No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Studies on Correlation of Grease Life between Shielded and Unshielded Conditions in Rolling Element Bearings
Abstract
div class="section abstract"> It has been reported that 90% of greases are used for the lubrication of rolling element bearings. Greases are important systemic components which greatly influence the life of the bearings besides the dynamic test conditions encountered throughout its operation such as load, speed, temperature and bearing design. The greases may be used in bearings running in open condition or using shields to prevent it being leaked or thrown off during operation.
The dynamic life of grease is determined by tests run on multiple sets at elevated temperatures till failure is encountered. These tests measure the grease life as well as the bearing life. Simulated tests in conditions close to real life applications are possible using this method. The FE9 test rig is one of the commonly used test rigs for finding the dynamic grease life. In this paper, grease candidates with differing composition were evaluated at different elevated temperatures in the open and shielded conditions to attempt to find out whether a correlation exists between these two operating conditions.
</div
ResearchGate has not been able to resolve any citations for this publication.
Based on the bionic non-smooth surface theory, this article carries out (1) design of the structure of bionic non-smooth sealing rings and toothed bars of the sealing structure and (2) finite element simulation study on the bionic non-smooth surface structure of roller-cone bits. The result shows that (1) when the parameter Y is equal to the rack angles, the maximum pressure of the Type B is smaller than that of the Type A, while the equivalent stress of the Type A is smaller than that of the Type B; when the parameter Y is equal to the tooth distribution, the maximum pressure and the equivalent stress of the rack angle of 30° are smaller than that of the rack angle of 20°; and when the rack angle is equal to the tooth distribution, the maximum contact pressure and the equivalent stress of the tooth decrease with the increase in the parameter Y. (2) Compared with the O-shaped sealing rings, the new tooth bars avoid the problem of over-large contact area. (3) The grid-shaped sealing structure can increase the wear resistance of rubber rings and delay their wear and aging, thus improving their service life.
Sealed deep groove ball bearings (SDGBBs) are employed to perform the relevant duties of in-wheel motor. However, the unique construction and complex operating environment of in-wheel motor may aggravate the occurrence of SDGBB faults. Therefore, this study presents a new intelligent diagnosis method for detecting SDGBB faults of in-wheel motor. The method is constructed on the basis of optimal composition of symptom parameters (SPOC) and support vector machines (SVMs). SPOC, as the objects of a follow-on process, is proposed to obtain from symptom parameters (SPs) of multi-direction. Moreover, the optimal hyper-plane of two states is automatically obtained using soft margin SVM and SPOC, and then using multi-SVMs, the system of intelligent diagnosis is built to detect many faults and identify fault types. The experiment results confirmed that the proposed method can excellently perform fault detection and fault-type identification for the SDGBB of in-wheel motor in variable operating conditions.
Aimed at good lubrication performance of angular contact ball bearing at high rotating speed, the research of bearing internal oil-air two-phase flow, air vortexes and blocks are crucial but insufficient. By setting up a high precise numerical model with different nozzle distribution and annular inlet flow, the oil-air two-phase flow inside bearing cavity was investigated in consideration of different sealing condition and intake systems. The temperature and air pressure distribution, air-flow pattern and oil volume fraction were all discussed. The results show that, lubricating oil is easier to access the contact region inside bearing cavity with the help of seal structure. At high rotation speed, the temperature and pressure distribution of bearing with dual-nozzle is superior to single-nozzle.
Recent years have seen a substantial increase in sealed-for-life bearing applications. These are applications in which bearings are expected to function reliably for prolonged periods without requiring relubrication or maintenance. It should be noted that sealed-for-life in this context refers to an expected bearing service life and that the term indicates an operational design goal as opposed to a performance guarantee. The sealed-for-life concept was once limited to small deep-groove ball bearings employed in consumer products like appliances, hand-held power tools and ceiling fans. It now encompasses a far broader array of bearings such as angular contact ball bearings in pumps and passenger car wheels; Y-bearing units in food conveyor systems and air conditioning units; roller bearing units in construction equipment, railroad locomotives and truck trailer wheels; and plain bearings (sleeve bearings) and linear motion products. Applications have also broadened to cover larger machines and equipment.
The leakage of grease from shielded rolling bearings is usually caused by grease being pushed out by ball or cage motion, centrifugal force, or grease flow due to high temperature. However, we have discovered two other mechanisms that cause significant leakage: (1) slippage of the grease lump caused by adhesion forces to the shield plate and inner race which typically occurs in case of slippery grease on the surface, and (2) the thixotropic flow of grease due to alternate grease deformation which could occur when the shaft has precession motion or inclines against the bearing.
Conventional bearing shaft seal systems used in gas turbine engines are often limited to a sliding velocity of about 100 m/s, differential pressure of 3 bar, gas temperature of 300°C and a seal life less than 8000 h. Advanced engines will require bearing shaft seal systems to operate up to sliding velocity of 200 m/s, differential pressure of 6 bar, gas temperature of 500°C and seal life in excess of 30 000 hours. For seals operating in these advanced conditions, a design with no rubbing contact will be required to achieve long life and reliability. A good validated approach is the use of a gas lift augmentation seal. The design objective for a seal of this type is to have the faces of the seal seek an equilibrium position to avoid any contact. The gap must be small enough to ensure a minimal air leakage, but it must be large enough to limit power dissipation, due to shear in the gas film, and face deformation by shaft displacement, misalignment and vibration. Dynamic seals for a bearing compartment have the following main functions: provide static and dynamic sealing in order to prevent oil leakage from the bearing oil compartment to the air compartment and consequently no oil smell pollution by the use of bleed air; control air leakage to the bearing oil compartment in order to improve performance of the engine and to reduce oil consumption; reduce volume of the oil tank and lubrication system and hence provide weight reduction; to operate in extreme conditions of temperature and with normal and reverse pressure; and reduce the mean time between overhaul (MTBO) and have a very long life. Techspace Aero and Burgmann have carried out design, development and testing of lift augmentation carbon seals and demonstrated that high life and performance levels of these seals are possible in a gas turbine engine environment.
The integral sealing of rotating rolling bearings is considered with particular emphasis given to the development of elastomer lip ring seals. The modern high volume seal designs are based on the sandwich construction of the 1940s and the rubber/steel bonded construction of the 1950s. The integral sealed unit provides a cost effective and space efficient solution to many sealing problems. Seals are described for use in deep groove ball bearings, automotive hub units and spherical roller bearings.
Grease lubrication is widely applied to rolling bearings. The consistency of grease prevents it from leaking out of the bearing, makes it easy to use, and will give it good sealing properties. The same consistency prevents an optimal lubrication performance. Most of the grease is pushed out of the bearing during the initial phase of bearing operation and no longer actively participates in the lubrication process, leaving only a limited quantity available, which is stored inside the bearing geometry and on the bearing shoulders (covers or seals). This stored volume strongly determines the remaining lubrication process in the bearing. The distribution of this volume is determined by the grease flow, which is very complex to understand due to the strong nonlinear rheology. There is no consensus on the next phase in the lubrication process. The grease may bleed and provide oil to the raceway; it may be severely sheared in the raceway releasing oil; or small fresh quantities of grease may be sheared off from the volume stored on the shoulder. In addition, the lubrication process may be dynamic. Grease has self-healing properties where fresh grease is supplied in case of film breakdown and self-induced heat development. This article describes the state-of-the-art knowledge on grease lubrication, including grease flow, film formation, film reduction, dynamic behavior, and grease life.
In this paper attention is given to empirically modelling the hydrodynamics of a tightly sealed squeeze-film bearing in a flexible support structure simulating an aero-engine assembly, with a view to assessing its damping performance. It is found that predictable experimental results are obtained by employing an end-leakage factor which relates the outlet pressure around the bearing circumference to the corresponding ‘long-bearing’ pressure. The present work complements that covered in an earlier paper (1), which was concerned with the performance of an open-ended or weakly sealed squeeze-film bearing in a similar support structure.
Grease is degraded during use in rolling element bearings and as a result the lubrication performance can deteriorate. Under severe conditions this can result in lubrication failure and, thus, the grease life will effectively limit the bearing life. At present there is a lack of detailed information regarding the changes that occur in the grease and the way in which this degradation affects lubrication performance and failure.This paper reports an initial study into grease degradation in bearings. The aim of the work was to characterize the changes that occur to the chemical and physical properties during use. A series of bearing tests using the modified DIN 51 806 test designated R2F(M) have been carried out using two greases: additized and non-additized. The tests have been run for different temperature and speed conditions for up to 300 hours. The aim was to examine the grease during normal running rather than after failure. At the end of the tests the bearings were dismantled and grease taken from different parts of the bearing for infrared spectroscopic analysis. This technique can characterize the degree of oxidation or degradation of the grease both in the bulk sample and from thin grease layers remaining on the bearing surfaces.The analysis has shown that the condition of the grease varies depending on the distribution within the bearing. The lubricant remaining in the cage pocket region was heavily degraded and contained very little thickener. The grease on the seals contained different amounts of thickener depending on the seal position. The lubricant remaining on the inner raceway surface was predominately base oil although there was some thickener present. These results are discussed in the light of proposed bearing lubrication mechanisms. Presented at the 56th Annual Meeting Orlando, Florida May 20–24, 2001
Sealed ball bearings are used widely for electric motors and automotive components. Appropriate grease is selected for the each application, considering grease life, bearing torque, sound characteristics, etc. Recently, as these components have become progressively more compact, the sealed ball bearings are required to operate at higher temperatures and rotational speeds. In such cases, grease life has become more critical in determining the bearing's overall life. Therefore, it is important to estimate grease life in order to select the appropriate grease and predict the life of the final product.In this paper, the grease life formulas for both urea and lithium soap greases were generated. The formulas were derived from grease life data generated on 6204 bearings with inner ring rotation. The formulas were composed of temperature, rotational speed and applied load terms. These terms were obtained, based on the test results, the temperatures from 100 °-180 °C, the rotational speeds from 10,000–20,000 revolutions per minute (rpm) and the axial loads from 67-670 N, respectively. The grease life formulas were further improved to be applicable to outer ring rotation bearings.It was found that the grease life in bearings with outer ring rotation was shorter than for bearings with inner ring rotation. The difference in cage rotational speed was found to affect the grease life. By adding a correction factor for outer ring rotation to the rotational speed term, the same grease life formula, independent of rotational type, can be utilized. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000
The lubricating life of a grease in rolling element bearings is limited by operation at high temperatures. The thermal and mechanical stresses imposed result in gross physical and chemical changes to the grease which contribute, eventually, to failure both of the lubricant and the bearing. The problem is very complex as both grease and bearing parameters contribute to failure and these are difficult to disentangle. Most of the research work in this area has been with bearing tests where samples of bulk grease have been removed for analysis after failure. Although this approach will yield results as to grease life and the condition of the grease at the end of the test it provides little insight into the fundamental mechanisms of failure.This paper approaches the problem from a simpler perspective. The aim is to develop experiments to artificially age greases under controlled conditions of thermal and mechanical stress, to characterize the changes that occur and to relate these changes to lubricating ability. This paper concentrates on thermal ageing: in future work mechanical working will also be studied.Thermal ageing tests have been carried out on simple lithium hydroxystearate greases and the resulting changes in their chemistry characterized by infrared spectroscopy. The lubricating performance of the aged greases has been assessed by measuring film thickness and oil release in a rolling contact under starved conditions. Presented at the 53rd Annual Meeting In Detroit, Michigan May 17–21, 1998
This paper deals with the influence of lubricating grease composition on grease service life and tribological performance characteristics in high-speed rolling bearings. First of all the test rig including the measuring system used to determine the lubricant film thickness in operation as well as the greases used in the study will be explained. Experimental results will then be used to analyse the influence of thickener type and content, base oil type and viscosity and anti-oxidants on grease service life, lubricant film thickness, bearing temperature and friction torque.
Bearing failures have accounted for an increased percentage of motor failures. This is due in part to improved stator and rotor construction, which may result in the bearings being the weak link. Also many bearings are being operated at increased loads, temperatures, and speeds. The environment is another major factor affecting bearing life. All too often the failed bearing is replaced without proper identification of the root cause of the failure. Hence, proper corrective actions may not be taken to minimize or avoid future failures, and extend bearing life. A methodology for identifying the cause of failure for antifriction bearings used in electric motors using antifriction bearings is presented.< >
Lubrication Strategies for Electric Motor Bearings
- H Bloch
A Comparison between Antifriction Rolling-Element, Grease- or Oil-Based Lubricated Bearings for Process Applications
- A H Bonnett
- T Albers
The Lube Coach Decision Parameters
- M Johnson