Showing papers in "Journal of The Society of Powder Technology, Japan in 1988"
109 citations
TL;DR: In this article, the authors investigated the effect of the compressive-abrasive motion of the ball charge on the compressed powder layer of a planetary mill and found that the ratio of the largest remaining particle size to the ball size is about 3×10-3.
Abstract: To clarify the mechanism and characteristics of a planetary mill grinding, batch grinding experiments were carried out using several kinds of balls each with a different specific gravity and size. The motion of the grinding media in the mill was observed and analyzed by using multistroboscope photography connected to an image analyzer, and the pressure force acting on the mill wall by the grinding media was measured by using a special pressure sensor.A surging phenomenon consisting of a pendulum-like oscillation of the grinding media in the mill is observed. It is found that the compressive-abrasive motion of the ball charge on the compressed powder layer is effective in producing very fine particles.An optimum fractional ball filling of the mill was demonstrated by the experimental results. It was proved that optimum filling results in the maximum applied force and the greatest motion distance with the greatest oscillation frequency of the ball charge on the powder layer.It was also found that the smaller the size of grinding ball, the finer the ground product that can be obtained. The ratio of the largest remaining particle size to the ball size is about 3×10-3.
14 citations
TL;DR: In this article, the specific rate of breakage of particles is described by the equation Si=a·xia·Q(z), where Q(z) is the probability function ranging from 1 to 0, which has been used by Austin for a tumbling ball mill.
Abstract: Grinding experiments on the sieved-size fraction of silica sand in a planetary mill are carried out. It is found that for large balls (≥∅4mm), the breakage of she fine size fraction can be described by first-order law, but when the particle size is larger than the ball size, the breakage is not of the first-order, but even for smaller balls, the breakage is completely non-first-order. Reasons for this non-first-order breakage are experimentally investigated and discussed. The specific rate of breakage of particles is described by the equation Si=a·xia·Q(z), where Q(z) is the probability function ranging from 1 to 0, which has been used by Austin for a tumbling ball mill. In this equation, S has a maximum value, and the particle size of the maximum is related to the ball diameter by xm=k1dB, where k1=0.05 irrespective of the specific gravity of the balls. In another words a 20:1 ball diameter/particle size ratio can give the optimum grinding condition for planetary milling, which is found to be the same as in stirred ball milling, but it is different from tumbling ball milling and vibration ball milling. The effect of the diameter and the specific gravity of balls can be expressed as a=k3(ρB/dB0.35).
13 citations
TL;DR: In this article, two different methods for the preparation of graphite fluoride-modified powders were studied in a dry treating system and it was found that fine graphite fluoride particles are homogeneously fixed onto the surface of each core particle.
Abstract: Two different methods for the preparation of graphite fluoride-modified powders were studied in a dry treating system. Nylon 12, polyethylene, and epoxy resin microspheres were used as core materials.Using the binary powders blending method (called the powder/powder system blending method) it was impossible to prepare the regular monoparticle layer of graphite fluoride on each core particle.On the other hand, with another method utilizing a strong impact force (the high speed impact treatment method) it was possible to easily prepare the fine arrangement of graphite fluoride particles on each core particle. From the results observed on the powder dispersability in water and SEM observation, it is found that fine graphite fluoride particles are homogeneously fixed onto the surface of each core particle. This tendency did not depend on the triboelectronic series of the materials.
11 citations
TL;DR: The tumbling agglomeration apparatus that was developed here used hydrogenated castor oil, stearic acid and carnauba wax as coating materials and investigated the effects of wax species, particle size, coating amount and heat treatment on the drug release.
Abstract: In order to control the release rate of the drug from the pharmaceutical dosage form, a useful method for coating the fine wax powder to the surface of the drug-containing granules with the binder solution is by using the tumbling agglomeration apparatus that was developed here. We used hydrogenated castor oil, stearic acid and carnauba wax as coating materials and investigated the effects of wax species, particle size, coating amount and heat treatment on the drug release.The release rate of the drug from the wax-coated granules could be extensively controlled by varying these conditions. Heat treatment was easy and useful to control the drug release. This method is applicable to the preparation of the controlled-release dosage.
8 citations
TL;DR: In this paper, the effects of the magnitude of blade interval, initial conditions of a particle, such as angular position and velocity, and particulate capture radius on classification accuracy were examined, and it was found that partial classification efficiency is improved as the blade interval is reduced.
Abstract: Trajectories of particles thrown into a forced vortex-type centrifugal air classifier are numerically calculated, and the effects of the magnitude of blade interval, initial conditions of a particle, such as angular position and velocity, and particulate capture radius on classification accuracy are examined.It is found that partial classification efficiency is improved as the blade interval is reduced. A particle trajectory is influenced by the angular position and circumferential velocity of a particle at its injection into a classification chamber.
7 citations
TL;DR: In this paper, the compressive crushing of powder beds was carried out to study a roller mill and the effect of applied load, the mass of feed and the particle size on the probability of crushing and on the crushing resistance were studied.
Abstract: Roller mills have come to be actively used for the fine grinding of solids. In this paper, the compressive crushing of powder beds was carried out to study a roller mill. The effect of the applied load, the mass of feed and the particle size on the probability of crushing and on the crushing resistance were studied. The sample used was quartz. The following results were obtained:1) When the applied load was constant, the deformation of the powder bed increased with the increase in the mass of feed and particle size.2) The probability of crushing increased with the increase in the applied load, but the rate of increase of the probability gradually decreased.3) The mass of the feed with a low crushing resistance was observed, and it had a certain range. This range narrowed with the decrease in the particle size.4) The crushing resistance increased with the decrease in the particle size.
5 citations
TL;DR: In this article, the fractal dimensions of twenty-eight different kinds of sample particles were compared with Wadell's working sphericity and the degree of circularity based on the same particle-projected figures.
Abstract: In order to quantitatively determine a particle's shape, the profile data of particle-projected figures were fed into the personal computer using the digitizer, and then the fractal dimensions of the particles were calculated by the divider method. The fractal dimensions of twenty-eight different kinds of sample particles were compared with Wadell's working sphericity and the degree of circularity (or the perimeter ratio) based on the same particle-projected figures. The results show that the fractal dimensions of samples are correlated with circularity. The fractal dimension becomes a useful means for the quantitative representation of a particle-projected shape as well as circularity.
5 citations
TL;DR: The relationship between the average coordination number and the void fraction in a randomly packed system of uniform-sized spheres was investigated by for different kinds of computer simulated results to judge whether or not the coordination number could be uniquely estimated from the voidage.
Abstract: The relationship between the average coordination number and the void fraction in a randomly packed system of uniform-sized spheres was investigated by for different kinds of computer simulated results to judge whether or not the coordination number could be uniquely estimated from the voidage. The relationship between the coordination number and the voidage depends on the types of the computer simulation program used our research results make it clear that the coordination number cannot be uniquely estimated from the void fraction. These computer simulated results were compared with the calculated results using some empirical or model equations which have already been reported in the literature. The model equations by Gotoh and Suzuki et al. and the empirical equations by Sunada et al. and Nagao were found to be in fairly good agreement with some of our simulated results.
4 citations
4 citations
TL;DR: In this paper, a spray-drying technique was used to transform emulsified vitamin E with surfactant and colloidal silica (Aerosil ®) in water into powder dosage form by a spray drying technique.
Abstract: Emulsified vitamin E with surfactant and colloidal silica (Aerosil ®) in water was transformed into a powder dosage form by a spray-drying technique. The type and the concentration of surfactant in the formulation mainly determined the shape and the size of the dried particles and their redispersibility in water. Those results were closely related to the state of aggregation of colloidal silica caused by the adsorption of surfactant in the feed fluid.
TL;DR: In this article, the removal of unburned carbon from fly-ash with a continuous density distribution by means of a fluidized bed with tapping is discussed, and the segregation process is approximated by the first order rate equation under the condition of optimum fluidization velocity.
Abstract: This paper is concerned with the removal of unburned carbon from fly-ash with a continuous density distribution by means of a fluidized bed with tapping.It is indicated that tapping the fluidized bed is effective maintaining a good fluidization state of fly-ash and to promote the segregation of unburned carbon. The segregation takes place mainly place due to the apparent density difference between fly-ash with more unburned carbon content and other fly-ash. It is further shown that the segregation process is approximated by the first order rate equation under the condition of optimum fluidization velocity, which is in the range 1 to 4 times the minimum fluidization velocity.
TL;DR: In this paper, a cascade-forming circulation flow of particles in a horizontal rotary cylinder was expressed inductively in terms of the characteristics that determine the profiles of the regions organizing circulation flow.
Abstract: The cascade-forming circulation flow of particles in a horizontal rotary cylinder was first expressed inductively in terms of the characteristics that determine the profiles of the regions organizing circulation flow. This was done with equations expressing the operational condition, that is, the hold up ratio and/or Froude number, making use of data published by other researchers.Secondly, through those studies, the motion of the particles in each region, and thereby of the entire circulation flow was analyzed. Methods to calculate the position of the whirl core, the retention time of particles in each region, and the theoretical power required for circulation in the rotary cylinder could be calculted.
TL;DR: In this article, the relationship between the flocculation state of the particles and the packing structure on the surface of gypsum mold was investigated, based on rheological and sedimentation behavior as a function of dispersant concentration.
Abstract: Generally a slip-casting process is closely related to the flocculation state of particles. The present investigation was undertaken in order to understand the relationship between the flocculation state of the particles and the packing structure on the surface of gypsum mold.The flocculation state of particles in an Al2O3 -slurry was discussed on the basis of rheological and sedimentation behavior as a function of dispersant concentration. It was found that these properties could be classified into three modes.On the slurries, the rate and pressure in the absorption of water, the increase in the packing layer thickness, and the porosity and permeability of the packing layer were measured in order to explain the packing structure on the surface of mold.From these measurements, the relationship between the flocculation state of the particles and the packing structure could be modelled.
TL;DR: In this paper, the binding strength of binary mixed powders was evaluated by using residual die wall pressure and measuring the bounding strength of the compacted powders, which was reflected in a saturated curve as the compaction pressure increased.
Abstract: The compressibility of powders was evaluated by using residual die wall pressure and measuring the binding strength of the compacted powders.The binding strength was reflected in a saturated curve as the compaction pressure increased. However, the residual die wall pressure increased in proportion to the compaction pressure. These phenomena explained the capping behaviors during tableting.In the binary mixed powders, the binding strength changed in a complicated way, but the residual die wall pressure changed simply with the composition of the mixture. The ratio of these two values was defined as the capping index, and the actual capping tendency was defined as the capping ratio. Good correlation was observed between this index and ratio.
TL;DR: In this paper, three sets of optical fiber probes have been installed in the mixer vessel to investigate the flow and mixing characteristics of the solid mixer, and it has been shown that two different mixing rate coefficients φ1 and φ2 represent the different mechanisms, convective and shearing or diffusive mixing.
Abstract: To investigate the flow and mixing characteristics of the solid mixer, three sets of the optical fiber probes have been installed in the mixer vessel. The mixer employed in this work was a rotary-cylinder type mixer wth rocking motion using a swinging bed mechanism. The concentration changes with time and the pattern of the mixing curves have been measured by using the tracer particles coated with dye powder. It has been shown that two different mixing rate coefficients φ1 and φ2 represent the different mechanisms, i. e, convective and shearing or diffusive mixing. The mixing characteristics of the mixer have been evaluated based on these two kinds of rate coefficients measured under various operating conditions.
TL;DR: In this paper, an equipment for measuring the wettability (i.e., the contact angle) of hydrophobic powder was newly developed, based upon the so-called constant flow method.
Abstract: Equipment for measuring the wettability (i. e. the contact angle) of hydrophobic powder was newly developed, based upon the so-called constant flow method. This equipment has a feature in which the specific surface area of the powder, the threshold pressure at which a liquid begins to penetrate the powder bed and its contact angle are calculated and printed out. This happens when the values related to the operational conditions and the physical properties of air, liquid and powder used in the measurement are put in advance into the computer installed in this equipment.The availability of this equipment was confirmed by investigating the effect of operational factors such as the feed rate of pure water, the porosity of the powder bed and its height on the contact angle of aluminum hydroxide powder treated with stearic acid. The relationship between the contact angle of the sample powder and the concentration of stearic acid, the mixing time, the dispersion state in pure water or the amount of DOP (dioctyl phthalate) absorbed was also obtained.
TL;DR: In this article, the amount of micropore and monolayer absorbed on the external surface of adsorbents was obtained from the αs-plots of argon adsorption isotherms at 77K on untreated or surface-treated silica gels and activated carbons.
Abstract: The amount of micropore and monolayer absorbed on the external surface of adsorbents were obtained from the αs-plots of argon adsorption isotherms at 77K on untreated or surface-treated silica gels and activated carbons. A three-parameter adsorption equation can be used to predict the isotherms reduced by their micropore amounts throughout nearly the entire relative pressure range. The amounts of monolayer thus obtained agreed with the amounts of external monolayer obtained from their αs-plots. The three-parameter adsorption equation can also be used to predict their bulk isotherms with a reduction of the amount of micropore. The amount of monolayer thus obtained agreed with the sum of the amounts of the micropore and monolayer on the external surface of the adsorbent. The micropore of activated carbon is found to be much finer than that of silica gels, and the cross sectional area of the adsorbed adsorbate molecule in the micropore of activated carbon is also found to be smaller than that of the usual adsorbate molecule, because of the strong interaction due to the wall of the micropore.
TL;DR: In this article, a procedure and apparatus have been developed to determine the concentration and size of particles suspended in a liquid using a He-Ne laser, nine kinds of powder samples and four kinds of liquid were used in the experiments.
Abstract: A procedure and apparatus have been developed to determine the concentration and size of particles suspended in a liquid.A He-Ne Laser, nine kinds of powder samples and four kinds of liquid were used in the experiments.The values of attenuation caused by particles of suspension were proportional to the amount of particles existing on the optical pass of a Laser beam. The attenuation values calculated, according to calculation program developed by the authors, were agreed well with the experimental values. The attenuation values with suspension containing two kinds of powders corresponded to the sum of the product of the weight fraction and the attenuation values for the individual powder.The particle concentration of suspension and the mixing ratio of binary powders were determined by measuring the attenuation values.The measurement of attenuation for suspension at a fixed level was carried out during gravity settling, and the size distribution of the particles based on the number was determined by analyzing the change in the attenuation values over time.
TL;DR: In this paper, a transmissometer was developed to measure dust concentration at stationary sources employing an LED ( Light Emitting Diode) and a self-compensation system for the degradation of the optical system.
Abstract: A transmissometer was developed to measure dust concentration at stationary sources employing an LED ( Light Emitting Diode) and a self-compensation system for the degradation of the optical system. The relationship between the optical concentration obtained by the tansmissometer and the mass concentration measured by a gravimetric method were investigated theoretically and experimentally.The experiments were carried out with four kinds of test dusts. Very good correlations between the optical concentration and the mass concentration were obtained over a wide range of dust concentration, about 10mg/m3-5g/m3. It was found that dust concentration can be measured accurately for a long period with this tansmissometer in which the self-compensation system for optical degradation is very effective. A comparison between the experimental values and calculated results showed good agreement between the phenomenon and the theory of light extinction. It was also found that the effect of dust properties, such as the refractive index and the particle size distribution, can be estimated by calculating parameter K.
TL;DR: In this article, the penetration characteristics of fly ash suspended in gas flowing through a fixed packed bed of granular materials were determined experimentally, and it was observed that calculated values of both the amount of dust accumulated and penetration in the moving bed agreed well with measured values when an appropriate correction factor was introduced.
Abstract: Penetration characteristics of fly ash suspended in gas flowing through a fixed packed bed of granular materials were determined experimentally. Gas velocities through the 0.4m thick bed of 5-16mm diameter particles ranged from 0.5-2.0m/s. Experiments were also performed in a moving packed bed in which the accumlation of fly ash was measured. These experimental results were compared with that of prediction by employing data from the fixed packed bed tests. It was observed that calculated values of both the amount of dust accumulated and penetration in the moving bed agreed well with measured values when an appropriate correction factor was introduced.
TL;DR: The area used for data processing of the flow pattern decreased, and the method of extracting useful information from the image data is discussed, and good response waves are obtained in the level control of hopper.
Abstract: Recently, the technique of image processing has been used for many purposes. This report is concerned with the flow pattern and level control of a hopper by using an image processing apparatus.The flow pattern of granules inside the hopper changes at the transitional bed height (Htr). Htr is the bed height at which flow pattern of granules changes from mass flow to core flow or vice versa. The flow pattern of granules is uniform in the upperpart of Htr. In this sense, it is easy to control the level of the hopper, because the surface of granules in the hopper is kept constant.The flow pattern was first observed by using a video camera and image processing unit. The position of Htr was measured. Then, the bed height of the hopper was controlled at the upper part of Htr. The time to operate the image and to transmit the image data to a personal computer, and which is necessary for the image processing, was reduced to maintain good response waves. In order to do so, the area used for data processing of the flow pattern decreased, and the method of extracting useful information from the image data is discussed.As for the results, we could obtain good response waves in the level control of hopper.
TL;DR: In this paper, a vibration type of tester for measuring the dynamic physical properties of powders has been developed and examined, which consists of an electromagnetic vibrator with a controller for the frequency and acceleration, a detecting sphere body attached to a load transducer and a micro-computer.
Abstract: A vibration type of tester for measuring the dynamic physical properties of powders has been developed and examined. The system of the tester consists of an electromagnetic vibrator with a controller for the frequency and acceleration, a detecting sphere body attached to a load transducer and a micro-computer.It has been shown that the patterns of the characteristic curve measured as the relationship between the vertical transmitted force through the powder bed and the frequency varied sensitively with changes in the physical properties of the powders. The mixing effect of a small amount of fine powder on the change in the peeks at the characteristic frequency has been measured by using two different types of mixers.
TL;DR: In this paper, an equipment for measuring the wettability (i.e., the contact angle) of hydrophilic powder was newly developed, based on the so-called CST(Capillary Suction Time) method.
Abstract: The equipment for measuring the wettability (i. e. the contact angle) of hydrophilic powder was newly developed, based on the so-called CST(Capillary Suction Time) method. This equipment has a feature in which the wetting liquid spreads horizontally and radially into the powder bed having a disk shape 2mm thick. The contact angle is calculated from the time (CST) which it takes for the wetting liquid to move from the 1st sensor to the 2nd one. The wetting front was detected by either an electrical conductance method or a reflecting light method.The availability of this equipment was confirmed by investigating the effect of the type of sensor, the distance between the two sensors, the porosity of the powder bed, and the temperature, etc. on the contact angle of untreated aluminum hydroxide powder or that treated with stearic acid.
TL;DR: In this paper, a mathematical model for a ring ball mill based on specific rates of breakage, breakage distributions, and primary and secondary classification actions was further refined and empirical expressions were presented for both primary and Secondary classification actions as a function of the mill and classifier geometry and operating conditions.
Abstract: The mathematical model previously developed for a ring ball mill based on specific rates of breakage, breakage distributions, and primary and secondary classification actions was further refined. In particular, empirical expressions are presented for both primary and secondary classification actions as a function of the mill and classifier geometry and operating conditions. In addition, the scale-up factor with the make-up feed rate determined in a pilot-scale mill was further developed for larger mills. Model simulations based on parameters measured in the Hardgrove mill with the present classification models and scale-up factors correctly predicted the circuit behavior of industrial-scale mill systems.Furthermore, some of the factors affecting the mill performance were investigated by the present simulation model. As a result, the feed size distribution and the total crushing load on balls were found to be dominant factors.