The design, development and vibration analysis of a high-speed aerostatic bearing

Frew, David Anthony (Stellenbosch : University of Stellenbosch, 2007-12)

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007.

Thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering Science (Mechanical) at the University of Stellenbosch.

Thesis

ENGLISH ABSTRACT: This thesis examines the development of a specialized, high-speed bearing in order to reduce vibration levels, reduce cutting times and increase blade stability during diamond sawing. The sawing process is required to be smooth, straight and unhindered – a task which is made difficult by the extreme hardness of the diamond as well as unseen grains which could potentially ruin the cut by deflecting the blade. This has an adverse effect on the quality of the cut and the yield obtained from the stone. The current equipment used for diamond sawing is very basic and a significant improvement can be made in terms of quality and sawing speed with the addition of an improved bearing. An aerostatic bearing was designed in order to achieve lower vibration levels and increased spindle speeds. A speed of 18 500 rpm was achieved with this bearing. A numerical model of the bearing was built with the aim of predicting the bearing’s dynamic behaviour. A finite element method (FEM) analysis was done to confirm the rigid body assumption made. Experimental modal analysis (EMA) was done to determine the frequencies and damping ratios of the natural modes of the rotor. The model was seen to predict the frequencies of the modes to within 6%. This model would be used for future design work to ensure that the frequencies of these modes are designed outside of the operating speed range of the aerostatic bearing. Tests were done to compare the vibration levels between the conventional machine and the aerostatic machine during sawing. The overall RMS acceleration was reduced by 70% on the housing of the aerostatic machine and by 50% on the diamond clamp.

AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die ontwikkeling van ‘n gespesialeerde, hoë-spoed laer om vibrasie en sny tye te verminder, asook om lem stabilitiet te verhoog in die diamant sny proses. Die sny proses moet glad, reguit en akkuraat wees, maar dit is nie altyd moontlik nie as gevolg van die variasie in hardheid van die diamant asook die naat in die daimant wat die lem maklik kan laat afwyk. Hierdie het ‘n negative effek op die kwalitiet van die snit. Die konvensionele diamant saag masjien is baie eenvoudig en ‘n groot verbetering in die snit kwalitiet en lemspoed is moontlik as ‘n nuwe laer ontwerp en implementeer kan word. ‘n Aerostatiese laer en rotor is ontwikkel om die vibrasie te verminder en die lemspoed to verhoog. ‘n Lemspoed van 18 500 rpm was verkry met die nuwe laer. ‘n Numeriese model is ontiwkkel om die beweging van die rotor dinamies te bereken. Die Eindige Element Metode (EEM) is gebruik om te bepaal of die aanname dat die rotor rigied is, wel aanvaarbaar is. Eksperimentele Modale Analise (EMA) is gebuik om die natuurlike frekwensies en die dempingsverhoudings vir die rotor te bepaal. Die model het die frekwensies tot binne 6% van die werklike waardes bereken. Hierdie model sal in die toekoms gebruik kan word vir die ontwerp van aerostatiese laers om te verseker dat die natuurlike frekwensies buite die spoedbereik van die aerostatiese masjien val. Toetse is gedoen om die vibrasievlakke van die huidige en die aerostatise masjien te meet tydens die snyproses. Die totale WGK versnelling het met 70% op die huls van die aerostatiese masjien, en met 50% op die diamant dop, verminder.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/4484
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