Rotary Mill Research Articles

Heterarchical modelling of comminution for rotary mills: part I—particle crushing along streamlines

Rotary mills aim to effectively reduce the size of particles through a process called comminution. Modelling comminution in rotary mills is a challenging task due to substantial material deformation and the intricate interplay of particle kinematics of segregation, mixing, crushing, and abrasion. Existing particle-based simulations tend to provide predictions that cannot cope with the large number of particles within rotary mills, their wide range of sizes, and the physics dictating the crushing of individual particles. Similarly, there is currently no deterministic modelling means to determine the evolving population of particle sizes at any point in time and space within the mill. The aim of this two-part contribution is to address these gaps by advancing a framework for a novel stochastic comminution model for rotary mills, which has a well-defined deterministic continuum limit and can cope with arbitrarily large numbers of particles. This work describes the basic physics and structure of the new model within a heterarchical framework for ball and autogenous grinding mills. The primary focus of this Part I paper is to develop a computational model for the integration of motion of material along streamlines inside a mill. Coupled to this process is the kinetic physics dictating particle crushing. In a subsequent work, Part II, segregation and mixing will be added to this model such that realistic behaviour from the mill can be observed.Graphical

Heterarchical modelling of comminution for rotary mills: part II—particle crushing with segregation and mixing

In granular media, the crushing of individual particles is influenced by the number of contacts with neighbouring particles. This well-known phenomenon of “cushioning” shields the individual particles from crushing when the number of contacts is high. However, in open systems that involve extensive granular flow and bulk motion, like those found in industrial mills, the neighbouring particles continually exchange positions due to segregation and mixing, thereby altering the number of neighbouring contacts and their sizes, affecting the crushing of individual particles. Therefore, a critical challenge for properly modelling comminution in such systems lies in tracking the fluxes of the various particle size classes. Here, we explore the physics that governs the mechanisms of segregation and mixing within the multiscale heterarchical modelling paradigm. Building upon the framework developed in Part I, which integrated the heterarchical aspects of the physics of crushing along streamlines, we further account for segregation and mixing, and demonstrate their impact on the comminution efficiency of autogenous grinding mills. In particular, segregation is shown to greatly enhance the extent of particle crushing within the mill. Accordingly, we posit that this mechanism cannot be ignored. In summary, the new model sheds light on previously obscured dynamics within industrial mills, as well as enables the field to predict the time evolution of the particle size distribution at any point in the mill domain. This modelling capability opens the doors to new developments for estimating and improving milling efficiencies.Graphical

Parameters of a combined plow rotor for the climatic conditions of the Bukhara region

In this article, pretreatment of the soil in Bukhara includes simultaneous softening, compaction and crushing of plant residues. As a result, the movement of agricultural machinery in the field is reduced, and the compaction of the subsurface layer is reduced by 5-7 times. For this purpose, the installation and grounding of an additional rotary mill assembly to the fork body is described. Pre-sowing processing consists in the justification of constructive and technological parameters and modes of operation of the crop-milling aggregate, which improve the quality and reduce the tensile resistance. Theoretical studies were carried out using the laws of mathematical analysis and theoretical mechanics. Multi-factor experiment planning methods have been used to conduct experimental research. The results of the study were processed using the methods of Mathematical Statistics.

Вплив механохімічної активації композиційного цементу на міцність будівельного розчину

The article discusses issues related to the use of technology for the production of mortar mixtures and mortars based on high-speed mixers, the operation of which causes mechanochemical activation of the binder. The rotary counterflow mill used in the work acts as an activator of the surface zone of both Portland cement grains and quartz sand grains and, thus, contributes to the intensification of the processes of structure formation of cement paste and mortar based on it. Based on the fact that one of the promising ways to reduce the cost of cement activation is to reduce the energy intensity of the dispersion process itself, the use of relatively low-energy rotary mills can be considered as an effective way to increase the activity of the binder. After the joint activation of Portland cement and unground quartz sand (the amount of which was adjusted from 0 to 50 % of the cement mass; activation period - 300 seconds), samples were made from equal-viscosity cement paste. It was experimentally established that the maximum strength of cement stone at 28 days of age was achieved when using composite cement with a 20 % content of activated sand. To determine the influence of the studied factors, such as the consumption of mechanically activated composite binder, the concentration of superplasticizer C-3 (0...1,5 %) and the consumption of microsilica (0...10 %) on the strength of the mortar in 2 and 28-day old, a 3-factor experiment was conducted. It was established that in the studied hardening period, the content of mechanically activated composite cement has the greatest influence on the compressive strength for the studied mortar compositions (from 1:3 to 1:1). The next most important influence on the strength of the mortar is the consumption of superplasticizer C-3. The increase in compressive strength of a mortar from the introduction of microsilica into its composition does not exceed 10-15 %. The combined effect of mechanical activation of the binder and the use of the C-3 additive ensures an increase in the strength of the mortar (mortar composition 1:1) at 28 days of age from 43,5 MPa (non-activated binder; no C-3 additive) to 63 MPa, that is, almost by 45 %. For a mortar of similar age with a lower consumption of composite cement (mortar composition 1:3), mechanical activation of the binder in the presence of 1,5 % C-3 additive ensures an increase in the compressive strength of the mortar from 21 MPa (non-mechanically activated binder; C-3 = 0 %) to 39 MPa.

Simulation Method for Particle Comminution Process Considering Dependence on Particle Size and Impact Velocity in Breakage Modes

Comminution process is widely used in industry to produce fine particles. We developed a mathematical model of comminution in order to analyze particle size reduction in an impact pulverizer. In our model, it is assumed that parameter a, which represents particle breakage modes, depends on both impact velocity and size of the particles. To obtain that dependence, particle-size distribution was measured experimentally before and after the breakage using a jet-mill. We implemented the mathematical model into the simulation based on computational fluid dynamics (CFD) and discrete phase model (DPM). It was confirmed that the simulation results coincide with the experimental ones in a rotary mill. Therefore, we conclude that it is important to consider the dependence of impact velocity as well as particle size on the breakage modes.

Properties of biomass powders resulting from the fine comminution of lignocellulosic feedstocks by three types of ball-mill set-up

Background: Lignocellulosic biomass has many functionalities that hold huge potential for material, energy or chemistry applications. To support advanced applications, the biomass must be milled into ultrafine powder to increase reactivity. This milling unit operation needs to be fully mastered to deliver high-quality standard end-products. Here we studied the relationship between the characteristics of the starting lignocellulosic plant material and the properties of the resulting ultrafine powder in different ball-mill process routes. Methods: Two lignocellulosic biomasses (pine bark and wheat straw) with contrasted compositional and mechanical properties were milled using three ball-mill set-ups delivering different balances of impact force and attrition force. The resulting powders were analysed for particle characteristics (size, agglomeration extent, shape) and powder flow properties (compressibility, cohesion) using a dynamic powder rheometer. Results: Pine bark is more amenable to a fast particle size reduction than the fibrous wheat straw. The resulting pine bark powders appear less compressible but much more cohesive than the straw powders due to particle shape, density and composition factors. The mill set-up working by attrition as dominant mechanical force (vibratory ball mill) produced a mix of large, elongated particles and higher amounts of fines as it acts mainly by erosion, the resulting powder being more prone to agglomerate due to the abundance of fines. The mill set-up working by impact as dominant mechanical force (rotary ball mill) produced more evenly distributed particle sizes and shapes. The resulting powder is less prone to agglomerate due to a preferential fragmentation mechanism. Conclusions: The attrition-dominant mill yields powders with dispersed particle sizes and shapes and the poorest flow properties, while the impact-dominant mill yields more agglomeration-prone powders. The mill set-up working with impact and attrition as concomitant mechanical forces (stirred ball mill) produces powders with better reactivity and flow properties compared to rotary and vibratory mills.

Feasibility study on the volume reduction of radioactive concrete wastes using thermomechanical and chemical sequential process

This study describes a method to reduce the volume of radioactive concrete wastes generated during the decommissioning process of nuclear facilities. The method involves thermomechanical and chemical treatment processes sequentially to separate the bulk aggregates from the cement binder; the latter of which contain the majority of the radioactive contaminants. The thermomechanical process acted to weaken the chemical bond between the cement and aggregate components in the concrete. Optimal thermomechanical treatment conditions were determined to be as follows: Isothermal pre-treatment at 550 °C for 1 h using crushed concrete followed by rotary mill grinding for 4 h at room temperature with a 75% loading volume. Such conditions were found to be effective at reducing the volume of the concrete waste, but could not remove the contaminants 137Cs and 60Co from the aggregates completely. Applying the chemical process to remove the contaminants using a hydrochloric acid solution, the clearance criteria for 137Cs and 60Co could be attained for the aggregates separated. Therefore, the radioactive concrete waste could be treated for clearance by the sequential treatment process, thus achieving an approximately 75% volume reduction of the radioactive concrete waste and ultimately lowering the cost of decommissioning and waste disposal.

Use of replaceable working equipment to expand the functionality of the excavator

Increasing the range of replaceable working equipment for hydraulic single-bucket excavators allows to expand the scope of application significantly, increase the efficiency of its usage, as well as the mobility of these machines. The purpose of the study is to design working equipment replacement items, used for hydraulic single-bucket excavator for digging frozen soils in the city Vladivostok. The main tasks of the study are to analyze frozen soils in the region and their existing structures, select a layout scheme for further design calculation, evaluate the economic feasibility of the proposed hydraulic excavator working equipment design replacement items, used for digging frozen soils in Vladivostok city. Keywords excavator, replacement equipment, frozen ground, urban conditions, rotary mill, vibro-ripper, hydraulic hammer, bucket-ripper, tusk-ripper, gripper-tongs working body

THEORETICAL ASPECTS OF THE DISPOSAL OF WOOD FIBER WASTE IN AERODYNAMIC MEDIA

The paper discusses the results of a study on the use of fundamentally new equipment (rotary knife mill) for the preparation of secondary fiber waste in the air and the possibility of their full use in finished products for various purposes. In order to justify the effectiveness of the preparation and the feasibility of using secondary wood fiber semi-finished products by a dry grinding method, the physical phenomena and regularities of the mechanism for the preparation of secondary wood fiber semi-finished products by the proposed method are determined and investigated, which characterize the technological process of preparation in air and their possible future use as semi-finished products or in the manufacture of finished products products. The process of dissolution of wood fiber waste was studied, the mechanical effect on wood fiber waste due to face-cross cutting (cutting, crushing, flattening, breaking) and aerodynamic phenomena (breaking, collision, dissolution, fibrillation), contributing to the formation of external and internal fibrillation of the secondary wood fiber, is described. increase in specific surface in the absence of high temperatures and pressure, without the addition of chemical additives, without the use of water and steam. The performed studies allow us to propose a new method and system for the preparation of wood fiber waste by dry grinding, justifying their economic and environmental feasibility.

Analysis of power parameters of a rotary mill

The paper (publication) presents a description of the developed design of a rotary mill with a complex mechanical and acoustic effect on the dispersed material, as well as analytical studies of the parameters of energy consumption of a rotary mill, based on the main physical processes occurring in it. The research was carried out by mathematical and simulation modeling of technological processes in the grinding chamber of the mill, as well as on various technological paths of the unit. To determine the main parameters that make up the total power consumption of the unit, an approach was chosen to differentiate the processes by their physical nature and contribution to the formation of the total power consumption of the rotary mill.The obtained results of mathematical modeling of processes occurring inside the technological paths of the unit allowed getting expressions for determining the main power costs of the unit depending on the characteristics of the unit design for each component of the total power required for effective operation of the unit at the required parameters of the dispersion of the finished product.

Distribution of Working Angles in a Rotary Mill

The control of rotary milling is shown to be a problem with numerous possible solutions. An approach based on the Harrington desirability function is proposed. The tool’s working angles are selected as the optimization parameters; their variation is analyzeyd. Theoretical distributions corresponding to the empirical data are chosen.

Cutting Geometry in a Rotary Mill

A method is proposed for determining the direction of the resultant velocity from geometric relationships in accordance with the kinematics of rotary milling. The effectiveness of the method is assessed by comparing the results with existing methods and with results obtained by direct graphic simulation.

A numerical study on particle behaviors of fluid flow in pulverizer

Abstract In the case of the developed countries, pulveriser systems exhibit a high level of sophistication, but competitive pressures threaten family farm units and rural communities. Also, the improvement of the added values of existing products has been concentrated. Until now, high-speed rotary milling machine which be capable of producing 20 kg/h of materials containing a large amount of fat without heat denaturation of about 20μm or less has not yet been commercialized in the world. There are two air stream mill techniques such as the jet and high-speed rotary mill methods among the air stream-type pulverizing method in the world markets. However, the high-speed rotary mill method is known as the only method of crushing the raw materials not only soybeans, but also coffee. In order to optimise the pulverised fluid flow, many aspects need to be taken into account. The objective of this paper is concentrated on a technique that can be finely pulverized to submicron size while maintaining the composition and nutrition without heat denaturation. First, a FEA (Finite Element Analysis) that the optimal number of revolution as input parameter is obtained through the impulse analysis to minimize the thermal denaturation has been carried out. Second, the optimum inlet velocity for producing particles less than 20μm is derived by checking the particle size distributions which employed particle behaviour analysis. Finally, the relationship between the flow and the kinetic characteristics of particles generated by crushing of soybeans for the development of high-speed rotary milling machine using the developed FEA models has been discussed

Correction of pressure drop in a heavily loaded hybrid bearing when starting by using a constant flow lubrication system- Application to a rotary cement mill

We analyzed a lubricated journal plain bearing supporting heavy loaded rotary mill. During start-up operating, after the shaft is lifted by high external pressure lubricant, the speed of the shaft grows from 0 to the operating hydrodynamic speed when, suddenly after the first thirty seconds of shaft rotation, the pressure drops in one recess causing excessive damage to the pad bearing interface. The aim was to understand and provide some answers to the pressure drop in order to give an appropriate correction. Misalignment between the shaft and bearing surfaces was considered and analyzed in first part of the study. According to the obtained results the proposed correction is to use a suitable constant flow lubrication system which avoids the pressure to drop in recesses. A real application was made on a partial pad bearing supporting a heavy rotary cement mill localized at the cement plant of Chlef in Algeria.

Optimal design of helical reducers for cement equipment

The trends in raising the technical level of multistage helical reducers for drives of cement, metallurgical and other heavy equipment are considered. An interactive method for optimizing the geometrical parameters of reducers with various gear ratios is proposed, which ensures equal strength of the stages in contact and bending endurance. It is shown that an increase in the hardness of the teeth requires an increase of the module and helical angle of the teeth, limitation of gear ratios, and to reduce the difference in center distances of adjacent stages. When creating a new generation of reducers, the transition to gears with carburized teeth leads to an increase in load capacity of 2.5-3 times. The examples of gear drive design for rotary kilns and ball mills are considered.

A Study of the Mechanical Properties of Railroad Wheels Manufactured from a Billet Broached in a Helical Rolling Mill

We describe the results of a full-scale experiment in the fabrication of 957 mm diameter railroad wheels from a pre-formed hollow billet obtained by piercing a thick-walled sleeve with an ingot. We found that a 474 mm diameter steel wheel billet can be smoothly pierced using a rotary piercing mill. The process of forming hollow billets when mass-producing wheels in press-rolling equipment also remains stable. The mechanical specifications of railroad wheels fabricated from hollow billets meet regulatory requirements.

Research into the Possibility of Producing Single-Phase Tantalum–Hafnium Carbide by SHS

The influence of mechanical-activation (MA) conditions on the microstructure and phase composition of Ta–Hf–C reaction mixtures and products fabricated from them by self-propagating high-temperature synthesis (SHS) is investigated. The Ta–Hf–C reaction mixtures are mechanically activated in centrifugal planetary mills with various drum revolution rates. It is revealed that an increase in the drum revolution rate from 250 to 900 rpm lowers the heterogeneity scale of the reaction charge, decreases the size of coherent scattering regions of tantalum and hafnium by an order of magnitude, and leads to a rise in the degree of microdeformation of their crystal lattices by a factor of 1.5–2.0. It is established experimentally that it seems impossible to initiate an SHS reaction in the Ta–Hf–C activated mixture at initial temperature T0 < 550 K. The combustion process is implemented only at T0 = 800 K, when the adiabatic combustion temperature reaches 3274 K in mixtures treated with a revolution rate higher than 678 rpm. Single-phase carbide (Ta,Hf)C with lattice parameter a = 0.4487 nm, which corresponds to 18.0 at % dissolved HfC in TaC, is formed from reaction mixtures activated according to optimal regimes. The hafnium oxide content in products does not exceed 1%. The sample structure has high porosity (larger than 30%) and small carbide grain size (smaller than 10 μm), which makes it possible to produce the (Ta,Hf)C powder by milling the SHS product in a ball rotary mill.

Design, Testing and Evaluation of Mobile Corn Mill for Village-Level Operation in the Philippines

The efficiency and availability of corn mills operating in the Philippines play a vital role in achieving food self-sufficiency in the entire country. Majority of operational corn mills are situated along the highway where three-phase electrical line is available. Current design of operational corn mills still utilizes emery stone for its degermination process, two-steel rollers for its milling process and oscillating sifter that all require huge amount of power. The purpose of this research was to develop a technically viable and financially feasible new type of mobile corn mill that can be used in the countryside particularly in the remote areas. The developed corn mill system is comprised of the degerminator, rotary mill, rotary grader and equipped with a pre-cleaner (destoner and winnower), two elevators and a suction blower. It is powered by 60 HP, 4-cylinder diesel engine. Performance test results revealed that the developed mobile corn mill has an input capacity of 940 - 1,100 kg/h with product recovery of 66-71 % and degerminator efficiency of 82-88 %. Cost of milling is estimated at Php0.86 per kg output. The estimated cost of the developed corn mill is Php850,000 per unit (US$1=Php50). The developed corn mill technology can be used by farmer cooperatives and local entrepreneurs that will engage in custom-milling business and the processing of corn for food and animal feeds.

Nitrogen as an alloying element improving material properties of the high carbon cast steel for ball mill liner plates

This paper presents an experimental analysis, which was carried out to evaluate the addition of nitrogen as an element complementing a chemical composition used for such cast parts. It has been demonstrated that nitrogen is very advantageous in the process of austenitizing and quenching, improving the stability and homogeneity of the alloy structure. Plates used as a lining of rotary mills operating in cement plants are castings, which acquire their properties mainly through proper heat treatment. Together with an appropriate microstructure and chemical composition, correct heat treatment allow to improve the wear resistance and significantly reduce the abrasive corrosion. Extensive investigations enabled establishing an optimum nitrogen content in the chemical composition of thick-walled castings used in cement industry. Results of experiments, managed for the steel of ledeburate type containing 0.8–1.2% of carbon, have found that the optimal level of nitrogen is in the amount of 0.07–0.10%. The proposed modification helped to reduce the amount of an expensive chromium, increase the hardness of the material (by about 2 HRC to 4 HRC), and to achieve the uniform microstructure and hardness, which noticeably improved the lifetime of the rotary mills plates.

Energetic and exergetic performance investigation of a cement facility for clinker production

In this study, the energetic and exergetic analyses of a cement plant for clinker production are investigated. The exergy destruction rate, energy and exergy efficiency of process components are presented by using the thermodynamic balance equations. The energetic and exergetic efficiencies of cement plant are calculated as 60.78%, and 46.11%, respectively. The rotary kiln, raw mill and cooler component have the maximum exergy destruction rate among the other process components. The exergy efficiency of rotary kiln, raw mill and cooler component are calculated as 57.36%, 33.52% and 49.46%, respectively. Also, to analyse the cement plant performance more comprehensively, the parametric studies are conducted to determine the impacts of different design variables, such as rotary kiln temperature and raw material mass flow rate, and feedstock coal chemical properties and varying of ambient temperature on the energy efficiency, exergy efficiency and exergy destruction rate of plant components.