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chapter 1 evolution of a successful design

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A foil journal bearing (Fig. 19.3l) consists <strong>of</strong> a very thin compliant bearing surface<br />

resting atop a series <strong>of</strong> corrugations.When it is compared to a conventional gas bearing,<br />

the foil bearing has a thicker film, higher load capacity, lower power loss, better<br />

stability, and superior endurance to high operating temperatures.<br />

19.2.2 Journal Shapes<br />

JOURNAL BEARINGS 19.7<br />

Although the journal is generally assumed to be perfectly circular, wear effects or<br />

poor manufacture can lead to journals with the shapes shown in Fig. 19.4a, b, and c.<br />

In addition, the possibility <strong>of</strong> developing pressure by grooving the surface <strong>of</strong> the<br />

journal has been investigated.Three grooved patterns that were found to yield good<br />

stability characteristics are shown in Fig. 19.4c, d, and e.<br />

(a) (b)<br />

(d) (e)<br />

FIGURE 19.4 Journal shapes. (a) Hourglass; (b) barrel; (c) tapered; (d) herringbone;<br />

(e) partly grooved symmetrical pattern: (f) partly grooved asymmetrical pattern.<br />

(Parts (d), (e), and (f) are from [19.1].)<br />

19.3 BEARING MATERIALS AND SELECTION<br />

CRITERIA<br />

19.3.1 Bearing Materials<br />

JOURNAL BEARINGS<br />

The ideal journal bearing material would have the following characteristics:<br />

1. High compressive strength to withstand the applied radial loading<br />

2. High fatigue strength to endure any cyclic changes in load direction and/or load<br />

intensity<br />

3. Compatibility with the journal material to minimize surface scoring and bearing<br />

seizure whenever the journal and bearing surfaces come into contact (e.g., during<br />

startup)<br />

4. Embedability to permit foreign particles in the lubricant to penetrate the bearing<br />

surface to avoid scoring and wear<br />

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(c)<br />

(f)

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