Optimum Grinding Research Articles

Theoretical aspects of energy consumption acoustic evaluation at the jet grinding

The objective of this work was to develop an acoustic method for evaluating energy consumption during the jet mill operation on the basis of the new generalized physical laws of material dispersion at it destruction. Theoretical explanation is given to the problem of energy consumption diminish in the mode of fine grinding. Dependences between the product dispersion and critical energy density in the course of destruction are described. The acoustic-emissive parameters of dispersion of the samples loaded by compression and results of acoustic estimation of the jet grinding are considered. Interrelation between the gas-jet mill performance and parameters impacting on the energy consumption are analyzed. Grounds are given for using a criterion of extremal control of the working process for maintaining maximal performance. An acoustic size effect of dispersion is formulated by the analogy with dynamic size effect of destruction (DSE). A new approach to evaluation of energy consumed by the jet mill is developed from positions of unity of nature and mechanism of the loaded body destruction with community of manifestation of physical laws of acoustic emission and effects of new surface formation on the destroyed particles. Leading role in the methodology of energy consumption evaluation is given to the coefficient gN (J/imp) of transformation of the consumed energy into acoustic radiation at optimal mode of the mill operations (at maximum performance), which is calculated as a ratio of the reduced work (energy) to the acoustic signal counts in the grinding zone. Current energy consumption ЕDt (J) for period Dt (s) of work is calculated with taking into account coefficient gN (J/imp) and average (for the interval Dt) acoustic activity (imp/s). It is possible to maintain minimum energy consumption at the jet grinding by the snap-acting control of jets loading up to the level of the measured acoustic activity in the grinding zone, at which a “conditionally permanent” value of coefficient gN can be achieved. The results of acoustic evaluation of effective surface energy at optimal grinding mode correspond to the range of estimation gs in the regularity of the DSE destruction. This fact confirms validity of the dispersion theory (including the acoustic size effect) use for evaluating current energy consumption in the course of the jet mill operation.

Modeling the development of rail corrugation to schedule a more economical rail grinding

Rail corrugation should be managed appropriately, as it causes noise, vibration, and degradation of track components and materials. Generally, rail corrugation is managed with the removal of rail surface roughness by rail grinding. However, in many cases, rail corrugation will reoccur after the rail is ground, thereby making the management of the phenomenon difficult for railway operators. For the proper management of rail corrugation, it is necessary to understand the development of rail corrugation and model it mathematically. However, this effort has not been made in previous studies. This paper investigates an efficient method for scheduling a regular grinding maintenance to manage rail corrugation. Using regularly measured data about rail surface roughness on a commercial line, a mathematical model was developed to estimate the growth of rail corrugation. This model was utilized to estimate the effects of the remaining roughness after rail grinding on the maintenance cost and to optimize the maintenance schedule. First, it was confirmed that the development of rail surface roughness of rail corrugation can be expressed in three phases and can be modeled by fitting the functions of growth curves to measurements of rail surface roughness recorded over a long period. Next, the rail grinding strategy was examined by applying this model to realize both effective and economical strategies for the maintenance of rail corrugation. This study confirmed that maintenance costs can be reduced by rail grinding that removes almost all of rail corrugation. In the case of ballasted tracks, it has been found that the optimal grinding schedule can reduce the cost of rail grinding as well as the cost of tamping. These findings can be applied by railway operators tasked with managing maintenance schedules for railway lines at a minimum cost.

Effect of Nano Charcoal Ash Coconut Shell in Bitumen as Alternative Binder

The effect of Nano charcoal ash (NCA) from coconut shell on the physical and chemical properties of bitumen as alternative binder was evaluated in this study. Six different Nano grades of charcoal ash were examined. The charcoal ash ground for the optimum grinding time had a median particle size of 148 nm. NCA dosage of 30% by weight of binder was used throughout the experiments. Nanoparticle size analysis and X-ray fluorescence were performed to determine the size and chemical properties of material. Dynamic shear rheometer, penetration, softening point, and penetration index were used to characterize the physical properties of NCA. Thirty hours of grinding time produced the optimum NCA, which could enhance the binder performance. Test results indicated that adding NCA from coconut shell to bitumen improved the binder stiffness up to 47% and significantly increased the softening point up to 12% compared with virgin binder.

Thermal damage control for dry grinding of MgO/CeO2 glass ceramic

MgO/CeO2 glass ceramic is a key solid catalyst and accelerant produced by raw mixing, prilling and pressure sintering. Grinding, as a high-efficiency machining method was used to obtain MgO/CeO2 glass ceramic components with accurate size to meet the size requirements of design. However, thermal damage occurring on the ground surface may change the properties of the components and affect their performance in subsequent applications. In this work, a grinding thermal model was established and validated by experiments. On the basis of this thermal model, the grinding temperature can be controlled to < 100 °C by selecting optimal grinding parameters and thus prevent grinding burn. The mechanism of potential chemical reactions on the grinding surface was further studied by analysing the transient temperature jump at a grain wear flat area and comparing the change in element mass fraction before and after grinding. The performance of a normal resin bond diamond wheel and a resin bond wheel with Ni–P alloy coating on the diamond grains was compared. Results showed that the latter intensified the redox reaction because of the catalytic actions of Ni and P, and the mass fraction of each elements on the workpiece surface shows obvious uneven distribution due to the surface spalling of Ni–P alloy. All these results indicated that key issues are the optimal setup of process parameters to control the grinding zone temperature and the selection of a proper grinding wheel to avoid catalytic elements such as Ni and P.

Improvement of grinding technology with vortex cooling of steels that are liable to crack propagation

Abstract Complexity of grinding process and phenomena entailing it not always allow reaching required technological results, especially while machining surfaces of parts made of tough-to-machine steels, which are liable to crack propagation. Cracks can occur in these parts during grinding due to considerable temperature difference along the section, which can cause formation of high temporary internal tensile stress. Application of cooled air in grinding process exerts considerable influence over temperature decrease in cutting area. In addition, it depends not only on heat exchange, but also on properties of cold air flow. The greatest effect of temperature decrease can be reached by injection of cold air flow in cutting area with implementation of vortex effect, which occurs in swirl flow of compressed air originating in vortex tube. The study of heat generation during machining by tools with discontinuous cutting surface and vortex air cooling was carried out. Obtained thermophysical parameters of vortex air cooling (increase in speed of stream flowing, expansion degree, share of cold stream and decrease in humidity of air stream) allow reducing heat density due to growth of cooling effect in grinding zone. On the base of experimental studies we developed recommendations for choice of optimal grinding modes by tool with discontinuous cutting surface and vortex air cooling of flat parts made of steels being liable to cracking.

Capillary penetration mechanism and machining characteristics of lubricant droplets in electrostatic minimum quantity lubrication (EMQL) grinding

In this work, the machining performance of an electrostatic minimum quantity lubrication (EMQL) technology in grinding of Cr12 die steel was systematically investigated in terms of grinding temperature and forces and grinding ratio, as well as surface quality and microstructures. The intensity of charging voltage was varied in order to obtain an optimal grinding performance. A model of capillary penetration of lubricant droplets to the abrasive-workpiece interface was proposed to reveal the lubrication mechanism of EMQL. It was found that EMQL at an electrostatic voltage of 4 kV significantly reduced the grinding forces and surface roughness, but increased the grinding ratio by 24.8% in comparison with a conventional MQL technology. The improved performance was attributed to the fact that EMQL promoted the penetration of lubricant droplets, achieving a better interfacial lubrication with low friction and grinding heat. The EMQL was also believed to reduce the surface micro-hardness of workpiece materials by enhancing the migration of dislocations, hence improving the cutting effect of abrasive grains.

Evaluating the grinding ratio and surface quality of Ti-6Al-4V under varying grinding pass count and depth of cut

Surface finishing of advanced difficult-to-machine materials through grinding is posing a significant challenge to the manufacturing industries. However, one of these materials, Ti-6Al-4V has a significantly high usage in several cutting-edge sectors. Thus, finding optimum grinding conditions for processing of this material becomes critical. Present article represents an experimental investigation dedicated towards analysing the effects of varying grinding pass counts and infeed values on the surface roughness, hardness, visible surface burns and grinding ratio of Ti-6Al-4V applying alumina wheel. Experiments are performed to reveal the trend of the surface properties and hardness of Ti-6Al-4V, ground at 10 μm and 20 μm infeed values with different sets of grinding passes. The results indicate that grinding at 15 pass count under 10 μm and 20 μm infeed values are the ideal set of parameters for the operating ranges considered herein.

Modeling and optimization of machining parameters during grinding of flat glass using response surface methodology and probabilistic uncertainty analysis based on Monte Carlo simulation

In this paper, the performance of diamond grinding wheels was investigated. The industrial diamond crystals with a size of 140/170 mesh were utilized. The microstructure of the grinding tool was observed using a Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Analysis Device (EDX). The experiments were designed using Box–Behnken method and optimum grinding parameters for glass were analytically determined. Experimental studies were carried out on a surface grinding machine in a flat glass factory. Grinding characteristics were examined with respect to surface roughness. The effects of grinding parameter on output responses were studied using analysis of variance (ANOVA). Probabilistic uncertainty analysis depends on Monte Carlo simulation was applied. Moreover, after the experiments using the optimized cutting parameters, the microstructure of the grinding wheels was analyzed. From results, the established model and optimization method could be employed for predicting surface roughness and this work is reliable and suitable for solving the problems encountered in machining operations. The lifetime of Cu-based grinding discs can be increased by adding Zn and Fe to the matrix material.

Spraying parameter optimization and microtopography evaluation in nanofluid minimum quantity lubrication grinding

To overcome environmental problems, nanofluid minimum quantity lubrication (NMQL) has been utilized as a burgeoning alternative technique to conventional flood machining, which consumes a large quantity of cutting fluid. Furthermore, spraying parameter optimization is a prerequisite of an effective NMQL grinding and a key to achieving a new sustainable grinding process. However, the spraying parameters of NMQL are multifarious and have varying degrees of influence on lubri-cooling performance. The main objective of this work is to first obtain good spraying parameters in NMQL grinding through the analysis of signal-to-noise ratio and analysis of variance based on orthogonal experiment results. Furthermore, an experimental verification is carried out on the basis of the relative optimization of several groups of spraying parameters from the orthogonal experiments. Power spectral density function (PSDF) and energy spectrum are used to analyze the workpiece and debris microtopography. Consequently, the optimal spraying parameter is obtained. The spraying parameter (palm oil as the base oil, 2 vol% nanoparticle concentration, 0.6 MPa air pressure, and 0.4 gas–liquid flow ratio) achieved the lowest proportionality coefficient (0.245) of PSDF in the low-frequency band and the highest (0.142) in the high-frequency band. Meanwhile, the optimal grinding performance is validated by the workpiece and debris microtopography and long-strip debris morphology.

Experiments on Rare-Earth Element Extractions from Umber Ores for Optimizing the Grinding Process

Ancient hydrothermal metalliferous sediments (umber) have recently attracted attention as a new rare-earth element resource. We conducted chemical leaching experiments on three different umber ores to optimize the hydrometallurgical extraction process, especially regarding the grinding process. The three umber ore samples, which were collected from Japanese accretionary complexes (Kuminiyama and Aki umber) and Troodos ophiolite (Cyprus umber), had different chemical, mineral, and physical properties, and showed different leaching behaviors. The experimental results revealed that the physical properties (density and P-wave propagation velocity) principally controlled the extent of REY (lanthanides and yttrium) extraction from the umber ore samples, and REY extraction from umber samples clearly increased with the decrease in the density and P-wave propagation velocity. The differences in physical properties of the umber samples are attributable to the pressure and thermal history of each ore sample, and it was revealed that umber samples which underwent strong metamorphism are not suitable for actual development. The results also suggested that the optimum particle size (optimum grinding level) of umber samples is simply predictable based on the physical properties. The results of this study should be valuable for future efforts to procure these important mineral resources.

Experimental study of metal ceramic (WC-Co) micro-tool fabrication by controlled inclined grinding (CIG)

As a kind of metal ceramic material, cemented carbide (WC-Co) has attracted attentions of many scholars for its excellent material property. In this paper, a new method named controlled inclined grinding (CIG) is proposed to fabricate a micro-substrate of cemented carbide. The machining mechanism during CIG was investigated; a lot of micro-substrates, whose diameter is from 8 to 120 μm, had been successfully fabricated; and the critical parameters for obtaining the suitable machining result are given. Two ultra-small micro-tools, with a diameter of 8 μm and 20 μm, respectively, and an aspect ratio (for both) of bigger than 50, had been fabricated by the CIG method. The relationship between tool contour and inclined angle (θ) was revealed, and the optimal inclined angle was found to be 0.5°. Differences when grinding at different wheel positions were studied and compared, and an optimal grinding position was found. A contrast experiment was designed and carried out by using the CIG method and traditional grinding method, and machined workpiece surface was observed by a profilometer and a scanning electron microscope (SEM); it is found that the machined surface of the CIG method was comparatively gentle and even, while the machined surface of the traditional method was violent and uneven. A surface roughness model for the CIG method was built, the corresponding expression was derived, and the surface roughness model was finally validated experimentally. The CIG method proposed in this study is not only a simple device but also cheap and efficient, and it is anticipated to be an optional method to fabricate micro-tool.

OPTIMIZATION OF CYLINDRICAL GRINDING PROCESS PARAMETERS OF SS316L AUSTENTIC STAINLESS STEEL BY TAGUCHI METHOD

The main objective of this study is to optimize the cylindrical grinding parameters that can be utilized to predict optimal grinding parameters to achieve minimum surface roughness of a material. A SS 317L Austentic steel round rod of 80 mm x 168 mm was considered for cylindrical grinding in this study. Cutting speed, depth of cut and feed rate were chosen as input variables while Surface roughness (Ra) selected as output response. An L9 orthogonal array was selected for this study and S/N ratios were analyzed to study the surface roughness characteristics. Nine experiments were conducted in the surface grinding machine with different values of input parameters obtained from the orthogonal array. The surface roughness values were optimized in the optimization software (Minitab version 17) and the optimal solution was obtained for minimum response. Minimum surface roughness is achieved with 100 rpm cutting speed, 0.03 mm depth of cut and 1 mm/s feed rate. The confirmation experiments were conducted for the optimal solution obtained from Taguchi experiment and the results are verified.

Grinding Optimization of Cassiterite-Polymetallic Sulfide Ore

Due to the differences in beneficiation methods and mineral properties between cassiterite ore and polymetallic sulfide ore, there is an inherent contradiction between cassiterite overgrinding and sulfide ore undergrinding. A method to optimize and characterize the grinding performance is presented in this paper. In this method, the grinding characteristics are defined by the qualified particle size range index under unit energy consumption. By changing the grinding time, grinding concentration, and filling ratio, the optimized grinding conditions were evaluated, and they were predicted and verified by the response surface method. The results corroborate that when the grinding time of cassiterite is 4 min and the grinding time of sulfide ore is 8 min, the grinding qualified size range index under unit energy consumption is the largest. Cassiterite is brittle and easy to grind due to low hardness, while sulfide is difficult to grind due to high hardness. Hence, the time to beneficiate tin ore is when the grinding time is 4 min, and that to beneficiate sulfide ore is when the regrinding time is approximately 4 min. In this way, the contradiction between overgrinding cassiterite and undergrinding sulfide ore can be alleviated on the basis of the most effective utilization of grinding energy. The optimal grinding concentration and filling ratio are 65% and 37%, respectively. The response surface prediction and test results are almost identical, with an error of ±2%. Thus, the effectiveness of grinding characterization method is verified.

Experimental Evaluation of the Lubrication Performance in MQL Grinding of Nano SiC Reinforced Al Matrix Composites

Metal matrix composites (MMCs) are materials which have been extensively used in the aerospace and automobile industries and have been categorized as hard-to-machine materials.Lubricants participate a significant role in machining, particularly in the grinding process. As a effect of the rising require for environmental safety and the growing number of health problems faced by workers, traditional lubricants are gradually being replaced. This research evaluate the performance of MQL grinding of nano SiC reinforced Al matrix composites using SAE20W40, Cashew nut shell oil and nano Tio2 filled Cashew nut shell oil as base oils. Experiments for grindability study were approved on a horizontal spindle cylindrical grinding machine using Response Surface Methodology. In this research, the influences of n grinding parameters including wheel speed, work piece speed, depth of cut and wt% nano SiC have been considered on the basis of the grinding forces and temperature to develop optimum grinding narration such as lubrication, high biological and ecological safety. The result shows that the application of nano fluid leads to the reduction of tangential forces and grinding zone temperature. Surface integrity of machined surface were studied using Scanning electron microscopy (SEM).

Acoustic method of jet grinding study and control

Jet grinding considers a rather energy-intensive production. For obtaining high mill productivity, it is necessary to control the process in order to prevent the transfer the energy intensity value to a critical one. This work shows the possibilities of jet grinding studying based on the process acoustic signal analysis and to develop a mill mode control system to achieve optimum productivity. There were determined that decrease in the activity and maximum amplitudes of the acoustic signals in the grinding zone is a sign of deviation from the optimal fine grinding mode, which leads to a decrease in the mill productivity and requires timely material loading. For control of ground product quality it’s necessary to control the frequency dispersion of signals corresponding to the control class, and check the absence or presence of signals corresponding to other size classes for zone behind the classifier. The developed automated control system of jet grinding allows implementing the optimal parameters of the mill operation by control the acoustic parameters of the grinding zone for optimum jet loading with material. The dispersion control of the ready product is based on acoustic monitoring of a two-phase flow in the product transportation zone.

Application of NSGA-II for optimisation of cylindrical plunge grinding process parameters

Cylindrical grinding (finishing) operation is widely used for obtaining accurate surface finish on components in automobile sectors. Present industries are facing a challenge of producing high quality components with low power consumption and low manufacturing cost due to increased competition. In this paper, optimum process parameters values are obtained for dressing depth of cut, dressing cross feed rate and grinding feed rate of cylindrical plunge grinding operation. Experiments were performed as per L9 orthogonal array with replica on computer numerical control angular head grinding machine. Mathematical model has been developed using response surface methodology for determining grinding responses. The results of RSM are further used to obtain Pareto front optimal solutions using NSGA-II approach. A novel method is developed to obtain grinding ratio. The established results are helpful to decide optimal grinding parameters.

Application of NSGA-II for optimisation of cylindrical plunge grinding process parameters

Cylindrical grinding (finishing) operation is widely used for obtaining accurate surface finish on components in automobile sectors. Present industries are facing a challenge of producing high quality components with low power consumption and low manufacturing cost due to increased competition. In this paper, optimum process parameters values are obtained for dressing depth of cut, dressing cross feed rate and grinding feed rate of cylindrical plunge grinding operation. Experiments were performed as per L9 orthogonal array with replica on computer numerical control angular head grinding machine. Mathematical model has been developed using response surface methodology for determining grinding responses. The results of RSM are further used to obtain Pareto front optimal solutions using NSGA-II approach. A novel method is developed to obtain grinding ratio. The established results are helpful to decide optimal grinding parameters.

A fundamental study of leaching kinetics and mechanisms of molybdenite assisted by mechanical activation

The mechanical activation was applied as a pre-treatment method to improve molybdenite (MoS2) leaching. The effects of grinding ball size, ball to powder mass ratio, milling speed and time, molar ratio of mineral to oxidants, as well as the influence of solution pH, temperature and leaching time were investigated in detail. The results showed an extremely low Mo extraction (less than 2% at acidic and neutral conditions) for MoS2 activated alone. However, Mo extraction was increased significantly after co-grinding of MoS2 with NaClO2 and Na2CO3, e.g., more than 58% in any leaching solution applied. Prolonging the grinding time improved Mo extraction but the efficiency was declined gradually, giving rise to an optimum grinding efficiency at 4 h with a molar ratio of 1:3:5 for MoS2:NaClO2:Na2CO3. Distilled water was selected as the leaching solution since this gave similar Mo recovery to other lixiviants. Higher temperature and longer leaching time were beneficial to Mo extraction. However, it was also found that too large grinding balls and high ball to powder mass ratio adversely affected MoS2 extraction. The kinetics analysis indicated that the leaching of activated MoS2 followed a chemical reaction controlled mechanism. The XRD and SEM analyses indicated that mechanical activation not only reduced the particle size of MoS2 but also triggered solid state reaction to produce soluble Na2MoO4, thereby improving Mo extraction significantly.

Development of Concurrent grinding for application in aqueous mineral carbonation

Vast reserves of peridotite and serpentinite rocks can be utilised for the safe and permanent sequestration of global CO2 emissions via aqueous mineral carbonation. These, and indeed most feedstocks used in mineral carbonation require ultrafine grinding and/or heat-activation, to engender significantly enhanced reactivity in the rock such that it can then be carbonated. Both activation processes are energy intensive and present significant obstacles to the commercial application of mineral carbonation. Here we show that these limitations can be addressed, at least in part, through the application of a concurrent or in operando grinding technique which does not require feedstocks which have been subjected to prior ultrafine grinding nor heat-activation.Concurrent grinding is shown to result in a significant increase in magnesite yields for non-heat activated feedstock, prepared such that fines (<20 μm particles) were excluded from the feed. We assert that concurrent grinding may be a suitable technique for the processing of feedstocks such as those containing significant proportions of forsterite and pyroxene, minerals which are unresponsive to thermal activation for use in aqueous mineral carbonation. This study also investigates the effect of different grinding media particle size on reducing the particle size distribution (PSD) of the feed. Optimum ratio of grinding media size to feed particle size, optimum grinding media and slurry concentrations, optimum time for grinding and optimum impeller designs are determined for the system under study. The quantitative effect of grinding media concentration, slurry concentration, pressure and temperature on magnesite yield has been investigated.

Optimization of Wet Grinding Parameters of Calcite Ore in Stirred Ball Mill

This study focused on ultra-fine grinding of calcite powder (CaCO3) using a vertical stirred ball mill. The influences of various operating parameters such as stirrer speed (rpm), ball filling ratio (J), powder filling ratio (fc), solid ratio (wt.%) and grinding time were studied under wet conditions. The experiments were carried out in a batch mode of operation. The experimental results were evaluated based upon product size (d50), specific surface area (m2/g) and width of particle size distribution. As a result of this work, the optimum grinding test conditions were found to be 840 rpm for stirrer speed, 0.70 for ball filling ratio, 0.100 for powder filling ratio, 50% for solid ratio and 20 min for grinding time. It was also observed that stirrer speed, ball filling ratio and grinding time were directly proportional whereas powder filling ratio and solid ratio were inversely proportional to product fineness and specific surface area. The width of particle size distribution decreased with decreasing product size for all grinding conditions.