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By Silvano Morelli, Giovanna Cassani, Renzo Bindi, Antonio Nicola

More than 70 km of main line and service tunnels have been excavated to date for crossing the Apennines between Bologna and Florence. A new design and construction approach, known as Analysis of the Controlled Deformation in Rock and Soils, (ADECO-RS), was adopted to tackle the extreme heterogeneity of the ground and the particular stress-strain conditions. The goal of this system is to obtain constant and predictable full section advance rates, even in very poor geology, with the highest possible level of safety and reliability. The execution of this gigantic project required the mobilization of 21 job-sites, with the concurrent operation of 30 excavation headings. The global production rates confirm the high quality of the design and the high level of industrialization reached during the construction stage, levels not previously obtained in similar conditions, using other approaches such as NATM.

Jan 1, 2003

By G. Bonifazi

In the present work the possibility to utilize the morphometrical and morphological characteristics of an articulate solids system in a slurry flow to monitorate and to control a continuous process is considered. This goal has been reached by mean of an optical system able to acquire, to handle and to process the pictorial information derived by a suitable hardware architecture designed to realize the best lighting, focusing and sampling conditions for the examined flow stream domain. The procedure has been tested using different flow stream slurries coming from different sections of a beneficiation plant. A suitable strategy and a consequent software architecture has been set up in order to assure to the system the necessary speed and the stability to achieve correct on-line measurements and control.

Jan 1, 1994

By S. Mischler, J. Organiscak, S. Klima, C. Seaman

"Researchers at the National Institute for Occupational Safety and Health’s Pittsburgh Mining Research Division (PMRD) performed comparative testing of six hollow cone water sprays from three manufacturers: static swirl chamber sprays from Spraying Systems (BD-3, BD-5) and Steinen-Hahn (SH-3, SH-5), and movable swirl chamber sprays from Repair King (RK-3, RK-5). Water flow testing was completed at three operating pressures (60, 80, and 100 psig) where both sets of sprays (3-series and 5-series) produced similar water flows, deviating less than 8% from the average water flow rate at each pressure. Airflow induction testing was completed at 80 psig using a hot wire anemometer to take air velocity measurements upstream of the spray nozzles. Respirable dust capture efficiency testing was completed in a 14.5-m3 (512-ft3) closed system dust chamber at 80 psig. The dust capture efficiency ranged from 7.2% to 9.9% for the 3-series nozzles, and from 5.3% to 7.1% for the 5-series nozzles. Sprays were also analyzed using a Cloud Aerosol and Precipitation Spectrometer (CAPS), which uses light scattering to count and size the airborne water droplets from each spray. In both cases, Spraying Systems sprays produced the largest mean droplet size, followed by Steinen-Hahn and Repair King sprays, respectively. INTRODUCTION Coal mine worker overexposure to respirable coal dust continues to be a problem in underground coal mining operations in the United States. The U.S. Mine Safety and Health Administration (MSHA) now requires coal mine worker respirable dust exposure to be no more than 1.5 mg/m3 average over the actual working shift (CFR 30-70.100, 2016). Potential overexposure to respirable dust by continuous miner, roof bolter, and shuttle car operators may be prevented if proper safety and health practices are implemented as detailed in the mine’s ventilation plan (CFR 30-75.371, 2016). Water sprays are a necessary component of an underground coal mine ventilation plan. They are important on the continuous mining unit for moving air and removing respirable coal dust from the breathable airstream. MSHA requires underground coal mines to include the number, types, location, orientation, operating pressure, and flow rate of operating water sprays in their mine ventilation plans (CFR 30-75.371, 2016). Water sprays can become clogged, requiring the sprays to be properly checked, maintained, and replaced in order to continue meeting the ventilation requirements described in the mine ventilation plan.In an effort to eliminate the problems with spray clogging, Repair King has developed self-cleaning movable swirl chamber hollow cone water sprays (RK-3, RK-5). The spray’s movable swirl chamber is designed to only open when water pressure is applied to the spray nozzle, preventing the nozzle from clogging. Anti-clogging sprays could improve mine production by reducing the amount of time spent servicing clogged sprays. Also, these sprays could improve health and safety of miners since they would continue to suppress and capture dust and continue to move airflow at the face, while a clogged spray loses this ability until it is cleaned or replaced manually. The objective of this research was to assess the comparability of the Repair King sprays with the most commonly used sprays in underground coal mines using performance criteria. An assessment of the sprays self-cleaning or anti-clogging capability was not conducted."

Jan 1, 2017

By C. J. Greet

Grinding with an electrochemically inert grinding media (i.e., high chrome white iron) shifts the pulp potentials to more oxidising conditions, increases the dissolved oxygen content and reduces the EDTA extractable iron concentration when compared with milling with electrochemically active grinding media (forged steel). These changes in pulp chemistry produce cleaner particle surfaces, reduce reagent consumption, and increase concentrate grades and recoveries. This paper presents a robust laboratory test program that not only demonstrates the changes in the pulp chemistry, but also provide an indication of the magnitude of the metallurgical improvements that are possible. While laboratory studies are interesting, the proof is in the pudding! So, the paper provides an overview of plant trials conducted at several porphyry copper operations around the world: Newmont’s Cadia and Red Chris Operations, as well as Evolution Mining’s Northparkes Operation. These successful plant trials clearly demonstrate that selection of the right grinding media alloy will yield savings in grinding media consumption and reagent consumption as well as increases in revenue through improved copper and gold recoveries. However, many of the porphyry copper mines on the Eastern Pacific are copper-molybdenum deposits. The paper presents laboratory test results for typical copper-molybdenum operations and extrapolate these numbers to what might be expected should a plant trial occur.

Feb 1, 2025

By Robert Mermelstein, Robert W. Kilpper

In a long term toxicology study SPF, F-344 rats were exposed 6 hours/day, 5 days/week for up to 24-months to a special test toner at 0, 1 (low), 4 (medium), and 16 (high) mg/m3, or Ti02 at 5 mg/m3, or Si02 at 1 mg/m3 by the inhalation route. The test toner was composed of about 90% random, high molecular weight acrylic copolymer and 10% high purity, medium color, furnace type, carbon black. It was enriched in fine particles such that the respirable aerosol concentrations (ACGIH) were to 0, 0.35, 1.4 and 5.6 mg/m3. There were no effects of exposure on survival, causes of death, body weight, food consumption or clinical chemistry and hematology parameters. There was no evidence for systemic or upper respiratory system toxicity as all of the changes were restricted to the lungs and associated lymph nodes. The lung tumor frequencies in the control (air and Ti02) and toner exposed groups were comparable. There were no changes at the low exposure level, which is the most relevant in regard to potential human exposures. The lung changes at the high exposure level consisted of decreased alveolar clearance, increased toner retention, increased lung weight, chronic inflammation, decreased pulmonary function and a moderate degree of focal fibrosis in all animals. The changes in the middle exposure level were smaller in magnitude than at the high level, and a very slight degree of fibrosis was found in 20% of the animals. In a follow-up investigation, female F-344 rats were exposed to one of three toner concentrations; control, low (10 mg/m3) or high (40 mg/m3) for 13 weeks followed by five, 13 week observation intervals. At the low exposure level, slight clearance retardation and modest inflammatory changes were observed at the end of exposure. They returned to normal values within six months post-exposure. In contrast, at the high exposure level, increased lung weight, decreased alveolar clearance and a disproportionate increase in toner retention, as well as an inflammatory response, were noted, which persisted throughout the post-exposure interval. While no significant histopathological changes were noted at the end of exposure, a very slight degree of fibrosis was observed in all of the animals in the high exposure group, after 65 weeks of observation. All of the above alterations are ascribable to "lung overloading", a generic response to excessive amounts of any dust retained in the lungs for a prolonged time interval. Published accounts in the toxicology literature document that long-term inhalation of large quantities of even innocuous particles such as Ti02, carbon black, petroleum coke, toner, and other polymeric and insoluble materials has resulted in a spectrum of generically similar pulmonary changes. Scaling of the rat-data, using 1 mg dust/g of lung as a threshold for "lung overloading", normal ventilatory parameters and 300-500 day human retention halftimes project "lung overloading" upon long-term exposure to insoluble respirable dust above 0.2-0.33 mg/m3. Other types of information are consistent with an exposure limit in the range of 0.4-1.0 mg/m3 for respirable dust. The absence of definitive toxicology data in support of the current OSHA respirable nuisance dust limit, coupled with the lack of sound epidemiology data, indicate the need to reexamine the validity of the current nuisance dust health standard.

Jan 1, 1991

By B. C. B. Pretorius

A heat load analysis of the very hot sub-shaft area of Loraine gold mine situated near Welkom, South Africa, showed. that the heat that needed to be removed to give acceptable wet-bulb temperatures at the working faces could not be done by the normal ventilation air alone, but would have to be complemented with extensive refrigeration. The paper outlines the considerations in selecting the cooling system adopted for this shaft.

Jan 1, 1980

By J. Rothschild

I would like to thank the Society of Mining Engineers for inviting me as well as the other distinguished panelists to spend a morning reviewing and discussing the handling and shipping of industrial minerals. I also would like to thank my management, Cometals. Inc. for permitting me to take time out from the daily hectic pace of marketing and trading to share with you some of our experiences and expertise. Cometals, Inc. is a wholly-owned subsidiary of Commercial Metals of Dallas. The transportation and handling costs of industrial minerals frequently are a major component of the value of the goods marketed and, therefore, it is only natural that close attention should be paid to them. Many of the industrial minerals require special handling to assure that the material reaches the consumer without being contaminated or getting wet. I invite you to accompany me through the various steps involved in "delivering the goods" to the consumer.

Jan 1, 1989

By J. S. Stachulak

Inco Limited operates nine underground mines on the rim of the Sudbury Basin. These operations are situated near the City of Sudbury, 589 km (365 miles) west of Montreal, and 363 km (225 miles) north of Toronto. The ores are mined primarily for nickel and copper, and the principal minerals are pentlandite, chalcopyrite, and pyrrhotite. Total ore production from underground is in excess of 51,000 tons per day. The total volume of fresh air supplied to the nine mines is six million cubic feet per minute. There are 50 main fans in operation at these mines, powered by electric motors totalling 11,200 kw (15,000 hp). The trend in metal mining during recent years towards mechanization and high-tonnage production methods has greatly increased ventilation requirements. The flow of air must quickly dilute and carry away diesel exhaust fumes, dust created by mining operations, and the fumes of the explosives used in blasting. Mechanical ventilation is required to obtain the necessary volume and control, as natural ventilation pressures alone are, for the most part, inadequate and unreliable. In the event of a mine fire or other needs, close control of ventilation is essential. There are two unique heating systems presently in operation at Inco: Creighton Natural Heat Ex- changer and Stobie Ice Stopes.

Jan 1, 1989

In conjunction with steady increases in production levels, longwall operators have applied greater quantities of ventilating air and spray water in an effort to control respirable dust and/or methane. Air velocities greater than 7.6 m/s (1500 fpm) have been measured on longwall faces. Operators have expressed concern over the potential entrainment of respirable dust at these high velocities. The greatest likelihood for entraining dust into the high velocity airstream may occur as shields are advanced allowing relatively dry particles to fall from the shield canopy directly into the airstream. Laboratory tests to simulate dust liberation during shield movement were conducted at the Pittsburgh Research Laboratory of NIOSH at velocities ranging from 2.0 to 8.2 m/s (400 to1600 fpm). Airborne dust samples were obtained with personal impactors to quantify the size distribution and concentration of the dust entrained at the various air velocities. Statistically significant increases in both total and respirable dust concentrations were measured as test air velocities were increased.

Jan 1, 2001

By Emily Sarver, Cigdem Keles, Jonathan Gonzalez

The study re-examines respirable coal mine dust samples using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). It finds that SEM tends to overpredict the abundance of dust from rock strata and underpredict coal content, possibly due to coal-mineral microagglomerates (MAGs). The findings suggest that MAGs could be valuable in improving dust controls in mines.

Feb 10, 2022

By A. E. Ketler

Conventional Atmospheric Monitoring System (AMS) installations for monitoring CO, CH4, O2 and air-velocity throughout underground mines are usually relegated to a modest 3-5 mile extent and with data communication speeds confined to a ponderous 1-5K baud range. New US-MSHA and state regulations require fast reporting of unsafe conditions, and the old 20-30 minute updates are no longer acceptable. To communicate farther and faster has always been a problem, because data reliability degenerates with excessive distances and high speeds. Because of this, very large mines often resort to costly optical-fiber media, using expensive OF cables and repeaters to obtain the necessary coverage. This entails high initial cost, as well as high maintenance and downtime costs to repair or replace broken optical fibers. Rel-Tek has pioneered with its DX-Bus communication data highway, which uses inexpensive twisted-pair telemetry cables, which can now communicate well into the 20-mile extent of the largest mines -- normally a brick wall for low-tech AMS systems. This extended range, enables the use of twisted-pair cables and provides a low cost alternative to OF systems. This paper discusses the DX-Bus, and its latest accomplishment, the ?B-LINK,? a unique high-speed communication repeater that maintains the 19.2K-Baud data rate. On-going innovations to our workhorse Millennia-DX computer software have kept pace with this extra speed/distance phenomenon, resulting in a dually-optimized AMS package: both hardware and software. Cost savings are substantial, and at no sacrifice of reliability ? nearly always at 100%. Sensor updates are measured in seconds, not minutes and hours. Twisted pair copper cable is cheap to purchase and install and a breeze to maintain. Rel-Tek uses the B-LINK's wide branching capabilities to enable the AMS to extend 20-miles both far and wide. Actual experience in large US coal mines -- both longwall and continuous mining operations -- confirms the large mine performance. The ventilation and safety benefits to the mining industry are immeasurable.

Jan 1, 2009

By Rainer Alles, Markus Keller

INTRODUCTION For overland conveyors of several kilometres length and as well as wide for conveyors designed for high mass flows, the cost for the conveyor belting share is 40% to 50% of the invested cost 173. The German Standard DIN 22101 is used for calculation and dimensioning of - conveyor belts and belt conveyor components. Developments in rubber technology and conveyor belt design required a revision of the standard released in 1982 121, which was published in August 2001 131. New research results and publications 16-9, 13-15] led to a better understanding of the material behaviour and their influences on conveyor belts. Test and calculation methods have been established to determine the most important parameters which are related to the performance of a conveyor belt line. These parameters are • The running resistance of the idlers • The indentation resistance of the belt • The dynamic splice efficiency • The distribution of belt load in the splices, transition zones and on pulleys. As a result, new rubber compounds with low indentation losses allow the use of reduced friction coefficients and thus lead to reduced power consumption, smaller drives and lower belt tensions. The deeper understanding of the flux of forces within belt splices led to both optimised splice design and optimised rubber compounds which significantly improve the dynamic splice efficiency. Therefore, in accordance with the standard, the benefits of these technologies and the better understanding of material behaviour allow a reduction of belt strength still maintaining sufficient safety factors. Thus engineers are enabled to calculate belt tensions more exactly and users are encouraged to pay more attention to starting and braking techniques. DETERMINATION OF DRIVE FORCE According to the DIN standards the resistance to motion generally has to be determined for each different section of the belt conveyor including upper and lower run separately. The necessary drive power P is calculated as [ ] with v as the conveying speed. The total of all resistances to motion of carry and return run can be determined as [ ] FHo and FHu are the primary resistances consisting of the running resistances of the idlers, the indentation resistance of the belt, the fulling of the conveyed material and the flexure of the belt. While indentation resistance and idler resistance are measurable, they have been deter- mined to be responsible for up to 70% of the primary resistances covered by FH. Further FN is the secondary resistance that covers, for example, the resistance of feeding points and scrapers. Fa are the total slope resistances and Fs is the total of all special resistances, resulting, for example, from belt steering devices. These three resistances should be neglected in the following discussion. For conveyors where a determination of the substantial parts of the resistances to motion is not possible, according to the new DIN standard [31 a determination of the drive power is acceptable by using the fictitious friction factor) [ ] In this formula the index i identifies the individual section of the conveyor, 1 is the length of the section and MR, MG and ML are the related masses of the idlers, the belt and the load in kg/m. The fictitious friction factor f determines the ratio between the overall resistance to motion and the total of moved masses within the

Jan 1, 2004

By Fred Pena

The VERTIMILL has proven itself to be a reliable performer in heavy duty industrial applications. Applications have been extensively used in the mining industry, flue gas desulfurization applications, and industrial minerals field. The machine is a vertically stirred machine that utilizes a screw operating in a grinding media. Grinding media types have ranged from several sizes of steel balls as the most common to pebbles or ceramic media. Mesh-of-grind and final product size are the determining criterion for the selection of the media size used. Product size consists have ranged from very coarse to super-fine grinds of less than 25 microns. Savings in consumption of power, grinding media, and liners when compared to a conventional ball mills, have been realized. Savings in consumption of reagents have also been demonstrated.

Jan 1, 1992

By A. L. Crandell

History The Cortez Mining District has a long history of mining activity dating back to 1862. More recently, Cortez Gold Mines had operated a cyanide leach, counter current decantation (CCD) recovery gold mill from January 1969 to February 1976. This type of plant has been standard in the US for treating higher grade, finely disseminated gold in Carlin type ores. The mill was initially operated from 1969 to 1973 at 1.5 kt/d (1650 stpd) on oxidized ore from the Cortez ore body. In 1973, the mill was operated at 2 kt/d (2200 stpd) on softer, less oxidized, high clay ore from Gold Acres, located 13 km (8 miles) west of Cortez, NV. In February 1976, the oxidized portion of the ore body at Gold Acres was depleted and the mill ceased operations. Successful heap leaching of the lower grade portion of the ores was practiced at both Cortez and Gold Acres to supplement the milling operations. Valuable experience was gained in the operation of these two heap leaching programs (Duncan and Smolik, 1977). The ore heaps at Gold Acres and Cortez were releached with a limited crew from 1976 to 1979. The surge in the price of gold in late 1979 sparked an interest to incorporate new techniques into treating lower grade and less oxidized carbonaceous ores at Cortez. In early 1980, heap leaching was started on low grade oxidized dump material left from the earlier Cortez mining operation. By June of 1980, testwork was completed on the London Extension Dump, a low grade, mildly carbonaceous dump at Gold Acres. It was decided to convert the mill at Cortez from the conventional cyanide leach CCD recovery plant to a carbon-in-leach (CIL) recovery system. In May 1983, ore processing from the Horse Canyon deposit began. The Horse Canyon ore body contains both oxide and carbonaceous ores and is located 22.5 km (14 miles) from the Cortez mill. The Cortez CIL circuit was expanded to handle a blend of oxide and carbonaceous ores from Horse Canyon. Ore selection In the last quarter 1979, gold prices were increasing to a point where restarting the Cortez mill, idled since 1976, appeared imminent. Several previously explored geologic reserves at various stages of development were available as possible sources of feed for the mill. Initial metallurgical testing of dumps and tailings from earlier operations was completed, and previously uneconomic deposits were explored. It was decided to pursue sources of ore with the least lead time to production and those with the least capital cost requirements. A master plan was developed to bring the four profitable ore resources into production. The plan called for: • Heap leaching of waste dumps from the Cortez mining operation; • Restarting the mill to handle the waste dumps from the London

Jan 9, 1986

By Song Jiang, Xianzhi Tan, Minjie Lian

"The ground water heat pump system lades underground hot water which can be heated or cooled by heat exchanger in water source heat pump air conditioner. This system replaces the model of heating of air-conditioning by refrigerator and boiler. In this paper, the formation conditions of hot water energy in Shan Dong are analyzed in order to achieve the purpose of energy conservation and emissions reduction by taking full advantage of water resources such as water pouring and return water of beatification during the productive process of underground metal mine. In order to analyze the issue better, the paper points out some ways and methods for geothermal water often used in underground metal mine. This paper also presents the advantages of the technology of water source heat pump that is applied into underground metal mine. Here is a case study of comprehensive utilization of water source in a certain underground metal mine in Ji Ning. This mine, according to its own actual situation, designs heat pump heat exchange system which is used for indoor heating of buildings and bath for staff. It turns out that the system can save 23% water per year, cut down 3.303 million KW electric energy, and reduce 4160t emission of carbon dioxide. It is concluded that the technology of water source heat pump has broad application prospects in underground metal mine. Therefore, the results show that it is an ideal way to change the present structure of cooling and heating source in metal mine.Introduction In recent years, overuse of fossil fuels has posed a grave threat onto the environment, which makes renewable energy a more important status in energy structure. Development and utilization of renewable energy has become an important direction. Water source heat pump technology is to use solar energy stored in water as cold/heat source to convert energy. Currently, this technology has been widely used in some advanced countries. However, due to facers of implementation technology and component costs, there is still a gap in water source heat pump technology between China and these advanced countries. According to (Blum et al 2011) that after in-depth study, water source heat pump technology has developed rapidly in China recently, and the gap is gradually reduced. Groundwater source heat pump system as a kind of high efficiency, energy-saving and environmentally friendly technology in recent years, more and more get the people's attention. At the same time, its practical application has also been rapid development. Based on (Ni et al 2015) that According to the relevant departments of the prediction, the technology will become the 21st century the most efficient heating and cooling technology."

Jan 1, 2017

By S. K. Nicol

The results of column flotation tests conducted on a bulk sample of ultrafines discarded from the fine coal desliming cyclones at the Riverside coal preparation plant of Theiss Dampier Mitsui Coal Limited are presented. A 9% ash concentrate was obtained from a 51% ash ultrafine feed at 75-80% recovery of combustibles in a single stage of column flotation. From this result it is predicted that installation of column flotation at Riverside would lead to the annual recovery of additional coal worth $US5.1M. The operating conditions for coal and copper column flotation are compared and some differences which may result in a variation in column design are noted.

Jan 1, 1987

By Harrison R. Cooper

The expanding use of digital control in the metallurgical industry is a significant recent development. From 1970 to 1975, approximately forty metallurgical plants throughout the world have adopted automation techniques based on digital controls (see Table 1). Several recent technical reports have described development of digital control systems in concentrator grinding control, 1,2 flotation,3 and smelter operations.4,5

Jan 1, 1975

By Hugh Boyd

Jet pulverization is a relatively new tool for fine grinding. It is not yet in general use in the mining and ore dressing fields, since most of the requirements in these areas have been for relatively coarse particle sizes. As the need for finer grinding increases - because of different ores, new products, and new values being sought - jet pulverization will, increasingly, be properly used.

Jan 1, 1969

By James Watson Baxter

Fluxes are used to promote pyrometallurgical processes that rely on adhesion (soldering or brazing) or fusion (gas and arc welding) to join metallic surfaces. In the adhesive processes, the metal surfaces to be joined are not melted; the join is formed using a filler metal with lower melting point than the base metal. Fusion welding involves use of heat in excess of the melting point of the base metal. The fused joint may be achieved either by simply fusing together metal surfaces brought in contact with each other or by introducing additional molten metal of similar composition to form a fused joint. ADHESIVE PROCESSES--SOLDERING AND BRAZING In order for molten filler metal, solder or braze, to spread in a manner that creates a successful join; the work surfaces on the base metal must be thoroughly cleansed. Fluxes remove stubborn oxide films and other surface contaminants, promote wetting of the work surfaces, add fluidity to the solder or braze, and enhance workability and ease of spreading. Brazing processes involve higher temperatures than those reached in soldering. Brazing fluxes, which must remain active and effective at the higher temperatures, differ from those employed in soldering. Some common fluxes used in adhesive processes are rosin for soldering tin and electrical connections, hydrochloric acid for use in soldering galvanized iron and other zinc surfaces, and borax for brazing. Soldering and brazing are similar processes, the primary difference being the temperature at which the joining operation is carried out. Soldered joints, produced with low-melting-point fillers (solders) that melt and flow at temperature less that 450°C (Althouse et al., 1988) can sustain loads of 1 to 1.7 MPa for extended periods of time (Anon., 1966). Brazing involves the use of filler materials with melting points commonly above 500°C and generally provides stronger joints than those obtained with solder. Both processes require local application of heat to melt and spread the filler so that the molten filler can wet (adhere to) the base metals by alloying and diffusion. Soldering Soldering is a means of joining metals by adhesion using a metallic bonding alloy as the filler, commonly a mixture of lead and tin. However, the adhesion of solder depends more on its ability to be keyed into minute surface irregularities than on alloying. The most familiar application is to provide and secure electrical connections. Soft solders can range from 1 to 70% tin with the remainder mostly lead. However, for general-purpose, soft-solder work, the alloy is commonly 50% lead-50% tin. Higher lead contents provide a wider range in the melting temperature and, for this reason, a 60% lead-40% tin alloy, which yields a mushy mixture, is used for wiped joints in lead sheet and pipe work. Conversely, 40% lead-60% tin alloys are used in soldering tin and other low- melting-point materials for which a narrower range of melting temperature is required. There are numerous other solder compositions such as tin-silver, 95% tin-5% silver and antimony-tin, 95% tin and 5% antimony (Carlin, Jr., 1992). Heat needed to melt and spread the solders is commonly provided by electrically heated, copper-tipped soldering irons or by means of torches; the solder is applied by hand, usually face-fed by means of wire. For wiped joints in plumbing and lead-cable splicing, the solder is manipulated with cloth pads. The molten solder wets the joint surfaces and is drawn, by surface tension, into minute fissures and capillary openings. Other applications involve use of induction heaters and furnaces with pre-shaped solder appropriately placed prior to fluxing and heating. In some processes, the joints are immersed in molten solder. Constituents and Role of Soldering Fluxes: Soldering fluxes generally fall into one of three categories: highly corrosive fluxes, intermediate fluxes, and noncorrosive fluxes. These same categories are sometimes designated inorganic, organic and rosin-based respectively (Althouse et al., 1988). Common constituents of each group are discussed briefly below. Corrosive Fluxes (Inorganic). Work with aluminum, magnesium, stainless steel, high alloy steel, aluminum bronzes, and silicon bronzes is carried out at temperatures in the upper portion of the range for solder operations. Soldering these materials requires use of highly active, corrosive fluxes to remove and prevent the formation of the especially stubborn, hard, oxide films that form on these materials upon exposure to the atmosphere. The corrosive fluxes consist of inorganic acids and salts that are applied either as pastes or dry. They are active at elevated temperatures and, since they remain active after the soldering is completed, must be completely removed. The main constituent of most corrosive fluxes is zinc chloride with a melting temperature well above the solidus temperature of most commercial tin-lead solders. It is made by the action of hydrochloric acid on zinc. When zinc chloride is used alone, un- melted particles of this corrosive salt get caught up in the joint and weaken it. For this reason, other inorganic salts such as ammonium chloride (NH4Cl) or sodium chloride (NaCl) may be added to lower the melting temperature. A mixture of zinc chloride and ammonium chloride is very effective because the excellent oxide reducing properties of ammonium chloride and the protective action of the molten zinc chloride combine to produce a fluxing action superior to that achieved when either is used alone. In addition to zinc chloride, ammonium chloride, and sodium chloride; common con-

Jan 1, 1994

By A. Smithson

It is generally accepted by British mining engineers that coal will continue to be worked by the. advancing or retreating longwall system for the foreseeable future. At the coal face, the emphasis will be on better machine utilization; increased equipment reliability; modular design and more standardization; remote control and monitoring; and a continuing drive to increase productivity and safety. Improvements at the face can be sustained only if there are corresponding improvements in efficiency elsewhere in the mine. Coal handling systems, for example, must be able to accept increased tonnages without creating bottlenecks. As workings move further from the shafts, the time taken to transport men and materials must be kept within reasonable limits. Development drivages must he on schedule to be ready for the planned opening of new faces, and face ends must keep up with faster moving faces.

Jan 8, 1981