MRO Magazine

Feature

Understanding Vibration

In the simplest terms, vibration in motorized equipment is merely the back and forth movement or oscillation of machines and components, such as drive motors, driven devices (pumps, compressors and so on) and the bearings, shafts, gears, belts...


In the simplest terms, vibration in motorized equipment is merely the back and forth movement or oscillation of machines and components, such as 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.

But how can the plant maintenance professional tell the difference between acceptable, normal vibration, and the kind of vibration that requires immediate attention to service or replace troubled equipment? With a basic understanding of vibration and its causes, the maintenance professional can quickly and reliably determine the cause and severity of most machine vibration and receive recommendations for repair.

Not always a problem

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 be no cause for concern.

When vibration is a problem

Most industrial devices are engineered to operate smoothly and avoid vibration, not produce it. In machines such as electric motors, rotary pumps and compressors, and fans and blowers, 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 testing

Many professionals may think there are only two options for vibration testing; high-end vibration analyzers that are expensive and difficult to use, and low-end vibration pens which aren’t particularly accurate. The latest technology includes handheld vibration testers with built-in expertise that are designed specifically for maintenance professionals who need to troubleshoot mechanical problems and quickly understand the root cause of equipment condition.

Common causes of machine vibration

Vibration can result from a number of conditions, acting alone or in combination. Keep in mind that vibration problems may be caused by auxiliary equipment, not just the primary equipment. Here are some of the major causes of vibration:

Imbalance. 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, casting flaws) or maintenance issues (deformed or dirty fan blades, 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.

Misalignment/shaft runout. Vibration can result when machine shafts are out of line. Angular misalignment occurs when the axes of (for example) a motor and pump are not parallel. 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, due 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.

Wear. 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.

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 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, wear and fatigue in equipment mounts and other components.

Understanding why vibration occurs and how it manifests itself is a key first step toward preventing vibration from causing trouble in the production environment. Typical vibration analyzers 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.

Advanced troubleshooting tools are designed specifically for maintenance professionals who need to troubleshoot mechanical problems and quickly understand the root cause of equipment condition. Ensuring smoother machine operation, with zero vibration, goes a long way in helping keep today’s facilities productive and running efficiently. MRO

Colin Plastow has been with Fluke Electronics Canada since 1987 in various support and product management positions. Today, as industrial product manager for Fluke, he brings his expertise in electronic test and measurement to customers in high-tech and industrial markets. He can be contacted at colin.plastow@fluke.com.

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