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By G. W. Govier

The origin and limitations of the conventional and empirical equation for the interpretation of the results of back pressure tests on gas wells are discussed. Difficulties in data interpretation arise from many causes, including Jack of flow stabilization, uncertainties in connection with the friction calculation, and the effect of turbulence near the sand face in the reservoir. A procedure is developed to ac-count for the turbulence effect. This is based upon the theoretical equation for laminar steady state flow and current knowledge of turbulent steady state flow. The procedure involves the expression of the equation for combined laminar-turbulent steady state flow in terms of a turbulence contribution factor. This factor. is shown to be dependent mainly upon the flow rate per unit of pay thickness and the reservoir permeability. The method of interpretation permits the use of judgment based upon the theory and present day under-standing of laminar-turbulent flow and is considered an improved method

Jan 1, 1961

By Xuehui Xia

Abstract -There are a number of sedimentary exhalative massive sulfide (SEDEX) deposits in the Proterozoic Langshan-Zhaertai rift at the western segment of the northern margin of the North China platform in China, including more than ten large, medium and small deposits located in a belt of 300 km EW by 50 km to 100 km NS, with large Cu, Pb, Zn, Ag, and S reserves. In several representative SEDEX deposits in the rift, the mineralizing elements are prominently zoned, horizontally or vertically, with Cu decreasing but Pb increasing from west to east, Cu decreasing but Zn increasing from bottom to top, and Zn restricted to the bottom half. The ore-hosting rocks, characterized by a clear manganese halo, have developed a polymetallic mineralization in positive relation with their carbon contents. Their isotopic aspects are: ?34S has relatively large positive values, fluctuating between +5‰ and +35‰, compared with Pb isotopic compositions which are less variable, with a model age of 1600 Ma to 1800 Ma, showing that they are mantle-derived. The mineralizing materials were associated undoubtedly with the contemporaneously faulting events in the rift. The deposits owe their origin to seafloor exhalation, with sedimentary rocks as their hosts.

Jan 1, 1999

By S. Makni, G. Gagnon, F. Couët, C. Rochefort

"Comminution represents a significant part of mineral processing plant operating costs. Yet, autogenous (AG) or semi-autogenous grinding mills (SAG) are difficult to control because of disturbances like feed size distribution and rock hardness. AMIRA, within project GeMIII, developed a comminution index from laboratory crusher data. The index correlated with the Bond ball mill work index and with the A×b parameter. The present work extends the use of crusher data as a grindability indicator to real-time industrial applications. The aim is to improve comminution operation using online hardness estimation. Because the operational work index is proportional to the ore work index, rock hardness variations can be estimated from the feed and product size distributions, the throughput, and the power draw of a crusher. Real-time estimation of rock hardness can help understand the dynamic behavior of AG and SAG mills. Multivariate time series were analyzed to understand the impact of hardness on a SAG operation. Results showed that the estimated hardness influences the SAG operation and its throughput. Moreover, non-linear dimension reduction was used to ease the process visualisation and search for potential control strategies. In the future, online hardness measurements should also impact the understanding of comminution circuits and improve their operation.INTRODUCTIONThe variability in hardness, and the feed size distribution, are two of the main disturbances affecting comminution circuits (Sbarbaro & del Vilar, 2010). Size distribution can be measured by imagebased granulometry systems such as WipFrag (Maerz, Palangio, & Franklin, 1996), or by 3D vision systems when the fines are difficult to discriminate by 2D segmentation (Faucher, Makni, Gagnon, Lavoie, & Roberge, 2015).There are few examples of online hardness measurements. One example was the work of Casali et al. (2001) who developed a hardness indicator. The ore grindability soft sensor used the fraction of each lithological class in the ore, as determined by image analysis, to predict the work index of the material. The model was developed using a moving window with a width of 12 months and trends were shown over many years with one data point per month."

Jan 1, 2016

By S. Y. Ezz, K. El•Guindi

A vertical tube, 8 m long and 2.5 cm in diameter, electrically heated to 650°C throughout the majority of its height, was used to study the-effect of ore feed rate and hydrogen flow rate on the reduction of fine iron ore particles. A correlation could be obtained between the combined effect of the amount of reducing gas and reduction time and the per-cent reduction. The results suggest that a method based on the reduction of fine iron ores while falling through up-streaming hydrogen cannot be recommended for industrial application.

Jan 1, 1969

By H. C. Gunning

SOME small vanadium-bearing deposits on the west coast of British Columbia about 100 miles north of Vancouver are of interest for several reasons. They are of a type that is, so far as we know, unique. They are difficult to identify as being vanadiferous so that, unless they are described, other similar deposits could easily pass unrecognized. Furthermore, although none of them has as yet been proven to be of commercial proportions, no good reason is apparent why larger, and therefore valuable, deposits should not occur under similar geological conditions. The original discovery on Quadra island was made in 1932 and has been recorded by H. V. Ellsworth and H. C. Gunning (l). Since 1932, prospecting in the area has revealed other similar deposits, one about a mile south of the original and another some ten miles to the east, near Menzies bay on Vancouver island. The Quadra Island showings are a mile and a half north of the head of Gowland harbour, a small inlet that is easily reached by gas boat from Campbell river, about four miles to the southeast on Vancouver island. The deposits were examined by the writers in the spring of 1943 in connection with field work sponsored by the Department of Geology, University of British Columbia. We are indebted to Mr. G. A. Dirom and Mr. Lothrop, of Vancouver, for helpful data on the Menzies Bay deposits, and to Dr. V. Dolmage for making a brief trip to Gowland harbour and discussing the deposits.

Jan 1, 1944

By R. M. T. Raja Ismail

Shipping and stevedoring industry is going to witness a massive increase in the amount of containers to be handled while land constraints become more critical. Offshore transfer operations hence offer a preferable solution to deal with the surge in cargos rather than to expand the port outwards. Recently, there has been increasing research interests on offshore crane automation. Suspended cargos in a ship-mounted crane system are caused to swing due to the vibratory motion of the ship induced by ocean waves, which can lead to collision between cargos and deck. Therefore, it is vital for offshore crane systems to satisfy rigorous requirements in terms of safety and efficiency. This paper presents the modelling and control development for offshore boom crane systems. A second-order sliding mode control law is proposed for trajectory tracking and sway suppression control, making use of its capability of actuator chattering alleviation while achieving high tracking performance and preserving strong robustness. The asymptotic stability of the closed-loop system is guaranteed in the Lyapunov sense. Simulation results indicate that the proposed controller can significantly reduce the effect of disturbances coming from gusty waves and other dynamic loadings.

Aug 1, 2013

By C. Larsen, E. Goodwin, E. Konigsmann

"This paper describes the development of an innovative effluent treatment process for cyanide and heavy metal removal from tailings wastewaters at Hemlo Gold Mines Inc. Golden Giant operation.The importance of minimizing dissolution of contaminants in the gold leaching circuit is discussed, as well as using recycled water in milling circuits to the fullest extent possible. Finally, a brief description of the role of natural cyanide degradation in the tailings pond is provided.Emphasis is placed on the need for overall water quality management to ensure minimum effluent treatment process costs and complexity while producing excellent quality effluents.1.0 INTRODUCTIONHemlo Gold Mines Inc. owns and operates its Golden Giant Mine located forty kilometres east of Marathon, Ontario. The Golden Giant mine is one of three gold operations exploiting the large gold orebody located in the Hemlo area. The milling facilities include two stage secondary crushing, three stage, closed circuit ball mill grinding with no reagents, thickening, cyanide leaching and carbon in pulp gold recovery unit operations. The average throughput is 3000 tonnes per day of 10 grammes per tonne gold ore. Figure 1.1 shows a schematic flowsheet of the operation."

Jan 1, 1989

By P. H. Jennings, J. C. T. Farge

Commercial tellurium commonly contains heavy base-metal impurities such as lead, copper, iron, etc., as well as selenium and oxygen. The base metals may be removed by vacuum distillation or by zone melting. Vacuum distillation is a convenient method for treating moderate quantities ( 100 kg.) for the production of a material having a total content of heavy metals in the 10-30 ppm range. By zone melting, it is possible to lower all the heavy metal impurities tm below the limits of spectrographie detection. Neither vacuum distillation nor zone melting is effective for the removal of selenium, but treatment of molten tellurium with hydrogen converts selenium to hydrogen selenide. This procedure is too slow to be considered except as an adjunct to zone melting. In the course of air-melting, many of the more easily oxidized impurities form a dross and may thus be readily removed. Substantial refinement with respect to iron, tin, chromium, aluminum, sodium, silicon, magnesium, calcium and manganese can be achieved in this way. Although tellurium can be electrodeposited from either acid or alkaline solutions of the dioxide, various factors militate against successful electro-refining, amongst which may be mentioned the brittleness of cast tellurium anodes and the tendency for the metal to be deposited in dendritic form, even at low current densities.

Jan 1, 1966

By H. R. Stoger

"In 1994 world trade grew by 9%, the fastest annual increase since 1976. Dry cargo shipping rates are at an all time high.Panamax size bulk carriers are receiving19 000 US dollars per day for trans Atlantic round trip voyages. This is good news for the ship owners but not such good news for the industrial users of ocean shipping.The main emphasis of this paper will be on bulk carriers, the charter market and what industrial companies can do to reduce their costs of ocean transportation which is critical to Canadian exporters. Let us look at the charter market in general.Bulk carriers come in four main sizes:1.The Capesize bulk carriers of 110 000 to160 000 tons that are primarily used to transport iron ore and coal;2.the Panamax bulk carriers of about 70 000tons dwt. This is the largest size (with a beam of 105 ft) that can transit the Panama Canal.3.the Handymax bulk carriers of 40/45 000tons dwt; and4.the Handysize bulk carriers of 20/35 000tons dwt.The handysize vessels are usually craned or geared and carry a variety of bulk cargoes including steel. Ship sizes have increased over the years and the mining industry now uses primarily capesize or Panamax bulk carriers.International chartering is conducted through an international network of shipbrokers. There is usually one broker representing the ship owner and another broker who represents the charterer. The major chartering centers are London and New York but a great deal of chartering activity is conducted in regional markets such as Hongkong, Oslo, Montreal and Hamburg.The Biffex Index or Baltic Freight Index is a good measure of dry bulk freight rates. The Biffex is composed of ten major routes. In May1995, the Biffex was at 2310 points. A year earlier it was at 1354, an increase of about 56%."

Jan 1, 1996

By S Sokhanvaran

Electrodeposition of silicon from a cryolite based electrolyte at a relatively low temperature (1000°C) is a promising approach to generate high purity silicon. In order to obtain fundamental data pertaining to electrowinning of silicon from Cryolite?SiO2 melts, density and electrical conductivity measurements were made. A range of temperatures and SiO2 contents was studied for each property. It was found that while density has an inverse relationship with temperature, the dependence for electrical conductivity is direct. Increasing silica content up to the saturation limit (~ 5 wt%) increases the density whereas further increase in SiO2, lowers the melt density. On the other hand, the conductivity is lower for the melts with greater SiO2 content, at any temperature.

Jan 1, 2011

By Xuanxue Mo, Kaihui Yang

"Abstract- The Laochang mine, located in the Sanjiang area of southwestern Yunnan Province of China, is a volcanogenic massive Pb-Zn-Cu sulfide deposit. It is hosted by a pyroclastic sequence of Barly Carboniferous age, namely the lower member of the Yiliu Group, which was intruded by syenite and rhyolite porphyry . The volcanic suite is basaltic or basaltic-andesitic in composition, has alkaline affinities, and is associated with the initial rifting along the margin of the Baoshan-Shanstate continental rnicroplate (Yang, 1989). The ores are typically Pb>Zn>Cu in composition, averaging 3.820Jo Pb, 3.51% Zn, from 0.01% to 1.85% Cu (0.107% av.), a high average content of Ag (113 g/t) and recoverable amounts of Au, Tl, Gd, Ga, Ge, In. A massive sulflde zone, in which lenticular and stratiform orebodies are localized in a sulflde-carbonate-silica shale unit or sulfldic tufflte horizon that usually overlies coarse-grained pyroclastic rocks, is underlain by a stringer sulflde zone developed in a subvolcanic intrusion or volcanic sequence. The sulfide mineral assemblages, from the top to the bottom of the deposit, are: realgar + orpiment - galena + sphalerite + pyrite- chalcopyrite + pyrite + pyrrhotite + arsenopyrite. Oxide and sulfate minerais occur rarely in the massive ores. The massive ores are generally fine-grained and banded, but coarse-grained ore, colloform and framboidal texture, and growth-zoned pyrite and sphalerite are common. Sedimentary features such as graded bedding, brecciated and deformed ore clasts, and chaotically emplaced blocks, are well preserved, indicating that the massive orebodies have undergone slumping and dis­ placement. Alteration is weak in the hanging-wall rocks, but strong in the stringer zone. Two dis­ tinctive alteration zones have been identified: the upper zone, characterized by an assemblage of quartz, carbonates, chlorite, albite, zeolite and sericite, and the lower zone containing diopside, trema­ lite, actinolite, gamet, clinozoisite, and epidote.The general features of the Laochang deposit are in accord with the descriptive mode! of VMS deposits (Lydon, 1984). However, it falls into neither the Zn-Cu group nor the Zn-Pb-Cu group chemically (Franklin et al., 1981). The depositional setting of the Laochang deposit is quite different from Cyprus or Besshi-type massive sulfide deposits. Laochang is hosted by alkaline lavas that were erupted in a submarine continental rift. Although some features of the Laochang deposit are similar to those of Kuroko-type deposits, there are remarkable differences in the alteration mineral assemblage, the proportion of ore-forming elements (lead enriched) and the amounts of oxides and sulfates. These suggest corresponding differences in ore fluid composition and the associated ore-forming environment. Thus, the authors suggest that the Laochang deposit may be a distinct type of VMS deposit."

Jan 1, 1993

By H. Watari

In 1998, a voluntary agreement was reached between the European Commission and the European Car Manufacturers Association (ACEA) to reduce average carbon dioxide emissions of new cars to 25% below 1995 levels by 2008, Agreements have also been reached between the European Commission and the Japanese Automobile Manufacturers Association (JAMA) and the Korean Automobile Manufacturers Association (KAMA), However, the target average of carbon dioxide emissions of less than 140g/km in 2008 is a very challenging goal, Therefore, total product weight reduction is an objective for many manufacturers, This can be achieved utilizing materials possessing high strength and low weight, One material that has recently attracted interest is magnesium alloys, The magnesium alloys are expected to play an important role as next-generation materials, which have possibilities of contributing to lighten the total product weight when magnesium products can be used to replace aluminum and mild steel products.

Jan 1, 2005

By J. W. Gregg, P. M. Dranchuk, D. L. Flock

"From preliminary investigations it has been observed that although evaporation losses may be estimated by comparing single values of certain physical properties of crude oils and their evaporation residues, such techniques possess little accuracy unless both the evaporation process and the variation of the property as a function of the process are completely known. The accuracy of estimation may be increased somewhat through the comparison of property mid-per-cent curves. Further increases in accuracy are possible if bottoms yield •curves rather than mid-percent curves are used. The use of both the mid-percent and bottoms yield curves however involves a prohibitive amount of effort in most cases. Examinations of distillation bottoms from Hempel type distillations carried to end points just short of the cracking point have indicated that these bottoms are not appreciably affected by the evaporation process. It was further observed that bottoms of identical API gravity, obtained from a crude oil and its evaporation residues behave as if they were pure components which were unaffected by evaporation. Based on these observations Hempel distillation bottoms of equal API gravity were obtained for a crude oil and its various evaporation residues from API gravity bottoms yield curves. The volume percent of these bottoms in the crude oil and its residues were used to calculate the evaporation losses suffered by the crude in order to yield the various residues. The results indicate that, although further refinements in technique are required, it is possible to calculate evaporation losses with an accept-able degree of accuracy through the use of this method."

Jan 1, 1960

By J. Grignon, C. Fleming

It is possible to reproduce the performance of an operating CIP or CIL plant in the laboratory, in small scale batch kinetic tests, coupled with mathematical models that translate kinetic data into predicted steady state gold profiles across multi-stage adsorption circuits. Once the performance of the commercial plant has been mimicked by the model, the plant operating parameters can be varied systematically in the model, and the likely response of the plant to the step wise change can be determined. In this way it is possible to inexpensively optimize the operating conditions of an existing plant, with no disruption to plant operations and no economic risk to the mining company. This approach had been adopted by IAMGOLD to optimize the performance of their Rosebel CIL plant following several major expansions in mill capacity since 2004.

Jan 1, 2011

By L. E. Djingheuzian

IN 1953, Lewis (1) published an article which brought forth a great amount of discussion by grinding engineers. In his contribution to discussion the present writer (2) suggested that, for the most efficient performance of a ball mill, there must be a .definite relationship between Cn, per cent critical speed, and V p, per cent mill volume occupied by the ball charge. Later, he ( 3) was able to publish some grinding data from Wright-Hargreaves milly which appeared to bear out this contention. It is with this view to establishing a fundamental relationship between Cn and Vp that the idea of this Forum was conceived. Accordingly, a questionnaire was prepared and copies of it were mailed to over eighty Canadian mill operators. This questionnaire did not include a question on dilution on the assumption that each mill operator was using the most efficient dilution for his operation, nor was a question on efficiency of classification included since it was thought that the inclusion of efficiency of dassification in the questionnaire at this preliminary stage might render the forum discussion,. while everybody was trying to find his bearings, too unwieldy. However, it is evident that, as discussions develop, this forum will have to define a uniform method for establishing most efficient classification in grinding circuits

Jan 1, 1957

By G. Major-Marothy

"INTRODUCTIONA beneficiation plant to upgrade earthy iron ores is being installed by the Iron Ore Company of Canada in Sept-Iles, Quebec.The crude ore for the plant will come from the Knob Lake area, located in Northern Quebec, where mining has been in progress since 1954.Some 170 million tons of ""direct 11 ores have been mined and shipped in the past eighteen years, with an overall silica content of 7 to 8 percent. No beneficiation - except the reduction of the top size to about 2 inches - took place during this period, but extensive research work has been carried out, in order to find a feasible process.Since “washing"", gravity separation, roasting and magnetic separation experiments did not indicate positive enough results, flotation was tried and found to be feasible.The beneficiation complex being installed will consist of grinding, flotation, dewatering - i.e.: thickening, filtering and drying - balling feed preparation, and agglomeration - i.e.: balling and induration.This process will result in a product superior to the ""direct shipping"" ores and will also expand the ore reserves by allowing material with a higher silica content to be utilized.THE OREThe Knob Lake ores are grouped by mineralogical composition and by grade.BLUE ORES, representing roughly two thirds of the reserves, carry their iron content mostly in the form of massive, blue hematite and martite.YELLOW ORES, about one sixth of the reserves, have predominantly hydrated iron oxides as the iron bearing minerals.RED ORES, the other sixth of the reserves, carry the iron mostly in the form of red hematite.The gangue in all ores is mainly quartz, but aluminum oxides and hydroxides are also present, particularly in the red ores."

Jan 1, 1972

By P. Trudel, M. A. . Cloutier

This lithogeochemical study demonstrates that the Gilman and Blondeau Formations in the Chibougamau area belong to a subalkaline suite of tholeiitic affinity poor in potassium. The Gilman Formation is composed mostly of basalts, with subordinate andesites and rare dacites, while the Blondeau Formation comprises all lithologies of the basalt-andesite-dacite-rhyodacite-rhyolite ensemble. Both AFM and Harker variation diagrams show that all these rocks originated by differentiation from the same magma reservoir, and are related to one volcanic episode, This study did not, however, identify hydrothermal alteration zones useful for regional geochemical prospect ion.

Jan 1, 1984

By Rayleen Riske

Why do we look for better reconciliation when times get tough? Why wait? Mine reconciliation should be a priority throughout the good times too. In fact, with good reconciliation, those good times are going to be even better and will help pave the way to success through those preventable bad times. Reconciliation throughout the entire mining value chain requires the capture, validation, and analysis of copious amounts of data. This task can be daunting for a team in a small mine, let alone reconciling across a suite of large mines. This paper will outline the different ways we can reconcile across the value chain, why we should reconcile over differing periods of time and how Snowden?s solution to proving reconciliation can be a simpler, reliable and transparent process. Snowden?s Reconcilor is proving to be a valuable tool on any mining scale, by capturing, validating, sorting and reporting data for timely decision making by the site geologist through to corporate management. By instigating vigorous reconciliation, you are setting your mine up for the future. Not only will you have the means to analyse your current processes and measures, but you will have the opportunity to identify and improve your mine?s performance from the resource model through to the final product.

May 1, 2010

By Mostafa Benzaazoua, Emilie Ré, Raphaël Mermillod-Blondin, Hassan Bouzahzah, Jean-François Wilhelmy, University of Québec in Abitibi-Témiscamingue

"We analyzed two copper and lead flotation concentrates from the LaRonde mill using MLA technology (Mineral Liberation Analyzer) to identify the contaminants and to quantify their size and liberation. The MLA mineral quantification was compared with traditional mineralogical techniques (Scanning Electron Microscopy, Optical Microscopy, X-Ray Diffraction and Chemistry). The accuracy of MLA data was then quantify in application to metallurgical decision (mineral identification, mineral quantification, particle sizing and liberation quantification). We prepared five well-known materials from pure minerals and analysed them by MLA. MLA concentrates analyses showed the lead concentrate is mainly contaminated by pyrite and sphalerite. These minerals are liberated above 70 % and present a floatable size around 15 to 35 µm. Surface activation by dissolved lead from galena is therefore assumed for these contaminants. The analyses of the known samples show that mineral quantification and size distribution given by the MLA are consistent with the chemical analyses and the laser particle sizer. The liberation measurement is affected by the stereological effect. Modelling quantifies the overestimation of the particle liberation. Based on the modelling, the stereological shift on liberation should not impact metallurgical conclusions on the concentrate contaminations.INTRODUCTIONTo face the diversity of mineral processing challenges, the process mineralogy includes phase quantification, measurement of mineral size, liberation by exposure and by grade, association, surface contact proportion and texture. In the last decades, two SEM commercial tools emerged: MLA and QEMSCAN R. Both are based on specific combinations of backscattered electrons and X-ray images as well as image analysis routines developed at CANMET (Petruk & Pinard, 1976, Petruk, 1989), CSIRO (Frost, O'Hara, Suddaby, Grant, Reid, Wilson & Zuiderwyk, 1977, Reid, Gottlieb, MacDonald, & Miller, 1984) and JKMRC (Hall, 1977, Gu & Sugden, 1995). Recently, TIMA (TESCAN) and Mineralogic MiningR (ZEISS) supplied automated mineralogy for mining industry (Bouzahzah, Benzaazoua, Graham & Cropp, 2015, Gottlieb & Dosbaba, 2015a). In parallel, home-made routine were developped to resolve mineralogy challenges in mineral process but also in geometallurgy and mining environment (Kahn, Mano, & Tassinari, 2002, Knight, Klassen & Hunt, 2002, Mermillod-Blondin, Benzaazoua, Kongolo, de Donato, Bussiere & Marion, 2011, Hunt & Bradshaw, 2015). SEM mineralogy become essential to operation by setting units on mine sites (MacDonald, Latti, Adair, Bradshaw, & Dunn, 2011, Goergen et al., 2013, Dobbe et al., 2014, Gottlieb & Dosbaba, 2015b)."

Jan 1, 2016

By Jayesh B. Patel, Zhongyun Fan, Hu-Tian Li

"Melt conditioned direct-chill (MC-DC) casting is a novel technology which combines vertical direct-chill (DC) casting with a high shear device directly immersed in the sump for in situ microstructural control. In this paper, the solidification mechanism of DC casting under varying conditions is discussed. The temperature profiles in the sump were measured under the steady state casting conditions by using sacrificing thermocouples. Detailed comparisons of the derived thermal condition are made. The individual role of grain refiner additions, natural thermosolutal convection and forced convection in the sump and the interplay of these factors in determining the solidification structures of DC cast billets are discussed. The MC-DC casting technology can be used to control microstructural constituents and casting defects in DC cast billets/ingots by in situ manipulating of the thermal and fluid flow conditions.INTRODUCTION Direct-chill (DC) casting of aluminium, has been the essential commercial process for producing feedstock suitable for subsequent processing, such as extrusion, rolling or forging. Fine and equiaxed grain structures in the as-cast billets/ingots are required to enable a fine and uniform distribution of second phase particles and microporosity. This leads to higher productivity, more cost-effective homogenisation and more efficient downstream thermomechanical processing. The addition of chemical inoculants has been the standard industrial operation prior to casting for grain refinement of Al alloys. However, it has been established that less than 1% of the grain refiner particles added actually act as heterogeneous nuclei to refine the grain structures, showing a very low grain refining efficiency (Greer, Bunn, Tronche, Evans, & Bristow, 2000). Moreover, the remaining particles from the grain refiner addition in the final casting may cause surface defects during downstream processing. A major issue of the metallurgical quality of large sized ingots/billets is the non-uniformity of microstructures even with chemical grain refiner additions. This is due to the fact that the grain structure formed in the different zones of the billet depends on the local chemical composition and local cooling rate. The local cooling rate can vary from 0.4~1 K/s at the centre of the billet to around 10–20 K/s at its surface zone (Nadella, Eskin, Du, & Katgerman, 2008). The large thermal gradient along radial direction between billet surface and interior of the melt during conventional DC casting induces thermal stress and cold cracking even with grain refiner addition. Therefore the control of casting defects, such as macrosegregation, porosity, cold/hot cracking and distortion of the billets/slabs, etc., is still challenging in industry, causing high scrap rate of DC cast ingots/billets even with grain refiner addition."

Jan 1, 2018