Copper Grade Research Articles

Validation of predictive flotation models in blended ores for concentrator process design

The use of geometallurgical modelling is becoming common in the design of a concentrator plant and during its operational phase. Predictive modelling aims to define optimized process parameters for the concentrator plant to accommodate the variability of the ore feed characteristics. The main objective of this study is to simulate the metallurgical response for distinct ore unit types and their blends using kinetic models derived from experimental flotation tests. Kinetic flotation tests, including both rougher and cleaner, were applied on four ore types containing different ratios of chalcopyrite, chalcocite and copper oxide minerals from Rich Metal Group’s Madneuli copper–gold mine, Georgia. The metallurgical performance of complex copper ores Madnueli XI and V differs from each other significatively due to the different mineralogical distribution of copper sulphides and oxides. The blend of ore units in various ratios affects the efficiency of the process by decrementing the recovery and mass pull due to copper oxide-sulphate in the ore Madnueli V. HSC Chemistry® software was used to simulate the metallurgical response of blended ores based on mineral compositions of the ores, Klimpel kinetic rectangular distribution model and flowsheet model. Simulated and experimental results of copper grade, copper recovery and concentrate mass pull correlated well with R2 values of over 0.95. These results demonstrate that the metallurgical response of ore blends can be simulated based on the flotation kinetics of distinct ore types. The use of predictive simulation can create savings during the test work phase and increase the flexibility and certainty in the process design stage.

A comparison between conventional blast hole sampling and diamond core drilling for copper grade at the Antapaccay mine

Even though the sampling technique result in potentially biased samples with poor precision of the metal grade and are classified as specimens and not samples, the manual sampling of rotary percussion blast hole chips is still widely performed in the industry for operational grade control purposes. The objectives of this investigation are to estimate the precision and“bias” of manual sampling by comparing the copper grade results of fifteen (15) diamond drill core samples versus fifteen (15) rotary percussion blast hole drilling chip samples. This also includes the determination of a practical manual sampling template with the highest precision to providean understanding of the distribution of the copper content within the cone of blast hole chips. The contouring plots of thecopper grades provides the selection of the best fit-for-purpose template with regards precision and operational resourcing requirements. The diamond drill core samples take into account the Increment Delimitation Error (IDE) andIncrement Extraction Error (IEE) and therefore can be considered as reference samples for the purpose of this review.

Buckling of dented bi-material pipe under bending Part I: Experiments and simulation

As a cost-effective solution for transporting corrosive hydrocarbons, mechanically lined pipe has been used in many offshore and onshore projects. The bonding between the carbon steel carrier and the non-corrosive liner is commonly achieved by mechanical expansion. As typical pipeline damage, the local dent brings deformation to the bimetallic composite, which is expected to undermine the structural integrity. This work investigates the influence of a local dent on the plastic responses and stability of a lined pipe system during bending. Part I presents the results of the experiments and numerical analysis involving a set of small-scale lined tubes. The lined tubes, made of carbon steel Grade GB45 (AISI 1045) and copper Grade T2, are manufactured using a custom hydraulic expansion facility. The products have finished diameters of 50 mm and an overall D/t of 16.5, with 1.0 mm thickness for the liner. A minor transverse dent is introduced to the specimen using a cylindrical indenter. The dented tube is subsequently bent to collapse in a four-point bending facility. It is found that the local dent tends to induce early collapse of both the outer tube and the liner, resulting in a noteworthy reduction of the bending capacity of the composite. Initially, the local dent grows stably instead of collapsing right away. With increasing bending, the liner develops a major buckle and several satellite dimples around it. Subsequently, the manufacture, indentation, and the succeeding bending to collapse are simulated using a custom numerical framework, and the experimental results are reproduced reasonably well. Part II will use the validated numerical model to conduct an extensive parametric study of the important variables of the problem for full-scale lined pipes.

Application of Thionocarbamates in Copper Slag Flotation

Thionocarbamates are the group of collectors that are mostly used for flotation of sulphide copper minerals, alone or in combination with xanthates depending on a mineralogical composition of the ore. In this paper, the results of the study of application of thionocarbamates in copper slag flotation are presented. Chemical analysis of smelter slag sample obtained from Flotation plant in Bor, Serbia, showed that it contains 3.56% of copper, of which over 73% is in the sulphide form, as well as 0.58 g/t of gold and 11.30 g/t of silver. XRD analysis identified fayalite and magnetite as main minerals present in the slag and SEM-EDS analysis showed that copper is mainly present in the form of sulphide minerals, thus making it suitable for flotation with thionocarbamates. Two thionocarbamates MX 980 and TC 1000 and one xanthate SIPX, along with their mixtures MX 980 + SIPX and TC 1000 + SIPX, were investigated. The influence of parameters such as collector type and dosage, grinding fineness, pulps’ pH and flotation time, on flotation indicators (recovery, yield and copper grade in concentrate) were determined. Smaller dosages of thionocarbamates (40 g/t) provided concentrates with high copper grades, 22.34% (MX 980) and 18.42% (TC 1000) and lower recovery rates, 83.98% (MX 980) and 87.78% (TC 1000), while the increase of dosages to 200 g/t led to the increase of recovery rates for more than 4% and a significant decrease in copper grades. The increase of grinding fineness from 50% to 70% of grain size < 0.074 mm showed a positive impact on flotation indicators, recovery rate, copper grade and yield, for all investigated collectors and their mixtures, while, with the further increase from 70% to 90%, recovery rates continued to increase while copper grades decreased. The increase of pulps’ pH had a positive influence, especially for MX 980, for which recovery rates increased with the increase of pH from 8 to 10 (12). A flotation kinetics test showed that flotation with TC 1000 was the fastest, i.e., recovery rate after 20 min of flotation was over 91%, while recoveries obtained with other collectors were a few percentage points lower.

Enhanced copper recovery from low grade copper sulfide ores through bioleaching using residues produced by fermentation of agricultural wastes

Enhanced copper recovery from low grade copper sulfide ores through bioleaching using residues produced by fermentation of agricultural wastes

Considering the action of frothers under degrading water quality

The stability of the froth is known to strongly affect flotation performance. Literature shows that both frothers and ions reduce bubble coalescence, and stabilise the bubbles that form, resulting in greater froth stability. Considering both variables act on the froth in a similar manner, it is becoming increasingly important to understand how frothers behave under conditions of increased ionic strength. Increasing the frother dosage stabilised the froth and increased the recovery of water and solids but had no impact on the recovery of copper and only a slightly positive influence on the recovery of nickel, with a simultaneous decrease in the grades of both copper and nickel. Increasing the ionic strength also stabilised the froth which increased the recovery of water and solids, but both the recoveries and grades of copper and nickel were unaffected. Examining both variables simultaneously revealed that ionic strength was more influential than frother dosage in the recovery of water with the opposite being true for the solids recoveries. This means that a simultaneous increase in ionic strength and decrease in frother dosage by the same amount will increase the water recoveries and decrease the solids recoveries. Such an increase will also slightly decrease the nickel recoveries while having no effect on the copper recoveries. Overall, managing the frother dosage under conditions of increased ionic strength, while still maintaining flotation performance, is possible. However, depending on the water quality, the frother dosage can be managed, this needs to be tailored to suit the requirements of the plant. Therefore, this study investigates the interrelationship between frother dosage and ionic strength within the context of flotation.

MUELLER BRASS C11000

Abstract Mueller Brass C11000 (electrolytic tough pitch copper) is an electrolytically refined, high conductivity copper that contains a minimum of 99.90% copper and a controlled amount of oxygen in the form of Cu2O. It has a minimum electrical conductivity of 100% IACS. Electrolytic tough pitch copper (C11000) is the most widely used grade of copper in electrical applications all over the world and represents over half of global copper use. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming and heat treating. Filing Code: Cu-931. Producer or source: Mueller Brass Company.

Quantitative Inversion Modeling Method for Grading Deerni Copper Deposits Based on Visible and Near-Infrared Hyperspectral Data

Quantitative metal grade inversion based on hyperspectral data is an effective approach to achieve the real-time in situ determination of ore body grades and has the advantages of low cost compared with traditional chemical analysis methods. However, the redundant nature of hyperspectral data and the parameter-limiting nature of machine learning algorithms reduce the modeling accuracy and precision, resulting in severe limitations on the application of hyperspectral techniques for the grade inversion of Deerni copper ore bodies. In this paper, we first obtained visible-NIR hyperspectral data for 190 ore samples using a spectrometer and determined the copper content of the sample set using chemical analysis; then, we processed the raw hyperspectral data using three dimensionality reduction algorithms and optimized a BP neural network based on an evolutionary algorithm. Finally, a Deerni copper grade inversion model was established using the hyperspectral data before and after dimensionality reduction, and the inversion accuracy and precision was compared and analyzed with that obtained by the BP neural network, the random forest and the variable hidden layer nodes models. The combination of the LLE dimensionality reduction algorithm and the optimized BP neural network algorithm achieves the highest modeling precision, with an R 2 of 0.950.

Sustainable Low-Cost Method for Production of High-Entropy Alloys from Alloy Scraps

In this communication,we propose a sustainable way to produce high entropy alloys from alloy scraps called Alloy mixing.We successfully demonstrate this method using a near equimolar CrCuFeMnNi HEA. Alloy scraps (304L stainless steel, Nichrome 80 and electrical wire grade Copper) obtained from various sources were melted together using vacuum arc melting along with minor additions of Mn and Cr to achieve the equiatomic composition.The alloy was characterized using X-ray Diffraction (XRD) and Scanning Electron Microscopy, which confirmed that the alloy produced through Alloy mixing exhibits a microstructure similar to that of the alloy with the same composition produced through conventional melting of pure elements

Geometallurgy of Cobalt Black Ores in the Katanga Copperbelt (Ruashi Cu-Co Deposit): A New Proposal for Enhancing Cobalt Recovery

Copper-cobalt deposits in the Central African Copperbelt belong to the Sediment-Hosted Stratiform Copper (SHSC) type and are situated in the Neoproterozoic Katanga Supergroup. This paper describes in detail the geology, geochemistry and hydrometallurgy of cobalt, with a special focus on the Black Ore Mineralised Zone (BOMZ) unit from the Ruashi Cu-Co deposit as a case study. Based on results from fieldwork and laboratory testing, it was concluded that the BOMZ consists of a succession of massive and stratified dolostones, which are weathered into carbonaceous clay dolostones and clays. The Lower “Calcaire à Minéreaux Noirs Formation” (Lower CMN Formation) consists of stratified and finely laminated dolostones, which are weathered at the surface into clayey to siliceous dolostones. The cobalt concentration in the weathering zone is due to supergene enrichment, a process that is linked to the formation of a cobalt cap. The ore consists of heterogenite associated with minor amounts of chrysocolla and malachite. Minor carrollite, chalcopyrite, chalcocite and bornite are present in unweathered fragments. The cobalt grade in both the BOMZ and Lower CMN decreases within depth while the copper grade increases. These grade changes reflect the variation in mineralogy with depth from heterogenite with minor amounts of malachite and chrysocolla to malachite, chrysocolla with traces of heterogenite, spherocobaltite, chalcocite, chalcopyrite, carrollite and bornite. Based on the Cu (100xAS Cu/TCu) and Co ratio (100 xAS Co/TCo), which is related to the ore mineralogy, oxide ores (Cu ratio ≥ 75%) and oxide dominant mixed ores (Cu ratio < 75%, containing the copper sulphide chalcocite) can be differentiated in both the BOMZ and Lower CMN. The absence of talc and the low concentration of Ni, Mn and Fe, on the one hand, and the high-grade Cu in the BOMZ, on the other hand, facilitate the hydrometallurgy of cobalt but require a specific processing. Consequently, the recovery of Co from the BOMZ requires the application of a processing method that is based on sulphuric acid (30 g/L) leaching under reducing conditions (300–350 mV) and the removal of impurities (Cu > 95% and Mn ≈ 99%) from the pregnant leach solution (PLS) by solvent extraction (SX) prior to the precipitation of cobalt as a high-grade hydroxide (40.5%). The sulphuric acid leaching of the BOMZ enabled achieving, after 8 h of magnetic stirring (500 rpm), a highest yield of 93% Co, with other major elements Mn (84%) and Cu (40%). The latter forms a main co-product of the Co exploitation. In contrast, the highest leaching yield for Fe remained smaller than 5%.

Study of Reagent Scheme, Entrainment and Their Relationship in Chalcopyrite Flotation in the Presence of Bentonite and Kaolinite

Entrainment has been considered as an important factor affecting clayey ore flotation. In this study, the effect of reagent dosage on chalcopyrite flotation in the presence of bentonite and kaolinite was investigated through entrainment. It was found that increasing the collector and frother dosage had little influence on copper recovery in the presence of bentonite, but decreased the copper grade substantially, owing to the increase in entrainment. With regard to kaolinite, increasing the reagent dosage increased the copper grade prominently, due to the decrease in entrainment. The substantial variation was related to the different interactions between the reagent and different clay minerals. The smaller surface area and hydration property of bentonite made most of the reagent remain in the solution, facilitating high entrainment, while kaolinite, with its larger surface area, adsorbed most of the reagent, which decreased the entrainment. The results of this study suggest a guideline of controlling reagent scheme in clayey ore flotation, based on the specific structure and properties of different clay minerals.

Forming of properties complex of copper wire by the method of combined deformation by torsion and tension

The object of research is the mechanical properties of copper wire M1 for electrical applications, subjected to combined torsional deformation with tensile tension. One of the most problematic aspects in the manufacturing of such a wire is its fracture during processing due to low strength and ductility. DSTU EN 13602:2010 regulates the ultimate tensile strength, relative elongation, the number of bends before fracture and the number of twists until failure. To increase the service life of the product it is necessary to increase strength and plastic properties. The methods of influence on the material by combined plastic tensile deformation with tensile was used in the study, the mechanical characteristics (ultimate tensile strength, true deformation before failure, relative elongation, relative reduction in area) and electrical conductivity were determined. Statistical analysis tools were used for modeling and graphical displaying of data. The proposed approach allows to select the modes of combined torsional deformation with tensile, providing the optimal combination of tensile strength and relative narrowing of M1 grade copper wire. Under certain modes of such deformation, with increasing degree of deformation, it is possible to increase the strength characteristics and at the same time obtain high values of plasticity. The obtained results of approbation of different combined deformation modes allow to consider it an effective tool for achieving high values of true rapture stress and ultimate deformation in order to improve the service characteristics of the deformed wire. It is shown that relaxation processes occur during such treatment, which leads to a decrease in stresses and a sharp increase in plastic characteristics. Clarification of the mechanisms of the characteristics formation allows to control the features of the structure and, accordingly, the level of mechanical properties to obtain a wire that combines high strength with high toughness. This makes it possible to develop deformation modes to obtain copper wire with special properties depending on customer requirements, for example: strong wire with low electrical resistance.

ТЕХНОЛОГИЧЕСКИЕ ПРОЦЕССЫ ПОЛУЧЕНИЯ ФУНКЦИОНАЛЬНЫХ ПОКРЫТИЙ МЕТОДОМ ЭЛЕКТРОКОН ТАКТНОЙ ПРИВАРКИ

Electric contact welding (ECW) is a promising resource-saving technology for obtaining functional coatings from the waste of tool-making and machine-building production. A clear methodology is a pre-requisite for selecting the materials, equipment, and tools used; stating the order and describing the operations (transitions) performed; and choosing technological modes (parameters). To develop a technique for obtaining, strengthening, and restoring machine parts, the authors studied functional coatings obtained by electric contact welding at the 011-1- 10 “Remdetal” installation. The duration of the welding pulse and pauses was set using the RVI-501 controller. The welding current strength was calibrated through a strip made of 5 mm thick copper grade with the welding current meter IST-02. Based on the analysis of the ECW zone resistance, he authors found that, for the steel belt U12, the optimal value of the compression force of the welding electrodes on the plowshare made of 65G steel will be 1.7 kN. To ensure the highest effi ciency of the ECW process and complete overlap of welding sites, and taking into account the mutual movement of electrodes and parts, the authors present the relationships that help pre-set the main parameters of electrical contact welding for all circuits and equipment options: the strength of welding current, its fl ow time and the pause between pulses, the compression force of welding electrodes, welding speed, overlap coeffi cients of welding points fl ow rate of the cooling liquid and their infl uence on the process fl ow and the quality of coatings obtained. The presented algorithm can be used in machine-building production and, in particular, repair production for designing technological processes of obtaining functional coatings during the hardening and restoration of machine parts.

DETERMINING A RESILIENT STOPE BOUNDARY FOR UNDERGROUND MASS MINING PROJECTS

Uncertainty-based stope boundary optimization is a complex part of underground mine planning, especially in mass mining projects and notably block caving. Besides, grade variation and grade uncertainty are significant sources of error in mining projects. This paper presents a procedure to determine a resilient block-cave stope boundary considering the ore grade uncertainties. The procedure applies the floating stope algorithm, the maximum upside/minimum downside, and the value at risk for design evaluation. The floating stope algorithm is customized for block caving and is used to determine the stope boundary over some simulated grade models. The idea fits into a multi-criteria decision-making problem. Finally, the most resilient stope boundary is selected by considering several criteria and the TOPSIS method. According to the results, the resilient stope boundary covers an area where the mineable reserve is 977 Mt with an average copper grade of 0.51%.

Microstructural Analysis and Mechanical Behaviour of Copper CDA 101/AISI-SAE 1010 Dissimilar Metal Welds Processed by Friction Stir Welding

In this work, low-carbon steel AISI-SAE grade 1010 with copper grade CDA 101 was joined by friction stir welding (FSW) using a tapered pin profiled tool. The rotational speed of the tool is 900 rpm, a traverse rate of 30 mm/min, and an axial force of 5 kN were used to produce the joints. The microstructural analysis and mechanical properties of the weld joints have been successfully examined. The optical microscopy, scanning electron microscopy, and X-ray diffraction (XRD) techniques were performed to examine the macropatterns and micropatterns of the welded joints. The tensile and hardness test was performed to evaluate the mechanical behaviours of the FSW joints. The fine ferrite grain features with uniform size were obtained in the microstructure of the nugget zone (stir zone). It is purely influenced by the alternating dynamic rearrangement (recrystallization) mechanism. High hardness was identified in the stir zone, even as the slightest stability was established in the heat-affected zone. The tensile investigation proposed that all the joints explored just lesser unbending nature than the parent material. The tensile strength of 181.5 MPa, the hardness of 144 VHN, and elongation of 14.03% were observed for the welded samples. The better properties for the weld joints were attained at 900 rpm spindle speed and tool traverse speed of 30 mm/min. The FSW is an attractive material joining process for both similar and dissimilar materials compared to other conventional types of joining processes, such as aerospace, marine engineering, shipbuilding, and industrial sector applications.

Influence of aluminum ion on the structural, optical, and electrical properties of CuO thin films for the PN-Junction diode application

Pure and (1, 3, and 5 wt%) Aluminum-doped copper oxide(Al:CuO) thin films were prepared using the JNS spray-pyrolysis technique using analytical grade copper chloride and aluminum chloride as a precursor. The monoclinic structure of the CuO film has been confirmed by an X-ray diffraction (XRD) study. The microstructure of the films is analyzed with the help of a scanning electron microscope (SEM). The optical characteristics of the grown films have been examined with the help of UV–vis spectroscopy, from which the bandgap of the materials of the coated films are calculated. Electrical properties such as conductivity and the diode activity of the films are studied using I-V characterization, which shows the improved electrical conductivity with the increase in doping concentration. Diodes are fabricated using pure and Aluminum-doped p-type CuO thin films coated on the n-type silica wafer by the JNS technique, and the rectification behavior is found to improved at a higher doping concentration of Al3+ ions.

Design cases for Russia’s largest mining and processing enterprises for copper ores

The article covers the design and construction of advanced processing facilities for JSC Russian Copper Company (RCC), one of the leaders in the field of mining and processing of copper ores in Russia. JSC «Mekhanobr Engineering» has been directly involved in the respective work. In 2015–2020, RCC’s largest mining and processing plants of Mikheevskiy GOK and Tominskiy GOK were put into operation. Mikheevskiy GOK was built in the shortest possible time, however the initial performance monitoring revealed certain specific features of the ore, which required a number of process improvements. «Mekhanobr Engineering» experts updated the design documentation for concentrator No. 1 and the tailings facilities. The enterprise is currently in operation, producing copper concentrates with the copper grade of up to 25 wt. %. For concentrator No. 2 of Mikheevskiy GOK, the entire documentation set and all field construction supervision activities were developed and conducted by «Mekhanobr Engineering». The copper recovery and concentrate grade design targets were achieved immediately after the commissioning. The design work for Tominskiy GOK included a certain modification of the process and main process equipment of the concentrator. For example, tailings slurry thickening was added. In 2018, «Mekhanobr Engineering» experts proceeded with preparing design documentation for the concentrator of Malmyzhskiy GOK, one of RCC’s largest enterprises. This design features some of the most advanced and efficient equipment sets in the world.

Characterization study and recovery of copper from low grade copper ore through hydrometallurgical route

Characterization studies were conducted on low grade copper ore with the aid of standard approaches. The Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) study specifies the semi-quantitative data of qualitatively analyzed chemical elements present in the ore sample. Optical Microscopy (OM) and X-Ray Diffraction (XRD) endorse the presence of chalcopyrite (CuFeS2) and pyrites along with other different mineral phases in the ore sample. Thermo Gravimetric Analysis (TGA) and Mossbauer spectroscopy studies confirm the formation of CuO and Fe2O3 after roasting at 700 °C. The better copper recovery from low grade copper ore was achieved through optimized leaching parameters. It was found that the particle size of −63+53 µm can be leached up to 94.96 % of copper using a lixiviant reagent mixture (30 vol. % hydrogen peroxide and 0.5 M sulfuric acid) under magnetic stirring for 30 min at a constant speed of 300 rpm, by keeping the liquid/solid (L/S) ratio at 20/2 ml/g. Moreover, the solvent extraction process works well with the pregnant leach solution, whereby, 98.9 % of copper extraction is possible, and the loading time is less than a minute. Meanwhile, 93.91 % of overall copper extraction efficiency was achieved through optimized leaching parameters and solvent extraction method.

Regulations, risk management and experience about tailings dams in Chile

Chile is the biggest copper producer in the world, the production of fine copper in 2018 was approximately 5.5 Mton and it is estimated that in 2025, 7.2 Mton of copper will be produced. This production, added to copper grades of less than 1%, causes 99% of the material that is processed to become mine waste such as tailings storage, heap leach pads and rubble deposits. Tailings are classified as high risk environmental waste, and these tailings are also located in a country of high seismicity. Due to this, Chile has a regulatory framework that allowed the improvement of the standards in the design, construction and operations of tailings deposits based on the know-how about the behaviour of these structures. Currently, a risk management system is being implemented to identify the risks and take decisions and actions to ensure the physical and chemical stability of these different types of storage. This article describes the Chilean experience about the behaviour of tailings storage under high magnitude seismic events. A summary about the regulatory framework and the recently implemented risk management is also presented.

Cтруктура и прочность мелкозернистой меди после криогенной прокатки и обработки однократными импульсами тока различной мощности

The effect of a treatment combining isothermal cryogenic rolling and single electro-pulsing on the structure and hardness of M1 grade copper with an initial grain size of 10 –15 μm was investigated. Copper was deformed at liquid nitrogen temperature by multi-pass rolling with a total reduction of 90 %. Subsequent electro-pulse treatment (EPT) was carried out in the interval of integral current densities (Kj) from 3.5 ×104 to 8.1×104 A2 s / mm4. Nearly two-fold strengthening of Cu under rolling was found due to the formation of a heavily deformed (sub)grain structure with a crystallite size of the order of 1 μm and a fraction of high-angle boundaries of about 30 %. With further EPT with an energy of 3.5 ×104 A2s / mm4, the processes of recovery predominantly occur, resulting in slight softening with a simultaneous strong decrease in micro-distortions of the crystal lattice and dislocation densities. Processing with higher energies resulted in a sharp drop in the hardness of Cu owing to an activation of in-situ continuous static recrystallization, forming regions of new fine defect-free grains, whose fraction increased with Kj, and intensified the formation of annealing twins. As a result of EPT with Kj in the range of 5×104 – 7×104 A2s / mm4, a uniform fine-grained structure with a grain size of near 2 μm and a fraction of high-angle boundaries of about 90 %, a third part of which were twins of Σ3, was obtained. With a further increase in pulsing energy to 8.1×104 A2s / mm4, normal grain growth to 4 μm with minor changes in the angular parameters of the structure were observed. The nature of structural and mechanical behavior of copper is discussed. A conclusion is made on the viability of the use of combination of cryogenic rolling and EPT to manufacture ultrafine- and fine-grain sheets of different strength out of copper.