Mill Operating Parameters Research Articles

Machining-Induced Distortion during Peripheral Milling of High Strength Aluminum Parts

In the aerospace and automotive industries aluminum sheet metal components are often produced by forming and post-machining. Due to the change in the complex stress state during manufacturing, part distortion is a major challenge. The overall objective of this work is to streamline the process chain to minimize production costs. For this, a determination of the material properties and analysis of the machining process parameters and their influence on the resulting distortion are required.First, tensile tests of the aluminum alloy EN AW-7075-T651 were performed. Subsequently, a series of machining tests were conducted to examine the effect of the machining process on the resulting part distortion. This paper presents machining-induced part distortion depending on the variation of the process parameters for down milling operations of thick aluminum plate material. It was found that the radial depth of cut and the cutting speed have a high impact on the resulting distortion, while the feed rate has a small influence.

RETRACTED: Experimental Study of Operational Parameters on Product Size Distribution of Tumbling Mill

To assess the effects of the mill operating parameters such as mill speed, ball filling, slurry concentration and slurry filling on grinding process and size distribution of mill product, it was endeavored to build a pilot model with smaller size than the mill. For this aim, a pilot mill with 1 m × 0.5 m was implemented. There are 15 lifters with 50 mm height and face angle of 30˚. In the present work, the combination of the balls (40% of the balls with 60 mm diameter, 40% of the balls with 40 mm diameter and 20% of the balls with 25 mm diameter) was used as grinding media with 10%, 15%, 20% and 25% of the total volume of the mill. The experiments were carried out at 60%, 70%, 80% and 90% of the critical speed. The feed of the mill is copper ore with the size smaller than 25.4 mm, which d80 and d50 of them are 12.7 and 8 mm, respectively and slurries with 40%, 50%, 60%, 70% and 80% of solid and the slurry filling between 0.5 and 2.5. The results showed that the best grinding and grading occurs at 70–80% of the critical speed and ball filling of 20–25%. Optimized grinding was observed when the slurry volume is 1–1.5 times of the ball bed voidage volume and the slurry concentration is between 60% and 70%. The mill grinding mechanism in this work is a combination of both impact and abrasion mechanisms.

A Review of the Milestones Reached by the Attainable Region Optimisation Technique in Particle Size Reduction

The attainable region (AR) is an optimization method adopted for use in comminution to achieve different objective functions, which all converge to optimising the production of the desired particle size distributions for downstream processes. The technique has so far mostly been used to optimise the breakage of particles in tumbling mills. It achieved the desired purpose by unveiling all possible outcomes derived from a combination of operational parameters that are bound by trajectories showing the limitations of a system. The technique has given the scientific community lenses to see the behaviour of different parameters in ball mills otherwise known as the black boxes due to their concealing nature. Since its inception, the AR technique has been applied to data obtained from the laboratory tests and simulated industrial mills and the results sometimes contradict or confirm the conventional milling practices in the industry. This makes the already conservative mining industry sceptical about its adoption. This review thus assesses the milestone covered as far as the AR development in comminution is concerned. It also helps to clarify the sources of the discrepancies between the AR results and the conventional knowledge concerning the optimisation of ball mill operational parameters.

Structural characteristics and functional properties of fiber-rich by-products of white cabbage modified by high-energy wet media milling

The recovery of residues and by-products of the food industry plays an important role in terms of sustainable management. For this reason, the aim of this study was to analyse the effect of wet milling parameters on dietary fiber concentrates of white cabbage by products or, more precisely, the stalks of cabbage. The input of hydraulic shear-energy during wet milling process leads to a partial modification of the structure of fiber components to obtain compounds with high water- and oil-binding properties. Furthermore, the wet milling parameters affect the functional properties of the fiber concentrates. A mathematical model was developed which relates the functional properties to the parameters of the colloid mill such as slurry concentration, milling time, agitation speed and particle size distribution. A slurry of the grounded material is forced into the milling gap. Grinding is autogenous as a result of collisions between rotating particles. All of the material in the process stream is being grounded finer than the gap setting and grinding can be optimized by adjusting mill operating parameters. The identification of the relations between milling parameters and functional properties is necessary in order to comprehend the processing characteristics of the material in the context of fiber enriched food products manufacturing.

Control system of multi-disc mill with a new structural solution

The study presents the issues involved in control and monitoring of functional characteristics of the process of grinding, on the example of a multi-disc mill, designed according to a new solution. The authors’ original system for control and monitoring of the mill operational parameters has been presented. The aim of this work is to develop a methodology for integration of the control, process and logistic modules of a multi-disc mill designed for industrial purposes. The structure of the control and monitoring systems has been analyzed. The structure was used for tests of the mill operational parameters whose results were used for evaluation of the mill operation.

Research on the relative productivity of a drum mill type SAG 8.5×5.3

The determination of the optimal operational mode of drum mills can be assessed by different criteria. The most important of them can be formulated as follows: “To be specified and established the values of the mill operational parameters regarding to which it is possible to be provided the user’s expected performance at the required quality of the final product and the same to be achieved at minimal energy consumption”. For the fulfillment of this condition, there has to be determined the laws of productivity variation, the final product quality and the energy consumption in function of the adequately chosen representative control parameters of the mill. There are obtained mathematical models, describing the most important technological parameters of the machine and are made conclusions about the factors influencing on them.

Effects of ‘impact’ and abrasive particle size on the performance of white cast irons relative to low-alloy steels in laboratory ball mills

In mineral grinding mills, media and liners are consumed by abrasion, corrosion, and fracture-related damage mechanisms. White cast irons (carbide-reinforced composites) can provide substantially greater wear life than martensitic steels of comparable bulk hardness, but the magnitude of benefit depends on abrasive mineral characteristics. Their performance might also be influenced by mill operating parameters. Since increasing mill rotation speed increases the proportion of high-angle impingement compared to sliding, and since ‘impact’ is commonly expected to promote fracture-related damage mechanisms in brittle materials, it might be assumed that increasing speed will degrade white cast iron performance. However, such assumptions require scrutiny. Using the laboratory ball mill abrasion test (BMAT), the effects of impact severity on relative performance of white cast irons were quantified. Contrary to intuitive expectations, increasing impact severity appeared to improve white iron relative performance. Micro-fracture is known to be influenced by the abrasive's mineral constitution; but the results demonstrate an influence from abrasive particle size — fine particles being less capable of damaging the eutectic carbide network. The observed effects of mill operating parameters were all explicable in terms of their effect on particle size; hence were manifestations of simple abrasive wear processes, not impact-related damage mechanisms.

Identification of Optimal Mill Operating Parameters during Grinding of Quartz with the Use of Population Balance Modeling

It is known that ball milling is an energy intensive process and great efforts have been made over the years to improve energy efficiency. The use of population balance models (PBMs) can assist in the design of mineral processing circuits and the scale-up of laboratory mill results to full-scale. However, since each model has its own capabilities and limitations, it is believed that a combined use will provide more accurate information for the reliable description of the process.

Optimization of Particle Size and Specific Surface Area of Pellet Feed in Dry Ball Mill using Central Composite Design

Objective: The dimensional properties of iron ore pellet feed including specific surface area and particle size distribution in the ball mill was studied using response surface area method. Methods/Statistical analysis: The effect of the operational parameters of dry ball mill including ball charge (20-40%), grinding time (30-50 min) and balling distribution (Small, Mixed and Large) on dimensional properties of pellet feed was meticulously examined and optimized using response surface methodology based on Central Composite Design (CCD). Responses were 80% passing size (D80) and Blaine (BL). A total of 30 grinding experiments were designed and carried out in the CCD method. Regression models and response surfaces were obtained for each response. Findings: The results predicted by these models showed good agreement with experimental values. In the studied range it was deduced that D80 is decreased and BL increased when grinding time and ball charge increased. Also, the production of fine particles improved using balling distribution of level B (mix balls), instead of one ball size distribution. 3D graphs were applied to visually evaluate each parameter effect on responses. The optimum conditions of ball mill operational parameters to reach the best pellet feed for each blast furnace burden and direct reduction iron (DRI) pellet feed were revealed using CCD optimization. The predicted values BL and D80 were found to be in a reasonable agreement with the experimental values, with R2 as correlation factor being 0.91 and 0.92 for BL and D80, respectively. Improvements: The optimum condition for having a suitable blast furnace burden was: Ball distribution level B, Ball charge= 21.8-22.4 %, Grinding time= 40.1-42.9 min. Also, the optimal condition for DRI pellet feed preparation was: Ball distribution level B, Ball charge= 21.8-22.1 %, Grinding time= 42.1-44.6 min.

Prediction of tumbling mill liner wear: Abrasion and impact effects

Liner wear occurs during the grinding process in tumbling mill. It has a significant influence on the overall economic performance of mills. It will be worthwhile to know the effect of mill operating parameters on the liner wear intensity. In the present work, an experimental–theoretical procedure is presented for evaluation of the liner wear due to abrasion and impact. A wear tester is used to measure the wear of specimen due to ball impacts. A relation is then extracted which gives the wear of specimen at the different impact conditions. This relation is used to evaluate the impact liner wear. Abrasion liner wear is evaluated using the procedure suggested by Radziszewski. To have the experimental data, a laboratory mill is used. A small specimen is inserted in the liner face of the laboratory mill to measure its wear during the mill operation. The cataract regime in mill is eliminated by a mechanism to measure the impact and abrasion wear separately. The comparisons show the appropriate accordance of predicted and measured liner wear, so the model can be used to determine the impact and abrasion wear portions of mill liners.

Determination of the specific breakage rate parameters using the top-size-fraction method: Preparation of the feed charge and design of experiments

The top-size-fraction method of determining the specific breakage rate of particles from the slope of a log-linear ‘first-order disappearance kinetics’ plot has been widely used. Generally, the feed charge is prepared from the material crushed in a jaw and/or roll crusher, and four to five batch grinding experiments are carried out sequentially to obtain about 95–99% reduction of the top-size-fraction. An analysis of a large volume of high quality batch grinding data available in the literature has shown that this approach suffers from several drawbacks. For this reason, the values of the specific breakage rate parameter, k1, reported by the researchers are found to be not sufficiently accurate for mill scale-up and design work. The present paper discusses the rationale behind a new approach proposed. It involves carrying out only one short duration batch grinding experiment using a feed charge that has been pre-ground for sufficient time under the same mill operating conditions for which the value of k1 is to be determined. The results of experiments carried out using two types of cement clinker and quartz are presented for several different combinations of the mill operating parameters. These results clearly demonstrate the merits of the proposed approach.

Optimization of Cutting Conditions in Multi-Pass Milling

In this paper, a new, optimization strategy is used for the determination of the optimum cutting parameters for multipass milling operations. This strategy is based on the “minimum production time” criterion. The optimum number of passes is determined via dynamic programming, and the optimal values of the cutting conditions are found based on the objective function developed for the typified criterion by using a hybrid genetic algorithm with SQP. GA is the main optimizer of this algorithm, whereas SQP is used to fine-tune the results obtained from the GA. Furthermore, the convergence characteristics and robustness of the proposed method have been explored through comparisons with results reported in literature. The obtained results indicate that the proposed strategy is effective compared to other techniques carried out by different researchers.

Computational prediction of performance for a full scale Isamill: Part 1 – Media motion and energy utilisation in a dry mill

The Isamill is a horizontal stirred media mill used for fine and ultrafine grinding. Discrete Element Method (DEM) simulation has been used in this paper to study the behaviour of the media and the collisional environment in a full industrial scale Isamill. The DEM modelling has been able to provide a general understanding of the force balances that control the mill performance and the quantitative variation of key performance measures such as power draw and peak collision energy with changes in mill operating parameters and media properties. The key factor controlling the behaviour of the media and mill performance is the force balance on the media adjacent to the rotating discs of the impellor. Gravity and any applied axial pressure gradient play a critical role by providing a restoring force that presses the media bed against the discs which enables energy transfer from the discs to the adjacent media. Three important aspects of the media flow are identified with the holes in the discs playing a critical role in media transport and generating high speeds media jets in the upper half of the mill.

A Mastercurve to predict annual ryegrass (Lolium rigidum) seed devitalisation when exposed to multiple single sided impacts

A strategy to control herbicide resistant weeds is to use an impact mill to devitalise weed seeds as they exit a combine harvester. To model the impact milling of weed seeds, the milling response was split into material and machine functions separating the effect of seed properties from mill design and operational parameters. The material function was determined by subjecting annual ryegrass seeds ( Lolium rigidum ) to multiple single sided impacts using a rotational impact tester. The number of impacts, impact speed and seed moisture content were varied. Seed devitalisation was measured by germinating seeds in soil bins in a controlled environment room. Seed devitalisation increased with the number of impacts, the impact speed and decreasing moisture content. Seed devitalisation did not depend on the order of an impact sequence when exposed to multiple impacts at three different speeds. A threshold minimum energy per impact of 0.3991 kJ kg −1 (equivalent to ∼ 28 m s −1 ) was observed, below which almost zero devitalisation occurred. A material function Mastercurve for devitalisation was developed using this threshold energy level and one other material parameter which described a seed's resistance to fracture. The Mastercurve was able to accurately predict ( r 2 = 0.94) devitalisation of annual ryegrass seeds (11.3% m.c.) by the number of impacts above the threshold speed and impact speed in any impact sequence. The Mastercurve presented will be able to be used in future studies with a machine function to design impact mills to mechanically devitalise annual ryegrass seeds. • Seed devitalisation increased with impact speed and number of impacts. • Seed devitalisation reduced with moisture content. • Mastercurve fit based on impact energy above minimum impact energy. • Minimum impact energy for seed devitalisation was 0.3991 kJ kg −1 or 28 m s −1 .

Multi-objective optimization of multi-pass face milling using particle swarm intelligence

In this paper, to facilitate manufacturing engineers have more control on the machining operations, the optimization issue of machining parameters is handled as a multi-objective optimization problem. The optimization strategy is to simultaneously minimize production time and cost and maximize profit rate meanwhile subject to satisfying the constraints on the machine power, cutting force, machining speed, feed rate, and surface roughness. An efficient fuzzy global and personal best-mechanism-based multi-objective particle swarm optimization (F-MOPSO) to optimize the machining parameters is developed to solve such a multi-objective optimization problem in optimization of multi-pass face milling. The proposed F-MOPSO algorithm is first tested on several benchmark problems taken from the literature and evaluated with standard performance metrics. It is found that the F-MOPSO does not have any difficulty in achieving well-spread Pareto optimal solutions with good convergence to true Pareto optimal front for multi-objective optimization problems. Upon achieving good results for test cases, the algorithm was employed to a case study of multi-pass face milling. Significant improvement is indeed obtained in comparison to the results reported in the literatures. The proposed scheme may be effectively employed to the optimization of machining parameters for multi-pass face milling operations to obtain efficient solutions.

Mineral Liberation and Particle Breakage in Stirred Mills

In this paper, the study of particle breakage mode versus mill operating parameters is addressed. Stirred mills grinding modes are mainly attrition but could be manipulated to include breakage by compression or impact loading. Macro and micro analysis of particle breakage and grinding mechanisms are correlated. Macro analyses convey information that relates grinding mechanism to particle size and shape. Micro analysis on the other hand relates the particle breakage mode to the fracture type whether transgranular or intergranular. Intergranular particle breakage leads to higher mineral liberation compared to transgranular breakage. Similar minerals would have more homogeneous properties that convey a stronger bond compared to dissimilar, heterogeneous mineral bonds. This paper presents the results of an investigation that assesses how operating conditions can affect trans- versus inter-granular breakage. It is deduced that with the standard stirred mill operation, the breakage mode is primarily abrasion. Breakage mode is characterized using morphology analysis as a tool. Accordingly, if mill operation is controlled such that compression and impact breakage modes are imposed, then there will be a potential to impose inter-granular breakage rather than trans-granular.RésuméDans cet article, on aborde l'étude du mode de fracture de particule en relation avec les paramètres d'opération du broyeur. L'attrition est le principal mode de broyage des broyeurs agités, mais on pourrait également inclure la fracture par compression ou par charge de chocs. L'analyse à l'échelle macro et micro de la fracture de particule est corrélée aux mécanismes de broyage. Les analyses à l'échelle macro donnent l'information qui relie le mécanisme de broyage à la taille et à la forme de la particule. D'un autre côté, l'analyse à l'échelle micro relie le mode de fracture de la particule au type de fracture, soit transgranulaire ou intergranulaire. La fracture intergranulaire de la particule mène à une libération plus élevée du minéral par rapport à la fracture transgranulaire. Des minéraux similaires auraient des propriétés plus homogènes donnant un lien plus fort par rapport aux liens de minéraux dissimilaires, hétérogènes. Cet article présente les résultats d'une investigation qui évalue comment les conditions d'opérations peuvent affecter la fracture trans- ou inter-granulaire. L'opération normale d'un broyeur agité donne un mode de fracture principalement par abrasion. Le mode de fracture est caractérisé par analyse de morphologie, comme outil. Donc, si l'opération du broyeur est contrôlée de telle manière que l'on impose un mode de fracture par compression ou par impact, il sera alors possible d'imposer la fracture inter-granulaire plutôt que trans-granulaire.

Experimental analysis of wet mill load based on vibration signals of laboratory-scale ball mill shell

Real-time measurement of the mill load is the key to improve the production capacity and energy efficiency for the grinding process. In this paper, experimental analysis of the wet mill load based on the vibration signals of the laboratory-scale ball mill shell is presented. A series of experiments are conducted to investigate the vibration characteristics corresponding to different grinding conditions such as dry grinding, wet grinding and water grinding. The power spectral density of the vibration signals is systematically interpreted. Experimental results show that the rheological properties of the pulp affect the amplitude and frequency of the vibration signal. The most important conclusion is that the frequency range of the shell vibration of the laboratory wet mill can be divided into three parts, namely natural frequency band, main impact frequency band and secondary impact frequency band. Finally, soft-sensor models between vibration signal and mill operating parameters of mill load are established using genetic algorithm-partial least square (GA-PLS) technology. After more work on industry scale ball mill is done, the soft-sensor modeling based on the mill shell vibration for operating parameters of mill load will improve the performance of the ball mill in the grinding process.

Mechanochemical effect of dolomitic talc during fine grinding process in mortar grinder

Dolomitic talc was milled in a mortar mill by varying the milling time, solid content, and vertical stress. The milled samples exhibited massive particle size reduction and came to a threshold value around 4μm, with wider particle size distribution. The breakage mechanism of the dolomite and talc phase was influenced by hardness, crystallographic structure, and Young's Modulus. The milled particles underwent massive mechanochemical effect where the degree of crystallinity ranged from 40% to 50%. The variation of lattice parameters of both phases was influenced by mill operational parameters and breakage mechanism of the particles in the mill.

Modeling and Optimization of Milling Process by using RSM and ANN Methods

Nowadays numerical and Artificial Neural Networks (ANN) methods are widely used for both modeling and optimizing the performance of the manufacturing technologies. Optimum machining parameters are of great concern in manufacturing environments, where economy of machining operation plays a key role in competitiveness in the market. In this paper, the selection of optimal machining parameters (i.e., spindle speed, depth of cut and feed rate) for face milling operations was investigated in order to minimize the surface roughness and to maximize the material removal rate. Effects of selected parameters on process variables (i.e., surface roughness and material removal rate) were investigated using Response Surface Methodology (RSM) and artificial neural networks. Optimum machining parameters were carried out using RSM and compared to the experimental results. The obtained results indicate the appropriate ability of RSM and ANN methods for milling process modeling and optimization.

Relation between mechanochemical dechlorination rate of polyvinyl chloride and mill power consumption

A sample of polyvinyl chloride (PVC) powder was milled with CaO powder in a planetary mill for various mill operational parameters. The milled product consisted of dechlorinated hydrocarbon and water-soluble CaOHCl. The dechlorination rate of PVC was determined by the concentration of Cl− ions measured in solution after dispersing the milled product in water. To evaluate the power consumption during PVC dechlorination, the mill power consumption was measured during each experimental run. In addition, media motion during planetary milling was simulated using the discrete element method (DEM), enabling calculation of the mill power consumption. The power consumption calculated by the DEM simulation compared well with the power consumption measured experimentally. The dechlorination rate correlated well with the specific mill power consumption, regardless of the sample weight. The dechlorination rate of PVC when milled with oyster shells (CaCO3) was observed to be faster than that of the PVC/CaO system, and oyster shells could be used as a reactant for the treatment of PVC wastes. This work should be useful for the design of a reactor for the dechlorination of PVC.