These bearings have two rows of barrel shaped (spherical) rollers which run on a common spherical outer and inner raceway, they are inclined at an angle to the bearing’s axis. Their design offers many features such as self-alignment, insensitivity to misalignment, tolerance to heavy radial and axial loads etc.
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Taperedrollerbearingshavetapered inner and outer ring racewaysbetweenwhichtaperedrollersarearranged, optimizingrollingconditions. Taperedrollerbearingsareutilizedinapplicationswherethereisacombinationofradialandaxial (thrust) loads.
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Cylindrical roller bearing from WXGZ® can be ideal for machine tools, compressors, cement pulverizers, and many other applications that require a heavy dynamic or static radial load capacity at high speeds. A cage-guided cylindrical roller bearing helps keep the rolling elements in place, which becomes more crucial as loads get heavier. A cylindrical roller bearing can support the light-thrust movement, with the double-row type also able to support axial loads in both directions.
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One of the most commonly used bearings, the open types are manufactured without seals to allow for the free circulation of either oil or grease, used in gearboxes and other environments where no foreign matter would be present and a lubricant supply is available. Rubber and metal seals are also avaliable.
The FVA-Workbench is a manufacturer-neutral tool for the simulation and calculation of transmission systems. As product development cycles become shorter, powerful modeling approaches and calculation algorithms become increasingly important. The predominantly analytical approaches in the FVA-Workbench deliver fast and reliable solutions to all important issues related to drive technology. For bodies that cannot be accurately described analytically, the results are supplemented by suitable numerical methods. The intuitive modeling techniques in the FVA-Workbench guarantee simulation of consistent, valid, and manufacturable gears every time.
The calculations are developed, analyzed, and validated in research projects by Forschungsvereinigung Antriebstechnik e.V. (FVA, the Research Association for Drive Technology). Through member contributions and public funding, the FVA is able to organize 17 million euros annually in research projects at leading German universities, chairs, and research institutions. The FVA-Workbench serves as a knowledge platform, making the results of FVA research projects available and accessible to all engineers. It is no longer necessary to read through and study countless pages of scientific documentation, making the development of innovative gearboxes considerably more efficient and user friendly.
The following article will explain the detailed calculation of rolling bearings in the FVA-Workbench, based on consideration of the profiling of roller bearings.
Profiling of Roller Bearings
In roller bearings, there is line contact between the rolling elements and the raceway. If the rolling elements are perfectly cylindrical (cylindrical roller bearings) or tapered (tapered roller bearings), this leads to local pressure peaks when the end side of the rolling elements comes into contact with the raceway (Figure 1a). This can result in local pitting damage in these areas (Figure 2). To avoid these pressure peaks, roller bearings are always designed with profiling along the longitudinal axis of the roller (Figure 1b). In addition to avoidance of high edge stresses, the profiling also has an influence on the following criteria:
Maximum roller-raceway contact pressure, especially with tilting
Modified reference rating life according to /2/
Tilting and lowering rigidity
Cylindrical and tapered roller bearings typically have a logarithmic profile in accordance with /2/. However, the actual depth and shape of the profiling can deviate significantly and is determined by the manufacturer, based on available knowledge for each bearing type. In order to consider the influence of different profiles on the above criteria in the bearing design phase, the FVA-Workbench provides the option to adapt the profile for each individual roller bearing. In addition to pre-defined profile shapes, profile curves provided by the bearing manufacturer or based on measurements can also be defined. Therefore, it is recommended to consult the bearing manufacturer in critical cases when making the final bearing selection.
The influence of different profiles will be demonstrated, using the calculation of the NJ 230 type motor-side output shaft bearing from the gearbox shown in Figure 3 as an example. Three different profile variations are calculated for the bearing:
32 μm logarithmic profile (corresponding to /2/)
14 μm logarithmic profile
Diagram 1 provides an overview of the calculation results for the 3 variants. The values are all relative to the corresponding profile specified in /2/ (here: 32 μm).
Additionally, the pressure distribution along the longitudinal axis of the roller in the inner ring contact of the most heavily loaded roller element is compared for the three variants in Figure 4, below.
The following statements can be derived from the results:
The profiling has no significant influence on the results of the modified rating life calculations (according to both ISO 281 and bearing manufacturer catalog calculations). Only minor differences may result from the fact that slightly different bearing forces may be calculated in the system due to the change in the bearing stiffness.
The distribution and the maximum value of the local contact pressures in the bearings are decisively influenced by the specification of different profiling. From the curves in Figure 4, it can be seen that the pressure in the middle of the roller increases with higher amounts of profiling. With lower amounts of profiling, the pressure distribution becomes more even. In this case, however, increased edge stresses may occur, especially at high tilt angles.
Since the value of the modified reference rating life according to DIN 26281 is based on consideration of the local contact pressure, a strong influence on the rating life values can also be seen here for each specified profile.
About FVA GmbH FVA GmbH is a joint venture of VDMA (Verband Deutscher Maschinen- und Anlagenbau, the Mechanical Engineering Industry Association) and FVA e.V. (Research Association for Drive Technology). Founded in 2010, FVA GmbH works hand-in-hand with top-level German research institutions and leading companies from the drive technology industry toward the practical application of knowledge gained from FVA research projects. Our core competencies are the development of calculation and simulation software for drive technology, processing and conversion of legacy code structures into modern software architectures, professional service and support, and hosting technical seminars and conferences.
List of sources /1/ A. Kessler: Schiefstellung und Axialschubverhalten von Zylinderrollenlager, Dissertation, Universität Hannover (2010) /2/ DIN 26281 – Rolling bearings – Methods for calculating the modified reference rating life for universally loaded bearings, Beuth Verlag (November 2010)
In most pump applications, it is not always necessary to run the pump at full speed. Flow rate has traditionally been decreased with flow control valves, but this has disadvantages. Nowadays the flow is often controlled by running the pump’s motor on a variable frequency drive (VFD). Besides well-controlled flow rates, VFDs offer:
Energy savings (from reduced motor speeds)
Improved seal and impeller life and reduced vibration and noise (from reduced pressure)
Greatly reduced water hammer (from smooth acceleration and deceleration)
But VFDs have their own downsides. One big problem is that they create stray voltage on the motor shaft. This shaft voltage can cause electrical damage to motor and pump bearings by discharging (arcing) through them. This electrical damage accrues over time, causing premature bearing failure.
The solution is to electrically bond the shaft to the motor frame with a shaft grounding device. This gives charge on the shaft a low-resistance path to ground, so current flows through the grounding device instead of arcing through the bearings. (Large motors, over 100 hp/75 kW also require one insulated bearing to prevent circulating VFD-induced currents.)
AEGIS® Shaft Grounding Rings are the most reliable form of shaft grounding available, and the only one that offers a 2-year extended warranty. AEGIS rings can be installed on existing motors, and several manufacturers also offer motors with AEGIS rings factory-installed, including vertical hollowshaft, severe duty, and even explosion proof models.
To learn more about the problem of VFD-induced bearing currents and the solution using AEGIS rings, see these case studies and best practices, or see the AEGIS Youtube channel.
As mentioned, AEGIS Rings come with a 2-year extended warranty against bearing fluting damage. No other form of protection against VFD-caused bearing damage offers a warranty like this.
To learn more about AEGIS shaft grounding and best practices for electrical bearing protection, sign up for a training. We offer both live webinars and on-site lunch-and-learn trainings.
When a rolling bearing is damaged during machine operation, the entire machine or equipment can seize or malfunction. Since bearings that fail prematurely or unexpectedly cause trouble, it is important to be able to identify and predict failure beforehand, so that preventive measures can be adopted.
When debris such as small metallic particles are caught in the rolling contact zone, Denting occurs on the raceway surface or rolling element surface. Denting can occur at the rolling element pitch interval if there is a shock during the mounting (brinell dents).
Debris such as metallic particles are caught in the surface
Shock during transport or mounting
Clean the housing
Improve the sealing mechanism
Filter the lubrication oil
Improve the mounting and handling methods
Part: Inner ring of a double-row tapered roller bearing Symptom: Frosted raceway surface Cause: Debris caught in the surface
Part: Outer ring of a double-row tapered roller bearing Symptom: Indentations on raceway surface Cause: Debris caught in the surface
Part: Inner ring of a tapered roller bearing Symptom: Small and large indentations occur over entire raceway surface Cause: Debris caught in the surface
Part: Tapered rollers of damage “Denting 3“ Symptom: Small and large indentations occur over the rolling surface Cause: Debris caught in the surface