Vibration of Machinery - Part 1

VIBRATION IS THE PERIODIC, BACK, AND FORTH MOTION (oscillation) of an object. We encounter vibration in many different ways in our daily lives while for a plant person, its measurement and root cause identification are important from a machinery reliable performance point of view. In plant #assetmanagement programs; vibration monitoring of rotating machines, pressure vessels, and other important structures is not only being performed periodically but trend analysis is also carried over multiple positions to decide expected life and any upgrades required to increase the life of assets.

Machines vibrate because of external and internal forces and transmission of energy. This transmission causes a periodic motion of rotors, pipes, casings, bearings, shafts, foundations, etc. all at the same time. Vibration; so small; the size of human hair diameter i.e. 130micron is also unacceptable in certain machines.

#vibrations cause stresses in machine parts, which can lead to fatigue failure. Severe vibration causes wear or damage on machine parts resulting in breakdown and costly repairs. In a #dairyprocessing plant, along with a network of pumps, there are #homogenizers, #centrifugal #separators, turbo #mixers, air #blowers, air #compressors, #refrigeration compressors, #generators, #conveyors along with packaging machinery are part of major rotating machines. Rotating machines involve #bearings, #shafts, and #couplings and most vibrations of these machines revolve around these parts.

Commonly following causes are related to vibrations:

1. Bearings issues: Bearing should be installed by heating to 110C and must be shrink-fit on shafts. The selection of bearings is another issue. #Bearing should be properly rated for speed and load. #Vfd bearing should be sealed type and/or insulated. Bearing shouldn’t be contaminated with dust, dirt, or product. In dairy plants; especially those motors which are installed in powder mixing areas, are prone to failure due to contamination.
2. Misalignment of driver and driven parts; while assembling machine always check heights of both parts, better is to laser align. If there are specific manufacturer instructions; follow them and stick to recommendations.
3. Lubrication failure; machinery suppliers provide information for #lubrication to be used and quantity of lubricant to be applied. Stick to supplier recommendations. If a bearing is above and in the product zone of food machinery; always use food-grade lubricant of H1 grade. Application procedures must also be followed. Old contaminated solid lubricant/grease should be completely removed by the newly applied #grease.
4. Loose or Tight Belts cause overstress on pullies. A proper tension should be maintained.
5. #Overcurrent on #motor or drive due to overspeed or high torque/load of driven part. Check tachometer if installed or stroboscope for speed confirmation of driven part. See how can you check driven part load like flow, and pressure and if it is a belt conveyor, overload can cause motor high amperes and tripping.
6. High vibration over a long period, sometimes this happens due to vibration during startup, ramp down or normal operation, resonance, harmonics, fluid turbulence, cavitation, etc.
7. #Unbalancing of rotors due to build-up of debris, wear with time, and broken or cracked parts. Variable speed drive machines sometimes operated at low speed don’t show any symptom of vibration but it becomes obvious when machine is operated at full speed.
8. No Isolation or improper vibration damper installation. For high-speed fans/blowers, and #milk #separators, axial thrust is controlled by thrust springs. Sometimes these spring housings become loose and spring function is compromised. Piping system vibration can be controlled by expansion joints, piping hangers, etc.

The vibration of machines is not limited to these above common reasons but there are other operational and process parameters that affect vibrations. Piping vibration during sterilization of aseptic tanks is a normal phenomenon but vibration of UHT interconnecting piping may be due to pressure pulsation from homogenizer or due to other process parameters. The tall structure of dairy process plants like calandria of evaporator and powder plants may also vibrate due to prevailing feed milk pressure variations. It is necessary to study the complete set of operational conditions prevailing around the equipment in question.