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1. General aspects of monitoring and diagnostics.

Question 1.9.

Would you be so kind to give us the information about the main advantages and disadvantages of Shock Pulse Method that as we know is one of the most efficient method of rolling element bearing fault detection?
(The question was asked by the specialists in machine diagnostics from the paper and pulp mills.)

The question is answered by Natalia Barkova:

The Shock Pulse Method was patented in 1968 and at that time it results in qualitative improvement in rolling element bearings diagnostics as it has the following advantages:

  1. It enabled to detect most types of defects in the incipient stage of their development because it used for diagnostics the high frequency vibration that does not need large oscillation forces for its excitation.

  2. It did not require long vibration measurements as to detect shock pulses it is sufficient to control the vibration during 2-3 bearing revolutions.

  3. It did not require the knowledge of bearing construction parameters (only its rotating speed).

  4. Did not require to construct a standard of nonfailure bearing of each type.

  5. The most simple and inexpensive measuring instruments could be used.

The mentioned advantages even nowadays distinguish this method among many other methods of diagnostics as the method that requires minimal expenses for technical means and operator's training with high efficiency. At the same time this method cannot nowadays be the leader in diagnostics efficiency and the volume of diagnostic information received.

As the main disadvantages of this method the following can be mentioned:

  1. Not all potentially dangerous bearing defects lead to shock pulses' appearance. This fact limits the possibility of their detection up to the moment when a chain of defects will develop and at least one defect of the chain results in the appearance of shock pulses. The consequence of this shortcoming is a low reliability of the bearing condition forecast, the necessity to measure the vibration often (not less than once in 5-10) days.

  2. The presence of shock pulses even in non defective bearings on low rotating frequencies (less than 50-100 RPM). It makes this method useless in diagnostics of such bearings.

  3. The necessity to separate the vibration, excited by the shock pulses, from the vibration, excited by friction forces. To do so one has to measure the high frequency vibration on frequencies over 25-30 kHz. Hence it is necessary to measure vibration as near as possible to the fixed race of the bearing, practically on the race itself.

  4. The decrease of efficiency in detecting the shock pulses when several defects are developing in the bearing as some pulses overlay on the others, e.g. the difficulty of developed defects detection by single vibration measurement.

  5. The possibility of false interpretation of dynamic loads, applied to the bearing from other machine units, for example from gearing, as bearing defect.

To overcome the disadvantages of Shock Pulse Method in bearing diagnostics but keeping its main advantages, VAST, Inc and Inteltech Enterprises, Inc. have transferred to other high frequency bearing vibration analysis methods, in particular, to the enveloping method.

 

 

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