance a rotor in one plane.
Setting up the machine mechanics
Work to adjust the mechanics of a balancing machine to the balancing of a rotor.
Setting the measuring device
Work to enter rotor and balancing-specific data into the measuring device of a balancing machine.
Electrical concentricity deviation
Systematic error of eddy current sensors during concentricity or shaft vibration measurement caused by residual magnetism or electrical irregularities of the measured part.
Sensitivity to imbalances
Measure of the change in the vibration of an (elastic) rotor due to a change in unbalance, expressed by the ratio between the change in the vibration vector and the change in the unbalance vector.
Replacement mass
Mass attached to the crank pins of crankshafts to simulate part of the rotating and oscillating masses of the piston/connecting rod assembly during balancing.
Spare rotor (dummy)
Accessories that replace a rotor assembly during balancing. The replacement rotor must have the same main dimensions, mass and rigidity properties as the original part.
Centrifugal balancing machine
Machine that generates measured values for the unbalance due to the centrifugal forces of a rotating rotor mounted in it.
Cardan shaft drive
Mechanical drive of a balancing machine consisting of a motor, optional gearbox and cardan shaft. The cardan shaft is connected to one end of the rotor to be balanced.
Total concentricity deviation
Difference between the maximum and minimum value of the radii of a rotor cross-section when measured with respect to a fixed axis of rotation.
Half feather key
Special key for balancing, which represents the unbalance effect of the part of the correct key in relation to the shaft or hub (see also ISO 21940-32).
Main axis of inertia
Depending on the unbalance condition of a rigid rotor, the main axis of inertia is offset and inclined in relation to the design axis.
Auxiliary wave
Precisely manufactured shaft that accommodates a rotor without its own journal for balancing.
High-speed balancing
Balancing of elastic rotors at speeds at which a rotor to be balanced can no longer be considered rigid.
Horizontal balancing machine
Balancing machine that measures the unbalance for horizontal alignment of the rotor axis.
Adjustment
In balancing, the process of adjusting a machine or device so that the measurement information is converted into unbalance units for the bearing points and/or the balancing planes of a rotor.
Calibration mass
Defined mass to adjust a balancing machine with a specific rotor or to adjust a balancing machine for a specific rotor.
Calibration rotor (master rotor)
Adjustment rotor derived from a real rotor with defined positions for the application of calibration masses; used for the regular inspection of a balancing machine.
Smallest achievable residual imbalance (KER)
The smallest value of residual unbalance that can be achieved with a balancing machine.
Component equalization
Correction of the unbalance at at least two angular positions if the angular positions are specified in a correction plane.
Force-measuring balancing machine
Machine on which rotors are balanced below the critical speed of the rotor-balancing machine bearing system.
Storage rack
Component of a balancing machine with the rotor bearing, which transmits the forces of the rotor to the machine bed.
Contract balancing (balancing service)
Service provided by a company to balance rotors on behalf of a customer or to examine their unbalance condition.
Local mass eccentricity
Distance of the center of mass of (imaginary) thin rotor disks from the shaft axis.
Center of mass or center of gravity
The point in an axially and radially extended (rigid) rotor at which its inertia effect against linear displacements can be replaced by a point mass.
Mass centering (balance centering)
Determination of the main axis of inertia of a rotor; information is used in the subsequent machining of the bearing journals, centering or reference surfaces so that the subsequent axis of rotation is as close as possible to the main axis of inertia.
Modal balancing
Method that uses the information about the bending eigenmodes in the vicinity of the respective critical speeds to balance elastic rotors.
Moment imbalance
Unbalance condition in which the central main axis of inertia intersects the shaft axis at the shear point; typically caused by two equally large unbalances that are 180 degrees opposite each other.
Compliant rotor
Rotor which, due to an unbalance distribution and depending on the speed, exhibits deformations that can no longer be neglected.
Zeroing
Method of compensating for the current unbalance values and thus - using software - generating a fully balanced rotor, e.g. to check the plane separation.
Permanent calibration
One-off calibration valid for all rotors within the weight and speed range of a force-measuring balancing machine.
Piezoelectric material
Hard ceramic material that produces an electrical charge when subjected to mechanical pressure. Used in force sensors to measure the effect of rotor imbalance in a balancing machine.
Polar diagram
Representation of the amount and angle of vibration and unbalance values measured at variable speed with the corresponding X and Y values in a circular diagram.
Polar compensation
Correction of the unbalance amount in a correction plane at a single angular position.
Practical equalization unit
Display of the unbalance amount for a specified compensation radius directly e.g. in mm drilling depth, number of washers etc..
Tasting mass
Usefully selected mass to determine the response of the rotor to an unbalance in a plane.
Test rotor (test rotor)
Rigid balanced rotor with suitable mass for adjusting and testing balancing machines; allows the exact, reproducible application of test or calibration masses.
Quasi-static imbalance
Unbalance condition in which the central main axis of inertia intersects the shaft axis at a point where the center of gravity is not located; e.g. caused by a single unbalance outside the center of gravity or in a form of dynamic unbalance where the static unbalance component coincides with one of the two moment components.
Concentricity deviation at low speed
The concentricity deviation of a rotor surface measured at a low speed at which no significant vibration caused by unbalance occurs; value is usually compensated for measurements at variable speed.
Step-by-step balancing during assembly
Method for balancing a rotor that consists of several removable components. The unbalance is corrected on the last mounted component until the rotor is complete.
Gravity balancing machine (center of gravity balance)
Machine that generates a measured value for the unbalance due to the gravitational effect of a non-rotating rotor mounted in it.
Side spindle balancing machine
Design of a balancing machine in which the rotor is mounted horizontally overhanging on a balancing spindle
Rigid rotor
With a rigid rotor, the deformations due to unbalance distribution remain negligible up to the maximum operating speed.
Static imbalance
Unbalance condition for which the central main axis of inertia is displaced parallel to the shaft axis.
Dead mass
Parts with mass of a balancing machine that are moved by the unbalance forces of the rotor to be balanced.
Unbalance
The condition of a rotor when imbalances in the bearings cause forces and/or vibrations to circulate with the rotor. Unbalance is specified in gmm (or similar units).
Unbalance in the nth eigenmode, nth modal unbalance
Unbalance distribution that only influences the nth mode of deflection of an elastic rotor.
Unbalance amount
Product of the unbalance mass and the radial distance of its center of gravity from the shaft axis without reference to the angular position.
Unbalance force
Force in the balancing plane of a rotor that is created by the unbalance in this plane at a certain speed.
Unbalance reduction ratio (URV)
Ratio between the decrease in unbalance due to a correction and the previous unbalance.
Unbalance tolerance of an intrinsic mold
Limit value for the equivalent unbalance of a natural form of an elastic rotor.
Unbalance tolerance, permissible residual unbalance
Permissible value of the unbalance amount in a radial plane for a rigid rotor.
Unbalance angle
Angle at which the unbalance mass is located in a coordinate system connected to the rotor.
Primordial imbalance
Angle at which the unbalance mass is located in a coordinate system connected to the rotor.
Comparative precision
For a balancing machine, a measure of the quality of the unbalance measurement for repeat measurements under changed conditions; evaluation using statistical methods.
Vertical balancing machine
Balancing machine that measures the unbalance for vertical alignment of the rotor axis.
Displacement measuring balancing machine
Machine on which rotors are balanced above the critical speed of the rotor-balancing machine bearing system.
Repeatability
For a balancing machine, a measure of the quality of the unbalance measurement in repeated measurements under the same conditions; evaluation using statistical methods.
Angle position sensor
Component of a balancing machine that generates a reference for measuring the angular position of the rotor.