This dissertation reports a study about vibration analysis of spinning discs in centrifugal atomization, which are known as atomizing discs. Centrifugal atomization is an important process to produce metal powders which have vast applications in powder metallurgy. The main focuses of this study are to establish a dynamic model to investigate the transient vibration of atomizing discs during centrifugal atomization process and evaluate the influence of disc vibration on powder formation. In centrifugal atomization, a lot of studies investigating powder morphology, powder sizes and the flow behaviour of the molten metal on spinning discs have been reported. Vibration of spinning discs in other applications such as CDs, circular saws and turbine rotors has been extensively studied. However, vibration of atomizing discs is lack of investigation and is normally regarded as undesirable because of its negative effects such as possible generation of loud noise and potential contribution to device failure. But, in real practice, the disc vibration definitely has an influence on the molten metal flow, which may benefit the disintegration of molten metal and therefore makes an impact on powder formation in centrifugal atomization. In this thesis, a dynamic model to represent atomizing discs as a spinning Kirchhoff plate subjected to moving weight and moving mass is developed for better understanding of generation and characteristics of vibration of spinning discs in centrifugal atomization. The transient vibration of two cases of atomizing discs with uniform and non-uniform thickness is numerically analyzed. Three stages in disc vibration have been found. The investigation also reveals that the amplitude of the vibration increases greatly when the hydraulic jump takes place in the active area of the disc, which suggests the clamping ratio should be larger than the critical jump radius ratio in atomizing discs. A possible case considering asymmetric loads and air damping which may lead to unstable vibration is also investigated. The mechanisms of powder formation in centrifugal atomization is then investigated on the basis of vibration analysis. A theoretical model to predict powder size is developed and validated by numerical simulations and by experimental comparisons. The correlations between the size of powders generated by atomizing discs and geometry and process parameters in centrifugal atomization, which can provide a guidance for atomizer designs, are proposed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:578047 |
| Date | January 2011 |
| Creators | Deng, Huaxia |
| Publisher | University of Liverpool |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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