Judder effect in bearings

[Donnis]

Hello everybody!
Anybody know where can I find informations about "Judder" effect (factors of influence, methods of reduction/elimination)?
Thanks a lot in advance!

 

[AHRBearing]

I believe the ntnamerica.com website has quite a few PDF papers on bearing behaviour and failure. Sorry I cannot point you to a specific paper.

AHR International Ltd

http://www.ahrinternational.com

 

[Donnis]

Thanks, AHRBearing, but I think I will search for something more specific, theoretical informations about this effect, like what produce it and what can I make to avoid or at least minimize it. I think this phenomenon is not very easy to explain and there are not so many informations about it, or I'm wrong?

 

[diamondjim]

Donnis,
You probably know about the following:
It seems to me the principle is outlined fairly well.

http://www-personal.engin.umich.edu/~jbarber/backgnd.html

In the HotSpotter, a finite element method is developed for determining the critical sliding speed for TEI of an axisymmetric clutch or brake. Linear perturbations on the constant speed solution are sought that vary sinusoidally in the circumferential direction and grow exponentially in time. These factors cancel in the governing thermoelastic and heat conduction equations, leading to a linear eigenvalue problem on the two-dimensional cross-sectional domain for the exponential growth rate for each Fourier wave number. The Fourier reduction method developed in HotSpotter permits a remarkably efficient solution of the frictional thermoelastic stability problem for systems in which the geometry is axisymmetric. The power of the method is demonstrated by the multidisk clutch example, direct numerical simulation of which would represent an extremely challenging computational problem. Values are obtained for the critical sliding or rotational speed and also for the exponential growth rate of each mode when operating above the critical speed. The method is easily applied to other examples and can therefore be used to assess the effect of design modifications such as changes in geometry and material properties on the thermoelastic stability of multidisk brakes and clutches.

 

[Oilmaintanse]

I will put it like this: There is in fact several ways of determing wether the bearing is damaged. With the use of acoustics detection methods this "Judder" can be traced and planned to be maintined. Still acoustics is considered a late stage detection method. In fact the damage has appeared long ago in the oil. By using microscope photographing of oilsamples x500 on 0,8 micron milliporefilters it is possible to predict a damage long before it has happened. It is in this way possible to detect early stages of varnish presens in the lub wich indicates it's time for action. This is how ever only a way of detecting and not a solution to the wearproblem. When you look for the right solution, just keep in mind, the clearings within the bearings is endeed quite small on the side of wich the payload is working. The luboil can be as thin as 52 atoms, and the density of the oil can be very high,(density near light metal) so keep it clean. A new oil in standard NAS1638 Class 8 will contain sufficient particlenumbers wich will after a while change the chemical substance of the lub and then the stucture of the metal surface in the bearing. So even if you deside to change the oil when it's time, be sure the new oil is clean. All structural damages in metalsurfaces of bearings has a pre- stadium wich happens in the luboil. I'll mention a practical example:The company Kemostaal had problems with some roller bearings, breakdown every 850 h. The bearings was changed to ceramic bearings, the breakdown was moved to every 1150 h. Then we did a research/study with the first rollerbearings. Supercleaning of the oil was performed while the compressors was running. The result was an increase of the operatingtime to three years and still running.