Condition monitoring helps manage over-lubrication.
SDT International

Ultrasound is a guide to precision grease replenishment in motor bearings. It is also known for its versatility for leak detection, valve assessment and electrical fault detection.

Acoustic lubrication is an integral component of ultrasound programs. Fewer than 95 percent of all roller bearings reach their full engineered life span, and lubrication is the culprit in most cases. In fact, poor lubrication practices account for as much as 40 percent of all premature bearing failures. Yet, when ultrasound is used to assess lubrication needs and schedule grease replenishment intervals, that number drops below 10 percent. What would 30 percent fewer bearing related failures mean for an organization?

To understand the role precision lubrication plays in bearing life extension, it helps to understand basics of bearings, their lubrication mechanism and how ultrasound helps.

The insides of a bearing consist of four components. The inner and outer raceways form a path for the rolling elements to glide on a thin film of lubricant. A metal cage separates the rolling elements, keeping them evenly spaced to distribute the load and stop them from crashing into one another. These components move in concert producing frictional forces from rotational inertia, surface load, misalignment, imbalance and defects. Zero friction is impossible, but optimal levels of friction are achievable with correct installation techniques and proper amounts of lubricant.

Ultrasound works on the FIT principle—it responds well to defects that produce friction, impacting and turbulence (FIT). For motor bearings, two of these phenomena apply: friction and impacting. Ultrasound detects high-frequency signals produced when two surfaces slide together or come in contact with any force. Stage 1 bearing failures happen at the micro level. Because ultrasound ignores low-frequency audible signals, it forms the perfect companion for measuring, trending and analyzing defects despite high levels of noisy interference encountered on the factory floor.

Ultrasound detectors detect friction and impacting as acoustic energy from rolling friction and defect impulses. When lubricant levels are optimum, the energy created is at its lowest. As frictional forces increase, so does the acoustic energy. Ultrasound instruments measure friction and impacting as energy using the scaled value dBµV (decibels/microvolt). The results are presented as condition indicators, and there are four of them:

  • root mean square (RMS)—an indicator of friction
  • maxRMS—an indicator of stability
  • peak—an indicator of impacting
  • crest factor—which surmises the relationship between friction and impacts

Condition indicators are most responsible for transforming ultrasound technology from a simplistic, “point the gun and pull the trigger” gadget, to being recognized as analysis and trending technology. Condition indicators add validity to trending by going beyond the single decibel. If a user currently uses an ultrasonic gun that does not have condition indicators, they should question the data.

Benefits of Optimized Lubrication Practices

Optimizing grease replenishment practices will deliver both fast and longer-term benefits. What are some of the indicators that your lubrication program is on the right track?

A Change in Quantity of Grease Consumed
Maintenance departments track their grease consumption to monitor and control costs. A change in consumption is a sure sign that the lubrication program is on the right track.

Most organizations are guilty of over-lubricating. Expect lower grease consumption as the program matures. Bad procedures lead to bearings routinely receiving more grease than they are designed to handle. The excess ends up being pushed into the motor casing or purged onto the floor.

Over lubrication happens when regreasing intervals are scheduled based on time instead of condition. Control lubrication tasks with ultrasound to monitor condition and maintain optimal friction. The time between greasing intervals increases, resulting in less grease used per bearing.

Fewer Lube-Related Failures
Organizations with optimized greasing programs experience fewer lube-related failures. Less fixing and fire-fighting translates to more creative time for maintenance. That time can be used to bring more machines into the greasing program. Additionally, with ultrasound, a user finds many nontrendable defects. For example, broken or blocked grease pipes and incorrectly fitted grease paths prevent grease from reaching the bearing.

Optimized MRO Spares Management
This lubrication program provides better control of grease consumption, fewer failures and more productivity for maintenance. A decrease in bearing-related failures improves spares optimization. Users can share the ultrasonic lubrication data with a maintenance, repair and operations (MRO) manager to create a plan to reduce the number of emergency parts on hand.

Increased Number of Machines Monitored
One benefit of an effective lubrication program is time: time allotted to monitoring machines instead of fixing them; time allotted to correctly assessing the real needs for lubrication and; time to look at the big picture.

Take for instance, criticality assessment. Many lubrication programs begin with small steps. All the “A” critical machines receive priority. But, what about the rest? With more time to plan, organize and schedule, the number of machines acoustically monitored for optimal lubrication increases.

Combine Acoustic Lubrication and Condition Monitoring
Acoustic lubrication can ensure precise bearing lubrication. The newest technologies on the market combine the power of onboard lubrication guidance with four condition indicators for bearing condition assessment.

Problems detected by lube techs can be reported to condition monitoring teams and elevated to maintenance once confirmed.

How To Get Started

A well-organized strategy and carefully planned execution of that strategy can get the ultrasound lubrication program off on the right foot.

Commitment is required from all levels and this becomes easier if the program demonstrates structure and cohesion. Clearly defining and communicating the objectives of the lubrication program, as well as reporting the progress, is the best way to create a precision lubrication culture that benefits the entire organization.

Start by asking, “Why start an ultrasound lubrication program and what improvements do we expect?” There is no one easy answer to the question. Saving money is an obvious benefit that gets the attention of management, but it is not specific enough.

An ultrasound lubrication program can save money by reducing grease consumption, raising awareness of the right types of grease to use, making more effective use of a lube tech’s time, reducing unwanted machine breakdowns caused by lubrication failures and extending bearing life expectancy.

Ultrasound-assisted lubrication of plant assets offers benefits that calendar-based lubrication does not. Lubrication serves a primary purpose, which is to create a thin layer of lubricant between rolling and sliding elements that reduces friction.

It makes sense that the best way to determine the lubrication requirement of a machine is to monitor friction levels, not time in service.

Optimizing lubrication of plant machinery with ultrasound will result in a significant reduction in grease consumption. Having an ultrasound program in place can lead to cleaner storage practices, sampling and avoiding mixing greases.

Properly lubricated machines require less energy to run. Reducing the amount of money spent on grease can lead to lower energy bills.

Machines that consume less electricity run cooler, and machines that run cooler often have longer life cycles.

Optimize bearing lubrication to extend the life of bearings by making sure they have the right amount of grease, but not too much. When everything is running according to plan, lube techs will spend less time greasing bearings that do not need it, resulting in decreased labor.

By monitoring the condition of the machinery’s lubrication, a user is collecting valuable condition data about the machine itself. Put this data to work, and advance reliability through optimized grease replenishment.