Milling Conditions Research Articles

Computational study on the mechanism for the synthesis of active pharmaceutical ingredients nitrofurantoin and dantrolene in both solution and mechanochemical conditions.

A combination of density functional theory (DFT) calculations and microkinetic simulations is applied to the study of condensation between N-acyl-hydrazides and aldehydes in acidic media to produce the active pharmaceutical ingredients (API) nitrofurantoin and dantrolene. Previous experimental reports have shown that the use of ball milling conditions leads to a reduction in the reaction time, which is associated with a significant reduction of waste. This result is reproduced by the current calculations, which additionally provide a detailed mechanistic explanation for this behavior.

Interactions and reactivity in crystalline intermediates of mechanochemical cyclorhodation reactions.

There is experimental evidence that solid mixtures of the rhodium dimer [Cp*RhCl2]2 and benzo[h] quinoline (BHQ) produce two different polymorphic molecular cocrystals called 4α and 4β under ball milling conditions. The addition of NaOAc to the mixture leads to the formation of the rhodacycle [Cp*Rh-(BHQ)Cl], where the central Rh atom retains its tetracoordinate character. Isolate 4β reacts with NaOAc leading to the same rhodacycle while isolate 4α does not under the same conditions. We show that the puzzling difference in reactivity between the two cocrystals can be traced back to fundamental aspects of the intermolecular interactions between the BHQ and [Cp*RhCl2]2 fragments in the crystalline environment. To support this view, we report a number of descriptors of the nature and strength of chemical bonds and intermolecular interactions in the extended solids and in a cluster model. We calculate formal quantum mechanical descriptors based on electronic structure, electron density, and binding and interaction energies including an energy decomposition analysis. Without exception, all descriptors point to 4β being a transient structure higher in energy than 4α with larger local and global electrophilic and nucleophilic powers, a more favorable spatial and energetic distribution of the frontier orbitals, and a more fragile crystal structure.

Enhanced green remediation and refinement disposal of electrolytic manganese residue using air-jet milling and horizontal-shaking leaching

The reclamation and reuse of electrolytic manganese residue (EMR) as a bulk hazard solid waste are limited by its residual ammonia nitrogen (NH4+-N) and manganese (Mn2+). This work adopts a co-processing strategy comprising air-jet milling (AJM) and horizontal-shaking leaching (HSL) for refining and leaching disposal of NH4+-N and Mn2+ in EMR. Results indicate that the co-use of AJM and HSL could significantly enhance the leaching of NH4+-N and Mn2+ in EMR. Under optimal milling conditions (50 Hz frequency, 10 min milling time, 12 h oscillation time, 400 rpm rate, 30 ℃ temperature, and solid-to-liquid ratio of 1:30), NH4+-N and Mn2+ leaching efficiencies were optimized to 96.73% and 97.35%, respectively, while the fineness of EMR was refined to 1.78 µm. The leaching efficiencies of NH4+-N and Mn2+ were 58.83% and 46.96% higher than those attained without AJM processing. The AJM used strong airflow to give necessary kinetic energy to EMR particles, which then collided and sifted to become refined particles. The AJM disposal converted kinetic energy into heat energy upon particle collisions, causing EMR phase transformation, and particularly hydrated sulfate dehydration. The work provides a fire-new and high-efficiency method for significantly and simply leaching NH4+-N and Mn2+ from EMR.

Optimizing ball milling parameters for controlling the internal microstructure and tensile characteristics of a laminated carbon nanotube/aluminum–copper–magnesium composite

This research investigates how different ball milling conditions influence the microstructure and mechanical properties of carbon nanotube/aluminum alloys. The study examines varying rotation speeds, specifically 200, 300, and 400 rpm. The results highlight the significant impact of milling conditions on grain size and mechanical properties. Notably, milling at 300 rpm/4 h and at 400 rpm/2 h led to higher tensile strength but lower uniform elongation compared to milling at 200 rpm/6 h. The alloy milled at 300 rpm/4 h displayed a refined microstructure, increased density, and the strongest fiber texture along the (111) direction. The presence of a moderate grain size facilitated ductility, resulting in the highest uniform elongation (∼9.1%) while maintaining high strength (∼515 MPa). This study provides valuable insights into the effects of ball milling on the microstructure and mechanical properties of metals and alloys, contributing to the optimization of milling conditions to achieve desired material characteristics.

Effect of Spindle Speed and Feed Rate on Surface Roughness and Milling Duration in the Fabrication of Milled Complete Dentures: An In Vitro Study

Milling machines have made denture fabrication possible with high accuracy in a short time. However, the relationship between the milling conditions, accuracy, and milling duration has not been clarified. This study aimed to clarify the effects of milling conditions on surface roughness and milling duration. The specimen was designed using CAD software and milled using PMMA disks. In milling, the parameters of finishing the specimen surface were adjusted. Three different spindle speeds and four different feed rates were set. Twelve combinations of each parameter were used for milling, and the surface roughness and milling duration were measured. Results showed that the surface roughness significantly increased with the feed rate on the slopes of the specimen. The surface roughness differed with the spindle speed on the left and right slopes. The spindle speed and feed rate did not affect the surface roughness on the flat surface. The milling duration was not affected by the spindle speed but decreased as the feed rate increased. In conclusion, by increasing both the spindle speed and feed rate, the milling duration could be shortened while maintaining a constant surface quality. The optimum milling conditions were a spindle speed of 40,000 rpm and feed rate of 3500 mm/min.

Influence of Tools and Cutting Strategy on Milling Conditions and Quality of Horizontal Thin-Wall Structures of Titanium Alloy Ti6Al4V.

Titanium and nickel alloys are used in the creation of components exposed to harsh and variable operating conditions. Such components include thin-walled structures with a variety of shapes created using milling. The driving factors behind the use of thin-walled components include the desire to reduce the weight of the structures and reduce the costs, which can sometimes be achieved by reducing the machining time. This situation necessitates, among other things, the use of new machining methods and/or better machining parameters. The available tools, geometrically designed for different strategies, allow working with similar and improved cutting parameters (increased cutting speeds or higher feed rates) without jeopardizing the necessary quality of finished products. This approach causes undesirable phenomena, such as the appearance of vibrations during machining, which adversely affect the surface quality including the surface roughness. A search is underway for cutting parameters that will minimize the vibration while meeting the quality requirements. Therefore, researching and evaluating the impact of cutting conditions are justified and common in scientific studies. In our work, we have focused on the quality characteristics of horizontal thin-walled structures from Ti6Al4V titanium alloys obtained in the milling process. Our experiments were conducted under controlled cutting conditions at a constant value of the material removal rate (2.03 cm3⁄min), while an increased value of the cut layer was used and tested for use in finishing machining. We used three different cutting tools, namely, one for general purpose machining, one for high-performance machining, and one for high-speed machining. Two strategies were adopted: adaptive face milling and adaptive cylindrical milling. The output quantities included the results of acceleration vibration amplitudes, and selected surface topography parameters of waviness (Wa and Wz) and roughness (Ra and Rz). The lowest values of the pertinent quantities were found for a sample machined with a high-performance tool using adaptive face milling. Surfaces typical of chatter vibrations were seen for all samples.

Effect of Size-Distribution Environment on Breakage Parameters Using Closed-Cycle Grinding Tests.

The so-called population balance model (PBM) is the most widely used approach to describe the grinding process. The analysis of the grinding data is carried out using-among others-the one-size fraction BII method. According to the BII method, the breakage parameters can be determined when a narrow particle size fraction is used as feed material to the mill. However, it is commonly accepted that these parameters are influenced by changing the particle size distribution in the mill. Thus, this study examines the breakage parameters through kinetic testing in different natural-size distribution environments generated by closed-cycle grinding tests that simulate industrial milling conditions. The differentiation of the milling environments was accomplished using various reference sieves in the closed-cycle tests. The experimentally determined breakage parameters were back-calculated and then used to simulate the closed-cycle tests using the MODSIMTM software. Additionally, the energy efficiency was evaluated based on the specific surface area of the grinding products and the energy consumption. The results of the kinetic tests showed that the breakage rate of the coarse particles increases as the aperture size of the reference sieve decreases, and consequently, the content of fines in the mill increases. The back-calculated breakage parameters can be reliably used to simulate closed-cycle circuits, thus helping control industrial milling operations.

Effect of High-Energy Milling on Ceria-Zirconia’s Redox Properties

Series of ceria-zirconia (CZ)-based nano-materials with a d50 in the range of 0.2 to 1.3 microns were made using the jar milling, Eiger milling, and steam jet milling (SJM) techniques. The effect of the milling conditions on the morphology and textural properties was studied. High-energy steam jet milling in a quasi-hydrothermal environment (with potential local temperature spikes over 500 °C) significantly impacted the CZ crystal structure by inducing lattice distortions. It was shown that the acquired lattice stress resulted in a significant increase in oxygen mobility, which was manifested by a TPR-H2 Tmax shift from 450–550 to 150–250 °C. CZ materials with fast oxygen mobility are metastable phases, and re-slurring nano-CZ powders in water and impregnation with precious metals had stabilizing effects on fast oxygen mobility. Efficiently enhancing the CZ redox activity milling process took place in the following order: Steam jet milling > Eiger milling > jar milling.

Microwave wood chip treatment use in chemical pulp manufacturing (technical-economic assessment)

The low permeability of many wood species causes problems in the chemical pulp industry. These include very long cooking times, high chemical consumption, large material losses, high energy consumption, and environmental pollution. New microwave (MW) wood modification technology can provide an increase in wood permeability for liquids and gases that solves many of these problems. MW wood pre-treatment can increase pulp mill throughput, reduce chemical and power consumption, increase pulp quality and yield, and improve environmental performance. Economic modelling of this new technology use in different chemical pulp mill conditions allowed to assess the effect of capital costs, electricity costs, labour costs and other cost components to specific total costs of MW chip processing. MW chip treatment costs for pulp mills with output 50,000 to 500,000 ait dry ton (ADT) per year at electricity cost range US$0.04 to US$0.24/kWh vary in the range from US$17.7 to US$60.8 per air dry ton of pulp. Electricity costs form the most significant part – 51- 69% of the total specific costs of MW chip processing at electricity costs US$0.08 to US$0.12/kWh. New technology applications in different Russian conditions can provide benefits up to 7 – 22 Mil US$ per year for pulp mills with output of more than 200,000 ADT/year. The ecological effect and high economic advantages of this MW technology provide a good opportunity for commercialisation.

Comprehensive investigation of the impact of milling time on microstructural evolution and tribological properties in Mg-Ti-SiC hybrid composites

This research delves into the effects of milling time on the properties of Mg-Ti dual matrix composites reinforced with nano SiC powders, processed via spark plasma sintering. The study, driven by the need for advanced materials with enhanced wear resistance for the aerospace and automotive sectors, focuses on microstructural evolution and wear characteristics. It aims to understand how varying milling durations influence particle morphology, crystallite structure, and consequently, tribological behavior. Initial observations indicate a decrease in average particle size to 5.72 µm, followed by an increase to 14.83 µm due to cold welding and particle trapping, demonstrating the dynamic nature of particle morphology under different milling conditions. X-ray diffraction analysis reveals a notable reduction in magnesium's crystallite size with increased milling, suggesting plastic deformation. This study underscores that smaller crystallite sizes do not always correlate with strain, especially in smaller dimensions. Additionally, the research records variations in density and hardness, influenced by milling time and particle dispersion, with hardness showing a complex variation, peaking at 108 HV. Overall, the findings highlight the critical role of milling duration in shaping the microstructure and determining the mechanical and wear properties of Mg-Ti-SiC composites. This investigation contributes to the optimization of wear resistance in these composites, enhancing their applicability in high-performance industrial applications.

An experimental investigation on machining-induced surface/subsurface characteristics of nickel based Inc-718 alloy: A novel hybrid approach in milling process

Nickel-based superalloy Inc-718 has become an indispensable alloy in critical sectors, especially in the aerospace industry, thanks to its unique characteristics. However, some properties of the alloy (especially low thermal conductivity and hot hardness) cause difficulties in its machinability. For this reason, comprehensive studies to improve the machinability of Inc-718 alloy by considering the microstructural properties are guiding. In this context, the present study uses various methods to increase the machinability efficiency of Inc-718, while also investigating their effect on microstructural properties. Firstly, the effect of the pre-heating process (hot), pure-MQL (PMQL), nanofluid-MQL (NMQL), and hybrid methods (hot+PMQL and hot-NMQL) on the surface roughness, cutting forces, tool wear, vibration, and temperature was investigated while milling Inc-718 surfaces. Then the utilization of Electron Backscatter Diffraction (EBSD) facilitated a comprehensive examination of microstructural behavior, with a specific focus on Euler-colored maps and phase distribution maps, providing valuable insights into the material's behavior under distinct milling conditions. As a result, hot+PMQL, hot+SiC-NMQL, and hot+Al2O3-NMQL provided an important contribution to the improvement of machinability characteristics. Also, it was seen that in EBSD analysis, a limited area is affected by heat in the hot machining environment. The crystal orientations of the pre-heated and hybrid machined Inc-718 alloy are highly similar to that of the dry-machined alloy. This similarity indicates that the removal of the heated layer from the workpiece during the milling process contributes to the preservation of the microstructure.

Image super resolution by double dictionary learning and its application to tool wear monitoring in micro milling

It is an effective means to improve the machining quality of product by monitoring the tool wear conditions in micro milling. However, due to the small size and high speed of the micro milling cutter, it is difficult to capture the clear image of tool wear by CCD camera. Therefore, a double dictionary sparse coding super-resolution (SR) method is proposed to improve the resolution of micro milling tool wear images in this work. Based on the traditional single dictionary, this work proposes the residual dictionary to reconstruct the residual image of the tool, achieving the double dictionary coefficient encoding reconstruction. In order to extract local features of low resolution (LR) tool wear images, the Gobor filter banks are designed, and then the PCA method is used to reduce dimension of extracted features. The dictionary learning based on a single high resolution (HR) image is realized, which reduces the dependence of super-resolution algorithm on large datasets. The effectiveness of Gabor filter and double dictionary for restoration tool wear image details is verified by experiments. Compared with proposed method, traditional interpolation method, sparse coding super resolution model [32] and super resolution convolutional neural network model [26], the PSNR mean value of those methods are 43.62, 42.19, 43.20, 43.21, respectively, which shows that the proposed method has excellent performance in super-resolution reconstruction of micro milling tool images for tool wear monitoring.

A Review of the Grinding Media in Ball Mills for Mineral Processing

The ball mill is a rotating cylindrical vessel with grinding media inside, which is responsible for breaking the ore particles. Grinding media play an important role in the comminution of mineral ores in these mills. This work reviews the application of balls in mineral processing as a function of the materials used to manufacture them and the mass loss, as influenced by three basic wear mechanisms: impact, abrasion, and corrosion. The effect of grinding media geometries and density on the mill performance was also reviewed to determine what the research has recommended as the most suitable grinding media for different grinding applications. Although considerable work has been carried out in that area, the influence of grinding media shape on the liberation of minerals, as well as the effect of various mill conditions on the performance of mixed grinding media shapes, are still poorly understood. Thus, the review opens up opportunities for further research to improve the grinding processes, especially considering that even a slight improvement in the process efficiency significantly reduces the production costs.

Reaction path in the mechanosynthesis of calcium phosphates using a biogenic calcium source

Calcium phosphates were produced by mechanosynthesis, using eggshell, H3PO4 and 6–83 wt%-H2O. Mixtures were milled at 600 rpm during 0.5–12 h. Resulting calcium phosphates occur within specific milling domains; H2O concentration determines onset and stability of monophasic hydroxyapatite. Within the tested conditions, brushite is the first detected calcium phosphate precipitated from solution. In 6, 40 and 56 wt%-H2O, monetite intermediates brushite's transformation to hydroxyapatite; in 71 and 83 wt%-H2O transformation is direct. Hydroxyapatite formation is favoured at the H2O extremes tested, 6 and 83 wt%. CO2 build-up in the confined jar and nucleation-and-growth events during drying are possible obstacles upon control of morphology and composition of synthesised particles. The potential of chicken eggshell as direct biogenic source and the ability of high-energy milling as corresponding processing route to produce calcium phosphates was demonstrated. This signals a route for reliable production of brushite, monetite and hydroxyapatite. A preliminary milling map was built, allowing to obtain desired final product under specific milling conditions.

Major and minor elliptical axes and bounding rectangle dimensions in clay brick powder particles from changing milling conditions

Starting from the observation that regular shape parameters such as equivalent diameter, area-perimeter ratio, circularity, compactness and roundness fail to adequately identify shapes of materials, alternative shape parameters are proposed to remedy this shortcoming. In this study, plugins in image analysis are extended to explore the major and minor elliptical axes and bounding rectangle dimensions in clay brick powder particles from changing milling conditions of different masses of clay bricks in ball mill. It turned out that with developed plugins in ImageJ, extracting such shape parameters of clay brick powder samples was not problematic. For the generated reciprocal aspect ratio (RAR) values ranging from 0.51 to 0.53, majority of the particles were noticed to be within the ellipse-inclined shapes. Using the feret major axis ratio (FMR) values for the formulated bounding rectangle dimensions, most particles appeared to be bound in rectangle-inclined shapes. Despite the generated major and minor elliptical axes and bounding rectangle parameters, grinding conditions in this research did not present any significant influence on such shape parameters of CBP specimens. It is believed that the developments of quantifying the major and minor elliptical axes and bounding rectangle dimensions of the CBP particles in this study are ground on solid foundations without need for extensive experimental works. The proposed developments are therefore valid and could be dedicated for characterising pozzolanic materials, because of their interests in cement-based composites.

Cover Feature: Mechanochemical Synthesis of Corannulene: Scalable and Efficient Preparation of A Curved Polycyclic Aromatic Hydrocarbon under Ball Milling Conditions (ChemSusChem 20/2023)

Cover Feature: Mechanochemical Synthesis of Corannulene: Scalable and Efficient Preparation of A Curved Polycyclic Aromatic Hydrocarbon under Ball Milling Conditions (ChemSusChem 20/2023)

Early chatter identification based on optimized VMD with multi-band information fusion and compression method in robotic milling process

Undesirable self-excited chatter has always been a typical issue restricting the improvement of robotic milling quality and efficiency. Sensitive chatter identification based on processing signals can prompt operators to adjust the machining process and prevent chatter damage. Compared with the traditional machine tool, the uncertain multiple chatter frequency bands and the band-moving of the chatter frequency in robotic milling process make it more challenging to extract chatter information. This paper proposes a novel method of chatter identification using optimized variational mode decomposition (OVMD) with multi-band information fusion and compression technology (MT). During the robotic milling process, the number of decomposed modes k and the penalty coefficient α are optimized based on the dominant component of frequency scope partition and fitness of the mode center frequency. Moreover, the mayfly optimization algorithm (MA) is employed to obtain the global optimal parameter selection. In order to conquer information collection about the uncertain multiple chatter frequency bands and the band-moving of the chatter frequency in robotic milling process, MT is presented to reduce computation and extract signal characteristics. Finally, the cross entropy of the image (CEI) is proposed as the final chatter indicator to identify the chatter occurrence. The robotic milling experiments are carried out to verify the proposed method, and the results show that it can distinguish the robotic milling condition by extracting the uncertain multiple chatter frequency bands and overcome the band-moving of the chatter frequency in robotic milling process.

On the scope of mechanochemical activation: The case of Cu/ZnO catalytic systems

ZnO was submitted to different conditions of high-energy ball milling to thoroughly study the outcome of mechanochemical activation. Structural modifications led to a decrease in crystallite size and an increase in micro-strain and specific surface area (SBET) with milling time. Different copper amounts were added on pristine (reference) and activated support by incipient wetness impregnation. Cu deposited over activated support showed an enhanced metal-support interaction since part of Cu2+ could be introduced into milled ZnO lattice, replacing Zn2+ ions and/or locating in lattice interstitials. Moreover, further analyses suggested an electron transfer from activated support to metal, generating a mixture of Cu2O–CuO species, particularly at the interface between metal and support. N2O chemisorption studies gave Cu particle sizes of 1.3, 1.9 and 3.5 nm (for 0.2, 0.5 and 1 wt% Cu, respectively) and thus a good metal dispersion over ZnO was achieved. Hence, support's activation by milling process showed to be an excellent approach to improve both metal-support interaction and metal dispersion of supported catalysts.

Mechanical performance of high-entropy (AlCrNbSiTi)N films fabricated by high-power impulse magnetron sputtering over a wide compositional window

We designed nine distinct compositions of AlCrNbSiTi high-entropy alloy targets by adjusting the Al, Cr, Nb, and Ti contents, while maintaining the Si content at 7.7 at.%. We fabricated (AlCrNbSiTi)N films using the high-power impulse magnetron sputtering (HiPIMS) technique. By analyzing the microstructure and properties of the films, we have identified an expanded compositional window. This expansion enables (AlCrNbSiTi)N films with varying composition ratios to consistently demonstrate excellent mechanical properties. This consistency proves advantageous in terms of both sputtering target preparation and coating applications. In this study, all films had a single face-centered cubic (NaCl-type) structure with a crystallite size of ∼6 nm and lattice constant of ∼4.22 Å. The hardness of the films varied between 25.9 and 27.6 GPa. The thickness of the oxide layer formed when the films were annealed at 800 °C for 2 h under atmospheric conditions was approximately 30 nm, regardless of the composition. We also examined the cutting properties of (AlCrNbSiTi)N coatings on carbide cutting tools. Under dry milling conditions and extended cutting distances, the (AlCrNbSiTi)N coatings exhibited a remarkable reduction in flank wear length, with reductions of 78%, 64%, and 68% when compared to the commercial coatings TiN, TiAlN, and AlTiN, respectively. Furthermore, these coatings remained intact without peeling during milling on a 304 stainless steel workpiece. This research demonstrates that the combination of HiPIMS and high-entropy (AlCrNbSiTi)N could provide hard coatings with excellent performance during cutting. The characteristics of the coatings are attributable to the fineness and high density of the films deposited by HiPIMS and the synergistic lattice distortion and cocktail effects, which are similar in the compositional window of the designed alloy system.

Prediction of milling force based on identified milling force coefficients and tool runout parameters in time-frequency domain

Milling force is the key variable related to machining performance. Mechanistic models are commonly used to predict milling forces. However, the identification process of milling force coefficients and tool runout parameters in this model is prone to local optimal solutions. This paper develops a time–frequency domain identification method, and then the prediction of milling force is implemented on this basis. First, a milling force model considering the influence of tool runout is established, where the milling force coefficients and tool runout parameters are identified based on the time–frequency domain identification method. The simulation and experimental data are used to compare the time–frequency domain identification method with the time-domain and frequency-domain identification methods, respectively. Then, the variation of milling force coefficients and tool runout parameters with milling conditions is studied, based on which the linear interpolation method of coefficients and parameters is used to predict the milling force. Finally, the effectiveness of the milling force prediction is verified by experiments.