A review of the specific performance characteristics of hard rock tunnel boring machines
- Authors: O'Connell, G. J.
- Date: 2015-09-09
- Subjects: Tunneling , Drilling and boring machinery
- Type: Thesis
- Identifier: uj:14078 , http://hdl.handle.net/10210/14510
- Description: M.Ing. , This dissertation provides a review of the most notable papers published with regard to the specific performance characteristics of Tunnel Boring Machines (TBM's) during the past twenty years. It is a literature study of a Bibliography of 57 publications, which were screened from an original list of 970 documents ...
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Mechanosynthesis of reaction products between tungsten carbide cobalt drill bits and hematite ore and their characterization
- Authors: Banganayi, Clever
- Date: 2012-08-16
- Subjects: Bits (Drilling and boring) , Milling machinery , Drilling and boring machinery
- Type: Thesis
- Identifier: uj:2586 , http://hdl.handle.net/10210/6036
- Description: M.Tech. , Mechanical alloying/mechanical grinding by means of high energy ball milling has been considered as a promising materials processing technique to synthesise materials. In this study it has been employed in an attempt to simulate the wear products formed during the drilling of hematite ore by WC-Co drill bits, so as to try and find an explanation for the rapid wear of these drill bits during the drilling of hematite ore. A PM400/2 high energy ball has been used to mill individual powders of hematite, WC and a mixture of WC-hematite, hematite-cobalt and WC-Cohematite powders. In the high energy ball milling of hematite alone particle size reduction of up to less than 10 nm was observed by both XRD and Mossbauer Spectroscopy (MS), no phase transformation was observed as a result of milling the powder up to - 30 hours. The high energy ball milling of WC also showed no new phases but particle size reduction and XRD peak size broadening. Mechanical alloying of WC-hematite revealed a more effective grinding compared to hematite alone. The hematite particles were reduced to nanosized particles as in the previous systems but the fraction of particles at nanosize level increased drastically from 59 % in the hematite alone system to 100 % in the WC- hematite system, after 30 hours of milling as observed from the increase in the abundance of the central supper paramagnetic doublet in the Mossbauer Spectra. A new phase was observed from both XRD and MS in the cobalt-hematite system and this phase was identified as CoFe 2O4 . An increase in the composition of cobalt from 20 %-50 % in the mixture showed an in increase in the percentage abundance of the CoFe 2O4 phase (38 %-55 % respectively) with increase in milling time. The formation of this phase might be one of the causes of the rapid wear of WC-Co drill bits during the drilling of hematite ores. Particle size reduction to nanosized particles has also been observed in the cobalt-hematite system. Mechanical alloying of WC-Co-hematite did not reveal any new phases in the samples milled for 30 hours and analysed by XRD. Peak size broadening was observed with increase in milling time. The MS results showed an increase in the intensity of the central doublet with milling time. The results also show decrease in the magnetic field of the hematite with increase in milling time. This has been associated to reduction in particle size with increase in milling time
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