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By M. K. Pathak, A. K. Mukhopadhyay, D. C. Panigrahi

Changes in machinery operating and design parameters often result in unexpected vibrations or changes in the vibration patterns. Vibration in a system is an undesirable element that can cause machinery distress. Potential damage can be prevented by identifying the vibration level that is due to the changed operational parameters. This is necessary for the safe and reliable operation of plant equipment. This paper presents a documented study on vibration events that resulted from alterations in operating and design parameters in a mine ventilation fan and analyzes the causes by defining the sequence of events that led to its performance deficiency. This paper is based on experimental effort to study the vibration behavior of a ventilation fan under varying operating conditions.

Jan 1, 1999

By G. A. Dawe, E. G. Kelly

Because of the nature of the breakage in the Barmac vertical spindle impactor, the 80% reduction ratio is very small, so that when an energy efficiency is calculated from Bond's method, it appears to be very low. However, the product size distribution contains a high proportion of fines. It is argued that the production of these fines accounts for the high energy consumption, and Bond's method is modified to account for this, by considering the crusher to be, effectively, a number of smaller crushers in parallel, each having a different reduction ratio.

Jan 1, 1990

By Frank F. Roxborough

The paper presents a brief account of the principal findings and an assessment of the practical value of a substantial international research effort into the mechanical excavation of rock that has been in progress over the past 30 years. This assessment together with an appreciation of the emerging trends in mechanical excavation suggests what are likely to be profitable lines of future inquiry.

Jan 1, 1985

By Rolando V. Cuaño

For geostatistical applications, heterogeneous spatial phenomena are better modeled as mixtures of populations. However, the modeling of the constituent populations can become complex. The alternative mixture model offers a simplified approach to the w modeling problem. The model is applied and tested on the Walker Lake data set. Compared to the univariate ordinary kriging model, the alternative model generates less biased block estimates.

Jan 1, 1996

By T. C. Eisele

Previous work by the authors has shown that the performance of a flotation column can be improved by the use of horizontal baffles. These baffles prevent axial mixing and also reduce "churning" of the froth by breaking up or preventing the formation of large air bubbles. In this paper, results from tracer experiments are presented that show the effects of horizontal baffles on the reproducibility and stability of the column operation. The baffles prevent random disturbances, such as unusually large air bubbles and turbulence, from rapidly propagating along the height of the column. Because these factors are responsible for much of the variations in column performance between tests, the result is that the horizontal baffles make the column performance more reproducible, with fewer short-term variations.

Jan 1, 1999

By C. A. Wiggins

The new Niagara Falls Intake Tunnel, mined in the highly fractured Lockport Dolomite, encountered prolific inflows of water contained in rock seams directly linked to the Niagara River. These inflows were pressurized and, more significantly, contained high concentrations of dissolved H2S gas. The contractors attempts to control the water/gas inflows included cement and chemical grouting from inside the tunnel. Ultimately, improving the rate of air exchange in the tunnel by increasing the fan capacity, in conjunction with a pattern down-hole pre-grouting program along the tunnel alignment allowed the contractor to control the concentration of H2S gas and complete the tunnel.

Jan 1, 1997

By C. Sun

In this study, numerical simulations of yield pillars employing the finite-element method with a time-dependent Drucker-Prager material model are conducted. The stress¬control mechanism of yield pillars on weak floor strata is studied. The development of a pillar yield zone, the distribution of pillar stress and the development of a failure zone in the weak floor strata are investigated. The study indicates that a properly selected yield pillar size may significantly reduce the peak stress induced in the weak floor strata and may effectively control the development of a failure zone in the floor.

Jan 1, 2000

By Mengxiong Guo, Xuxin Shao, Yong Bao

In the paper, the adsorption properties of dissolved ions on the surface of collophane and dolomite are studied using zeta potential measurement, ESCA and UV adsorption spectrum both in distilled water and in the supernatant of each other. The effect of dissolved ions on the flotation separation of collophane and dolomite under SCO depressant and oleate is discussed on the basis of above analyses.

Jan 1, 1993

By M. M. Hajdasinski

In his recent paper, Torries (1998a) came to the defense of the much-criticized internal rate of return (IRR) as a project evaluation and ranking criterion. Torries also offered his own approach to the IRR-based project ranking, which he believes to be a more practical alternative to the conventional incremental-ranking approach, which Torries considers to be misleading. In an earlier paper (Hajdasinski, 2000), the author demonstrated that Torries' arguments vindicating the IRR concept are invalid. This paper provides logical and numerical evidence that the same is also true with regard to Torries' IRR based project-ranking approach.

Jan 1, 2000

By W. K. Tolley, D. G. Kotlyar

Silver is an economically important component of many complex, massive sulfide ores. The beneficiation of this type of ore is now almost entirely accomplished by flotation. Silver recovery is often low, and little is known about the flotation behavior of the silver-bearing minerals. Floatability studies were conducted using silver-bearing tetrahedrite and lead-zinc ore. The effects of xanthate-collector concentration, conditioning time, potentiostatic control of the mineral potential and control of the pH on mineral floatability were evaluated. The floatability of the silver-bearing minerals was shown to depend on collector concentration and mineral potential. The effect of controlling the mineral potential during the flotation process is discussed.

Jan 1, 1996

By John W. Conn, Harry C. Verakis

An explosion in an underground coal mine can have a devastating effect on the main fans used to provide mechanical ventilation. The Code of Federal Regulations, Title 30, Part 75.310 (CFR, 1992), specifies that each main mine fan shall be offset by at least 15 feet (4.6 m) from the nearest side of the mine opening unless an alternative method of protecting the fan is approved in the ventilation plan. Also, each main mine fan shall be protected by one or more weak walls or explosion doors. This paper presents venting and fan configuration designs which provide a comparable degree of safety for explosion protection. Design flexibility is enhanced and a means for consistency in safety judgements is afforded.

Jan 1, 1993

The concept of classification in wet, closed circuit ball milling is expanded beyond the performance of the classifying equipment to include all aspects of the fines removal system of the grinding circuit. Design and operating parameters that effect fines removal are identified and discussed, and a quantitative index for circuit classification effectiveness is presented.

Jan 1, 1987

By P. R. Hervey, J. W. Foise

Quartz is the second most widely used electronic material, with approximately 3,000 t (3,300 st) of single crystals used each year. Most of the quartz used in electronics is synthetic and is manufactured using a technique called hydrothermal growth. This paper reviews the basics of hydrothermal growth, the feedstocks used for these crystals and the challenges to improving the growth process. This paper also reviews the processing of these crystals, the markets and applications where they are used, and the global outlook for these markets.

Jan 1, 2002

By Mark W. Springett

The sampling of precious metal deposits entails inherent problems due to the low mineral abundances, high mineral specific gravities, skewed grade distributions and wide ranges of mineral particle sizes. Sampling practices and precautions are discussed with particular attention to each of the tripartite stages of sampling - sample acquisition, sample preparation and sample assaying. Practical examples of approaches to the sampling problem are given and some examples of significant sources of error are provided from gold and silver deposits in North America.

Jan 1, 1992

By M. Cai

Transformation of the measured borehole deformations induced by stress relief relies on the traditional assumption that the rock is continuous and homogeneous. Systematic and quantitative tests were carried out to check the performance of devices commonly used for measuring borehole deformations within different types of discontinuous rock conditions. Test results provide a reliable basis for considering the influence of discontinuities on in situ stress measurement and for choosing the best measuring device for a given rock type and condition.

Jan 1, 1998

By N. M. Grant, W. G. Prast

Jamaica has extensive deposits of marble, gypsum, and limestone, offering prospects for commercial sales to nearby US markets, notably the Gulf Coast and Southeast. Stare-owned and private Jamaican industrial minerals producers have made limited sales to date but expect to increase exports during the balance of the 1980s. Restraints include Jamaican government controls on access to essential foreign exchange for new capital investments and distribution of profits. Jamaican efforts to identify market opportunities in the US are reviewed, and the outlook for further exports of carbonates is discussed.

Jan 1, 1987

By P. Lausch, R. A. Mercer, J. F. Archibald

An innovative, polyurethane-based, spray on rock-lining material, designated Mineguard™ by its developers, is being manufactured to provide rapidly deployable area support coverage for specific use in underground hardrock mines. This form of surface-coating agent is intended to replace both shotcrete and the screen component of bolt-and-screen support systems. Due to the rapid rate of application, ease of installation and ability to achieve a 90% cure within seconds of application, Mineguard™ has considerable potential for use in mining and excavation operations that require a rapid rate of advance and a high degree of automation.

Jan 1, 1996

By R. A. Haney

The Mine Safety and Health Administration (MSHA) has conducted studies both in coal and non-coal mines to evaluate methods for sampling diesel particulates in underground mines. The agency is investigating size separation techniques to distinguish between diesel particulate and respirable coal mine dust. Additionally, ashing techniques have been used to distinguish diesel particulate from mineral dust in metal and non-metal mines. As part of these studies, personal exposures to diesel particulate for various mining occupations have been measured. This paper describes the measurement techniques and summarizes the exposure levels for various underground mining operations.

Jan 1, 1993

By R. K. Mehta, C. W. Schultz, R. R. Mallepali

Stirred ball mill feeds used for ultrafine grinding applications require a fine size separation step to avoid overgrinding. This paper presents the selectivity curves obtained for oil shale and complex sulfide ore using a 460-mesh (30-µm) Derrick vibrating screen. The selectivity curves generated from the experimental data show increasing selectivity with larger size for the oil shale but not for the sulfide ore. These unusual selectivity curves are similar to the mechanical air separator, fishhook selectivity curves described by Luckie and Austin. A two-stage, in series, classification model describing the fishhook selectivity curve has been used in proposing the classification mechanism for fine vibrating screens when a heterogeneous, multicomponent sulfide ore undergoes size separation.

Jan 1, 1994

By J. T. Gepford, K. A. Prisbrey, T. Scott, M. Spangler

Using neural networks for plant control is challenging. The objective was to show how to make a neural network effective, even with noise, lag times, and unmeasured disturbances in the plant. The procedure was to evaluate the neural network in a laboratory flotation vision system and in a plant refractory gold autoclave system. Although the resulting neural network easily conquered simple laboratory data, the noisy plant data was much more difficult, and adaptive linear models were equally effective. We concluded that the neural network needs support by combining it with other tools found in the best control packages.

Jan 1, 2000