Volume 9, Issue 6, 01 June 1938
Index of content:
9(1938); http://dx.doi.org/10.1063/1.1710427View Description Hide Description
9(1938); http://dx.doi.org/10.1063/1.1710430View Description Hide Description
9(1938); http://dx.doi.org/10.1063/1.1710431View Description Hide Description
Studies in Lubrication. I. The Theory of the Thick Film Lubrication of a Complete Journal Bearing of Finite Length9(1938); http://dx.doi.org/10.1063/1.1710433View Description Hide Description
A successive approximation theory is developed for the hydrodynamics of journal bearing systems of finite length, the expansion parameter being the journal eccentricity. This is applied through the second approximation to full journal bearings of lengths exceeding the bearing perimeter. The existence of the lubricant source and associated end leakage is explicitly taken into account, it being assumed in the actual analysis that the source is set 90° in advance of the maximum film thickness. It is found that contrary to prevailing opinion, based on the infinitely long bearing theory, the friction coefficients and eccentricities for the systems are not uniquely determined by the ``Sommerfeld variable''—(r 2/c 2)(μN/P), where r=journal radius, c=radial clearance, μ=lubricant viscosity,N=journal speed in r.p.s., P=bearing load per unit projected bearing area. It depends also on the leakage flux or source strength. For the position of source assumed in the analysis the friction coefficients and eccentricities increase with increasing source strengths. Further, the load carrying capacities of the finite length bearings are shown to be considerably less than for the infinitely long bearings, and decrease with increasing source strength if the source is placed in the low pressure part of the film. Finally, the theory shows how the consideration of the source of the lubricant permits a resolution of the difficulties with respect to the negative film pressures predicted by the infinitely long bearing theory. The numerical calculations show that the third and higher approximations may be neglected for eccentricity ratios not exceeding 0.4. General formulas are also developed for the asymptotic behavior of the friction coefficients on both the journal and bearing at very low eccentricities or large values of the Sommerfeld variable. These apply to bearings of all lengths and to partial as well as full journal bearings.
9(1938); http://dx.doi.org/10.1063/1.1710434View Description Hide Description
In treating film lubrication, Reynolds and Sommerfeld confined themselves to surfaces of infinite width, for mathematical reasons. Michell obtained the solution for a plane surface of finite width; the importance of this lies in the fact that leakage of lubricant through the lateral edges of a finite bearing reduces considerably the load supportable by the bearing. Solutions are obtained here for general cases of rectangular bearings with surfaces curved in both directions; for the Michell sector type of thrust bearing plate, in a case which allows consideration of the effect of the variation of film thickness with the radial distance from the center of rotation; and for the fitted finite journal bearing. General methods are exhibited suitable for handling other cases. In particular, the equations for the finite journal bearing in the general case are partially developed. Solutions for the journal bearing are shown to require laborious computation, so that an approximation to the film thickness is preferable; such an approximation, which can be handled relatively easily, is treated, and the solution obtained.
9(1938); http://dx.doi.org/10.1063/1.1710435View Description Hide Description
This paper describes a method for determining the dynamic current voltage characteristic curves of glow discharge tubes. The technique differs from that previously used for the oscillographic study of glow tubes in that the manner in which the current varies with time is under control. This is accomplished by the use of a vacuum tube to limit the current passed by the glow tube. The rate at which the current rises and falls, the current amplitude, the frequency of repetition of the current cycle, and the interval between cycles can be varied at will by changing the wave form of the voltage applied to the grid of the control tube, and the grid bias of the control tube. A number of oscillograms obtained by this method are shown, and the form of the characteristics is explained on the basis of time taken for ionization and deionization of the gas.