What Causes Excessive Vibration in Industrial Machinery
All machines will have some degree of vibration when working, however excessive vibrations, or an increase in vibration levels beyond what was previously experienced by a particular piece of equipment, could suggest there are developing mechanical issues.
Some common reasons for excessive vibrations would include:
Imbalanced pieces (the weight distribution is un-even)
Pieces out of line (misaligned)
Worn parts
Loose parts
Parts mounted improperly
If left unchecked, excessive vibrations will continue to exacerbate equipment wear and tear, decrease overall productivity, and ultimately lead to an untimely loss of service.
What is Machinery Vibration?
Machinery vibration refers to the back-and-forth movement of either an entire machine or specific machine part around a stationary point. There are many types of machinery that generate some form of vibration. These types of machinery include but are not limited to motors, pumps, fans, compressors, conveyor systems, etc.
In terms of determining what constitutes "normal" vibration levels; this is dependent upon various factors including the design of the machine itself, the machine's operational speed, the type and quantity of load being applied to the machine, and/or environmental conditions.
In general, understanding what a machine's "baseline" characteristics are will make it much easier to identify variations from those baseline levels.
When Does Machinery Vibration Become an Issue?
It is not possible to establish an absolute reference point for defining acceptable vibration levels for all machinery.
Rather than establishing a universal standard for vibration levels, it is more common for individuals responsible for maintaining industrial equipment to utilize published guidelines from manufacturers regarding established parameters for vibration levels, or comparison to industry-recognized standards.
It is also beneficial to maintain records of past vibration readings made using similar conditions and compare future readings against past data.
An individual should investigate potential vibration issues when any one of the following occur:
There is an unexpected increase in vibration levels.
Stronger vibrations appear at specific speeds.
Unusual noise patterns are produced in conjunction with increased vibration.
Visible movement is noticed in the equipment.
An increase in vibration appears immediately after performing new installations or maintenance.
A reduction in overall equipment performance is observed simultaneously with increased vibrations.
While continued use of vibrating equipment does not necessarily mean immediate replacement or shutdown; a notable variation from historical baseline data may still represent an emerging mechanical issue.
Common Causes of Excessive Machinery Vibration
Rotating Component Imbalance
Imbalance exists when the weight of the rotating component(s) is unevenly distributed throughout. Each time the imbalanced component rotates, its heavier portion moves outward and induces a repeating vibrational pattern.
The most common causes of imbalance are:
Material accumulation on the fan blades of blowers, pumps, and fans.
Damaged fan blades due to mechanical failure.
Missing or damaged balance weights.
Design errors or manufacturing imperfections.
Uneven wear and tear on rotating components.
Typically, as the operating speed of an imbalanced piece increases, so too will its vibration intensity. Balancing or repairing the imbalanced rotating component can typically eliminate the associated vibration issues.
Equipment Misalignment
Alignment refers to the relationship of two or more interconnected components (for example: a motor shaft and a pump shaft). Misalignment results when these components do not share a common centerline.
Possible causes of misalignment include:
Improper initial assembly.
Thermal distortion caused by heating/cooling cycles.
Movement/flexure of the supporting structure (baseplate).
Component shift/movement over time.
Corrective actions may include employing advanced alignment procedures to precisely locate the misalignment, then accurately realigning the components.
Worn or Damaged Bearings
Bearings enable smooth rotation by minimizing resistance generated by moving parts. When a bearing deteriorates excessively, it may induce periodic vibrations as the affected area continuously travels through the load-bearing region.
Causes of bearing-related issues may arise from:
Lack/surplus of adequate lubricant.
Contamination within the bearing housing.
Incorrect initial bearing installation.
Overloading.
Pre-existing misalignment.
Prolonged periods of vibration often precede catastrophic failures affecting adjacent components (shafts, seals, housing components).
Worn Gears, Belts, and Couplings
As well as bearing systems, other mechanical elements may also exhibit vibrational behavior as they degrade. A faulty tooth on a gear may generate a repeatable vibrational signal whenever it interacts with another gear tooth. Likewise, improperly adjusted belts may create erratic motions, whereas damage to coupler joints may lead to looseness issues.
Since these components continually transmit forces across distances; even localized deterioration can have widespread effects on equipment functionality.
Loose Components
Components attached loosely can permit greater-than-normal movement during operation.
Looseness can be the primary reason for elevated vibration or alternatively; pre-existing high levels of vibration may progressively loosen connections. This creates a self-reinforcing loop where additional wear is induced due to increased motion.
Re-tightening loose components may be required; although it is essential to understand why looseness occurred initially.
Bent or Damaged Shafts
A dented shaft will not rotate symmetrically about its central axis. As a result, it will create repetitive motion patterns resulting in additional stresses placed upon bearings/seals/couplers, etc.
Shafts may become distorted due to excessive loading, contact with external objects, mishandling, or prior equipment malfunctions. Even slight degrees of bending may be challenging to detect without precise measurement tools.
Based on the extent of damage; the shaft may need to be straightened.
Foundation, Mounting, and Soft-Foot Problems
Industrial equipment must be installed upon a stable base. A cracked foundation or poor anchoring of support brackets can allow equipment to move during operation.
Additionally, soft-foot can also contribute to vibration; this is defined as when one or more equipment feet rest on top of a non-uniform mounting surface causing uneven pressure. Attempting to tighten a foot resting on a mount that is not designed for that particular application can alter the shape of the machine frame potentially affecting alignment.
The underlying problem must be resolved before attempting to resolve associated vibration issues.
Resonance
Every machine has natural frequencies that can cause it to vibrate more strongly when triggered. Resonance occurs when an operating frequency approaches one of these natural frequencies.
Under resonance conditions, even low-amplitude excitations can amplify dramatically. Potential contributors to resonance include:
Alteration of operating speed.
Modification of mass properties.
Strengthening of components involved in resonance.
Removal of the primary source inducing resonance.
Why Excessive Vibration Should Not Be Ignored
Excessive machinery vibration represents both a potential indicator of a developing mechanical malfunction and a further contributor to damage in other areas of the machine.
For instance, imbalance generates vibrations that can eventually lead to loosening of fasteners, bearing damage, and alterations to alignment. Some potential consequences include:
Premature failure of bearings/seals.
Damage to shafts/couplers.
Increased energy consumption.
Reduced machine productivity.
Decreased product quality.
Safety risks.
Unexpected down-time.
Higher costs for repairs.
As time elapses and excessive vibrations persist, minor mechanical issues may rapidly escalate into major failures.
How Machinery Vibration Is Diagnosed
The component experiencing the strongest vibration is not always the original source. Vibration can travel through couplings, piping, baseplates, foundations, structural supports, and connected machinery.
Diagnosis may involve inspecting the equipment, measuring vibration, checking shaft alignment, examining bearings and couplings, and evaluating mounting conditions.
Vibration analysis can provide additional information. Amplitude indicates the severity of the vibration, while frequency and direction can help identify its source. Comparing current readings with previous measurements can also reveal gradual changes in equipment condition.
Because several mechanical problems can create similar symptoms, machinery should be properly evaluated before corrective work begins.
Addressing Excessive Machinery Vibration
Excessive vibration should be treated as an early warning that machinery may require inspection. Identifying whether the cause is imbalance, misalignment, component wear, looseness, foundation instability, or another condition allows the appropriate corrective action to be taken.
Finding and correcting these problems early can improve equipment reliability, extend component life, and help industrial facilities avoid preventable downtime.
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