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Vibration in motorised equipment is the back-and-forth movement or oscillation of machines and components, according to Fluke.

These components could be drive motors, driven devices (pumps, compressors and so on) and the bearings, shafts, gears, belts and other elements that make up mechanical systems.

Vibration in industrial equipment can be both a sign and a source of trouble.

Other times, vibration just goes with the territory as a normal part of machine operation and should not cause undue concern.

However, it is difficult for the plant maintenance professional to tell the difference between acceptable, normal vibration and the kind of vibration that requires immediate attention to service or replace equipment.

With a basic understanding of vibration and its causes – and equipped with the new Fluke 810 vibration tester – the maintenance professional can determine the cause and severity of most machine vibration and receive recommendations for repair.

This is all carried out without the extensive monitoring and recording required for typical, long-term vibration monitoring programs.

Vibration is not always a problem; in some tasks, vibration is essential.

Machines such as oscillating sanders and vibratory tumblers use vibration to remove materials and finish surfaces.

Vibratory feeders use vibration to move materials.

In construction, vibrators are used to help concrete settle into forms and compact fill materials.

Vibratory rollers help compress asphalt used in highway paving.

In other cases, vibration is inherent in machine design.

For instance, some vibration is almost unavoidable in the operation of reciprocating pumps and compressors, internal combustion engines and gear drives.

In a well-engineered, well-maintained machine, such vibration should not be a cause for concern.

Most industrial devices are engineered to operate smoothly and avoid vibration, rather than producing it.

In these machines, vibration can indicate problems or deterioration in the equipment.

If the underlying causes are not corrected, the unwanted vibration itself can cause additional damage.

In this article, Fluke is not focused not on machines that are ‘supposed’ to vibrate as part of normal operation but on those that should not vibrate: electric motors, rotary pumps and compressors and fans and blowers.

In these devices, smoother operation is generally better and a machine running with zero vibration is the ideal.

Vibration can result from a number of conditions, acting alone or in combination.

Vibration problems may be caused by auxiliary equipment – not just the primary equipment.

A ‘heavy spot’ in a rotating component will cause vibration when the unbalanced weight rotates around the machine’s axis, creating a centrifugal force.

Imbalance could be caused by manufacturing defects (machining errors or casting flaws) or maintenance issues (deformed or dirty fan blades or missing balance weights).

As machine speed increases, the effects of imbalance become greater.

Imbalance can severely reduce bearing life as well as cause undue machine vibration.

Vibration can also happen when machine shafts are out of line.

Angular misalignment occurs when the axes of a motor and pump are not parallel, for example.

When the axes are parallel but not exactly aligned, the condition is known as parallel misalignment.

Misalignment may be caused during assembly or develop over time, owing to thermal expansion, components shifting or improper reassembly after maintenance.

The resulting vibration may be radial or axial (in line with the axis of the machine) or both.

As components such as ball or roller bearings, drive belts or gears become worn, they may cause vibration.

When a roller bearing race becomes pitted, for instance, the bearing rollers will cause a vibration each time they travel over the damaged area.

A gear tooth that is heavily chipped or worn, or a drive belt that is breaking down, can also produce vibration.

Vibration that might otherwise go unnoticed may become obvious and destructive if the component that is vibrating has loose bearings or is loosely attached to its mounts.

Such looseness may or may not be caused by the underlying vibration.

Whatever its cause, looseness can allow any vibration present to cause damage, such as further bearing wear and wear and fatigue in equipment mounts and other components.

The effects of vibration can be severe.

Unchecked machine vibration can accelerate rates of wear (thus reducing bearing life) and damage equipment.

Vibrating machinery can create noise, cause safety problems and lead to degradation in plant working conditions.

Vibration can cause machinery to consume excessive power and may damage product quality.

In the worst cases, vibration can damage equipment so severely as to knock it out of service and halt plant production.

However, there is a positive aspect to machine vibration, according to Fluke.

Measured and analysed correctly, vibration can be used in a preventive maintenance program as an indicator of machine condition and help guide the plant maintenance professional to take remedial action before disaster strikes.

To understand how vibration manifests itself, a simple rotating machine such as an electric motor should be considered.

The motor and shaft rotate around the axis of the shaft, which is supported by a bearing at each end.

One key consideration in analysing vibration is the direction of the vibrating force.

In Fluke’s electric motor, vibration can occur as a force applied in a radial direction (outward from the shaft) or in an axial direction (parallel to the shaft).

An imbalance in the motor, for instance, would most likely cause a radial vibration as the ‘heavy spot’ in the motor rotates, creating a centrifugal force that tugs the motor outward as the shaft rotates through 360deg.

A shaft misalignment could cause vibration in an axial direction (back and forth along the shaft axis) as a result of misalignment in a shaft coupling device.

Another key factor in vibration is amplitude – or how much force or severity the vibration has.

The further out of balance the Fluke motor is, the greater its amplitude of vibration.

Other factors, such as speed of rotation, can also affect vibration amplitude.

As the rotation rate goes up, the imbalance force increases significantly.

Frequency refers to the oscillation rate of vibration or how rapidly the machine tends to move back and forth under the force of the condition or conditions causing the vibration.

Frequency is commonly expressed in cycles per minute (CPM) or hertz (Hz).

One hertz equals one cycle per second or 60 cycles per minute.

Although Fluke referred to its example motor as ‘simple’, even this machine can exhibit a complex vibration signature.

As it operates, it could be vibrating in multiple directions (radially and axially), with several rates of amplitude and frequency.

Imbalance vibration, axial vibration and vibration from deteriorating roller bearings could all combine to create a complex vibration spectrum.

The Fluke 810 vibration tester is an advanced handheld device designed and programmed to diagnose the most common mechanical problems of unbalance, looseness, misalignment and bearing failures in a variety of mechanical equipment, including motors, fans, blowers, belts and chain drives, gearboxes, couplings, pumps, compressors, closed-coupled machines and spindles.

The tester detects vibration along three planes of movement and then provides a plain-text diagnosis with a recommended solution.

The diagnostic technology in the Fluke 810 analyses machine operation and identifies faults by comparing vibration data to an extensive set of rules developed over years of field experience.

Typical vibration analysers and software are intended for monitoring machine condition over the longer term, but they require special training and investment that may not be possible in many companies.

The Fluke 810 is designed specifically for maintenance professionals who need to troubleshoot mechanical problems and quickly understand the root cause of equipment condition.

Fluke Calibration

Fluke Corporation was founded in 1948, specialising in electrical test and measurement products. Early in its history, Fluke recognised that the very best electrical metrology would be needed to support its products and undertook to develop this capability. From this activity, the calibration business was born. Over the years, many breakthrough calibration products were introduced, establishing Fluke as a leader in electrical metrology.

In 2000, Fluke acquired Wavetek Precision Measurement. In 2001, Fluke’s calibration business expanded into the temperature field with the acquisition of Hart Scientific and then into pressure and gas flow with the acquisition of DH Instruments (2007), followed by Ruska and Pressurements (2010).

The unified business’s unmatched breadth and depth in metrology puts Fluke Calibration in a unique position to deliver today’s and tomorrow’s calibrations solutions to customers who demand the very best, supported by an organisation they can count on for the long term.

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