Rubber compounds are elastomers usually highly filled with carbon black. Similar to two-phase particulate-filled thermoplastic melts,3138 they are non-Newtonian viscoelastic media with inherent yield-stress.3944 Rubber compounds are highly thixotropic in nature. The yield stress and non-Newtonian and thixotropic behavior are dependent upon the concentration of the carbon blacks, their activity, particle size and their distribution and shape.32,33,41 Due to the presence of the yield stress, rubber compounds show solid-like behavior at stresses below the yield stress and viscoelastic-fluid behavior above it. In particular, Figure 2 shows a dependence of viscosity on shear stress for styrenebutadiene rubber (SBR) filled with carbon black. The rheological behavior observed in this figure is typical of rubber compounds. At low shear-stresses, the gum SBR exhibits a constant shear-viscosity, while carbon-black-filled SBR shows an unbounded value of the shear viscosity, indicative of the presence of a yield value. At high shear-stresses, the compounds and the gum rubber show a decrease of viscosity, the behavior typical of a non-Newtonian fluid.
There have been some efforts towards developing a constitutive equation to describe the observed rheological behavior in two-phase systems. However, these attempts have so far led to a qualitative description of the real behavior of rubber compounds. In particular, development of a fluid model with yield stress has a long history.4548 By combining the Von Mises yielding criterion with the NavierStockes Newtonian-fluid equation of motion, a three-dimensional Bingham fluid model has been developed.4951 This theory has been improved by introducing viscosity as a function of the invariants of the rate of deformation tensor,52 in order to accommodate non-Newtonian behavior after yielding. Further, the time-dependent yield value has been introduced53 to explain thixotropic behavior. An attempt54 has also been made to extent Oldroyds plastic non-Newtonian viscous constitutive equation52 to describe a plastic material exhibiting viscoelastic behavior beyond the yield value. In recent years, there have been further theoretical and experimental studies of the rheological behavior of particle-filled melts exhibiting yield behavior, viscoelasticity and thixotropy.5560 Huttons yield-viscoelastic constitutive equation54 has been extended by including explicit expressions for the time-dependent yield-stress and non-linear memory function. The White model5557 has been tested on several particulate-filled polymers, but in a narrow range of strain rates.
In some rubber compounds and pure elastomers a further complication arises due to the presence of the slip effect during flow along the solid boundary, such as occurs in processing equipment.43,6265 Typically, the slip velocity for a particular rubber compound depends on temperature, shear stress, shear rate and pressure.66 In particular, the presence of hydrostatic pressure reduces slip velocity, while an increase in shear stress and temperature leads to an increase in slip velocity. As an example, Figure 3 shows data obtained on an EPDM-based rubber compound (EPDM is ethylenepropylene diene monomer). Slip velocity can reach values as high as 10cms1 at high shear-stress. The occurrence of slip effects in processing equipment, e.g. in injection molding, may lead to several undesirable phenomena such as non-homogeneity of the compound, poor mixing or unstable feeding. At the same time, the slip effect can be beneficial in reducing the pressure needed to fill the mold or push a compound through the dies. In the capillary rheometer, the presence of the slip effect leads to a dependence of flow curve on the capillary diameter. Namely, flow curves obtained in capillaries of a smaller diameter are shifted toward lower shear-stresses or higher shear-rates in comparison with those obtained in capillaries with a large diameter. Although the problem of slip has a long history,62 it is still not well understood, especially for the case of injection molding of rubber compounds.
As a processibility indicator, many rubber molders rely on the Mooney viscosity.2 However, the Mooney viscosity is not indicative of the complicated rheological behavior of rubber compounds, since it determines viscosity at one particular shear rate. In injection molding the flow curve measured over a wide range of shear rates is required.67 Shear rates which rubber compounds experience in the molding system can be as low as a few reciprocal seconds and as high as tens of thousands. Obviously, viscosity determined at one shear rate, such as the Mooney viscosity, cannot characterize the viscous behavior of a rubber compound.5,9,67 In this regard, the use of capillary rheometers can be quite beneficial for the evaluation of the processibility of rubber compounds.31,68 In particular, the Instron capillary rheometer has been employed for these purposes.4,67,69 The recent development of the Monsanto processibility tester, which has been specifically designed for rubber compounds, has provided an important tool for measuring the viscous properties of rubber compounds under injection molding conditions.9,7073 In addition, the development of the capillary or slit rheometer on the base of injection molding screws is another alternative.74,75 In this case, a capillary or a slit die with pressure transducers installed along its length can be attached to the injection screw. The injection unit can be used to push rubber compounds through the die at various velocities thus giving a range of high shear-rates realized during molding. The experiments can be conducted under isothermal and non-isothermal conditions. Thus, such a rheometer would allow measurement of the flow curves at various temperatures. In this case, even a change of flow curve during the early stage of vulcanization can be detected. The latter is highly important for cavity-filling simulation.
For many rubber compounds, the power-law model is known to be a good approximation in the high shear-rate region only. Thus, a more general form of the rheological equation is needed. Several equations are employed for injection molding of rubber compounds to fulfill this requirement. In particular, the Rubbers and Plastics Research Association (RAPRA)76 uses a so-called Klein viscosity equation,19 which is a second-order function of temperature and shear rate, namely
Here, Aij are material constants. The drawback of this model is that it predicts a maximum viscosity at some low shear-rate and a minimum viscosity at some finite value of temperature. In addition, this viscosity function shows crossover points in flow curves corresponding to different temperatures. Thus, in order to correctly apply this viscosity model, a careful consideration should be given to the range of temperatures and shear rates over which it is applied.
is the zero shear-rate viscosity. This equation can be applied to a wide range of shear rates and includes four material parameters, namely A, Tb, * and n. In particular, it has been widely used in the simulation of injection molding of thermoplastics77 and, most recently, of rubber compounds.73 However, even the latter equation is not applicable to those rubber compounds which exhibit yield stress leading to an unbounded value of viscosity at low shear-rates. In order to correct this deficiency, the Cross equation has recently been modified by incorporating yield stress.79 This led to
where Y is the yield stress, and A and B are material constants. Evidently, these three constants should be temperature dependent, although this was not specified in ref. 79 which dealt with isothermal flow.
In addition to viscosity, extrudate swell is an important characteristic of the behavior of a rubber compound. According to Oda et al.,80 the extrudate swell is a criterion for determining the allowable gate-size to avoid undesirable jetting during cavity filling.
Rubber compound formulations have generally evolved over many years with new additives and fillers combined with old. A typical rubber formulation may have two or three different types of rubber adding up to 100 parts and then curatives, fillers, process stabilizers, accelerators, antiozonants, antioxidants, lubricants, processing aids, acid and base neutralizers, and colorants, to name a few, are added on top in the old part per 100 (PHR of 100 parts of rubber) formulation scheme. Understanding all of the potential interactions and imparted attributes of these additives, during processing, curing and in the end-use application, is more of an art than a science. At the very least it would require a large design of experiment to map the interactions of a multicomponent system such as this and so much of this knowledge is learned by experience and maintained cerebrally. To show the complexity, Table 4.2 is an example formulation for a fairly simple tire compound.
Often side reactions or unexpected consequences occur when adding new materials to such a complex formulation. For example, soda lime borosilicate HGMs can have a moderately high pH of 9.510. Yet the formulation in Table 4.2 already has a fairly basic oxide additivezinc oxide, used in part to accelerate and control the rate of the cross-linking reaction. It acts as an acid absorber balancer to the acidic sulfur vulcanizing agents. Adding another fairly basic additive to this mixture may change this delicate balance and cause scorch (too fast a viscosity build) or poor mill-ability (tooslow of viscosity build). Commonly, when adding HGMs to rubber compositions, it is recommended to test cure rates through the use of an MDR rheometer to evaluate the potential effect of the pH on viscosity.
Among all processing industries, only in the ore and mining industries is the accent more on wear resistance than corrosion. In mining industries, the process concerns material handling more than any physical or chemical conversions that take place during the refining operations. For example, in the excavation process of iron ore, conventional conveyer systems and sophisticated fluidized systems are both used [16,17]. In all these industries, cost and safety are the governing factors. In a fluidized system, the particles are transported as slurry using screw pumps through large pipes. These pipes and connected fittings are subjected to constant wear by the slurry containing hard minerals. Sometimes, depending on the accessibility of the mineral source, elaborate piping systems will be laid. As a high-output industry any disruption in the work will result in heavy budgetary deficiency. Antiabrasive rubber linings greatly enhance the life of equipment and reduce the maintenance cost. The scope for antiabrasive rubber lining is tremendous and the demand is ever increasing in these industries.
Different rubber compounds are used in the manufacture of flotation cell rubber components for various corrosion and abrasion duty conditions. Flotation as applied to mineral processing is a process of concentration of finely divided ores in which the valuable and worthless minerals are completely separated from each other. Concentration takes place from the adhesion of some species of solids to air bubbles and wetting of the other series of solids by water. The solids adhering to air bubbles float on the surface of the pulp because of a decrease in effective density caused by such adhesion, whereas those solids that are wetted by water in the pulp remain separated in the pulp. This method is probably the more widely used separation technique in the processing of ores. It is extensively used in the copper, zinc, nickel, cobalt, and molybdenum sections of the mineral treatment industry and is used to a lesser extent in gold and iron production. The various rubber compounds used in the lining of flotation cells and in the manufacture of their components for corrosive and abrasive duties are:
The specified rubber compound is mixed and calendered and plied up to the desired thickness, then sheeted out on a two-roll rubber mill, or extruded. These unvulcanized rubber blanks are then prepared in for subsequent molding operations one of the following ways:
The above methods have the following features and/or drawbacks: Method 3 gives maximum production and minimum rejection; Method 1 is more tedious, and results in more remilling of waste; Method 5 may lead to ply separation in hard stocks; Method 2 is the simplest, but rejections are higher, due to joint separation at the bias cut portion and, with soft stocks, air trapping is expected; Method 4 is prone to lamination faults at the joints.
Vulcanization is done in case hardened mild steel or Nitralloy molds. Large and small O rings can be molded concentrically in the same mold. The flash at the parting line is either stripped off by hand or by trimming in a tumbling barrel using solid carbon dioxide. The rubber is frozen so hard that friction from its motion against the walls of the tumbling barrel removes the flash completely. Large O rings demand hand buffing.
In reinforced rubber compounds, unlike gum (unfilled) rubber, the elastic modulus is generally dependent on the strain amplitude. G approaches a limiting value at very low amplitude, which is higher than the limiting value approached at high DSA. The extent of this augmentation (G) depends on the loading and surface area of the carbon black, but not significantly on structure (Medalia 1978). At a normal loading of a reinforcing black the augmentation can be substantial; for example, with N220 (iodine number 126) at 50phr in SBR-1500, G is 44% higher at a DSA of 0.5% than at a DSA of 10%, while with N568 (iodine number 47) the augmentation is only 13% (based on measurements at 25 C and 0.25Hz). The augmentation is less at higher temperatures, greater at higher frequencies.
The augmentation of elastic modulusoften referred to as the Payne effectis attributable to the network of carbon black which is broken down at high amplitudes. Mixing procedures which improve the separation dispersion diminish G; for example, a two-stage mix in the above formulation with N220 gives only a 29% augmentation. Confirmation of the network as the source of augmentation comes from the electrical conductivity, which is higher for higher surface-area carbon blacks, and decreases with improved separation dispersion.
As mentioned above, rubber compound is vulcanized after mechanical mixing process. Therefore, especially just after vulcanization, residual stress exists inside of it. When thermo-dynamic impact is applied to it, it is expected to transform so that the residual stress is released.
Regarding reinforcing fillers, the interaction with rubber molecules is not rigid. They therefore easily alter their arrangements in a rubber compound. As a result, the orientation of the filler arrangement and the transition of the adsorbed state of molecules on the fillers to a more thermodynamically stable state can be observed. The former is known to cause the deterioration of crack resistance of rubber compounds to a specified direction.
Cure characteristics of rubber compounds must include a delay in the onset of cross-linking to allow sufficient time for the stock to flow at elevated temperatures to fill mold cavities. Then the cure should proceed rapidly to minimize the required time in the mold. Special measurements of scorch time at high temperature may be necessary to assure that a compound is usable for injection molding, since the stock may be subjected to high temperatures for a considerable time before injection into the mold.
Compounds should be designed for good mold release, and should not leave residues on mold surfaces, which could lead to subsequent sticking of parts and unacceptable surface quality. The choice of cure system plays a large part in this. The original diamine cure systems generally give mold dirtying and poor quality surfaces on parts after a few heats, thus these systems are little used. Bisphenol cures can be formulated for good release, and are widely used for molded parts. Peroxide systems give variable results. The relatively slow cures of fluoroelastomers with bromine cure sites often give demolding problems, while the fast cures with iodine cure sites can give clean demolding. Mold release agents may be incorporated into compounds. These agents are incompatible with the fluoroelastomer at molding temperatures, so that they migrate quickly to the interfaces between stock and mold surface to facilitate release. When such internal mold release agents are effective for a given compound, they are preferable to external mold release agents, which must be sprayed on mold surfaces periodically.
Volatiles may be released from the cured stock when the mold is opened, so adequate local ventilation should be provided to protect operators. A concern with peroxide cures is the release of methyl bromide and/or iodide. The amounts of these materials can be minimized by keeping the ratio of radical trap (usually TAIC or TMAIC cross-linker) to peroxide high enough so that methyl radicals are intercepted by the trap, rather than by halide groups on polymer chains. Peroxide decomposition also results in significant amounts of low-molecular-weight organic compounds, such as acetone and isobutene, which will be evolved on demolding of the hot cured parts. In bisphenol cures, inorganic base levels should be set high enough to avoid significant hydrogen fluoride evolution.
For good control of dimensions and surface characteristics of parts, molds should close tightly and cleanly at the flash line. Surfaces should be free of nicks and pits. Hard chrome plating of mold surfaces is recommended to minimize mold fouling.9 However, chrome plating at sharp edges may show excessive wear. Molds made of nickel chrome alloy have hard wearing surfaces with good release characteristics.15 Mold platens which hold mating mold plates should be free of distortion. The platens should be provided with heaters that allow good control of mold temperature.
Compared to other elastomers, fluoroelastomers have higher thermal expansion coefficients and are cured at higher temperatures, so higher shrinkage is usually observed in cured fluoroelastomer parts. Shrinkage increases with higher molding temperatures and decreases with higher levels of filler and metal oxides in compounds. A bisphenol-cured VDF/HFP dipolymer compound with 30phr MT black shows 2.53.2% shrinkage after molding at 177204C (380390F). An additional 0.50.8% shrinkage occurs after postcuring in an oven at 204260C (399204F), as water and other volatiles are removed.6 Shrinkage may be higher for fluoroelastomers with higher fluorine content. For close control over dimensions, shrinkage should be measured for a given compound and molding conditions, to allow proper design of mold cavities. Some fabricators may use molds designed for nitrile rubber to make fluoroelastomer parts. This may necessitate restrictions on fluoroelastomer composition, filler level, and cure temperature to get finished parts within size tolerances.
The physical properties of rubber compounds are highly dependent on the test conditions. Some of the problems associated with rubber testing are apparent in the typical stressstrain curves, obtained during cycling to constant load, see Figure 9 (1=initial stressing curve, 2=first retraction curve, 3=second stressing curve, 4=second retraction curve). These are for three natural rubber compounds of different carbon black loading, and demonstrate the stiffening effect of carbon black.
The nonlinearity of rubber elasticity is also apparent, the slope of each curve being initially steep (Young's modulus), but decreases in the middle region, before increasing again at high elongations as the ultimate elongation is approached. Thus, rubber stiffness (whether defined by the tangent or the more usual secant modulus) must have the extension defined to be useful. The curves are also markedly dependent on whether the strain is increasing or decreasingthe difference being a consequence of the internal viscosity (hysteresis) of the rubber compound, where the area between the curves is an indication of the energy lost. The slopes on the second and subsequent extension cycles are always lower than on the first due to the breakdown of crystallinity or of the carbon black structure (the Mullins effect).
In dynamic tests, rubber properties vary with the temperature, frequency, and strain amplitude of the test. Thus, the elastic modulus initially decreases with strain as described above, but increases progressively as the temperature is reduced (prior to a sharp increase of a factor of 1000 as the Tg is approached), or as the frequency of a dynamic test is increased. This frequencytemperature dependency is fundamental to elastomers, and applies to most physical properties. Analysis over a range of test conditions leads to the well-known WLF transform (Williams et al., 1955), which, if Tg of the rubber is known, allows test results obtained under different conditions to be harmonized.
Natural rubber will almost certainly be used in cases where the compound does not have to withstand high temperature, direct sunlight or ozone, and where it does come into contact with oils, solvents, fluids or chemicals. Synthetic rubbers, which have better resistance than natural rubber to these factors, are used where they will be encountered routinely. Typical applications of some synthetic rubbers are given below:
The use of the right rubber compound is important for manufacturing long-lasting and cost-effective products. A lot of developments have occurred in rubber compounding to improve the final performance. However, it is important to know the basic principles of rubber compounding to further develop new novel materials with excellent properties . Here, we have given a brief report on the basics of rubber compounding and their various characterisations. The need for the development of an economic and environmental friendly way addressing the global challenges of the 21st century is one major areas that is given prime importance.Progress in the area of green composites which reduces the harmful environmental effects during its life time is one such development that have gained wide appreciaton. Within various compounding strategies available right now one of the fascinating and hopeful areas that gives good scope for the development of materials with excellent properties is the introduction of nano technology in rubber compounding. The future development, while formulating different methodologies, should take into consideration a wide range of potential economic, environmental, and societal implications of the technology.
Three different technologies in tailing management were analyzed and compared.Six different scenarios in tailing management were developed.Two analysis methods were applied: life cycle costing and environmental valuation.Belt press technology with 10% renewable energy generated the greatest benefits.
Sustainable mining management is increasingly seen as an important issue in achieving a social license to operate for mining companies. This study describes the life cycle cost (LCC) analysis and environmental valuation for several coal mine tailings management scenarios. The economic feasibility of six different options was assessed using the Net Present Value (NPV) and Benefit-Cost Analysis (BCA) methods. These options were belt press (OPT 1), tailings paste (OPT 2), thickened tailings (OPT 3), and OPT 1 with technology improvement and renewable energy sources (OPT 1A-C). The results revealed that OPT 1A (belt press technology with stack cell flotation) was the first preference in terms of LCC while OPT 1C (belt press technology with stack cell flotation and 10% wind energy) generated the highest benefits value (BCA) compared to the other options. The LCC and BCA components and the volume of GHG emissions were used to determine the best option. Normalization of these three elements resulted in the selection of Option 1C as being the most cost-effective option.
Barium slag (BS) has high carbon content with value-added of recycling.Sulfuric acid was used as pH regulator and could precipitate soluble barium ions.Carbon grade was 63.25% and recovery was 82.70% under optional parameters.Recycling of carbon effectively minimizes the discharge of BS.
Barium slag is a kind of solid waste derived from the carbon reduction process of producing barium salt. Carbon is one of the main components in barium slag with a content of more than 10%. In this study, a barium slag was characterized using XRF, XRD and SEM-EDS, and froth flotation test was introduced to recover the carbon in the barium slag. In the process of froth flotation test, diesel was selected as a collector and terpenic oil was selected as a frother for carbon separation. The flotation influences of pulp pH, collector dosage, frother dosage and flotation time were investigated. The results showed that the obtained carbon concentrate had a carbon grade of 63.25% and its recovery was 82.70% under the conditions of pH 8.50, diesel 600g/t, terpenic oil 500g/t, and flotation time 5min. SEM-EDS analysis results revealed that the flotation concentrate was coarse and its particle sizes had a homogeneous distribution. The findings of this research provide a new pathway for barium slag utilization. The carbon obtained from the flotation test in this study can be recycled as raw materials, while the reduction of the remaining tailings can be utilized as building material additives.
For its extensive practical experience, 911 Metallurgisthas a clear understanding of what successful mineral processing engineering is and how to go about achieving it. Your goal is the production of a material that is marketable and returns you and your investors sustainable revenues.
Although improvements to the metallurgical processes have been made over the years the fact is that the unit operations, the machines, those too often called black boxes involved have not evolved or changed much since inception. Ore is reduced in size, chemicals are added and minerals separated and upgraded to produce a marketable product. Much of this process is mechanical and generally mistaken for some dark alchemy.We are the Anti-Alchemists.
Our vast experience has been gained through operation and start-up of both small and large scale mining/metallurgical operations in a range of commodities in thebase metals (Cu, Pb, Zn) and theprecious metals (Au, Ag,)
A solid metallurgist understands, the most important aspect of an operating process is its stability. Simple to say, but generally the most ignored in mineral processing. Linked unit operations require each to be stable, and each contains a different set of variables that have to be contended with. Thanks to some degree of stability: operating changes can be made and evaluated; increases in throughput can be made; and equipment performance improved. The more complicated the processes become, the more difficult it is to achieve and maintain stability. In mineral processing, unlike most processing operations, we have limited control of the main input, the feed ore. In most cases this inherently is variable and usually outside of the processors control.
Because you are too close to your own story, you might not see the forest for the trees and have chaos mistaken for stability. We, you, and your group have been battling plant problems for weeks, you start to accept chaos as a daily state of affair and consider it your new stability.
Each mineral processing plant is different: with varied ore types, mining equipment, and management (operating) philosophy. The evaluation and prioritisation of variables that affect the plant performance is the primary function. Implementing changes within the constraints imposed can be difficult, as resources may be limited.
Invariably the ability to solve problems can be confusing due the large numbers of variables that may impact the processes. In most cases problems are not metallurgical in nature but rather operational and mechanical. Problem solving is a process and in many operations this ability is absent. All too often many changes are made together without a solution resulting, on more confusion. Most plants learn to live or survive their problems, not to solve them.
Our engineering team has a global experience in the mining industry across all facets of the mine life-cycle. Our focus is to add value to your project and company by understanding your needs, employing innovative ideas and applying sound engineering while maintaining an economically driven approach. We have a combination of senior level professionals, experienced project managers, and technical staff to execute projects efficiently. We work in a partnership with our clients to achieve their company goals and operational milestones in a timely and cost effective manner.
At first sustainable mining could be perceived as a paradoxminerals are widely held to be finite resources with rising consumption causing pressure on known resources. The true sustainability of mineral resources, however, is a much more complex picture and involves exploration, technology, economics, social and environmental issues, and advancing scientific knowledgepredicting future sustainability is therefore not a simple task. This paper presents the results from a landmark study on historical trends in Australian mining, including ore milled, ore grades, open cut versus underground mining, overburden/waste rock and economic resources. When complete data sets are compiled for specific metals, particular issues stand out with respect to sustainabilitytechnological breakthroughs (e.g. flotation, carbon-in-pulp), new discoveries (e.g. uranium or U), price changes (e.g. Au, boom/bust cycles), social issues (e.g. strikes), etc. All of these issues are of prime importance in moving towards a semi-quantitative sustainability model of mineral resources and the mining industry. For the future, critical issues will continue to be declining ore grades (also ore quality and impurities), increased waste rock and associated liabilities, known economic resources, potential breakthrough technologies, and broader environmental constraints (e.g. carbon costs, water). For this latter area, many companies now report annually on sustainability performancefacilitating analysis of environmental sustainability with respect to production performance. By linking these two commonly disparate aspectsmining production and environmental/sustainability datait becomes possible to better understand environmental sustainability and predict future constraints such as water requirements, greenhouse emissions, energy and reagent inputs, and the like. This paper will therefore present a range of fundamental data and issues which help towards quantifying the resource and environmental sustainability of miningwith critical implications for the mining industry and society as a whole.
The feasibility of lithium-ion battery remanufacturing is evaluated.Remanufacturing of electric vehicle batteries is environmentally beneficial.The potential cost saving is about $1.87kg1 cell produced.The purchase price for spent batteries is a crucial factor to the profitability.
The environmental threats posed by spent lithium-ion batteries (LIBs) and the future supply risks of battery components for electric vehicles can be simultaneously addressed by remanufacturing spent electric vehicle LIBs. To figure out the feasibility of battery remanufacturing, this paper quantifies the environmental impacts and costs of the remanufacturing of lithium-nickel-manganese-cobalt oxide battery cells and compares the results with the production of batteries from virgin materials. Based on the EverBatt model, a China-specific database of hydrometallurgical remanufacturing process is established. The results indicate that the reductions in energy consumption and greenhouse gas emissions by battery remanufacturing are 8.55% and 6.62%, respectively. From the economic standpoint, the potential cost-saving from battery remanufacturing is approximately $1.87kg1 cell produced. Through a sensitivity analysis, LIB remanufacturing is found to be economically viable until the purchase price of spent batteries rises to $2.87kg1. Furthermore, the impact of battery type variability is prominent, whereas the influence of recovery efficiency is limited.