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Mathematical models for bit life of polycrystalline diamond compact (PDC) drill bits were developed for drilling small holes in hard abrasive media. Based on the wear-out criterion of an average 0.060 in. (1.5 mm) flank wear land, bit life equations were formulated in three forms: bit life versus rotary speed and feed rate, bit life versus rotary speed and penetration rate, and wear rate versus cutting speed and cutter engagement area. The traditional linear-logarithmic model proved inadequate to describe bit life, whereas the quadratic-logarithmic model provided the best bit life prediction equation. Consequently, it would be possible to predict the optimum economical drilling conditions more accurately by employing a quadratic-logarithmic based bit life equation. The equation demonstrated the ability to predict the bit life precisely under different modes of wear.

CITATION: Votteler, R. G. & Brent, A. C. 2017. A mining perspective on the potential of renewable electricity sources for operations in South Africa Part I—the research approach and internal evaluation process. Journal of the Southern African Institute of Mining and Metallurgy, 117(3):285-297, doi:10.17159/2411-9717/2017/v117n3a10.

The studies on the pyrolysis of polyethylene (PE), polypropylene (PP), and waste PE, PP with the continuous pyrolysis apparatus equipped with the 90 and 20mm pitch twin screw were carried out.There plastics were pyrolyzed to the hydrocarbon mixtures with a wide range of carbon number, under the reaction Condition which temperature and the feed rate of materials and the rotation rate of twin screw were 500-600°C, 1-5kg/hr, and 3-30rpm, respectively.The pyrolysis of PE, PP and these wastes were resembled each other in respect of the pyrolysis products. In any case, the component and the yield of product were greatly influenced by the temperature, but the rotation rate of twin screw and the feed rate of material did not have a pronounced effect on the yield of low molecular weight products.The gaseous products were obtained in 10-80wt% yields, which increases with greatly increasing the temperature, and they were contained 60-80 wt% olefins, and had high calorific value from 15, 000 to 20, 000 kcal/Nm3.The fractions distlling under 200°C were obtained in 10-40wt% yields. The contents of olefins, aromatics and paraffins in these fractions were 50-90wt%, 2-40wt%, and 5-30wt%, respectively. The contents of paraffins in the fractions decrased appro-ximately in propotion to increase in the temperature. In most cases, these fractions contained a large quantity of olefins and not fitted to fuel.The residue distilling at above 200°C were composed of hevay oils and waxes, having 200-350 of mean number molecular weight.

Spider webs must be able to absorb the energy of impacting insects, and similarly, rock support must absorb the energy of ejected rock in rockbursts. A consideration of the properties of spider webs shows that spider silks (threads) are extremely strong, typically three times as strong as common steel. Spiders also construct their webs with yielding mechanisms to enhance their energy-absorbing capability. In this paper, the techniques employed in web construction are compared with those used in rock support in excavations prone to rockbursting. It is shown that the design of rockburst support could benefit from some of the capabilities used by spiders in the construction of their webs.

The paper presents some research work on applying the oxygen enrichment technique to hot stoves that was carried out in one European RFCS project. In the presented work, both theoretical and practi ...

Structural changes during the deformation-induced synthesis of nanocrystalline Fe–10Cr–3Al alloy powder via high-energy ball milling followed by annealing and rapid consolidation by spark plasma sintering were investigated. Reduction in crystallite size was observed during the synthesis, which was associated with the lattice expansion and rise in dislocation density, reflecting the generation of the excess grain boundary interfacial energy and the excess free volume. Subsequent annealing led to the exponential growth of the crystallites with a concomitant drop in the dislocation density. The rapid consolidation of the as-synthesized nanocrystalline alloy powder by the spark plasma sintering, on the other hand, showed only a limited grain growth due to the reduction of processing time for the consolidation by about 95% when compared to annealing at the same temperature.

AbstractDifferent voltammetric methods have been used to investigate the anodization of Cd in NaOH solutions (0.01‐1 M, 25 °C), which is observed to produce a hydrous cadmium hydroxide‐cadmium oxide layer and soluble Cd species.

AbstractDie Abhängigkeit des Ruhepotentials vom Sauerstoffpartialdruck sowie das potentiostatische Verhalten in mit O2 und He gesättigter Lösung werden untersucht.