Tolerance ring bearing-mounts decrease vibration
A
Rencol Tolerance Rings product story
Edited by the Engineeringtalk editorial team
Feb 23, 2009
Saint-Gobain Performance Plastics Rencol has completed a research programme confirming that tolerance ring bearing-mounts decrease vibration compared with press-fit and glue alternatives.
By fine-tuning the characteristics of the joint between the bearing and the housing, the tolerance ring helps reduce the vibration within the bearing, which reduces noise.
This mounting has a positive effect on the electric motor and bearing life, enabling it to run quieter and smoother for longer.
Initial results suggest that the stiffness of a joint using a tolerance ring is lower than that of a press-fit or glue bearing-mount and therefore the transmitted force through the bearing into the housing is reduced.
In addition, with a tolerance ring-mount, the dampening effects effectively absorb more of the vibration energy, resulting in less noise.
Stuart Kelly, appliance product manager at Rencol, said: 'Tolerance rings offer better repeatability, lower RMS (root-mean-square) noise level, lower RMS vibration level at high speeds and the ability to control the frequency band in which the resonance occurs.
Electric motor failure can occur for a number of reasons, though an IEEE survey of faults on induction motors suggests that by far the biggest cause is the bearings, making up 51 per cent of all recorded failures.
Bearings have several failure modes: vibration, shock loading and mechanical stresses increase the rate of wear, while thermal fluctuation causes radial loading as clearances vary because of thermal expansion and contraction.
In an electric motor, vibration can by caused by the brushes or an imbalance of mass within the motor.
But most vibrations come from the moving parts, such as the axle and bearings.
The source of the vibration largely determines its frequency and amplitude and is transmitted through the bearings into the housing.
A significant proportion of the noise created by an electric motor is due to these vibrations, though not all.
Some of the noise could be due to air disturbance and other factors, which are unavoidable.
Engineers at Rencol explored the noise and vibration benefits brought on by the use of a tolerance ring to mount bearings in an electric motor.
Since desirable vibration and noise performance depends on the application of the electric motor, the focus of the research was to avoid resonances occurring within the specified operating range.
In addition to improving the perceived quality of the electric motor and the positive effects the bearing mount has on the motor and bearing life, tolerance rings can reduce costs to the manufacturer.
The radially sprung nature of the tolerance ring enables the manufacturer to relax the tolerance on the housing.
This allows the manufacturer to use 'as moulded' parts rather than invest in costly finishing operations to control the tolerance to a smaller range.
The improved bearing life allows the manufacturer to reduce costs further by specifying lower quality and cheaper bearings into the electric-motor design, while achieving the same life as high quality bearings.
With the introduction of the Waste Electrical and Electronic Equipment (WEEE) Directive at the beginning of 2007, OEMs are now turning their focus on the ability to rework or recycle component parts within their end equipment, in particular the electric motor.
The customary use of adhesives in component mounting - not just the bearings, also the stator, sensor and gears - makes it virtually impossible to dismantle the motor into its constituent parts.
As such, manufacturers are looking at the benefits of tolerance rings to ease assembly and to enable the motor to be taken to pieces.
In almost every bearing-mount application, the problems so often associated with the glue and press-fit alternatives can be completely eliminated by using tolerance rings.
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Tolerance rings - from concept to production
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Tolerance rings take the strain out of motors
Chris Needes looks at some of the innovative ways in which tolerance rings are currently being used in electric motors.
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