The Reliability in Action department features case studies submitted by our readers. To have your article considered for inclusion in a future issue, e-mail it to parnold@noria.com. This issue's article was written by Dave Garner, the global solutions development manager for Dow Corning Molykote:
A successful lubrication program rests on one basic concept: the correct amount of the correct lubricant at the correct place at the correct time. For anyone who has spent time in a maintenance or reliability role, this is not as simple as it sounds. Today, ultrasonic technology provides pump and system pros unparalleled insight into the condition of the lubricant in an operating unit of machinery. As lubrication quality diminishes during operation, friction creates vibratory energy at a frequency around 30 kilohertz (kHz), creating an ultrasonic beacon. Devices are available to measure and record ultrasonic signals, and "shift" (or heterodyne) the ultrasonic signal down into the audible range. This lets you hear the otherwise inaudible, tell-tale signal of inadequate lubrication.
Ultrasonic readings taken on a dry screw vacuum pump show a 7 dB rise and subsequent return to normal after bearing relubrication.
By taking periodic ultrasonic measurements and trending those values, you can gain insight into the actual condition of the machine's lubricating system during operation. Typically, bi-weekly or monthly ultrasonic readings are taken and trended. Ultrasonic emission increases of around 7 decibels (dB) indicate the lubricant has depleted to a point where friction has notably increased.
Ultrasonic technology is also useful in preventing over-lubrication. As the grease is pumped in, ultrasonic levels reduce to a point at which a squirt of grease results in a slight increase in dB. After the slight increase, the dB level resumes its decline until an additional squirt results in another slight increase followed by another decline. Subsequent squirts of grease are added until the levels increase and do not decline. This indicates that the bearing cavity is filled to the point that the rolling elements are continuously plowing through the new grease. Additional grease will over-lubricate the system.
Infrared images taken before and after relubrication.
Pros responsible for a facility's lubrication face challenges ranging from simple lubricant storage to procurement and application engineering. Often, fundamental concepts of lubrication get lost in the cultural practices and plant procedures intended to provide reliability. Ultrasonics help you deliver the correct amount of the correct lubricant to the correct place at the correct time, extending machinery reliability, reducing waste and minimizing costs.
