Vibrations always accompany the work of spinning machines, which cause gradual degradation of some parts of the device. Vibration diagnostics aims at collecting a set of information concerning the degree of wear and tear of specific sub-assemblies.
Depending on the purpose of measurement and type of examined machines, the temporal course of displacements are of major importance, also velocities or acceleration of vibrations. For the overall evaluation of the spinning machine, the rms value of velocity of vibrations is essential, which reflects majorly the destructive energy. Measurement of rms value of vibrations by referring to boundary values for specific group of machines, allows to evaluate the dynamic condition of the device. There are 4 classification areas A, B, C, D, which can be assigned to conditions of the device called good, satisfactory, transitory acceptable and unacceptable.
These kind of measurements can be performed using uncomplicated and relatively cheap instruments like vibration pens.
Answers to following questions have essential importance in vibration diagnostics:
- What are the reasons of high values of vibrations?
- How long can one use the device quite safely?
- What correcting actions are need to be preapred (the scope of works, spare parts etc.) for optimal (costs and time needed) removing the danger?
- What actions need to be undertaken in future to avoid such problems?
The answers to above-mentioned questions can be found only by detailed analysis of vibrations spectrum, which is the transformation of temporal course of vibrations in frequency spectrum. This kind of action, classic in mechanical diagnostics, allows to split the signal generated by the machine to components. Knowing the basic operational parameters of the machine and its construction, the specific components of vibrations spectrums’ can be assigned to elements generating them or monitoring of the machine.
Identifying the source of vibrations allows defining the actual level of failure danger, foreseeing its results within the device, but especially undertaking proper correcting actions, which eliminating the problem. The most common reasons of too high levels of vibrations, essential as far as failure danger is concerned, are:
- lack of shared alignment of propelling and propelled shafts of the device,
- clearances or damages of bearings.
The typical image of spectrum is featured on the picture below. Clearly dominating first harmonic component of vibrations, in this case, is a result of not balancing the spinning masses of the machine.
Extremely important function of vibration diagnostics is defining the
condition of bearings, which allow to optimize the expenditures
connected with its replacement. Knowing the type of a bearing installed
in the machine and rotational speed, the vibrations created by the
separate elements of the bearing are identified (outer bearing race,
inner bearing race, bearing cage, rolling element).
Below, the identified frequencies of vibrations generated by the above-mentioned elements of the bearing are marked. In this case a damage of outer bearing race was recognized (the frequency denoted as BPFO).
Optimal benefits coming from vibration diagnostics are obtained by
implementing so-called machines monitoring. Comparing the data collected
periodically allows to determine the tendency in reference to the
machine as a whole unit or/and its specific elements (for example a
bearing).
In the below picture there are vibrations values, which were measured
during the routine measurements. The yellow line indicates the danger
level, described as dangerous.
The red line is a equivalent of the critical state. As you can see, after crossing the danger level the proper preventive steps were undertaken, after which the condition of the machine became stable.
