Tracking temperature and vibration
By By Colin Plastow
Machines in trouble usually provide telltale evidence that you can read in order to diagnose their problems. Two of the most useful indicators are temperature and vibration. Most mechanical components emit a certain amount of heat and vibration...
February 1, 2013
By By Colin Plastow
Machines in trouble usually provide telltale evidence that you can read in order to diagnose their problems. Two of the most useful indicators are temperature and vibration. Most mechanical components emit a certain amount of heat and vibration in the normal course of operation. But excessive heat, cold or vibration can tip you off to underlying problems, so you can fix them before they lead to a breakdown and bring production to a halt.
Today’s latest test tools, such thermal imagers and vibration testers, can help measure heat and vibration and even interpret the data. They can tell you what the underlying problem may be and guide you in making repairs.
An abnormally hot or cold spot — or an unusual thermal pattern — on process equipment often indicates an emerging problem. That makes handheld thermal imagers, which capture two-dimensional images of the apparent surface temperatures of objects, useful tools for regular predictive maintenance of pumps and other equipment.
With thermal imaging, you can discover and diagnose various issues, including high-resistance electrical connections, obstructions that impede airflow, bearing issues on motors, tank levels, and many other mechanical problems.
One way to prioritize infrared scanning is to begin with critical assets whose failure would threaten people, property or product. Then determine what conditions add stress, and monitor those assets more frequently.
For example, the sludge and particulates found in many processes put extra stress on motors, affecting bearings, windings and insulation. That stress can show up as heat detectable by a thermal imager. Such motors should be scanned more frequently than others.
What to look for
A handheld thermal imager such as the Fluke Ti32 Thermal Imager can be used to look for hot spots, cool spots and other anomalies. Be especially aware of similar kinds of equipment operating under similar conditions but at different apparent temperatures. Such deviations might signal problems.
A good approach is to create inspection routes that include all critical assets. Each time you inspect a piece of equipment, save a thermal image of it and the associated data on a computer and track its condition over time. That way, you’ll have a baseline for comparisons that will help you determine whether a hot spot (or cool spot) is unusual.
You’ll also be able to verify when repairs are successful. Whenever you use a thermal imager and find a problem, use the associated software to document your findings in a report that includes a digital photograph as well as a thermal image of the equipment. That’s the best way to communicate the problems you find and to suggest repairs.
When vibration is a problem
Vibration can be normal in machine operation — or it can be both a sign and a source of trouble. Most industrial devices are engineered to operate smoothly and avoid vibration, not produce it. In electric motors, rotary pumps and compressors, fans and blowers, zero vibration is the ideal. 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. But how can the plant maintenance professional tell acceptable, normal vibration from the kind of vibration that requires immediate attention to service or replace troubled equipment? The answer requires an understanding of the various causes of vibration.
Common causes of machine 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. The cause could be a manufacturing defect or a maintenance issue. Imbalance can severely reduce bearing life and cause undue machine vibration and heat.
• Misalignment/shaft runout – Angular misalignment occurs when the axes of a motor and pump are not parallel. When the axes are parallel but not exactly aligned, that’s 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. Misalignment can cause coupling wear and failure.
• Wear – As components such as bearings, drive belts or gears wear, 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.
• 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. Looseness can allow any vibration present to cause wear and fatigue in bearings, equipment mounts and other components.
Characteristics of vibration
To understand how vibration shows up, consider a simple rotating machine like an electric motor. The motor and shaft rotate around the axis of the shaft, which is supported by a bearing at each end.
One key consideration in analyzing vibration is the direction of the vibrating force. An imbalance would most likely cause a radial vibration as the ‘heavy spot’ in the motor rotates. A shaft misalignment could cause vibration in an axial direction (back and forth along the shaft axis), due to misalignment in a shaft coupling device.
Another key factor in vibration is amplitude, or how much force or magnitude the vibration has. The farther out of balance a motor is, the greater its amplitude of vibration. Other factors, such as speed of rotation, can also affect amplitude. As rotation speeds up, the imbalance force increases.
Intelligent monitoring and analysis
The effects of vibration can be severe. Unchecked machine vibration can accelerate rates of wear (e.g., reduce bearing life), damage equipment, create noise, cause safety problems, and degrade plant working conditions. In the worst cases, vibration can knock equipment out of service and halt plant production.
Measured and analyzed correctly, vibration can be used in a preventive maintenance program as an indicator of machine condition, and you can target remedial action before disaster strikes.
For example, the hand-held Fluke 810 Vibration Tester is designed and programmed to diagnose the most common mechanical problems of imbalance, looseness, misalignment and bearing failures in a wide variety of mechanical equipment, including motors, pumps, fans, blowers, and more. It quickly detects vibration along three planes of movement, then provides a plain-text diagnosis with a recommended solution.
The diagnostic technology in the instrument analyzes machine operation and identifies faults by comparing vibration data to an extensive set of rules developed over years of field experience. It’s all done with the intelligence built into the tester, without the long-term monitoring, recording and analysis required for typical long-term vibration monitoring programs. MRO
Colin Plastow is the industrial product manager for Fluke in Canada. He may be contacted by e-mail at firstname.lastname@example.org.
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