Grinding Energy Research Articles

Investigating the effect on power draw and grinding performance when adding a shell liner to a vertical fluidised stirred media mill

A comparative testwork programme was conducted using a laboratory scale vertical fluidised stirred media mill. The mill was operated with and without the presence of a disc liner on the shell. Results showed that when the mill was operating with pin and disc type stirrers, the addition of a stationary liner to the mill shell significantly increased the mill power draw. In grinding experiments conducted with silica, it was found that the production rate was enhanced as a result of the higher power draw. No detrimental effect on the grinding energy efficiency was observed. It was postulated that the addition of the disc liner increased the stress intensity of the milling operation. The results of this study show that the addition of stationary internal disc liners have a potential to increase the production capacity of fluidised stirred media mills. Further work is recommended to confirm that these observations are valid at a larger scale and in continuous milling configuration.

Precision grinding process for gyro motor shaft of dynamic pressure air bearing

There are some problems of low accuracy, low efficiency and high cost in the precision machining for gyro motor shaft of dynamic pressure air bearing with high hardness and high brittleness, for the above questions, the research of high precision grinding technology is carried out. Firstly, the diamond grinding wheel is designed by studying the influence of different parameters on workpiece shape, surface quality and specific grinding energy, etc. Secondly, through the orthogonal test, the optimum process parameters affecting the surface roughness, roundness and cylindricity of motor shaft are determined. Finally, the grinding experiments of 20 motor shafts are completed by using the optimal parameters. The results showed that the qualified motor shaft with roundness 0.09μm, cylinder 0.32μm and roughness(Ra) 0.037μm is obtained when the workpiece speed is 308r/min, feed rate is 0.003m/min and grinding depth is 1μm.

Laser-assisted grinding of reaction-bonded SiC

The article presents the development of a novel laser-assisted grinding (LAG) process to reduce surface roughness and subsurface damage in grinding reaction-bonded silicon carbide (RB-SiC). A thermal control approach is proposed to facilitate the process development, in which a two-temperature model (TTM) is applied to control the required laser power to thermal softening of RB-SiC prior to the grinding operation without melting the workpiece or leaving undesirable microstructural alteration. Fourier’s law is adopted to obtain the thermal gradient for verification. An experimental comparison of conventional grinding and LAG shows significant reduction of machined surface roughness (37%–40%) and depth of subsurface damage layer (22%–50.6%) using the thermal control approach under the same grinding conditions. It also shows high specific grinding energy 1.5 times that in conventional grinding at the same depth of cut, which accounts for the reduction of subsurface damage as it provides enough energy to promote ductile-regime material removal.

Performance comparison of seeded-gel and CBN grinding wheels for cylindrical plunge grinding of 100Cr6 steel

The selection of the grinding wheel is an important step during the process planning of grinding operations, especially for high-quality small components of hardened steel. The correct choice of the grinding wheel and the proper selection of cutting parameters can provide ground surfaces with high quality and positively affect the economic aspects of the process. The present work compares the performance of seeded-gel and CBN grinding wheels in external cylindrical plunge grinding of 100Cr6 steel in a range of high peripheral speeds, where it is possible to use both grinding wheels. The comparison was made taking into account the workpiece surface roughness and indices like the grinding ratio, specific grinding energy and grinding efficiency. The use of the CBN grinding wheel resulted in lower surface roughness values than those obtained with the seeded-gel grinding wheel. For both grinding wheels, there was a tendency that increasing peripheral speed reduces the surface roughness values. The best performance of the seeded-gel grinding wheel was found at 150 mm3/min/mm, where the grinding efficiency increased with the peripheral speed, and the highest value of all the performed experiments was achieved at 80 m/s. This value was approximately three times the grinding efficiency of the CBN grinding wheel under the same cutting conditions. The highest grinding efficiency for the CBN grinding wheel was achieved at 200 mm3/min/mm and 80 m/s. The grinding efficiency of the seeded-gel wheel dropped for this cutting condition due to higher wheel wear.

Studying the effect of different operation parameters on the grinding energy efficiency in laboratory stirred mill

In this study, considering different operational parameters for stirred media mill, change in specific energy was compared to the change in Rx values, i.e. the cumulative weight of the material undersized to a specific sieve. R values, namely R38, R75, R106, were measured before and after grinding in stirred mill. The change in Rx (ΔRx, %) values were calculated and they were used to evaluate the certain unit of effectual energy (Ecb). This abovementioned calculation is performed by proportioning the Specific Energy (SE) to ΔRx values. The effectual part of SE is considered to be the ratio of the energy needed only for size reduction in grinding and it should be related to the ΔRx. The relative Ecb ratios of different grinding conditions give the relative specific energy efficiency ratio (SEe). The relative specific energy efficiency ratio is inversely proportional to specific grinding parameters and ground product particle sizes. The relative specific energy efficiency can be considered as the relative amount of energy for various grinding conditions. The variation between relative energy amount and the previously specified particle size provides a realistic comparison of different grinding parameters. The abovementioned variation could be employed to understand the resistance particle size which is a new concept to describe the particle size at which the maximum effectual SE is directly used. In the context of this study, it was aimed to figure out the interrelation between specific energy efficiency and PSD variation along with the resistance particle size.

Investigation of the surface integrity, flexural strength on the grinding of alumina for biomedical applications

This paper presents the analytical and experimental investigations on different factors such as surface integrity, flexural strength and grinding energy and cost of Alumina through the use of various diamond grinding wheels. For obtaining the analytical model for single-grit grinding, the effect of strain rate and grinding temperature are also included in the formulation. Moreover, the experimental tests are conducted with four different diamond grinding wheels to grind Alumina blocks. The applied force during grinding is measured. Then, the other important parameters, including surface roughness, wheel wear, and grinding cost are analyzed. According to the obtained results, a good agreement between the experimental and analytical results were achieved in all cases. Furthermore, it was found that controlling the grinding condition would be resulted in 11% reduction in the subsurface damages (SSD) according to the images of Scanning electron microscope (SEM) results at the distance of 150 μm under the ground surface. A converging improvement trend of the surface integrity and flexural strength was also observed. Also, approximately 29% improvement was attained for the flexural strength in optimum condition. In addition, the optimal condition for grinding was determined, in which 66% decrease in surface roughness and 75% decrease in grinding cost were accomplished.

Convective Heat Transfer Coefficient Model Under Nanofluid Minimum Quantity Lubrication Coupled with Cryogenic Air Grinding Ti–6Al–4V

Under the threat of serious environmental pollution and resource waste, sustainable development and green manufacturing have gradually become a new development trend. A new environmentally sustainable approach, namely, cryogenic air nanofluid minimum quantity lubrication (CNMQL), is proposed considering the unfavorable lubricating characteristic of cryogenic air (CA) and the deficient cooling performance of minimum quantity lubrication (MQL). However, the heat transfer mechanism of vortex tube cold air fraction by CNMQL remains unclear. The cold air fraction of vortex tubes influences the boiling heat transfer state and cooling heat transfer performance of nanofluids during the grinding process. Thus, a convective heat transfer coefficient model was established based on the theory of boiling heat transfer and conduction, and the numerical simulation of finite difference and temperature field in the grinding zone under different vortex tube cold air fractions was conducted. Simulation results demonstrated that the highest temperature initially declines and then rises with increasing cold air fraction. Afterward, this temperature reaches the lowest peak (192.7 °C) when the cold air fraction is 0.35. Experimental verification was conducted with Ti–6Al–4V to verify the convective heat transfer coefficient model. The results concluded that the low specific grinding energy (66.03 J/mm3), high viscosity (267.8 cP), and large contact angle (54.01°) of nanofluids were obtained when the cold air fraction was 0.35. Meanwhile, the lowest temperature of the grinding zone was obtained (183.9 °C). Furthermore, the experimental results were consistent with the theoretical analysis, thereby verifying the reliability of the simulation model.

Potential Benefits in Copper Sulphides Liberation through Application of HRC Device in Ore Comminution Circuits

The article presents results of investigations on a high-pressure comminution process carried out in the roller press device, aiming at potential improvement of effectiveness of downstream beneficiation operations. The major point of interest of the paper concerned an assessment of the useful mineral liberation in relation to the volume of operating pressing force in the press device. Obtained results of mineral liberation were compared to flotation effects and downstream grinding process in a ball mill. Environmental influence in terms of dust emission was also analysed. The feed material was crushed in the high-pressure roller crusher (HRC) device under four different values of pressing force (Fsp): 3.0, 3.5, 4.0 and 4.5 N/mm2. Each product then underwent the liberation analysis, together with determination the energy savings through calculation of Bond’s working index, flotation recoveries and grinding kinetics. Results of investigations showed that both the most favourable crushing results and mineral liberation level were achieved for the highest values of operational pressing force. Nevertheless, the observed effects were less than linear together with further increasing of Fsp in HRC device. However, the obtained results of investigation unambiguously showed that pressing force affects the obtained crushing results: comminution degrees and flotation recoveries were higher while the duration of downstream grinding operation and grinding energy consumption were lower.

Evolution of grinding energy and particle size during dry ball-milling of silica sand

The energy efficiency of dry fine grinding process of powders dramatically declines with decreasing particle size, and represents a growing concern in various cutting-edge technical applications for pharmaceutical and cosmetic products, advanced-ceramics, and food industry. In this paper, we report on a detailed experimental analysis of the long-term grinding behavior of silica sand as a model material in an oscillatory ball mill for a broad range of the values of vibration frequency and amount of powder. We show that the re-agglomeration of fine particles unambiguously explains the anomalous increase of grinding power consumption. We also find that the agglomeration phenomena are correlated with the volume fraction of the class of finest particles. A nonlinear comminution model is shown to capture this effect for the prediction of the evolution of the specific surface area.

Exploratory investigation on the use of low-cost alternative media for ultrafine grinding of coal

ABSTRACT In this study, the energy efficiency of three alternative grinding media including, coarse silica beads, fine silica beads, and granular sand, were evaluated and compared against standard stainless steel. Stirred mill test results show that both silica beads and granular sand were more efficient than stainless steel in producing ultrafine particles following the order of coarse silica beads>granular sand>fine silica beads>stainless steel. The finest product size corresponding to a P80 value of 2.33 μm was generated by coarse silica beads with a nominal size of 420 × 1190 μm, which also consumed the least amount of grinding energy. The specific energy input was reduced by almost 50% as opposed to that of stainless steel, while the operating work index was reduced by 87%. Overall, the test data indicate that grinding media density, media particle size and shape all play a role in determining the optimized grinding behavior of the coal material.

Investigation on induction brazing of profiled cBN wheel for grinding of Ti-6Al-4V

Profiled monolayer cBN wheel was induction brazed for grinding of titanium dovetail slot in this study. Aimed at acquiring a uniform temperature distribution along the profiled surface and reducing the thermal deformation of the brazed wheel, a finite element model was established to investigate the temperature uniformity during induction brazing. A suitable induction coil and the related working parameters were designed and chosen based on the simulation results. Ag-Cu-Ti alloy and cBN grains were applied in the induction brazing experiment. The results showed geometric deformation of the brazed wheel was no more than 0.01 mm and chemical reaction layer were found on the brazed joint interface. Further validation tests were carried out by grinding of Ti-6Al-4V alloy. Compared to the electroplated wheel, the brazed wheel showed better performance such as low specific grinding energy and good ground quality in grinding of Ti-6Al-4V alloy. Abrasion wear was found to be the main failure mode for the induction brazed wheel, while adhesion and grains pull-out were the main failure mode for the electroplated wheel.

Experimental study on specific grinding energy and particle size distribution of maize grain, stover and cob

Reducing the particle size of biomass is of great significance for rational and efficient utilization of biomass. In this study, maize grain, stover, and cob were comminuted at different speeds (2000-2800 r/min) by hammer mill with a mesh size of 2.8 mm. The mechanical energy for smashing three selected samples was obtained directly through the sensor and data testing system. Experimental results demonstrated that the maize cob had the highest total specific energy while the maize grain had the lowest (135.83-181.10 kW·h/t and 27.08-36.23 kW·h/t, respectively). In addition, for the same material, higher hammer mill speed generated more specific energy consumption. And the effective specific energy of maize stover had a similar trend to the total specific one. However, the effective specific grinding energy of maize cob and grain increased initially and then decreased with the increase of rotating speed. The fitting curves of the specific energy to mill speeds were determined, and the range of determination coefficients of the regression equation was 0.933-0.996. Particle size distribution curves were drawn by sieving the pulverized particles of the three samples based on a series of standard sieves. Fourteen relevant parameters characterizing the particle size distribution were calculated according to the screening data. Calculation results demonstrated that larger rotational speed leads to smaller particle sizes. Combining the size parameters, distribution parameters, and shape parameters, it was found that the distributions of the three samples all exhibit a distribution of “well-graded fine-skewed mesokurtic”. The Rosin-Rammler function was considered to be suitable for characterizing the particle size distribution of maize grain, stover, and cob particles with a coefficient of determination between 0.930 and 0.992. Keywords: maize grain, maize stover, maize cob, specific energy, particle size distribution, comminution DOI: 10.25165/j.ijabe.20201304.5327 Citation: Xue Z, Fu J, Chen Z, Ren L Q. Experimental study on specific grinding energy and particle size distribution of maize grain, stover and cob. Int J Agric & Biol Eng, 2020; 13(4): 135–142.

Processing Characteristics of Different Vegetable Oil-based Nanofluid MQL for Grinding of Ni-Cr Alloy

ABSTRACT Machining of hard materials generates high temperature in the cutting zone. Lubricants play an important role in the reduction of temperature in the cutting zone, thereby producing cooling and lubricating effects. Effective lubrication enhances the tool life thereby reducing the machining cost. Conventional lubricants are mineral-based oils that are non-biodegradable. Industries are focusing to reduce the consumption of these oils by exploring different alternatives. Dry grinding and Minimum Quantity Lubrication (MQL) technique are the alternatives of focus. Dry machining has limitations in hard to machine materials due to a steep rise in temperature. Thus, MQL is an alternative that can be applied to the machining to achieve the desired objective of lubrication and cooling. In the present work, nano-particles based nanofluids were prepared by dispersing 0.5 wt% and 1 wt% CuO nano-particles in the vegetable oils to grind Ni-Cr alloy. Surface roughness, G-ratio and Grinding Energy were evaluated under different conditions of lubrication. Due to high-pressure mist of MQL and rolling effects of nano-particles at the wheel and workpiece interface, there is significantly reduction in values of surface roughness, temperature, grinding energy with enhanced G-ratio comparatively to flood lubrication. Moreover, biodegradable oil-based Nanofluid MQL serves the purpose of environment-friendly machining.

Combined mechanical grinding and enzyme post-treatment leading to increased yield and size uniformity of cellulose nanofibrils

The low yield and size nonuniformity of cellulose nanofibrils (CNFs) prepared by mechanical grinding restrict their extensive application in many fields. In this study, microfibrillated cellulose (MFC) with varying grinding time (0–2.5 h) was post-treated with endoglucanase (EG) to improve the yield and size uniformity of the CNFs. With the same grinding time, the yield of the CNFs post-treated with EG increased approximately one-fold, and the diameter of the microfibrils decreased according to the SEM and TEM images. The yield of the CNFs ground for 0.5 h and post-treated by EG was similar to that of the sample ground for 2.5 h, and approximately 26.1 kWh/kg mechanical grinding energy were saved by the EG post-treatment while obtaining the same CNF yield. There was an abundance of micropores that affected the specific surface area of samples, and the width of the micropores was centered between 1.3 and 2.0 nm. The crystallinity index (CrI) of the MFC decreased gradually from 74.90 to 69.30% with prolonged grinding time, whereas the CrI of the samples post-treated by EG slightly increased between 1.7 and 3.0%. The tensile strength and elongation at break of the films prepared by the EG post-treated samples slightly decreased, while the Young’s modulus and transmittance increased. This study provides a valid and an eco-friendly biological method to improve the yield and size uniformity of CNFs and reduce energy consumption.

Investigation on machined surface quality in ultrasonic-assisted grinding of Cf/SiC composites based on fracture mechanism of carbon fibers

As a kind of carbon fiber-rich material, the machined surface quality of Cf/SiC composites is greatly affected by the fracture mode of carbon fibers. Therefore, exploring the material removal mechanism of Cf/SiC composites in grinding through the different fracture mechanisms of carbon fibers from the perspective of microstructure is necessary. In research, the micro-scale fracture mechanism of carbon fibers and the transformation of mechanism were explored. The difference in fracture behavior of carbon fibers caused different energy consumption in material removal, which is instructive for monitoring the machining process with specific grinding energy. The difference of machined surface morphology was directly caused by the difference of material removal mechanism, which can be effectively characterized by the machined surface roughness. The transition of the material removal mechanism was determined by the maximum undeformed chip thicknesses. Ultrasonic-assisted grinding promoted the removal of carbon fibers in nano-scale brittle fractures by reducing the maximum undeformed chip thicknesses, thereby improving the quality of the machined surface.

Microwave treatment of rocks: effect on specific gravity, whiteness, and grindability

Heating of ores usually improves the liberation of minerals and reduces grinding energy consumption. One of the heating methods is using microwave electromagnetic radiation, which may change the rock’s physical properties. This paper investigates the effect of microwave heating of rocks on their physical properties. The physical properties monitored were specific gravity, whiteness, and grindability due to their importance for the downstream processes. Two rock types were investigated: coral as the soft rock and quartzite as the hard rock. The rock samples tested were treated for different time intervals in a microwave oven (frequency — 2.45 GHz, P = 1.7 kW). The results showed that specific gravity of the soft rock decreased by 1.82 % after the microwave treatment (150 s), while that of the hard rock was not affected. It was also found that the maximum change in rock whiteness for the soft rock is 8.65 % after the microwave treatment (150 s), while that of the hard rock was 6.02 % after a 120 s microwave radiation exposure period. Following a 60 s microwave radiation exposure, the soft rock demonstrated the work index of 20.99 % against the value of 45.03 % of the hard rock. The results of FTIR and XRD analyses suggest that changes in the physical property and a phase shift of minerals may be responsible for the improvement in the work index and whiteness of the rocks studied. This project was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah. The authors are very grateful to the DSR for their technical and financial support.

Profile grinding of DZ125 nickel-based superalloy: Grinding heat, temperature field, and surface quality

• Increase of grinding speed and undeformed chip thickness decreases grinding heat. • Temperature field is characterized by experiments and simulation. • DZ125 is well ground by HEDG with good quality and residual compressive stress. • DZ125 blade root is ground with material removal rate over 50 mm 3 /(mm·s). During the high-efficiency deep grinding of a turbine blade root, localized thermal damage of the profile surface could easily occur owing to the complexity of the grinding dynamics and cooling conditions in the grinding zone. Therefore, it is worthwhile to investigate the generation of the grinding heat, the grinding temperature and its distribution, and the grinding surface quality, particularly for superalloys used to produce aero-turbine blades. In this study, the specific grinding energy and grinding heat flux during the profile grinding of a fir tree-shaped root of a DZ125 superalloy turbine blade were investigated. The grinding temperature at four points on the profile were measured and the results were used to conduct a three-dimensional simulation to analyze the temperature distribution on the machined surface and in the direction of the cutting depth. The effects of the heat source shape and contact length on the temperature distribution were also examined. A moderately high material removal rate was found to be beneficial to the surface quality, with a maximum material removal rate of 50.6 mm 3 /mm·s producing a surface roughness of Ra 0.6 μm without saturation or microstructural changes. Residual compressive stress was also achieved on the ground surface.

Torrefaction: a sustainable method for transforming of agri-wastes to high energy density solids (biocoal)

The depletion of fossil fuel reserves and greenhouse gas emissions led to limit the use of fossil fuels, including natural gas, coal, or petroleum, and demand a clean and sustainable source of energy. Many efforts are being made by the researchers to address these issues through the use of natural renewable resources (or lignocellulosic biomass), such as agricultural wastes and forest residues as a cleaner source of energy. But its poor properties like low energy density, high moisture content, irregular shape and size, and heterogeneity make it difficult to use in its natural form. Torrefaction, a simple heat treatment procedure, is widely employed to the natural bioresources to improve its thermal properties to be used as an energy source in the domestic power plants. The quality of the resultant torrefied solids (the so-called biocoal) is depending on the settings of heating conditions under the absence of oxygen, which can be improved by selecting and adjusting the processing conditions precisely. Typically, the process brings down the moisture content up to < 3 wt%, and increases the grinding energy up to 90%. Mainly, the calorific value and fixed carbon content of torrefied biomass increase by roughly 15–25 wt%, which makes it more appealing than non-torrefied biomass. The review emphasizes the available biomass torrefaction technologies, and it’s potential in the field of bioenergy generations. It also covers few case studies of biomass torrefaction and its application in the power generation sectors.

Energy conservation and environmental sustainability during grinding operation of Ti–6Al–4V alloys via eco-friendly oil/graphene nano additive and Minimum quantity lubrication

Conventional cutting fluids cannot fit the principles of green manufacturing in terms of cost, energy-saving, environmental and health impacts. Therefore, it is planned to develop high-performance cutting fluids based on biodegradable, health-friendly nanofluids that exhibit sufficient lubrication and cooling properties. Palm oil-based nanofluid containing different percentages of graphene nanoplatelets (GNPs) were prepared and evaluated utilizing the Minimal quantity lubrication (MQL) mode. The cutting, tribological and microstructure tests revealed that GNPs with the content percentage of 0.1 wt% decreased the specific grinding energy by 91.78% compared to dry cutting. Furthermore, the palm oil/0.1 wt% GNPs based nanofluid could lessen the specific cutting energy by 80.25% compared to commercially high-performance Acculube LB2000 because of the sharp reduction in the friction coefficient.

Influence of grinding parameters on Inconel 625 surface grinding

Nickel-based alloys have been increasingly employed due to their ability to maintain high mechanical strength and high chemical inertia at high temperatures. However, these outstanding properties can impair their machinability, so they are termed difficult-to-machine materials. Since machining of nickel alloys becomes even more difficult when the grinding process is needed, and because of poor thermal conductivity of both workpiece and the abrasive grinding wheel, more attention from machinists is required to determine proper grinding parameters that should be more moderate than those usually selected for grinding hardened steels. Because of the peculiar properties of Inconel 625 alloy, such as resistance to aqueous solutions, hot corrosion, high strength and resistance to creep, it makes it well suited for a wide range of applications, such as aerospace and marine applications as well as oil and gas industries. The grinding operation is generally the first option to enhance the combinations of narrow dimensional and geometric deviations in most of aeronautical components. In this context and motivated by the lack of information about grindability of this alloy, this work evaluates the influence of the several grinding parameters on surface integrity, grinding forces (Ft and Fn) and specific grinding energy of nickel-based, Inconel 625 alloy. A fractional factorial design of experiments (DOE) was adopted to use the wheel speed, work speed, depth of cut, abrasive mesh and grinding direction (up and down grinding) as measures of variation in the grinding process. Surface integrity was assessed in terms of surface roughness (Ra and Rz), observations of SEM images and microhardness. The results showed that Inconel 625 is highly susceptible to work hardening during grinding. The grinding wheel speed (vs) was the parameter of greatest effect and the best results were obtained when vs=15 m/s.