With industrial operations continually striving to maximize the output and reliability of machinery and production processes, the performance of rotating equipment is critical as a contributing factor. Implementing best practices offers a practical path forward.
Among best practices, accurate shaft alignment, use of correct tools when mounting rolling bearings, proper bearing lubrication, effective shaft sealing, and proactive monitoring of machine conditions play vital roles. Potential operating problems can be prevented, reliability improved, and optimized performance realized.
Align Machinery Shafts Properly and Accurately
Whenever an electric motor, turbine, or other driver is coupled to a pump, generator, or similar equipment, the centrelines of rotation of the two machinery shafts must be in line with one another. Otherwise, parallel (or offset) misalignment, angular misalignment, or a combination of the two will cause stress on the shafts and adversely impact machinery health and operation. Misaligned shafts can lead to premature bearing or coupling failure, shaft fatigue, damage to seals, increased vibration levels, friction, overheating, and energy consumption.
Properly and accurately aligned shafts of rotating machinery will serve to reduce excessive axial and radial forces on rolling bearings, minimize the amount of shaft bending from point of power transmission in the coupling to the coupling end-bearing, minimize wear in coupling components, reduce potential for mechanical seal failure, maintain proper rotor clearances, eliminate the potential for shaft failure from cyclic fatigue, and help keep vibration, noise, friction, and higher energy consumption at bay.
The demands for accuracy, simplicity, and reliability in methods used to enable, detect, and fix shaft misalignment have paved the way for highly precise laser alignment systems, which introduce highly affordable and easy-to-use solutions to align shafts of rotating machinery quickly and with pinpoint accuracy.
Laser technology alignment tools have been equipped with displays for real-time alignment values, allowing users to confirm results of alignment corrections as they are performed, and they require no special training. Other notable features have been integrated into such tools, including quick-start guides, fast measuring unit positioning capabilities, and built-in tolerance checking and memory facility to allow for results to be stored and shared by downloading.
Use Correct Tools for Mounting Bearings
If a rolling bearing is mounted improperly, without using the correct techniques and tools, the bearing’s service life will be jeopardized. The numbers tell the story: an estimated 16 per cent of all premature bearing failures can be directly attributed to poor fitting and the absence
of the correct fitting tools.
Since they are precision components, bearings should be mounted using correct techniques and technologies. The methods for proper mounting of a bearing are commonly referenced as “cold” or “hot,” consistent with their enabling technologies.
Cold mounting, or mechanical mounting, is generally recommended for small and medium-sized bearings (with outside diameters up to four inches); methods involving heat mounting will be appropriate for relatively larger bearings, and hydraulic techniques should be considered when mounting especially large bearings. Tools have been developed to accommodate each particular method.
In cold mounting, the practice of using a standard hammer and pipe for the job has been discredited due to the damage that can occur. This practice can cause debris to enter the bearing or, if not done properly, a pipe can slip and impact the internals of the bearing. Best practice for reliable installation: employing fitting tools to avoid harmful brute force and applying the proper force to both bearing rings, isolating the rolling elements from impact.
Hot mounting, where a bearing is preheated, provides a practical solution to allow for a bearing’s expansion and easier installation, while maintaining specified interference fit after the job is completed. Induction heaters can integrate various features to help prevent bearing damage during the heating process. The heaters stand in direct contrast to less effective (and potentially dangerous) methods, including an open flame, hot oil baths, and ovens or hot plates.
For mounting larger sized bearings, hydraulic assist tools are recommended. Hydraulic devices allow for more control and further help to maintain precision, accuracy, and repeatability; minimize the risk of damage to bearings and shafts; require less manual effort; and promote greater operator safety.
Properly Lubricate Bearing Arrangements
Selecting and delivering the proper lubricant in the correct amount at the required time interval is essential in realizing optimized rolling bearing performance, reliability, and service life and in promoting ideal rotating equipment performance.
Lubricant separates a bearing’s rolling and sliding contact surfaces, prevents wear, and reduces friction and heat generation. Lubricant also protects against corrosion, helps keep out contaminants (in the case of grease), and carries away heat (in the case of oil).
When feasible, grease will be the preferred bearing lubrication choice, because it is easy to apply, easier to retain within a bearing’s housing, and improves sealing against solid or moisture contamination. Oil lubrication will usually be specified when high speeds, high temperatures, or lubricant life and cleanliness preclude the use of grease.
It is imperative that the correct type of grease be used with the necessary thickener and base oil viscosity in the proper amount at the prevailing operating temperature of an application. Greases can further be formulated to achieve distinct characteristics by varying oil viscosities, soap, and additives to accommodate application requirements and operating conditions.
Mineral oils represent the most common oil lubricant choice for bearings due to their good performance for a wide range of applications. Synthetic oils will usually be selected in extreme cases, such as very low or very high operating temperatures, or when the oil service life needs to be extended. Rust and oxidation inhibitors are typical additives for extending the life of lubricating oils, and extreme pressure (EP) and anti-wear (AW) additives are used to reduce bearing wear and to extend bearing life.
In service, sufficient lubrication is equally important as selecting the proper type of lubricant. Lubricant-delivery technologies encompass manual re-lubrication (such as grease guns) or serve continuously by automatically supplying quantities of fresh lubricant on a regular basis.
Over time, lubricant in any bearing arrangement can gradually lose its lubricating properties due to mechanical work, aging, and/or the buildup of contamination.
This underscores the maintenance-related need for grease to be replenished or renewed, or for oil to be filtered and changed at regular intervals.
Adhere to the Basics of Shaft Sealing
Industrial shaft seals protect bearing arrangements and contribute to the overall reliability of rotating equipment and systems. Both the material of a seal and operating conditions will influence choices and application success. Hundreds of different radial shaft seal designs and material combinations have been standardized to a large degree and custom versions have further expanded the universe. There is no shortage of seal candidates.
When a seal must be replaced, however, best practices can provide a big assist. Among the guidelines, never reuse a worn seal, always verify that the original seal was correct for the job, confirm a seal will be able to accommodate an application’s speed and fluid media, compare operating temperature against lip material specifications for compatibility, determine that lubricant is appropriate for the seal’s lip material, and vent a seal’s cavity to prevent pressure buildup and blowouts. As with bearings, proper tools should always be used for seal installation.
Proactively Monitor Machinery Health
Industrial maintenance strategies have clearly shifted over the years from reactive to proactive approaches. The historical strategy of preventive or time-based maintenance has largely given way to predictive and/or proactive maintenance, which is based on the condition of rotating equipment when in operation. This strategy is grounded in the principle that while machinery failure may be unpredictable, emerging failure is detectable.
Condition monitoring technologies support predictive maintenance objectives by equipping operations with the surveillance tools to collect data reflecting the health of machinery and uncover faults for timely fixes before they can worsen.
Data collection options range from basic handheld or standalone units to more sophisticated, connected, and networked systems. Some devices and instruments focus on assessing the more significant physical operating parameters, such as vibration and temperature, while highly engineered systems at the other end of the spectrum can be configured to monitor and diagnose many more. The capabilities expand with integration into computerized maintenance management systems, the use of specialized software programs, and application modules and accessories targeting specific types of analysis.
For especially critical assets, continuous online condition monitoring systems offer indispensable lifelines. Online systems (hardwired or wireless) deliver up-to-the-minute information by delivering data 24/7 and storing scheduled and/or alarm data via permanently mounted sensors. The data can then be transmitted via the hardwired or wireless system to a host computer running relevant software packages.
All these best practices can pay significant dividends in optimizing the performance of rotating equipment. Additional insights can be gained by enlisting the support of qualified industry experts equipped with the know-how and experience to meet the most demanding application conditions and requirements.
Mark Cutler is Applications Engineering Manager-Industrial Market at SKF USA Inc. He can be reached at email@example.com.