Lubricated, journal bearing

Herzig" also studied the effect of dispersed molybdenum disulphide in a hydrodynamic bearing, and showed that, where full fluid film lubrication Is not present, dispersed molybdenum disulphide can decrease friction. The coefficient of friction in an oil-lubricated journal bearing is related to the Sommerfeld Number ZN/P where Z Is the viscosity, N the rate of rotation, and P the bearing pressure or specific load. Figure 13.2 shows some empirical relationships between coefficient of friction and the Sommerfeld Number for an oil with different concentrations of dispersed molybdenum disulphide in a foil bearing . 

Recent work Semi-lubricated journal bearings consisting of a shaft rotating in a porous metal sleeve of sintered bronze or aluminium containing lubricating oil within the pores of the porous metal are restricted to low loads, low-to-medium velocity and temperatures up to 100 C [48]. 

Analysis of the externally pressurized gas-lubricated journal bearing is involved, tedious and quite specific to the particular problem. Details can be found in the monograph by Pinkus and Sternlicht [4]. 

Since the late 1970 s the occurrence of film reformation in plain journal bearings has been a topic of research Interest for workers in the Institute of Tribology at the University of Leeds. Possibly no freely available design procedures for liquid lubricated journal bearings incorporate an explicit consideration of the effects of such film reformation. Some design routines (1) do attempt to quantify the consequences of the reformation both in thermal and flow rate terms, however, the reliability of such predictive techniques is still uncertain particularly at critical boundaries representing design limitations. 

The fluid film force in the bearing can be determined from the published data on the performance of gas lubricated journal bearings and this must balance the out-of-balance load,... 

Equations 3, 4 and 5 are solved iteratively using a computer program which contains data on the performance of gas lubricated journal bearings, the functions fj (L/D, H, e) and f2(L/D, H, e). The process converges rapidly, but under-relaxation is necessciry at high eccentricity ratios. 

During inspection, all journal bearings should be closely inspected. If the machine has not suffered from excessive vibrations or lubrication problems, the bearings can be reinstalled and utilized. 

Radial bearings or journal bearings are usually pressure-lubricated. Most compressors use two bearings on opposite ends of the rotor assembly or on... 

F(ir axial compressors, the journal bearings are of the plain sleeve type for the larger, slower speed compressors. They are of the tilting pad type for the smaller, higher speed machines. The sleeve bearing is normally housed io a spherically seated carrier. The bearings require pressure lubrication as do most of the other compressors. 

These are expensive but, in precision applications, they offer the low friction and lack of play that are characteristics of the more usual rolling journal bearings. Grease or adhesive oil usually effects lubrication. 

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. 

Externally pressurized gas journal bearings have the same principle of operation as hydrostatic liquid-lubricated bearings. Any clear gas can be used, but many of the design charts are based on air. There are three forms of external flow restrictors in use with these bearings pocketed (simple) orifice, unpocketed (annular) orifice, and slot. 

Morishita, S., Matsumura, Y, and Shiraishi, T., Control of Eilm Thickness of a Sliding Bearing Using Liquid Crystal as Lubricant, Journal of Japanese Society of Tribologists, Vol. 47,2002,pp. 846-851 (in Japanese). 

G., Squeeze Film Lubrication of a Short Porous Journal Bear- [38]... 

Christensen, H. and Tender, K., The Hydrodynamic Lubrication of Rough Journal Bearings, Journal of Lubrication Technology, Trans. ASME Series F, 01. 95,1973,p. 324. 

Figure 11.11 Different lubrication situations in a journal bearing. Left At low velocities and high loads, boundary lubrication with a high friction coefficient dominates. The shaft climbs the journal on the right side. Right At high speeds and low loads hydrodynamic lubrication leads to much lower friction. The build up of the hydrodynamic wedge moves the shaft to the upper left.

ZN/P curve—general graphic representation of the equation p = (f) ZN/P, where p (die coefficient of friction in a journal bearing) is a function (f) of the dimensionless parameter ZN/P, (viscosity x speed)/pressure. This is the fundamental lubrication equation, in which the coefficient of friction is... 

Samuelson, F., Lubrication of Journal Bearings with Water-Base Lubricant, Proc. General Discussion on Lubrication Lubricants, p. 269, I.Mech.E., London, 1937. 

The silicone-thermoplastic IPN composites exhibit superior mechanical properties (Table IV), and the network structure of the silicone prevents migration. The value of the IPN has been demonstrated in a molded journal bearing for use in high-speed paper-handling equipment. For example, part wear was reduced to a greater extent in a PTFE-lubricated, silicone-nylon... 

Journal bearing oil film thickness and wear Lubricant issues related to journal bearings have been extensively studied using bearing rigs through oil film thickness... 

Hutton, J.E., Jackson, K.P. and Wdliamson, B.P. (1984) The effects of lubricant rheology on the performance of journal bearings. ASIE Preprint No. 84-LC-IC-l. 

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