Operating Conditions of Journal Bearings Under Fluctuating Loads

Pattie, D. R (1952) Operating Conditions of Journal Bearings Under Fluctuating Loads. PhD thesis, University of Glasgow.

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At the outset, since no previous practical work was available, it was necessary to evolve apparatus and instruments with which investigation of fluctuating loads on journal hearings could he commenced. Since the problem is beset by many mechanical difficulties, it seemed expedient to make some simplification, and this was achieved by employing a larger diametral clearance than is commonly found in practice, and also by omitting friction measurement. The main object was to plot the pressure distribution throughout the bearing, and towards this end a balanced-pressure-piston type of instrument was devised. Transient pressures could be accurately measured whether above or beneath atmospheric pressure, and since the element was placed in the shaft and the apparatus so constructed that the shaft could be traversed axially, the whole area of the bearing could be searched. Fluctuating loads were applied to the bearing in two directions by spring and lever systems, and sensitive instruments were devised to measure the applied loads. Displacement of the bearing was measured in two directions, again with an instrument specially developed, and like the other instruments, capable of giving instantaneous readings. All these instruments contain electrical contacts and operate in a low voltage circuit with headset. Simultaneous measurements of pressure distribution, applied load, and attitude were obtained. Tests were made with a single fluctuating load and also with both loads operating to give a rotating load effect. Investigations were made with shaft stationary, shaft rotating at same speed as load, and with shaft rotating at twice speed of load. Good agreement was obtained between integrated pressure load and measured load. In the first tests, the bearing was submerged in an oil bath with no other oil supply, but tests were later made with oil supplied under pressure. It was found that, in general, the bearing does not remain full of oil, but is cavitated. A purely pulsating load produces a large low pressure region on the unloaded side of the bearing in which the pressure approaches absolute zero. A rotating load, which is similar to the normal case of a bearing under steady load, also gives a large low pressure region covering more than half the bearing surface, but in this case the pressure is only slightly beneath atmospheric pressure with the exception of a narrow region following the pressure peak in which the pressure approaches absolute zero. The oil film in a submerged bearing is gradually displaced by air which comes out of solution and is trapped in a low pressure region of the bearing, but in some cases a stable condition is reached. When oil is supplied under pressure through an oil hole, cavitation is not eliminated, but a larger quantity of oil is maintained in the bearing and the load carrying capacity thereby increased. While the load carrying capacity was found to be considerably less than that indicated by theory, it was shown that the critical case predicted by theory does exist; this occurs when the shaft rotates at twice the speed of the load, the oil film supporting no load under these conditions.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Mechanical engineering
Date of Award: 1952
Depositing User: Enlighten Team
Unique ID: glathesis:1952-78851
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 14:46
Last Modified: 30 Jan 2020 14:46
URI: https://theses.gla.ac.uk/id/eprint/78851

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