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A Study of Factors Affecting the Particle Size for Water Atomised Metal Powders
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The production of metal powders by water atomisation is a well established process, which can be used to produce a wide range of particle sizes. A careful control of the particle size distribution is necessary, to atomise powders with a high quality and at a low production cost. Therefore, it is necessary to have a substantial knowledge of the relation between operational parameters and the particle size, to be able to produce water atomised metal powders with consistent and high yields.

The main purpose with this thesis was to increase the knowledge about factors which affect the mass median particle size (d50) for water atomised metal powders. The specific objectives with the study were to develop a theoretical d50 model and to investigate the relation between the particle size and the physical properties of the liquid metal.

Pilot scale experiments for liquid iron showed that alloy additions of carbon and sulphur decreased the d50 value, at a maintained liquid steel temperature before atomisation. Moreover, it was indicated that the reduced particle size at increased %C and %S contents may be related to a decreased viscosity and surface tension of the liquid metal, respectively. An alternative explanation could be that raised superheats at increased carbon contents increased the total available time for atomisation, which may have contributed to a reduction of the d50 value.

The theoretical d50 model developed in this work showed a very good correlation to the current experimental data. The model considers the influence of surface tension, viscosity, melt stream diameter, water pressure, water jet angle and water to metal ratio. This model was further used to analyse how the d50 value was influenced by the viscosity and the surface tension. A reduced viscosity from 4∙9 to 2∙1 mPa s decreased the d50 value with 33%. In addition, the particle size was estimated to decrease with 21% by decreasing the surface tension from 1840 to 900 mN m-1.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , 31 p.
Keyword [en]
water atomisation, metal powders, particle size, modelling, viscosity, surface tension
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-94533ISBN: 978-91-7501-395-4 (print)OAI: oai:DiVA.org:kth-94533DiVA: diva2:525925
Presentation
2012-06-08, MAVES Konferensrum, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
Q 20120529Available from: 2012-05-29 Created: 2012-05-09 Last updated: 2012-05-29Bibliographically approved
List of papers
1. Influence of liquid metal properties for water atomised metal powders
Open this publication in new window or tab >>Influence of liquid metal properties for water atomised metal powders
2012 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The main focus of the present study was the influence of liquid metal properties on the particle size during water atomisation. Experiments for liquid iron showed that alloy additions of carbon and sulphur decreased the particle size. Moreover, it was indicated that the reduced d50 value at increased %C and %S may be related to a decreased viscosity and surface tension respectively. An alternative mechanism could be that raised superheats at increased carbon contents increased the total available time for atomisation. This may also have decreased the particle size. The influence of surface tension and viscosity on the d50 value was further analysed with a theoretical d50 model proposed in a previous work. A reduced viscosity from 4∙9 to 2∙1 mPa s decreased the d50 value with 33%. In addition, the particle size was estimated to decrease with 21% by decreasing the surface tension from 1840 to 900 mN m-1.

Publisher
37 p.
Keyword
water atomisation, metal powders, particle size, modelling, viscosity, surface tension
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-94531 (URN)
Note
QS 2012Available from: 2012-05-09 Created: 2012-05-09 Last updated: 2012-05-29Bibliographically approved
2. Prediction of particle size for water atomised metal powders: parameter study
Open this publication in new window or tab >>Prediction of particle size for water atomised metal powders: parameter study
2012 (English)In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 55, no 1, 45-53 p.Article in journal (Refereed) Published
Abstract [en]

This work aims to investigate how some significant atomising parameters influence the mass median particle size d50 of water atomised metal powders. More specifically, these were water pressure, melt flowrate, water jet angle, liquid metal viscosity and surface tension. Existing models for the prediction of d50 during water atomisation were reviewed. The selected models were fitted and compared with atomising experiments of liquid iron containing 0.5–4.4%C. Experimental results and model calculations were used in a parameter study to investigate how the different parameters influenced d50. The effect on d50 was large for the water pressure, medium for the viscosity and low for the melt flowrate and surface tension. Model calculations indicate that the jet angle has a large effect on d50, which should be verified by additional studies. The model proposed by Bergquist (B. Bergquist: Powder Metall., 1999, 42, 331–343) showed the best agreement with the current experimental data.

Keyword
Powder metallurgy, Modelling, Water atomisation, Metal powder, Particle size
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-53622 (URN)10.1179/1743290111Y.0000000016 (DOI)000302546300008 ()
Note
QC 20120528Available from: 2011-12-29 Created: 2011-12-29 Last updated: 2017-12-08Bibliographically approved

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