Bearings. Journal factors

Hydrodynamic principles for gas bearings are similar to those involved with Hquid lubricants except that gas compressibility usually is a significant factor (8,69). With gas employed as a lubricant at high speeds, start—stop wear is minimized by selection of wear-resistant materials for the journal and bearing. This may involve hard coatings such as tungsten carbide or chromium oxide flame plate, or soHd lubricants, eg, PTFE and M0S2. 

With the increased speed and horsepower capabilities of modem chain drives, the role of lubrication has increased in importance. The precision roller chain is actually a series of connected journal bearings and it is essential that lubrication minimizes the metal-to-metal contact of the pin/bushing joints of the chain. Many factors affect lubrication performance and chain life including heat, improper lubrication, windage, contamination, and oil viscosity. 

It is perhaps worthwhile to dwell briefly on the use of the journal-bearing configuration in practical lubrication applications. In such circumstances, the rotating inner cylinder is normally allowed to float to seek a position in which the hydrodynamic force precisely balances the load. We have analyzed the eccentric cylinder problem based on the picture in Fig. 5-1, in which the line of centers between the two cylinders is in the horizontal direction. In that configuration, there is a net vertical force but no horizontal force. Moreover, examination of (5-48) shows that the magnitude of the vertical force for a given pair of cylinders (so that a and e are fixed) is determined by 9 and A. The A dependence is contained in the factor... 

All of these factors are easily controlled in the design of such apparatus. Initial film thickness is controlled by hydrodynamic action of the blade, defined as that resulting from the balance of centrifugal force, water resistance, and a journal bearing type of lift. Rate of evaporation is controlled by the selection of the operating temperature difference across the heat transfer tube and the rate of film renewal is controlled by choice of output speed of the gear motor which drives the blade. 

Journal bearings made of a modified APD material have substituted rolling bearings in friction joints of drying drum wringer rolls and other equipment exposed to hostile media at 60-90° C temperatures. The service life of APD-based bearings exceeds that of roller bearings 1.5 times with a cost reduction factor of two. 

Hight of the control volume at the point A Correction factor for warped stream lines Width of the Journal bearing pad Pressure in gauge Inertia parameter... 

The above factors are best explained by consideration of the requirements for hydrodynamic similarity. The dimensionless load capacity parameter has been commonly used for steadily loaded hydrodynamic Journal bearings ... 

Resin Glass Content, wtX TFE Content, wt% Wear Factor /f (EquilBirium), p.min Vftelbeh/ Coefficient of Friction Limited by Journal Half Bearing Tooth Strength, psi... 

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