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| 2. |
- Gao, Ming-Wei
(författare)
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Optimization, scale up and simulation of tumbling mills
- 1990
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Grinding is a fundamental process in the mineral industries. Grinding mills are often very large machines. Their efficiency and energy consumption therefore are of major importance. Problems of large ball mills are discussed in this thesis. The employment of ball mills with a diameter over 5 meters in industry began only a decade ago. The abnormal behaviour of these big mills surely surprised many who had an optimistic view of them. However, the problems have to be overcome since the trend of increasing mill size is still prevailing. An optimization of the grinding process deals with a large number of co-operating parameters. Statistical approach provides a powerful tool for doing this. Its application on the simultaneous study of four important grinding parameters is described in this thesis. In the last part of the thesis a study on the population balance model is presented. Tremendous research has been carried out on this model. However, its application for designing grinding mills still requires more effort on the understanding of the selection and breakage functions. Heterogeneous materials were selected to be the experimental samples in this thesis. It is the author's opinion that the future of the population balance model depends on its ability to survive the applications on scaling-up fullscale mills for grinding those complex materials.:
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| 3. |
- Gao, Ming-Wei, et al.
(författare)
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Simulation of batch grinding of iron ore
- 1990
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Ingår i: Mineral Processing and Extractive Metallurgy. - 0371-9553 .- 1743-2855. ; 99, s. 142-146
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Tidskriftsartikel (refereegranskat)abstract
- A batch-grinding process treating a natural magnetite ore was simulated by a population-balance model. Different methods of determining selection and breakage functions for the ore were investigated. Grinding tests were performed with seven monosize fractions in a pilot-scale ball-mill. The back-calculated selection function was compared with experimentally measured values of the selection function, S, and the breakage functions so determined were checked against the results of the simulation. It appears that if the breakage functions of a material are not normalizable, it is necessary to carry out a sufficient number of monosize grinding tests to allow reliable selection and breakage functions to be estimated. Graphs. 8 ref.--AA
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| 4. |
- Gao, Ming-Wei, et al.
(författare)
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Study on the effect of parameters in stirred ball milling
- 1993
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Ingår i: International Journal of Mineral Processing. - 0301-7516 .- 1879-3525. ; 37:1, s. 45-59
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Tidskriftsartikel (refereegranskat)abstract
- Ultra-fine grinding involves a large number of parameters in its operation. In this paper, four important parameters of the Drais stirred ball mill, i.e., the bead density, slurry density, mill speed, and the effect of dispersant were selected for investigation. The experimental work was based on a factorial design and 27 milling tests were conducted. It is found that the bead density has an optimum value of 3.7 g/cc in this investigation. A lower slurry density and a smaller amount of dispersant appear to be better conditions. The mill speed should be as high as possible within the speed limit tested in this work for the best process efficiency.
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| 6. |
- Larker, Rickard, et al.
(författare)
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AEM investigation of ceramic/incology 909 diffusional reactions after joining by HIP
- 1994
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 29:16, s. 4404-4414
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion bonding by hot isostatic pressing (HIP) was performed between Incoloy 909 and five different ceramics. Two of the ceramics were composites made from powder mixtures of Si3N4 and either 60 vol% TiN or 50 vol% TiB2, while three were monolithic materials, namely Si3N4 with 2.5 wt% Y2O3 as a sintering additive, Si3N4 without additives, and Si2 N2O without additives. A diffusion couple geometry was developed to facilitate the preparation of thin-foil specimens for examination by analytical electron microscopy (AEM). Diffusion bonding was performed by HIP at 927°C (1200K) and 200 MPa for 4 h. The formation of reaction layers was very limited, being less than 1 μm in total layer thickness. Two reaction products were found by AEM; a continuous, very thin, (≤100 nm) layer of fine TiN crystals at the initial ceramic/metal interface, and larger grains extending about 100–500 nm into the superalloy and forming a semi-continuous layer of a G-phase suicide containing mainly nickel, silicon and niobium.
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| 7. |
- Larker, Richard, et al.
(författare)
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Diffusion bonding of Si3N4/TiN and Si3N4/TiB2 composites to Incoloy 909
- 1992
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Ingår i: 4th International Symposium on Ceramic Materials and Components for Engines. - London : Elsevier. - 1851667768 ; , s. 340-347
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Konferensbidrag (refereegranskat)abstract
- Hot isostatic pressed (HIPed) mixtures of Si3N4/60%TiN and Si3N4 /50%TiB2 were joined to Incoloy 909 (42%Fe, 38%Ni, 12.9%Cr, 4.7%Nb, 1.5%Ti, 0.4%Si) by hot isostatic pressing at 927 deg.C and 200 MPa. Microstructure (TEM and STEM) and diffusion profiles are reported and discussed. The work is relevant to the use of graded ceramics to reduce thermomechanical stresses in silicon nitride /superalloy joints
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| 8. |
- Li, Wei-Bin, et al.
(författare)
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Cause and effect of non-uniform densification during hot isostatic pressing
- 1992
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Ingår i: Powder Metallurgy. - : Informa UK Limited. - 0032-5899 .- 1743-2901. ; 35:1, s. 47-52
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Tidskriftsartikel (refereegranskat)abstract
- Hot isostatic pressing (hipping) is an extremely efficient way of densifying ceramic and high alloy metallic powders, or for healing porosity in castings. However, depending on the parameters of pressure, temperature, rate of heating, and sample size, hipping can result in a non-uniform mode of densification. This mainly occurs when a rapidly heated sample, or a sample of large dimensions, densifies quickly at the surface to produce, if effect, a fully dense, hard shell. It is shown that there can be a number of negative factors resulting from this, including reduced rates of densification, sample sample shape change, non-uniform shrinkage, and the development of residual stresses in the sample. Criteria for predicting whether or not non-uniform densification will occur are presented and evaluated. Steel and Cu are discussed.
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| 9. |
- Li, Wei-Bin, et al.
(författare)
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Instantaneous and residual stresses developed in hot isostatic pressing of metals and ceramics
- 1991
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Ingår i: Hot isostatic pressing. - : ASM International. ; , s. 47-54
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Konferensbidrag (refereegranskat)abstract
- Hot isostatic pressing of metallic or ceramic porous preforms occurs by the densification of a shell at the surface of the preform, which then thickens until the whole sample is fully densified. It is shown that the development of such a dense shell can reduce the pressure acting to densify the remaining porosity. Furthermore, this pressure difference can lead to anisotropic creep of the shell, and this may be a contributory cause of shape change of samples during HIPing. The stresses occurring during cooling of the sample and the residual stresses, are calculated as a function of various input parameters. It is found that the cooling stresses can be particularly large and tensile, and may be the cause of surface cracking observed in certain HIPed ceramic samples.
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| 10. |
- Meijer, J., et al.
(författare)
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Phase transformations by high-intensity sub-microsecond laser pulses.
- 1992
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Ingår i: Proceedings of the laser materials processing symposium, ICALEO '92. - Orlando, Fla : Laser institute of America. - 0912035498 ; , s. 228-236
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Konferensbidrag (refereegranskat)abstract
- In certain alloys, the 'laser shocking' causes work hardening, an increase in dislocation density and phase transformations. Of the materials tested, and austenitic Hadfield manganese-alloyed steel target was found to have the strongest tendency for a martensitic phase transformation. In contrast with conventional transformation hardening, there is no tempering in the case of repeated application. Whilst most material is vaporized, some surface melting will occur. The rate of re-solidification of the molten material is such that an almost completely amorphous structure results. The martensitic transformation has been confirmed by using optical, scanning and transmission electron microscopy, OM, SEM and TEM/STEM. Two different lasers, a Q-switched Ruby and a Q-switched Nd:YAG were used for the experiments. Calculations of impact/momentum, peak pressure and peak temperature were performed using the finite difference method. The model used for simulating the process has been proved to be useful in understanding the transformation mechanism.
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