Performance studies of externally pressurized air thrust bearings

by Ho, Kwong-wai

(Uncorrected OCR) Abstract of thesis entitled

II rerformance Stud ics of ?xterna.lly

Pressurized Air 'l'h:r.ust Dearings II

subni tted by : Ho Kwong-\vai

for the degree of

Haster of Philosophy

at the Unive:rsity of Hone Kong in AUGUst, 1976.

Based on Havier-Stokes equations, lumped paraneter analysis

and Routh's criterion, general equations were derived governing

the performance of capillary compensated multi-pocket hydrostatic

air thrust bearincs in the unstable and stable regions for three

cases, viz., a bearing vTi th any number of pocleets, a six-pocket

be~ring and a four-pocket bearing. The equations were solved by

neans of a high speed diei tal computer, eiving analytical results

for stability maps, load capacity, bearing clearance, pooket

pressure, bearing stiffness, "Teight flo"Tratc and p0\1er consumption

for different capillari restrictor size, pocket d~pth, shaft

speed, load and air supply pressure.

A specially designed test rig 'das built to investigate

experimentally the performance characteristics Of a four-pocket

and a six-pocket hydrostatic air thrust bearings. By varyinc

systematically the same parametersas in the analytical investigation,

experimental results describinc the be~ring characteristics

were obtained.

As reGards the stability characteristics, both analytical

and experimental results indicated that increase in pocket depth

tended to enlarge the unstable regions for the bearings, increase (uPfer i.in,?t)

to vibrationLRnd

the pocket pressure an~

Joad correspondin~ ({O.,,,. C???;{)

vi1)rationio On the other l;';;:d, -

J-

reduce trle frequency of

""

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the effect of incre~sint capillary size was to raise the

f~equency of vibration corresponding to the lower linit of the stability TI8.pS and to reduce the pocket pressure and load fa:;:: triO OCCUITencc of vib:!:'ation.((,LpperLl~"t)

\'n1el'l the bearings operated in the stable regions, the influence of increasing capillary size was to increase the bearing clearance. Effects of pocket dep~h and shaft speed

were, however, very limited. In addition to observing the existence of isothernal conditions in the bearing sys ten, it \o1as. found

that the pocket pressure was directly proportional to the

applied load and the stiffness value was highest for,bearings

\{ith the s8allest capillary restrictor diaueter of 0.0292 in. Bearings.,operating under heavier loads and highor sU:DPly :9ressures required correspondingly higher pm?er COl1su:r.1ption.

Conparison ~between the' results of the four-pocket and six-pocket test bearings revealed that the farner had ','smaller unst2."ble j~eGioris and higher values of pocket pressure and frequency

of vibration. At consta.nt load, the six-pocket bearin&; operated at a larger clearance and higher flO\'lrate. Although tl1e theory

slightly over-estimated the unstable region, reasonably good

agreement was obtained between the analytical anQ experiuental

results.

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