Vibration: A cause for concern?
March 1st 2011

Vibration in industrial equipment can be a sign and a source of trouble.At other times, it is a normal part of machine operation and should not cause undue concern.

But how can the plant maintenance professional tell the difference? Fluke offers some suggestions

With a basic understanding of vibration and its causes and equipped with a vibration tester such as the new Fluke 810, the maintenance professional can quickly and reliably determine the cause and severity of most machine vibration and receive recommendations for repair. It's all done with the intelligence built into the tester, without need for extensive monitoring and recording required for some long-term vibration monitoring programs.

Vibration problems Most industrial devices, such as electric motors, rotary pumps and compressors, fans and blowers, are engineered to operate smoothly and avoid vibration. 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.

Vibration can result from a number of conditions, acting alone or in combination. These are some of the major causes: Imbalance – A 'heavy spot' in a rotating component will cause vibration when the unbalanced weight rotates around the machine's axis. Imbalance could be caused by manufacturing defects or maintenance issues (deformed or dirty fan blades, missing balance weights). The effects of imbalance become greater with speed.

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

Misalignment/shaft run-out – Vibration can result when machine shafts are out of line. Angular and parallel misalignment may be caused during assembly or develop over time, due to thermal expansion, components shifting or improper reassembly after maintenance. The resulting vibration may be radial or axial or both.

Wear – As components such as ball or roller bearings, drive belts or gears become worn, they may cause vibration. A gear tooth that is heavily chipped or worn, or a drive belt that is breaking down, can also produce vibration.

Looseness – 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 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 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 production.

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

The new handheld Fluke 810 Vibration Tester, for example, is designed and programmed to diagnose the most common mechanical problems of unbalance, looseness, misalignment and bearing failures in a wide variety of mechanical equipment, including motors, fans, blowers, belts and chain drives, gearboxes, couplings, pumps, compressors, close-coupled machines and spindles. It quickly detects vibration along three planes of movement, then provides a plain-text diagnosis with a recommended solution. The diagnostic technology in the device analyses machine operation and identifies faults by comparing vibration data to an extensive set of rules developed over years of field experience.

Some vibration analysers and software are intended for monitoring machine condition over the longer term and require special training and investment that may not be possible in some companies. Fluke's tester is designed for maintenance professionals who need to troubleshoot mechanical problems and quickly understand the root cause of equipment condition.

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