Grinding Load Research Articles

PI Control For Rotation Speed Stability Of Induction Motor In Disc Mill Type Coffee Grinder

In a coffee processing production process, roasted coffee beans can now be ground using a motor-driven grinder. For an industrial scale, a Disc Mill typecoffee bean grinder is generally needed because it is able to get coffee grounds faster and smoother than other types. However, a Disc Mill typecoffee bean grinder has a disadvantage if the grinding load increases, it will affect the rotational speed of the motor so that there is the potential for congestion in the Disc Mill blade. Therefore, a control method is needed to maintain the speed stability of the induction motor. The control method used is Proportional-Integral(PI). To obtain the exact value of the parameter used the Ziegler-Nichols method of oscillations. The PI controller using the Ziegler-Nichols method is considered capable of obtaining a relatively stable system response and get a shorter reference value. System testing with tuning values Kp = 0.108 and Ki = 0.13 was carried out at a speed of 1400rpm. A stable system response was obtained with a rise time of 4 seconds, a settling time of 5 seconds, a peak time of 9s, a maximum overshoot of 2.85% and a steady state error of 0.89%. With the application of the PI method, the Disc Mill type coffee bean grinding motor can maintain the stability of the rotational speed compared to without control.

Определение коэффициента демпфирования ударного импульса при измельчении горных пород

Introduction. The physical properties of rocks, which determine the choice of the type of mill, as well as its operating parameters, are considered. The importance of studying the damping properties of the crushed material and their influence on the energy intensity of the grinding process is noted. Research methods and materials. The differential equation of motion of the crack wall, previously obtained by the authors of the article, is applied when it is exposed to a shock wave with amplitude σ and duration τ. The classical theory of damped oscillations of the system is used to determine the damping decrement of the shock pulse amplitude. A series of experimental studies was carried out on a laboratory sample of a drum mill to determine the magnitude of the shock pulse damping coefficient. Rocks from various deposits in Russia with strictly defined strength characteristics were used as the crushed material. Research results. Dependences of the amplitude of the shock pulse on time are constructed for the grinding of granite raw materials, carbonate rocks and soft rocks (gypsum) in a drum mill. The following conclusions were drawn: 1. When grinding strong and very hard rocks in a drum mill, a strong impact occurs (with a large amplitude and duration of the shock pulse) and with its weak damping when propagating in the rock. 2. When grinding carbonate rocks, doubling the angular velocity of rotation of the grinding chamber leads to an increase in the amplitude of the shock pulse by about 1.5 times. 3. The duration of shock wave propagation in both cases is approximately equal. 4. The frequency of grinding media collisions increases significantly. This indicates a sharp increase in the energy intensity of the grinding process. 5. When grinding soft rocks in a drum mill, almost half of the input energy is spent on overcoming the damping properties of the material, and small, frequent pulses, which consume half of all energy, are not able to grind the material to the desired size. Discussion. Based on the conducted studies, graphs of dependencies between the main parameters of the drum mill were constructed. The dependences of the duration of the shock pulse on the average diameter of the particles of the crushed material are constructed. The analysis of these dependences made it possible to conclude that the duration of the shock pulse is in a parabolic dependence on the value of the average particle diameter of the crushed material. The dependences of the damping coefficient on the damping decrement of the shock pulse amplitude are constructed. The analysis of these dependences allowed us to conclude that the shock pulse damping coefficient increases almost linearly with an increase in the damping decrement of the shock pulse amplitude. The dependences of the damping coefficient of the shock pulse on the average diameter of the particles of the crushed material are constructed. The analysis of these dependences allowed us to conclude that the shock pulse damping coefficient is in a quadratic dependence on the value of the average particle diameter of the crushed material. Conclusion. In this article, based on the classical theory of damped oscillations of such system, the principle of determining the damping coefficient of the shock pulse propagating from the grinding body deep into the grinding load of the drum mill is scientifically substantiated. Resume. Experimental determination of the value of the damping factor of the shock pulse, along with the use of the energy criterion for the destruction of the rock, makes it possible to calculate the amount of energy required to destroy the rock particles to a given size. Suggestions for practical application and direction for future research: The results of the research can be used at the enterprises of the mining sector of the industry to improve the efficiency of processing mineral resources and reduce the energy intensity of the process of grinding rocks in drum mills.

Sharpening mechanism of extremely sharp edges for diamond micro mills

• This study explores the sharpening mechanism of extremely sharp edges for PCD micro mills. • The transient temperature model of laser cutting PCD is constructed for studying the material removal mechanism . • The uniform graphitisation , micro abrasion , and smaller material stress near edge contribute to the extremely sharp edges. • The PCD micro mills with cutting edge radius of r β = 0.21 μm are fabricated indicating better sharpness compared with r β = 1–5 μm reported hitherto. The fabrication of extremely sharp cutting edges for ultra-hard micro mills is crucial for suppressing the severe size effect, restraining burr formation, and improving the surface quality of widely used micro components in micro milling. In this study, a hybrid machining technique, laser-assisted precision grinding, is proposed to improve the grinding efficiency and increase the sharpness of the cutting edges of polycrystalline diamond (PCD) micro end mills. A transient heat model of laser ablation was constructed to investigate the laser-cutting mechanism of PCD with a cobalt binder. Facilitated by suitable heat conduction, cobalt absorbs photon energy to heat itself and transmits thermal energy to the surrounding diamond, resulting in uniform graphitisation and cobalt oxidation on the cut section. Hence, the affected layer on the cut section can be easily ground using a low grinding load. Moreover, the subsequent grinding mechanism of the laser-cut section was demonstrated. The diamond was removed via micro-abrasion without any intercrystalline cracks or grain dislodgement, and the abrasive grain size was optimised to achieve superior ground surface quality. Thus, the uniform graphitization, micro abrasion, and smaller material stress near edge contributed to the extremely sharp edges. Furthermore, PCD micro end mills with a diameter of 400 μm, aspect ratio of 2, and cutting-edge radius of approximately 0.2 μm were fabricated, showing a superior sharpness compared with that of the end mills with an edge radius of 1–5 μm reported hitherto. Subsequently, micro-milling experiments were conducted on oxygen-free high-conductivity copper (OFHC) using the self-fabricated PCD micro end mills. Almost no burrs were observed, and the surface roughness of the machined groove was 19.8 nm, indicating the superior cutting performance of the fabricated PCD micro end mills.

Digital light processing-based additive manufacturing of resin bonded SiC grinding wheels and their grinding performance

In this study, an additive manufacturing process based on digital light processing was employed for a quick, flexible, and economical fabrication of resin bonded SiC grinding tools. The grinding wheel has been fabricated using laboratory manufacturing processes that utilize ultraviolet-curable resins and conventional abrasives. Also, desirable geometries and features like integrated coolant holes, which are difficult or even almost impossible to manufacture by conventional processes, are easily achievable. Grinding experiments were carried out by different process parameters, and with two different grinding wheels, i.e., with and without cooling channels with different concentrations (25 wt.% and 50 wt.% grains) to evaluate the grinding efficiency of the produced tools. Grinding forces, tool wear, tool loading, and ground surface quality were measured and analyzed. The wear rates of the grinding wheels with cooling channels were generally less than those without cooling channels, particularly in the deep grinding processes with large contact areas. Grinding tests on a hardened steel have shown that the integration of cooling lubricant channels almost prevents the wheel loading. In addition, by increasing the cutting speed (from 15 to 30 m/s) and decreasing the feed rate (from 10 to 2 m/min), the grinding wheel wear was significantly reduced. Furthermore, surface grinding of aluminum resulted in surface roughness values (Ra) in the range of 1 μm to 2.5 μm, while a Ra of about 0.2 μm was achieved by grinding hardened steel (100Cr6) with the same grinding conditions. Using the higher SiC-grain concentration (50 wt.%), it was determined that the surface roughness was 50% finer. Additionally the tool wear was significantly reduced (up to 30 times depending on the process parameters). The wear characteristics of the grinding wheel were analyzed through a novel image processing system. Significant correlations were found between the wear flat of grains and the increase in grinding forces due to the tool wear.

Sensitivity of oil shale particle surface to the applied load in ball mill

ABSTRACT The size reduction is a mandatory step in oil shale processing. In this study, the sensitivity of oil shale and its organic matters to the applied load in grinding was tested in a ball mill not only by using the different number of grinding media balls as an effective load but also by using balls made of two materials, namely, steel and ceramic. The ground product was characterized in terms of its mean size (d50) as well as it was subjected to flotation tests, and the properties of the floating product in terms of the loss-on-ignition and recovery percentages were determined. Furthermore, the Fourier transform infrared (FTIR) was used to show how the grinding media load can affect the surface properties of the ground product and correlate that to the flotation results. The results indicated that a delicate grinding load is needed for this sample of oil shale. The higher the load, the lower the loss-on-ignition (LOI) of the ground product and the lower the d50 of the ground product, and its higher recovery in flotation proposes that the produced fines are rich in gangue minerals of inorganic nature.

Real single grain grinding FEM simulation for case-hardened steel based on equivalent contact area analysis

Abstract Grinding is an indispensable phase in the gear production chain as it allows very stringent requirements characteristic of the automotive sector to be satisfied. The main goal of this finishing process is to ensure compliance with the surface integrity and dimensional tolerance specifications of the product. A single-grain grinding FEM model has been implemented to predict grinding load values based on real grain geometry using a set of Johnson & Cook coefficients able to represent the flow stress curve of a typical gear case-hardened steel 27MnCr5. Grain geometry acquired through computed tomography was imported into three-dimensional process simulation software DEFORM-3D. As the use of real grain geometry leads to time-consuming simulations, an equivalent defined geometry grain was implemented to compare cutting behavior and calculate maximum force values through real contact area analysis under the same process parameters. Calculated loads were subsequently compared with experimental results, showing good agreement with a maximum percentage difference less than 13% for two different grain geometries. Grinding force measurements were performed in a single-grain configuration on a CNC surface grinding machine adopting a wheel speed of 384 rad/s, feed rate of 8.6 mm/s and a depth of cut of 0.1 mm.

ВЛИЯНИЕ РАЗНЫХ АССОРТИМЕНТОВ ДВУХШАРОВОЙ МЕЛЮЩЕЙ ЗАГРУЗКИ НА ПРОИЗВОДИТЕЛЬНОСТЬ ШАРОВОЙ МЕЛЬНИЦЫ ОТКРЫТОГО ЦИКЛА

The ball mill has an energy efficiency of no more than 3.5 % (taking into account the measures taken to intensify the process of grinding the material). This is due to the imperfection of the design of the grinding unit, which consists in the fact that it is impossible to completely convert the mechanical energy accumulated by the grinding load into grinding energy (i.e., energy directly spent on the destruction of material particles). Most of the stored energy is converted into heat, noise, and vibration. The existing directions of intensification of the grinding process are as follows: improvement of the design, internal equipment of the cement mill; changes in the physical and chemical properties of the grinding medium; improvement of the grinding scheme. The authors of this article work in the direction of improving the internal equipment, which is reflected in the scientifically based selection of the range of grinding media for the fine grinding chamber, since the rational composition of the grinding load can significantly reduce the energy consumption of the grinding process. The authors continue to study the possibility of using a two-ball loading in a fine grinding chamber. This article provides a brief overview of the different ranges of two-ball grinding loadings, which differ from each other only in the range of grinding media. The possibility of a significant increase in the productivity of the mill when replacing the traditional grinding load with a rational two-ball is shown

Probing the effect of abrasive wear on the grinding performance of rail grinding stones

• Three grinding stones were fabricated individually using zirconia alumina, brown fused alumina and white fused alumina. • The main wear forms of rail grinding stones are blamed on attrition wear, abrasives pulled-out and fracture, the bond wear, material adhesion and clogging. • The grinding stones using brown fused alumina and white fused alumina exhibit better self-sharpness ascribed to the abrasives pulled-out and fracture. • The splintering mechanism of zirconia alumina is intergranular and transgranular fracture, while the brown fused alumina and white fused alumina are cleavable fracture. Grinding behaviour and wear mechanism of self-fabricated rail grinding stones (GS) using zirconia alumina (ZA), white fused alumina (WA) and brown fused alumina (A) were investigated in detail. The results illustrated that the grinding efficiency grew from GS-ZA and GS-A to GS-WA, and the GS-ZA gave the best ground rail surface quality. GS-ZA primarily consumed as attrition wear, while abrasive pull-out and fracture were dominant for the GS-WA and GS-A, thus making a better self-sharpness. The splintering mechanism of ZA was intergranular and transgranular fracture, and the macro-fracture and micro-fracture were presented by WA and A, respectively. Based on the experimental results, some suggestions about regulating the grinding performance of different GS, such as improving the grinding load of GS-ZA, reducing grinding heat of GS-WA, and the abrasive/bond interface modification of GS-A, were finally proposed.

Resource-energy-saving technologies and equipment for complex processing of man-made materials

Using the fundamental kinetic laws of materials grinding processes, a resource-energy-saving technology for complex processing and mechanoactivation of mineral components has been developed. For the technology, patent-protected energy-efficient grinding units for selective grinding of materials have been developed: press-roll grinders (PRG) for volume-shear deformation (VSD) of materials and obtaining their microdefect structure; drum ball mills (DBMs) with internal energy-exchanging devices (IEDs), which implement impact-crushing-abrading action with less 10–20 % grinding load. A technological complex was developed for mechanoactivation of fine-grained materials and obtain nanostructured composite mixtures from them: “PRG–VSD”– vibration-centrifugal unit (VCU) of selective grinding at each stage – vortex-acoustic dispersants (VADs) for obtaining ultrafine particles < 5 μm with mechanical-aerodynamic and acoustic grinding. Resource-energy-saving technology has been tested for complex thermomechanical processing of quartzite-iron-containing was teat the Lebedinsky mining and processing plant for production of pigments-fillers for the purpose of volumetric dyeing of products.

Improvement of the construction of vibration-centrifugal unit

The article presents the scientific and technical studies to create an effective system for balancing the lever mechanism of the centrifugal grinding unit with the possibility of automatic adjustment during the technological grinding process for changing the size of the grinding load in the working chambers.

ВЛИЯНИЕ ПУСТОТНОСТИ МЕЛЮЩЕЙ ЗАГРУЗКИ ШАРОВОЙ МЕЛЬНИЦЫ НА ДИСПЕРСНЫЕ ХАРАКТЕРИСТИКИ КЛИНКЕРА

Currently, most cement mills operate in a closed circuit. Installing a separator without a significant modernization of the mill allows to increase its productivity (by about 20 %) and improve the grain size distribution of the cement; therefore the improvement of the separation process, especially abroad, is of great importance. The advantage of converting a mill to a closed circuit is not limited to the above described positive sides. The separator allows to reduce the weighted average diameter of the ball and the degree of adhesion of the material, provides the ability to control the fineness of cement without changing the range of grinding bodies. As a result, the efforts of scientists are directed towards improving the design of separators, while they usually do not pay enough attention to the main characteristics of the grinding load and adjust them considering the presence of separation system. Many scientists have established the fact that the optimal composition and characteristics of the grinding load can increase the productivity of the ball mill by 10–20 % without reducing the fineness of the cement grinding. Switching the mill to a closed circuit while using a rational grinding load, both in the first and in the second chamber will achieve an additive effect of increasing the energy efficiency of the grinding unit. The authors of this article pay special attention to the packing density of grinding media in the second chamber, because the increase in the value of this indicator does not always lead to a positive effect. On the basis of experimental data, the article proves the absence of an unambiguous relationship between the porousness of the grinding load under equal conditions and the value of the parameters characterizing the fineness of grinding.

歯科用合金の複合研削に関する研究 : (第3報) 研削面性状に及ぼす砥石の粒度, 研削荷重, 電流密度の影響

歯科用合金の複合研削に関する研究 : (第3報) 研削面性状に及ぼす砥石の粒度, 研削荷重, 電流密度の影響

Determination of the boundary conditions of the grinding load in ball mills

The prospects of application in ball mills for grinding cement clinker with inclined partitions are shown. It is noted that ball mills with inclined partitions are more effective. An algorithm is proposed for calculating the power consumed by a ball mill with inclined inter-chamber partitions in which an axial movement of the ball load takes place. The boundary conditions in which the ball load is located are determined. The equations of bounding the grinding load are determined. The behavior of a grinding load is considered in view of the characteristic cross sections. The coordinates of the centers of gravity of the grinding load with a definite step and the shape of the cross sections are determined. It is theoretically shown that grinding load in some parts of the ball mill not only consumes, but also helps to rotate the ball mill. Methods for calculating complex analytical expressions for determining the coordinates of the centers of gravity of the grinding load under the conditions of its longitudinal motion have developed. The carried out researches allow to approach from the general positions to research of behavior of a grinding load in the ball mills equipped with various in-mill devices.

Influence of servo characteristics on crack generation in ultra-precision grinding of optical glass lenses

Generally, manufacturing process of optical glass lenses, which are used for single lens reflex cameras, is classified into grinding and polishing for removing cracks generated by grinding. Thus, it is desired not to generate the cracks in grinding as much as possible. Because grinding condition with cracks differs depending on the material properties of the workpiece, suitable grinding condition needs to be selected based on a lot of experimental verifications. In addition, the controller’s gain of the tool spindle with grinding wheel may be intentionally set to low value in ultra-precision grinding. Thus, the spindle speed may decrease even under servo control because of grinding load. In this study, the influence of servo characteristics on crack generation is evaluated in ultra-precision grinding of optical glass lenses. Concretely, an optical glass lens was machined using an ultra-precision 5-axis grinding machine and servo information of tool spindle was monitored during the process. Comparison of the obtained servo information and the surface observation of the workpiece revealed that the spindle speed decreased and the number of the cracks increased at the outside of the workpiece. The experimental results suggested the possibility of estimating the grinding load and predicting the surface quality by monitoring the variation in the spindle speed.

Influence of microstructure and grinding load on the bulk toughness and fracture behavior of PCBN abrasive grains

In this article, the theory of Voronoi diagram is used to represent the microstructure of the polycrystalline cubic boron nitride (PCBN) abrasive grains. The crack propagation process of PCBN abrasive grains is modeled explicitly using cohesive zone theory. Accordingly, the numerical simulation of the facture behavior of polycrystalline cubic boron nitride (PCBN) abrasive grains under grinding load is conducted. The results indicate that the elongated microcrystalline CBN particles and crack branching contribute to the effect of size distribution of the contained microcrystalline CBN particles on the bulk toughness of the PCBN abrasive grains. A greater angle between the inner defect and the load direction leads to a severer impairment of the inner defect to the bulk toughness. As to the influence of the grinding load on the bulk toughness, the additional emerged microcracks play a decisive role.

Investigating the effects of grinding time and grinding load on content of terpenes in extract from fennel obtained by supercritical fluid extraction

This paper investigated effects of grinding time (GT) and mass of raw material in mill (ms) on both global SFE yield from Fennel and its main volatile oil content namely Anethol and Fenchone. For this purpose, extractor of SFE equipment was filled with milled Fennel obtained at various values of ms, from 15g to 35g, and GT, from 15s to 20min. Extractor was subjected to pressure of 200bar, temperature of 313K, and supercritical CO2 flow rate of 1.67×10−4kg/s for 10min. Then, extract composition was evaluated by Gas Chromatography (GC) analysis. Moreover, for better understanding how GT and ms affect SFE yield and extract composition, their effects were initially investigated on temperature raising and diameter of Fennel seeds during grinding process. It was found that ms and GT have considerable effects on Anethole and Fenchone content of Fennel extract.

Determination of power mill spent on the creation of the longitudinal motion of the grinding load

In this article, a method of grinding material stepwise realized in the roller press mill and a ball mill, equipped with energy-exchange units (LEU). It was found that when using a ball mill, equipped with LEU, depending on the angle of rotation of the drum periodically changes its load level of grinding media in the chambers, and in the zone of active influence of LEU is lifted and to give them the longitudinal- transverse movement, characterized by, created in traditional mills. The technique of determining the power consumed by the mill is further equipped with energy-exchange units consumed for longitudinal movement of the grinding bodies in the grinding of materials, previously ground to a roller press mill. Presented equation for its calculation. The influence on the additional power consumption of the length of the first chamber, the angle of energy-exchange devices and load factors cameras grinding bodies. Comparative results obtained by experiment and calculations.

Stress characteristics and fracture wear of brazed CBN grains in monolayer grinding wheels

Compared to electroplated cubic boron nitride (CBN) grinding wheels, monolayer-brazed CBN wheels have a distinguished advantage in high bonding strength to super-abrasive grains. However, fracture-induced grain wear can occur during grinding. This study aims to understand the mechanism of such fracture, and hence to predict the fracture based on a stress analysis. A two-dimensional finite element (FE) model was developed to investigate the stress characteristics and fracture wear of the grains. The effects of grain embedding depth, grain wear, bond wear, grain size and grinding load on the stress distribution were investigated. It was found that grain macro-fracture wear is dominated by the brazing stresses in the junction region of a CBN grain, and that the peak brazing stress reduces with the increase in the grain embedding depth, grain size and undeformed chip thickness. This suppresses the possibility of grain macro-fracture wear in grinding.

A dynamic threshold-based fuzzy adaptive control algorithm for hard sphere grinding

Grinding wheel wearing fast and metal adhering were severe in hard sphere grinding, which led to wheel overload and clogging. If a fixed-feed grinding was used, the normal pressure between the workpiece and the grinding wheel increased rapidly. Once the grinding load on the grinding wheel was greater than the strength of the retaining bond bridges, a large amount of grains dropped out, which can even damage the wheel. This led to the sphere surface to be scratched. In this study, a dynamic threshold-based fuzzy adaptive control algorithm (DTbFACA) is proposed for hard sphere grinding to avoid scratches on the workpiece. The grinding force was indirectly obtained by measuring the motorized spindle current which was used as a feedback to control hard sphere grinding process. The current threshold in DTbFACA was obtained and online-rectified automatically. The depth of cut and the cup wheel swing speed that affect the motorized spindle current was online-adjusted by fuzzy algorithm. The experimental results indicated that DTbFACA can avoid scratches on the workpiece without sacrificing the sphere form error and grinding efficiency. DTbFACA has been implemented on MD6050 sphere grinding machine tool in production.

A preliminary investigation on the application of air-coupled ultrasound to evaluate surface condition of the grinding wheel

This paper deals with the application of the ultrasonic reflection method of non-destructive evaluation to monitor the condition of a grinding wheel surface. As the grinding process continues, the grinding wheel wear and loading changes the texture of the grinding wheel surface which changes the reflective characteristics of the grinding wheel surface. Ultrasonic signals are made to impinge on the surface of a grinding wheel and the amplitude of the reflected waves is evaluated to reveal the changes in the surface condition of the grinding wheel. A variation of the intensity of reflected waves with the increase in wheel wear helps us determine the redressing time for the grinding wheel. The intensity of the echo amplitude clearly indicates the changes in the grinding wheel condition. This indicates the suitability of this method for in process monitoring of the grinding wheel surface condition to evaluate the dressing time in order to avoid the production of defective products.