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By Eric Sitorus, Septian Prahastudhi, Roy William, Wieda Azani

In July 2020, massive slope failure occurred in the southeast corner Grasberg open pit. This was the final episode in the breakthrough of Production Block 2 South (PB2S) of the Grasberg Block Cave to connect to the surface. This breakthrough had been rapidly evolving during the first half of 2020 and occurred as expected with no adverse impacts to safety or operations. To manage and safeguard the exposure to the workforce and operations, numerous hazards were identified and anticipated. The failure of the sill pillar between the open pit and PB2S cave was identified as the main area of interest and was closely watched during the failure process. This paper reviews the systematic approach developed to convert monitoring data into information around the collapse of the GBC PB2S cave sill pillar. The data that was interpreted consisted of micro-seismic, piezometric, ground-based radar and observational inspections. Geological structures on the boundary of the PB2S cave were clearly involved in the breakthrough process. As the cave propagation reached these structures and triggered instability, the resulting acceleration and breakdown were clearly shown by IBIS radar units associated with high movement in the slope. The focus of this paper is on the evolution of changes seen in the micro-seismic data and how it was used to understand the rapidly changing conditions of the sill pillar. The seismic parameters evaluated were event distribution, Es/Ep value, and the seismic moment tensor inversion. The changes of breakthrough indication seen in these parameters were substantiated by Shear Wave Splitting (SWS) analysis that showed a close correlation with the fractured zone above the PB2S cave as indicated by the increasing anisotropy.

Jan 1, 2022

By R P. Bewick

Many future and current block and panel caves extract ore from veined rock masses. These rock masses are composed of open joints forming blocks or rock with healed networks of veinlets. These two types of discontinuities pose a challenge for rock mass characterisation and classification due to difficulties in distinguishing actually open joints from healed but weak veins when diamond core drilling and excavation blasting practices disturb the rock mass. The inability of separating characteristics of open joints and healed veins has often resulted in an underestimation of the rock mass quality and as a consequence led to inappropriate assessments of rock mass response to mining (ie rock mass behaviour) and consequently deficient excavation stability assessments and ground support designs. In this paper, guidelines are provided to improve the characterisation and classification of veined rock masses. It is shown how veined rock masses can be mischaracterised resulting in often incorrect forecasting of rock mass behaviour. Following this, the classification of veined rock masses is examined. It is shown how the primary classification systems (ie Q – Barton, Lien and Lunde, 1974; rock mass rating (RMR) – Bieniawski, 1976) may not lead to reliable ratings in veined rock masses if care is not taken to differentiate between open joints and veins of varying strength. Examples are provided to illustrate how the Q and RMR systems are insensitive to veining. Finally, an example of characterising a veined rock mass for design purposes is presented.CITATION:Bewick, R P and Kaiser, P K, 2016. Characterisation and classification of veined rocks for rock mass behaviour assessment, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 825–834 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By Gray N. B

The need to improve existing metallurgical processes and to develop new processes to meet the economic challenges that lie ahead requires the application of the tools of process analysis viz. mathematical models, physical models, pilot plants, laboratory measurements and plant tests. Examples of the application of these techniques to processes are described in this paper. Several of these techniques, combined with basic knowledge, are necessary to make improvements and for existing processes this always involves plant measurements. Also because metallurgical processes include extraction, refining, alloying, casting, mechanical working and heat treatment, an interdisciplinary approach to research and development is essential. This paper argues that metallurgical engineering is a discipline that is uniquely able to encompass the broad spectrum of chemical- and physical-metallurgy processes and is therefore essential to the health of the metallurgical industry.Regrettably many metallurgical engineering departments are not offering courses on process analysis, control, optimization, etc so necessary to meet modern industrial challenges.

Jan 1, 1985

By Glenn C. Waterman

Richard Strong (Oliver Iron Mining Div., U. S. Steel Corp.)—Mr. Waterman states (p. 59, Trans., January 1954): "Core-sludge combining factors have been calculaied for any combination of core-sludge recovery on the basis of several logical assumptions: 1—The sludge sample loses reliability geometrically as sludge recovery drops. 2—The sludge sample should not be used if the percentage of sludge return is less than the percentage of core recovered. 3—A core sample should receive a weighting at least equal to the percentage of core recovery." Assumptions 1 and 2 seem justified at Chuquicamata and most geologists would agree to the validity of assumption 3. However, contrary to the statement quoted above, the core sample does not in general receive a weighting at least equal to the percentage of core recovery when the Chuquicamata methgd is used. Furthermore, the basic Chuquicamata method is identical to the Longyear or relative volume core-sludge assay combining method. Finally, the Chuquicamata method does not, in its present form, reflect true geometric loss in sludge sample reliability according to the relationship L = AR (N-1) The basic equations representing the two steps of the Chuquicamata method can be combined algebraically as follows (using the symbology of the original article except as noted): Vol A + B Assay 2 = ASA = Assay 1 Vol A VolB Core Assay [I] Vol A CA.F + ASA (100 —F) Combined grade =[21 100 Pct where F and (100 — F) are the core and adjusted sludge assay factors from Fig. 3. Substituting Eqs. 1 and 2 and collecting terms Combined grade = Vol B Vol A + B CAF (100—-F) + Assay 1 (100-F) Vol A Vol A 100 pct Eq. 3 is a unified and general statement of the Chuquicamata method. The true core factor includes not only the factor F from Fig. 3 but also the quantity VolB ------------- (100 — F), which is implicit in the value of Vol A the adjusted sludge assay. This quantity is real and positive for all values of F and core recovery less than 100. Therefore the true core factor is always less than F except when F is equal to 100. If sludge recovery is 100 pct, Eq. 3 can be further simplified as follows: Let F = percentage of core recovered. Let Vol A = Vdh (100 Pct — Pct CR) where Vdh is the total volume of the sampled interval and let Vol B = (Vdh — Vc.) Pct CR where V, is the core volume in the sampled interval at 100 pct core recovery. Then combined grade = Vo V. CA Pct CR- + Assay 1, 100 Pct — Pct CR Vdh Vdh [4] 100 Pct Eq. 4 shows that when sludge recovery is 100 pct the laboratory sludge assay receives significant weight in the Chuquicamata method, even at 100 pct core recovery. The maximum weight assigned to the laboratory sludge assay depends on drillhole size, as follows: Eq. 4, with suitable changes in symbology, is identical to Royce's formula 8,' which is a statement of the Longyear or relative volume method of combining core and sludge assays. If Mr. Waterman's assumption 3 is of paramount concern to the geologist, the Royce method (for core recoveries of 60 pct and above) or a method employing the percentage of core recovered as a core weighting factor are the only recognized methods known to the writer which achieve the desired result. A modification of the latter method embodying Mr. Waterman's assumptions 1 and 2 would result from applying the factors from Fig. 3 directly to the laboratory core and sludge assays.

Jan 1, 1956

By D. B. Dow

The study of oil production methods with reference to the amount of oil originally pressent in the oil-bearing, formations has developed the fact that-ordinary methods-of production remove only a part of the oil actually present. In fact, it is generally realized that when a field is abandoned more oil remains in the sand than has ever been removed. As a consequence of this realization, the petroleum engineer has devoted considerable tine in recent years in devising methods for increasing the percentage of recovery. His studies have indicated that in most cases the total production of a field is dependent upon the available gas rather than upon the available oil. Mien the gas in the sand is exhausted, oil production ceases even though there may be enormous quantities of oil remaining unrecovered. Consequently, any method of conserving the gas or increasing the supply of gas will increase the ultimate recovery from a field. The practice of producing oil under vacuum increases the effectiveness of the gas remaining in the sand, as well as furnishing more gas by evaporating the light fractions of the crude. Pumping ' compressed gas or air down selected wells of a lease has been found to increase the production of oil from the surrounding wells. Studies of oil and gas ratios have indicated that much of the available gas has been wasted as far as its effectiveness on oil production is concerned. his has led to the development of "stop cocking"3 and the practice of producing under back pressure3, which methods aim, to obtain more effective work from the gas with reference to the amount of oil delivered to the well.

Jan 1, 1926

By L. Xu

Since the establishment of the standard dust concentration of 2 mg/m3, a strong effort has been made by mining engineers and researchers to provide better dust control equipment and procedures for underground coal mines. Particular areas of success have been control of dust generation by better coal-cutting strategy, better design of water sprays for dust suppression and air movement, use of scrubbers, and improved design of face ventilation systems. A drastic improvement occurred over time such that the average dust concentrations for continuous miner operators dropped from 6.5 mg/m3 in 1968 to 1.3 mg/m3 in 1980 and for auger, cutter, longwall, and roof bolter occupations from 2.7 mg/m3 in 1973 to 1.6 mg/m3 in 1980 (Niewiadomsky, 1983).

Jan 1, 1990

By L. T. Loe, A. S. Norsk, Mo i. Rana

High production rate and good stability demand the optimization of all phases of electric pig iron smelting. This is important with respect to slag chemistry, which to a large extent regulates the process temperature in electric smelting. Controlled basicity and slag volume. and a satisfactory screen analysis of the reduction material and sinter, are of the utmost importance for smooth furnace operation. Large variations in slag volume and in B/ A and C/Fe ratio will have an influence on the furnace resistance and thus the specific energy development in the furnace, which lead to variable reduction of SiO.. The result will be variable hot -metal quality and un-stable furnace operation.

Jan 1, 1970

By Brommerm Tracey, Britt Elin Gihleengen, Elsa Olivetti, Hans Ole Riddervold, Randolph Kirchain, Geir Øyen

"Compositional uncertainty in secondary materials and variable processing conditions inhibits secondary material utilization in the production of aluminum alloys. Efforts to implement optimization models that direct batch planning have limited industrial presence due to factors such as the insensitivity of these optimization models to dynamic plant circumstances. This paper describes a chance constrained model formulation that generates lower cost, robust batch plans with significant flexibility towards changes in processing conditions. The principal attribute of the chance constrained formulation is its inherent mitigation of risk by diversifying the batch plan. This paper compares aluminum remelter batch planning using the chance constrained formulation with a traditional deterministic model and a manual batch planner. With the expectation that volatile material prices, restricted scrap material availability, and pressure by consumers and legislation for increased recycled raw material input will continue in the future, batch planning tools that inherently diversify a production portfolio will become increasingly advantageous for industrial aluminum remelters.IntroductionAluminum remelters must develop strategies to incorporate lower cost secondary materials into finished alloys to remain competitive amidst increasingly demanding market and regulatory conditions. Determining the optimal combination of incoming raw materials to produce an alloy that meets compositional specifications presents remelters with a complex problem that has driven the development of computational tools commonly referred to as batch planning or blending algorithms. The ubiquity of the ingredient or raw material blending problem in production has motivated ongoing development of batch planning algorithms since the classic nut-mix problem in the 1950's [1]. The most common model formulation for industrial aluminum remelters are deterministic, linear optimization programs [2]. These blending problems determine the optimal combination of raw materials by minimizing cost subject to constraints around demand, availability, and compositional specification. Despite extensive research and moderate computational requirements, batch planning algorithms are inconsistently used in industry. Insufficient incorporation of the complexity of real world remelting conditions into these models provides an obstacle for their implementation [3]. For example, many batch planning algorithms do not explicitly incorporate the impact of compositional variation of the raw materials on overall batch cost. Additionally, they do not allow for endogenous specification of tolerance to error in batch planning, so provide little flexibility where a batch planner would like to incorporate materials of greater uncertainty. Incomplete accounting for quality variability undervalues secondary materials leading to overly conservative use [ 4, 5]."

Jan 1, 2011

By Edith Lafontaine

Modern underground mines operate fleets of mobile production equipment including drill jumbos, long-hole drills, load-haul-dump machines, trucks and bolters. Their availability has a substantial impact onto production cost and thus onto mine profitability. Through appropriate collection of pertinent data and information, use of adequate performance measures and their analyses, mine operators can identify the most promising and cost effective opportunities to get more from their equipment and to reduce the overall cost. This paper presents results of the study aimed to review and analyse means and measures used to quantify equipment availability and its contributing factors (reliability, maintainability and maintenance support) in several Canadian underground mines. It overviews current reporting procedures, sources, quality and quantity of the data and information collected as well as examines performance measures and their definitions used by the surveyed mines. Problems concerning data acquisition as well as meaningfulness and usefulness of the above mentioned metrics are also discussed. The paper concludes with some suggestions and recommendations concerning several aspects of equipment availability assessment. It is believed that the latter may become a more useful tool for mine operators in their efforts to reduce production cost than it seems to be the case at present.

May 1, 2007

By S. M. Shelton, A. L. Engel

The carnotite deposits of western Colorado and adjacent sections of Utah and Arizona were formerly an important source of radium and uranium until displaced by the exploitation of foreign deposits in the Congo and northern Canada . Recently interest has been renewed in domestic carnotite ores as a source of vanadium . Carnotite is a canary - yellow, crystalline , pulverulent mineral occurring in sandstones in the Colorado - Utah district as an incrustation on the faces of joints and fractures and deposited around and between individual sand grains , often strongly adhering to the surface of the grains . Chemically, it is a variable combination of potassium, uranium , and vanadium oxides with water of crystallization . It is soft and friable , and occurs in fine - grained or earthy form . In spite of a specific gravity of 4.1 , gravity concentration has not proved practical as a means of beneficiation because of the earthy texture of the mineral . Vanadiferous sandstones occur with minerals ranging from roscoelite (vanadium mica) , containing little uranium , to high- uranium and low -vanadium carnotite . There is considerable local variation in the texture of the ores . The treatment of carnotite ores has been described previously , with attention directed to the elimination of waste in mining and the extraction of radium . The suggested methods included those suitable for the recovery of vanadium , since both radium and vanadium occur in the same minerals . Moore and Kithil suggested crushing from 40- to 80 - mesh with rolls , accompanied by a rubbing action to loosen the carnotite adhering to the sand grains . Fine grinding was to be avoided because it diluted the final product too much . The crushed and rubbed material was to be washed and

May 1, 1942

By J. Janin, J. F. Bougard

Development of improved transportation networks in major urban centers has led more and more to underground construction, the only reasonable solution for decreasing surface traffic congestion. Excavations required by these projects usually cause decompression of the surrounding soil mass which results in subsidence of several centimeters. While these magnitudes of subsidence have no consequences in undeveloped areas, they are often unacceptable in urban areas where existing buildings, structures and utilities are endangered. Recent tunneling projects for the extension of the Paris Metropolitan Transit System (R.A.T.P.) underground network were carried out with this in view and gave rise to the development of a number of innovative techniques for minimizing ground decompression and subsidence. As shown in Figure 1, the recent R.A.T.P. expansion program includes a new express metro, 46 km long, crossing Paris from East to West, and the extension of many existing metro lines in the suburbs. From the start, R.A.T.P. was faced with many unique technical problems for which there was little precedent experience. The structures to be built have large dimensions, with cross-sections typically ranging from 40 to 300 m2, and exceptionally to 600 m2. The new lines are often very deep because the shallow profile is already congested by the existing metro, interceptors, sewers and a very large number of utilities. As a result, new construction is often below ground water level by as much as 20 m. Moreover, the geology varies widely from hard limestone with compressive strength over 1500 kg/cm2 to inconsistent water bearing sand. Finally, curves in the East-West line must have a minimum radius of 500 m which frequently forces the alignment to pass below existing structures, buildings and monuments.

Jan 1, 1974

By W. G. Davenport

H20 is present in many flash furnace inputs. Examples are: (a) moisture in concentrate and flux (b) humidity in blast (c) moisture in hydrocarbon fuel, particularly coal, Appendix IV. H20 may also leak into the furnace from damaged water-cooling jackets. H2O, especially that it be included H2O, exerts a strong cooling effect on the flash furnace. It is important our calculations. As will be seen from the calculations, gaseous and liquid H2O both increase flash furnace industrial oxygen and oil requirements. This is because gaseous H2O (humidity in blast) must be heated from its input temperature to the flash furnace off gas temperature. Liquid H2O must be evaporated and heated.

Jan 1, 2001

By Zhikai Wang, Wensheng Lyu, Peng Yang

"To better understand the mechanical behavior of the compression deformation of backfill under high stresses corresponding to large depths, consolidation compression tests were performed for cemented tailings backfill with a cement-sand ration of 1:10 and 30% water under confined conditions. After applying different loading stress functions from 0.5 MPa to 32 MPa, the final axial deformation of the test specimen of backfill was obtained, and the micromorphology of backfill was studied before and after consolidation by scanning electron microscopy. Additionally, fitting analysis was performed for backfill confined compression deformation data and device model constitutive equations by the minimum square law. The constitutive model was revised according to the analysis results. The research results indicate that, as the load increases, the void ratio e obeys the functional relationship e=alnt + b (where a and b are fitting constants and t is compression time). Under the high-stress conditions of confinement, the constitutive model of backfill consolidation and creep can be used to describe the creep behavior of the backfill. Under high-stress conditions, after the consolidation of the confined backfill, the space between the tailing particles diminishes, the particles becomes more compact, and particle slippage occurs. INTRODUCTION With the depletion of shallow mineral resources, the mining industry has gradually shifted to deep mining (Zhang, Li, An, and Huang, 2010). Furthermore, with the continuous introduction of sustainable development policies regarding development and utilization of mineral resources, the mining industry must protect the limited available land and make full use of mineral resources as much as possible (Sijing, 1994; Zhihua, 2009). Backfill mining technology offers an unparalleled advantage in fully recovering mineral resources, controlling pressures, and improving environmental protection. As a result, this method has been widely used in various countries in the world (Burd, 2002; Benzaazoua, et al., 2008). Of the underground mines in the world, 45% of the large and medium-sized non-ferrous-metal mines and 37% of the gold mines use backfilling (Fuhrman, et al., 2014; Khaldoun, Ouadif, Baba, and Bahi, 2016). In addition, 45% of underground non-ferrous-metal mines and 37% of the gold mines use the filling method (Mchaina, Januszewski, and Hallam, 2001). According to incomplete statistics, more than 80 metal mines operate at a depth of more than 1 km; the depths of several typical deep mines are shown in Figure 1 (Burd, 2002; Fall, et al., 2009)."

Jan 1, 2017

By Sedat Esen

"This paper presents a critical review of the fragmentation data obtained from some large open pit copper and gold mines. Database ncludes 35 mines with Uniaxial Compressive Strength values ranging from 19 MPa to 227 MPa (2756 psi to 32923 psi). Variation in the fragmentation data and the causes are discussed in detail. Quality assurance/quality control (QA/QC) in drilling and blasting was shown to have significant impact on fragmentation. In addition, controllable blast design parameters including drill pattern, powder factor, blast timing, stemming length, etc as well as the large blast sizes havesignificant potential to improve fragmentation. Feed size requirements of crushing and grinding circuits were discussed in detail. The paper discusses the effects of different size fractions (top size, 80 %passing size and % passing 10 mm (0.5 in)) on the downstream processes and the role of the fragmentation model in the mine to mill process. Blast domains based on rock strength and structure canbe established by using a fragmentation model which is calibrated using measured fragmentation data. This allows the blast engineer to compensate for changing rock characteristics and stabilize the ROMfragmentation size and result in increased crusher and mill throughput. Two case studies were presented to demonstrate the benefits achieved in downstream processes. Main benefits were reduced downtime at crusher circuits, improved mill throughput as well as reduced total operating cost. A simple relationbetween uniaxial compressive strength and powder factor was proposed using the database for the optimized mines as a guideline to allow site engineers to compare their sites against the other sites."

Jan 1, 2017

By James A. Finch, Xiangzhou Ding, Yue Hua Tan

"The Jameson Cell is one of the choices of flotation machine in coal, base metal processing and other specialist applications. This paper determines the effect on vacuum pressure and bubble size of two design variables, orifice size and downcomer length, and the operating variable air-to-water (AWR) ratio. The main findings are: orifice size and downcomer length impact the vacuum but have limited effect on bubble size; AWR < 1 favours high vacuum, conditions are identified where vacuum is maintained at AWR > 1, and water flowrate has slightly greater impact on bubble size than air flowrate.INTRODUCTIONFroth flotation, the most common technique for mineral separation, has been in use for over a century. The process takes advantage of the difference in wettability of mineral surfaces to achieve the separation of valuable minerals from non-valuable minerals, or gangue. Numerous flotation machines have been invented and patented over the years. The Jameson Cell, invented by Professor Graeme Jameson in the late 1980s, is one successful example. First trialed at Mount Isa Mines (Queensland, Australia), Jameson Cells have been installed at operations around the world for the recovery of fine coal (Mohanty and Honakeri, 1999; Cowburn et al., 2006; Hacifazlioglu and Toroglu, 2007; Uçurum 2009), minerals of copper (Farr 1992; Atkinson et al., 1993; Harbort et al., 1997), lead/zinc (Rohner, 1993; Munro, 2003) and gold (Bennett et al., 2012; Lauder et al., 2003), and in water treatment (Yan and Jameson, 2004), solvent extraction de-oiling (Miller and Readett, 1992; Miller et al., 1997; Harbort et al., 2003; Young et al., 2006), oil sands processing (Neiman et al., 2012), and various food industries (Brenneman, 2014). One of the largest units is the 650 cm diameter separation tank with 24 downcomers installed in an Anglo American operation (Osborne and Euston, 2015). Scale up is relatively straightforward: to increase capacity the number of downcomers is increased with corresponding increase in size of separation tank.The Jameson Cell comprises two main parts: a vertical tube (downcomer) which provides self-aspiration and intense bubble-particles contact, and a (separation) tank where particle-bubble aggregates disengage from the pulp. The intense bubble/slurry mixing in the downcomer with air holdups reaching 60% (Marchese et al., 1992) accelerates particle collection enabling the greatly reduced cell volume compared with mechanical flotation cells and columns. The disengagement of the particle-loaded bubbles from the slurry in the separation tank is usually aided by addition of washwater."

Jan 1, 2018

By J. H. Kelley

In this paper, we show that the methane emission and the dust generation in under-ground mining currently and in the future pose operational, health and safety conditions which adversely Impact face productivity and worker satisfaction. One solution is the use of a dual-aircourse system of ventilation. In this concept, one aircourse captures and exhausts to the surface the dust generated and the methane emitted in coal/mineral fragmentation while a second aircourse provides workers with cleaner air for breathing and comfort. Various dual-aircourse configurations adapted to the Variable Wall Miner are analyzed and compared with conventional mining in gassy seams, indicating a marked reduction in the required air quantity and the number of aircourses.

Jan 1, 1996

By Raymond M. Stateham

The Bureau of Mines evaluated temperature increases on the heads of resin-grouted bolts as indicators of the integrity of the anchoring of the bolt. Expected increases were calculated by the finite difference method; the calculations were checked by bolthead temperature measurements, both in the laboratory and in the field. The accuracy of the calculations varies with the validity of assumptions necessary to the process. Measurements in the laboratory produced a temperature rise of about 4.00 F on the head of a 4-foot bolt when installed with a full column of resin. This increase remained for about 30 minutes. Similar increases were noted on bolts installed at the White Pine mine, White Pine, Mich., but bolthead temperature increases in the mine lasted only about 10 to 15 minutes. When partial columns (reduced amounts) were used, the temperature increases were smaller.

Jan 1, 1976

By G. W. Jones

[One of the mJor c~ctivities of the Bureau ~f l;ine;: is the j.a-onotion of sdetp in mining a.nJ other inclus tries. 13 cor&apos;ncc tlcn td t~l tiiene activities the 3~.sccu r:e termine? t&apos;le cwl.os:lon ha~arls 95 n,o;r.?xs tibla Tases, vzpor s, aid scli3s aqi iavestig~ ter rnrI.?ns of controlling s-~fi. prevpri ting eqlosians.]

Jan 1, 1941

By Takashi Saito

Since early 1970?s skirt suction foundations (skirted foundation / bucket foundation) have been used as support for large fixed substructures or anchors for floating structures in offshore hydrocarbon development projects. In recent years skirt suction foundations are recognized as one of the solutions in foundations applicable to bridge substructures installed in waters, because skirt foundations have a wide variety of functions such as control of settlement during service life, less impact to environments during operation at installation site. This paper introduces general features of skirt suction foundations, and then discusses design practice of them for the application to bridge substructures, with reference to experiments in both laboratory and field.

Jan 1, 2013

By Graham Bright

The rapid increase in reliability, the low cost of operation, the ready application of safety devices, and the growing availability of central-station power have made the question of installing a hoist of the electric type no longer debatable. Where adequate electric power is available, there are few cases where it would be advisable to install a steam or air hoist. The type of electrical equipment depends largely on the nature of the power supply, its capacity, and the form of the power contract under which power is purchased. In a large majority of cases, the available electric power is alternating current, three phase, 60 cycles. There is, however, considerable 25-cycle power in use; and in a few instances constant voltage direct current is the only power available for a small or an occasional medium-size hoist. Where a new hoist is to be installed, the designer of the mechanical parts can readily take care of the maximum stresses likely to be imposed by the motor. Where the hoist is already installed and operated by steam or air and it is desired to substitute an electric motor for the engine, a careful check should be made to determine the advisability of using the old mechanical parts. In most cases it is better to install a complete new hoist than to attempt to use old mechanical parts. A steam engine has a definite maximum torque, which the hoist has been designed to withstand, while a motor may be able to deliver momentary torques beyond the strength of the mechanical parts of the hoist. The selection of the proper type of electrical equipment can only be made after complete information is obtained and certain calculations made to determine the capacities required. There are several methods used in making hoist calculations, but no matter what method is utilized a fair degree of familiarity with hoists and hoisting conditions is necessary before an intelligent analysis and proper selection can be made. Forms Used in Hoisting Calculations Some of the hoist calculation methods are long and complicated. Where such calculations are seldom made, it is better to use the

Jan 1, 1922