X90 mobile modules
240
X90 mobile system User's manual V 1.20 - Translation of the original manual
Causes of oscillations:
Imbalance
Per DIN ISO
1)
, an imbalance is present in a rotating system if forces or oscillation movements are transferred to
the bearing as a consequence of imbalanced centrifuges.
Imbalances on a rotating structure not only cause forces on the bearing and foundations, but also oscillations in
the machine. These oscillations have a harmonic nature, with the excitation frequency corresponding to the rotary
frequency of the imbalanced rotor.
Alignment errors
The main function of coupling is to connect 2 shafts in order to achieve a statically determinate complete system. In
addition to transferring torque, couplings also offset misalignment (radial, axial, angular) to a certain extent. How-
ever, if the misalignment exceeds the compensation capability of the coupling, additional loads such as increased
bearing forces, forced shaft deformation and axial forces occur for the machine elements involved.
Oscillations have a harmonic nature and are bound to the rotary frequency of the misaligned shafts and the multiples
of this frequency. Misalignment can be measured using the rotary frequency of the misaligned part or its harmonic
oscillations.
Impacts
Foreign objects as well as loose or colliding parts can cause shocks between rotating and stationary parts. These
shocks repeat periodically once or several times each time the shaft revolves.
The frequency of these shock repetitions corresponds to the rotary frequency of the shaft or its harmonic frequency.
Roller bearing damage
Most bearing damage results from changes on the surface (pitting). By rolling over the damaged area on the
inner ring, outer ring, cage or rolling element, pulse-shaped shocks occur that make the bearing structure and its
components vibrate.
Each of these shocks appears in the oscillation signal through the typical course of a shock sequence. Character-
istic values can be obtained from these measurements that give an indication of the condition of the bearing.
The excitation frequency on the inner ring, outer ring, cage and roller bearing damage is specified by the bearing
manufacturer.
Magnetic induction
A rotating magnetic field causes counterforces in the stator of the machine. This electric magnetic stimulation often
causes oscillations on the electric motors that are hard to detect.
Inverters also often lead to an inference of oscillations, the cause of which is of an electrical magnetic nature.
Effects
Machines and systems with moving parts cause mechanical oscillations. The effects on the immediate location
and surrounding area include tremors and structure-borne sound, often creating a disturbing noise development.
Increased vibrations can lead to malfunctions in the machine, particularly in measurement and control devices. If
this causes the measuring equipment to resonate as well, incorrect measurements will result and manufacturing
quality will suffer.
In addition, stress will develop on the components of the machine. Unwanted vibrations lead to increased wear
with partly plastic distortion of components and increased crack formation all the way up to failure.
Noticeable oscillations are felt through the equilibrium organ and sense of touch. Long-term exposure can impair
working performance and well-being, even leading to health damage.
1)
1925 DIN ISO 1925: Issue: 1996-11 Mechanical oscillations - Balancing technology - Terms (ISO 1925:1990 + AMD 1:1995)
