Executive Summary
Measuring bearing torque performance is a complex but critical task that impacts many industries. Poor performance results in energy loss, heat generation and ultimately costly downtime. Techniques that can improve bearing torque performance include choosing the correct lubricant for the job, carefully controlling the amount of lubricant used and following OEM recommendations. There are challenges to overcome in achieving better bearing torque performance; the equipment needed for testing is not only expensive but often inaccurate, leaving room for improvement and innovation in the areas of testing and modeling.
Q.1 Please describe any techniques or practices that have helped you with bearing torque performance.
Using a controlled amount of oil/grease intended for a given bearing, ensuring the structural existence of bearing cover radiators that facilitate lowering the temperature of the zone occupied by the bearing, control and maintenance of proper radial clearance value, maintenance of proper bearing tension, if required.
Lubricant rheological parameters, detailed contact model, surface properties.
Correct quantity of grease to be filled in the antifriction bearings has great impact on the bearing performance and life.
Analysis of the penetration of used greases.
Lubricant resistance, NLGI grade, base oil viscosity, temperature, lubricant friction coefficient, load, speed.
Could be to inject an adequate amount of lubricant grease and maintain relubricating with less grease than I set before.
Machine motor.
Select correct lubricant viscosity.
Bearing torque performance would be one of the considerations when we evaluated grease.
From the user’s point of view, following OEM’s preload or endplay bearing installation recommendations assures long bearing life.
Modeling based—high pressure rheological measurements of viscosity and density. New lubricants have drastically difference properties than those assumed for classical tribo- logical equations. In application—precision flow rate control for oil-based systems. Actual load monitoring to reduce bearing load fluctuations when possible. Accurate setting methods. Preload/endplay will affect thermal growth margins.
The right lubricant in the right amount in the right conditions. It is very important that the lubricant meets the characteristics indicated by the OEMs both in its balance of viscosity, soap, NLGI, etc. Another important factor in performance is the cleanliness of the lubricant, ensuring that it reaches the lubrication points clean.
Better cleanliness of the lubricant. Better extreme pressure (EP) properties. Optimum viscosity at operating temperature. I used aerostatic bearings for micro-turbine rotation stability.
I developed a numerical solution algorithm to optimize bearing design parameters in order to achieve maximum stable inertial force (using linear stability analysis). This led to the enhancement of micro-turbine rotation frequency from 25 kHz to 100 kHz.
Selection of suitable base fluids, additives and thickeners. Consideration of the oil separation and flow properties of a lubricating grease (yield point and shear viscosity), if possible, over the entire temperature range of the application.
Selecting the most efficient grease. Selecting low energy bearings. Optimizing bearing life for the application, i.e., not overdesigning the bearing resulting in added weight, momentum and inertia.
Use of friction modifiers in greases, use of low viscosity oils, use of viscosity modifiers.
It is helping to extend bearing service life.
Moving to a grease with a better rheological profile helped to reduce churning losses in the bearing. It also did not get as hot during running in.
Q.2 Please describe a tribological problem that you solved using bearing torque performance.
Selection of the system of rolling bearings of the gear shaft loaded with various forces, taking into account the possibility of reducing the frictional resistance of a given bearing inversely proportional to the load value (possible by selecting the geometric parameters of the bearings, but it was limited by the available free space within the bearing system).
Bearing internal optimization.
Have you noticed any restrictions on the current techniques with bearing torque performance?
Yes
46%
No
54%
Based on an informal poll sent to 15,000 TLT readers.
In case of forced draft (FD) fan bearings failure, the cause was traced to overfilling grease. The grease quality and properties were found to be correct, but only the incorrect quantity caused the operation failure.
Bleeding of greases mixed with each other.
To use synthetic lubricant.
With the help of motor mechanic.
Reducing a machine start-up time and power consumption where the drive is an on-demand situation requiring many stop-start operations an hour.
Bearing torque was measured when we conducted the grease selection for a specific field.
In some applications, bearing endplay may end up in bearing cage wear. So, using the proper bearing preload is essential.
A hard plastic recycling machine had many downtimes because it worked to the limit (the plastic was very hard). Changing the lubricant with better cleanliness, better EP properties and operating at the optimum viscosity improved the efficiency by up to 96%.
I solved a stability problem of a micro-turbine by using an aerostatic bearing.
Breakaway and running torque of rolling bearings at low temperatures. Friction torque at increased speeds.
Improved grease bearing lubricant life when optimizing bearing for application. Reducing bearing internal friction by design and selection of correct bearing type, size and integral sealing type.
We have studied the aging of windmill lubricants and improved it.
Lab demonstration showing reduction in friction torque by the use of friction modifiers for railroad greases.
It was not solving, but mainly preventing, a technical problem.
Moving to a softer but shear stable grease instead of a standard #2 grade reduced torque and the bearing ran cooler with longer life.
Q.3 Please describe the greatest benefits to be derived from the improvement in the bearing torque performance.
Extending the durability of the bearings.
Less maintenance.
Longer bearing life.
Reduced friction and wear for energy saving.
Reduction of power loss, temperature reduction.
Less amperage, less temperature and more bearing life to change.
Wheel balancing.
Reduced stress on drivetrain and reduction in energy used.
Improve the power loss.
I can infer that the improvements in bearing torque performance will produce reduced fuel consumption/electric drain.
System level optimization. What else can I reduce/remove as a result of decreased bearing torque? For example—external cooler size, pump size, sump size. All these add up to weight.
A safe and profitable operation, a predictable operation, that there are no stops due to failures that require the entire production line.
Reliability.
Understanding of performance peak in terms of bearing number and nozzle restriction number to achieve maximum stable performance.
Improving the efficiency of technical units, especially those with low drive power such as actuators in vehicles.
Reduced energy consumption, improved bearing life and increased mean time between bearing replacements.
We are talking about friction reduction and, hence, energy savings.
Energy saving.
Extended service life, less unnecessary repairs.
Reducing bearing torque reduces running temperature and extends life.
Q.4 What are the gaps that may need to be addressed going forward to accurately predict bearing torque performance?
Ongoing tracking of radial and axial clearances and roughness between all cooperating rubbing surfaces (perhaps using X-ray camera technology associated with digital 3D image processing?).
Lubricant rheological parameters, detailed contact model, surface properties, random deviations for all influence parameters.
Analysis of used oil or grease in regular intervals.
To think in future overload and maybe training in which grease or lubricants oil in general to use in different applications.
Spinning and gears.
Accurately measure the film thickness in a grease lubricated bearing.
Researching best practices.
Who would benefit most with more accurate prediction of bearing torque performance? Select all that apply.
OEMs
52%
End-users
81%
Lubricant manufacturers
48%
Bearing manufacturers
56%
Based on an informal poll sent to 15,000 TLT readers. Total exceeds 100% because respondents were allowed to choose more than one answer.
Bearing longevity is directly related to proper preload or endplay, depending on the application. Ideal bearing torque performance does not necessarily translate into longer bearing life.
Increase in readily available thermalelastohydrodynamic lubrication (TEHL) solution methods that incorporate real surfaces modeling and real lubricant properties. Surface finish definition beyond roughness average and bearing area curves. Real surfaces play a major role in mixed mode friction, born of surface asperity interaction, which is where the majority of bearings operate in terms of film thickness regime.
Recognizing that it is important to maintain constant training that allows recognizing the root cause and symptoms.
Equipment and rigs to make measurement more accurate and affordable.
Better mathematical modeling of nozzle/orifice shape effect (source term in Reynolds equation) in the numerical calculation of bearing stability will help in achieving more stable performance. Further, the precession motion needs to be modeled for such micro-turbines.
Better test methods must be developed to be able to predict churning of lubricating greases in roller bearings. The lubricating grease developer can then derive which thickeners and other formulation components have a beneficial effect on low friction, particularly in the case of high-speed rolling bearings. Excessive churning of grease increases the friction losses of roller bearings, especially roller bearings at high speeds.
Awareness. The reputable bearing companies have application engineering teams and application engineering tools to help customers calculate bearing torque for different parameters and can guide customers to optimize bearing torque.
The inside temperature monitoring and control.
Improve measuring techniques. Use of hydrostatic bearings for measuring friction torque in rolling element bearings.
Trying to measure bearing torque on individual bearings is a challenge, and mostly losses are within the uncertainty of measurement. More sophisticated instrumentation can be used, but that adds to the cost of the measuring equipment.