Role of Base Plate Rotational Speed in Controlling Spheroid Size Distribution and Minimizing Oversize Particle Formation During Spheroid Production by Rotary Processing

The occurrence of material adhesion and formation of oversize particles in the product yield during one-pot spheroid production by rotary processing leads to a less predictable process and a decrease in the usable portion of the total product yield obtained from each production run. The use of variable speeds of the rotating frictional base plate during the spheronization run was investigated for achieving optimal spheroid production. When the base plate speed was increased during liquid addition, the greater centrifugal forces generated improved liquid distribution and the mixing of the moist powder mass, resulting in a decrease in the amount of oversize particles formed. When the base plate was maintained at a high speed throughout the run, the amount of oversize particles and mean spheroid size increased, and a greater “between batch” mean spheroid size variability was also observed. The findings showed that, when higher speeds were used, the residence time must be adjusted accordingly to avoid excessive coalescence and growth while maintaining even liquid distribution. A “low-high-low” speed variation during rotary processing may be used to produce spheroids with a narrow size distribution and with a minimal amount of oversize particles in the total product yield.     

Wet spheronization by rotary processing--a multistage single-pot process for producing spheroids

Spheronization is an agglomerative size enlargement process for producing spherical agglomerates that have many technological and therapeutical advantages. Rotary processing is an efficient multistage, single-pot spheroid production method. The rotary processor can be used for spheroid production, drying as well as coating. In the course of spheroid production, centrifugal, fluidizing, and gravitational forces act upon the product from different directions and collectively contribute to the spheroid formation process during rotary processing. The outcome of the process depends on the complex interactions between the equipment, formulation, and process variables.     

Accuracy of self-reported data for estimating crash severity

Estimated traveling speed and speed limit have typically been used in population-based surveillance data to estimate crash severity. The accuracy of these measures in predicting crash severity is unknown. The Partners for Child Passenger Safety (PCPS) surveillance system offers a unique opportunity to compare these measures, as well as a novel measure of crash severity, “self-report” delta-V, to the accepted measure of delta-V estimated during detailed crash-investigations in 118 crashes. This “self-report” delta-V was computed from the estimated traveling speeds and direction of impact obtained from telephone interviews with drivers. These “self-reported” delta-V estimates are modestly associated with crash-investigation delta-V estimates, with the degree of association a function of the direction of impact: when the respondent was struck from the rear, the degree of association is strong; frontal, side, and single-vehicle crashes yield weaker associations. This “self-reported” delta-V measure, however, is a substantial improvement over use of estimated traveling speed or speed limit only.     

Image analysis algorithm and verification for on-line molecular sieve size and shape inspection

An online machine vision inspection method is proposed to implement feedback control of molecular sieve growth process in rotary drum granulation. An experimental platform, comprising of a high-resolution digital camera and an image analysis system, has been developed to confirm the validity of the method on particle size distribution (PSD) and sphericity measurements. Experiments were performed with non-uniform molecular sieve particles (1–3 mm diameter) obtained from production line. The particle images are first obtained through digital camera and are then processed by image analysis system. After separating the overlap particles and removing non-target particles of the images, the molecular sieve size and shape are computed in less than 0.9 s. The validity of the size measuring accuracy is confirmed through comparing with the results from micrometer. The experimental results show that the repetitive precision of the proposed inspection system is about ±1%, the diameter measurement error between image method and micrometer is about ±3%, single image inspection speed is around 0.9 s/frame. The proposed method is reliable to provide feedback information for control system in rotary drum granulation.     

Effects of cement size distribution on capillary pore structure of the simulated cement paste

The evolution of tricalcium silicate (C₃S) microstructure during hydration is tri-dimensionally simulated based on an “Integrated Particle Kinetics Model”. The hydration degree, the contact surfaces between the hydrated particles, the hydraulic radius and the capillary pore size distribution of the simulated cement paste at various degrees of hydration are calculated. Three examples of the C₃S microstructure development with different size distributions are presented. The effects of the cement size distribution on pore structure of cement paste are demonstrated and the results are discussed. In these examples, the cement size distribution varies between 3–40, 5–40 and 10–40 μm, respectively.     

水平井眼中旋转钻柱运动特性的实验研究

根据相似原理,设计建造了水平井底部钻柱运动状态的模拟实验装置。利用该装置进行了水平井钻柱在不同钻压、转速条件下钻柱运动状态的模拟实验。实验结果表明:水平井底部钻柱在不同转速下表现出近似圆形摆动,“8”字形摆动和扁“8”字形摆动3种运动状态。随着转速的增加,钻柱的摆动由近似圆形摆动向“8”字形和扁“8”字形摆动转化;钻压和转速是影响水平井底部钻柱运动状态的2个重要因素。转速越高,越容易形成“8”字形摆动,增加钻压有利于底部钻柱“8”字形摆动的形成;水平井底部钻柱的运动范围始终处于井眼的中下偏右部。     

Numerical study of size-driven segregation of binary particles in a rotary drum with lower filling level

Discrete element method (DEM) simulations of size-driven segregation of binary particles in a rotary drum were conducted to investigate the influence of filling level, size ratio, and rotation speed on the segregation performance. Segregation experiments with different filling levels were used to verify the DEM model and analyze the influence of filling levels on segregation. The granular bed was divided into five layers to study the axial segregation in the rotary drum. The total velocity fluctuation was used to discuss the granular behavior from a mesoscopic perspective. A segregation index was adopted to quantify the segregation performance with different parameters. It was found that binary particles in the drum with different filling levels have different segregation patterns. A core of small particles was formed in the middle of granular bed for the case with a higher filling level, while there is no core formed for the case with a lower filling level. Results obtained indicate that the size-driven segregation in the drum with lower filling level increases with the increase of size ratio. Within the rolling regime, the rotation speed has little influence on the final segregation index of particles.     

Characteristics and atomization behavior of Ti-6Al-4V powder produced by plasma rotating electrode process

In the present research, the characteristics and atomization behavior of Ti-6Al-4V powders produced by plasma rotating electrode process (PREP) with different rotation speeds were investigated. Three kinds of particles in the as-PREPed powders are observed: spherical particles, satellite particles and irregular particles. The mean particle size of the PREP powder decreases and its distribution becomes narrower gradually with increasing rotation speed. PREP powder at higher rotation speed demonstrates lower fractions of both satellite particles and irregular particles. By observing the residual electrode tip, it is considered that the irregular particles with corner or flat shape are possibly caused by the tearing of liquid film under the action of centrifugal force and shear force during the atomization process.     

Relationship Between Particle Size and Dissolution Rate of Bulk Powders and Sieving Characterized Fractions of two Qualities of Orthoboric Acid

We have carried out a study of the particle size distribution and aqueous dissolution rate of two commercially available qualities of orthoboric acid, labeled “crystal” (ABC) and “powder” (ABP). In a previous work, we have shown that the two commercial qualities of orthoboric acid chosen as model compound (“powder” and “crystal”) are related to the same crystal network in spite of their dvferent names. However, these two qualities have very different size particle distributions, as previously determined by sieving and confirmed by the present laser light scattering study. Dissolution testing is performed under sink conditions and show that the bulk ABC quality dissolves far more rapidly that the bulk ABP quality, For each quality, dissolution rates of four sieved particle size fractions (0-90 μm; 90-125 μm; 125-180 μm; 180-250 μm) were compared. Concerning the ABC quality, comparisons were also done with three other particles size fractions: 250-355 μm, 355-500 μm, and 500-710 μm. This study used the dQ/dt versus t profile. Dissolution profiles of the fractions enclosing particles with a size superior to 125 μm are very close. On the other hand, fractions enclosing particles with a size smaller than 90 μm present a different profile and a slower rate of dissolution.     

Rotary oscillations of a spheroid in an incompressible micropolar fluid

The paper discusses the flow generated by rotary oscillations of a spheroid (prolate and oblate) in incompressible micropolar fluid. The velocity and microrotation components are determined explicitly in terms of spheroidal wave functions and are expressed in infinite series form. The couple on the oscillating spheroid is evaluated and numerical studies are undertaken to examine the effects of the geometric parameter and material constant parameters of the fluid.     

Ion formation by high velocity impacts on porous metal targets

In impact ionization studies the target normally consists of a metal surface of compact solid density. In the present experiments, we investigate the use of a layer of a highly porous structure of nanometre-sized grains, sometimes also called “metal black”, as an alternative target. In our comparative experiments, spherical iron particles (0.1<d_p<1.5 μm) were shot with velocities 2–30 km/s onto both a compact solid silver plate and a silver metal black layer of about 7 μm thickness (grain size 20–40 nm, mean density ≈1 g/cm³), deposited on a compact solid gold plate. Impact generated ions were analysed by means of time-of-flight mass spectrometry. The results reveal important advantages of the porous black layer, such as better mass resolution and a larger amount of ions from the impacting particle. Therefore metal blacks may be very suitable targets for the purposes of identification and characterisation of the impacting particle's composition. An attempt is made to give a physical explanation of the results in the frame of existing empirical ionization models. The study is part of a programme to improve devices for in-situ analysis of fast moving cosmic dust particles.     

气流磨生产过程中喂料速率对粒度的影响

为在流化床式气流磨进行生产时合理选择喂料速率,以获得较好的产品,通过小型气流磨加工滑石粉实验,分析不同分级轮转速下磨腔料位、产品中位径与喂料速率之间的关系,以及喂料速率对产品粒度的影响。结果表明,提高分级轮转速,可以很明显地减小产品中位径;当物料粉碎过程进入稳定状态以后,分级轮的每一个转速都对应一个喂料速率的临界值,在一定的分级轮转速下,把喂料速率调整到最佳值,可以获得粒度更细、分布更窄的产品;喂料速度控制不好将引起分级轮电机过载,产品粒度不稳定,设备产能降低。     

PARTICLE-SIZE DISTRIBUTION INFLUENCE IN HIGH-SPEED EROSION OF ALUMINIUM

The paper discusses the influence of the abrasive particle-size distribution on typical high speed abrasive-waterjet erosion parameters. The size distributions of the used abrasive particles are modelled by a Rosin-Rammler-Sperling (RRSB) grain-size distribution containing the distribution parameters D and n. Both parameters are independently varied to characterise different particle-size distributions. Aluminium specimens are eroded by abrasive-waterjets at velocities of 320 m/s, and the erosion depth, depth distribution, and the surface roughness are measured. The depth distribution and the surface roughness are very sensitive to the particle-size distribution parameters, whereas the average erosion depth is not influenced significantly. These results offer the possibility to select an “optimum” grain-size distribution for maximum surface quality at fixed kinematics conditions.     

Evaluating the effect of feed particles size and their hardness on the particle size distribution of semi-autogenous (SAG) mill’s product

The main target of this research was to provide the optimal size of mills’ feed with acceptable accuracy, in order to find the size range of particles to achieve the maximum grinding product. Nowadays, experimental semi-autogenous (SAG) mill and drop-weight test are used for evaluation of grinding circuit regarding changes in feed particle size distribution, size of the ball, speed of mill, prediction of energy required, and product size distribution for complete grinding in AG and SAG mills. In this study, the effect of initial size ranges of feed (+13.2–315?mm) on the amount of grinding product and its size distribution has been evaluated, in order to find the size range of particles to achieve the maximum grinding product. The results showed that the feed size range of 19–22.4?mm had the highest amount of grinding product and breakage index number in different energy levels and the validity of results was evaluated with ball drop-weight test, as well.     

Acceleration discontinuities at an elastic/plastic loading interface

The conditions governing the motion of an elastic/plastic loading interface propagating into the elastic region with an associated acceleration (and strain-rate) discontinuity are set up. It is shown that for the general class of elastic/plastic solids considered, the speed of propagation of the interface must lie in one of three ranges, speeds in the fastest range being associated with the “creation” of a plastic regime. Detailed consideration is given to an interface with its normal along a principal axis of the tensor whose components define the normal to the yield surface in strain-space. The speed of the interface is determined for arbitrary acceleration and strain-rate discontinuities, and the effects of incident acceleration waves are discussed.     

Viewing Strategy and Window Effects on Dynamic Visual-Inspection Accuracy

Equally-spaced product units, moving on a belt at a uniform velocity, were exposed for visual inspection over a fixed viewing window. Viewing windows were equal to the product unit interspacing and twice this distance to give respectively 1 and 2 product units within the window. Three different belt speeds were used. Subjects performed short runs of visual inspection using their self-directed strategies of viewing the sequence of product units and then these subjects repeated all conditions of this task using a “directed viewing strategy.” Improved viewing discipline was expected from this “directed” strategy and eye motion monitoring was employed to verify that the subjects used the “directed” strategy. Inspection errors of each type were observed under twelve experimental conditions. Both types of errors were found to be greater with: 1) the smaller viewing window, 2) self-directed viewing strategies in contrast to the “directed” strategy, and 3) higher belt velocities. Contrasts were also made between error types and between high- and low-performing subject groups. Inferences on the apparent cost of each error type were made from these data and compared with rational objectives. Economic implications are shown for these viewing-strategy and viewing window effects.     

Production of Narrow Size Distributions in Classifier Mills

ABSTRACT

In various technical processes particles with well-defined, narrow size distributions are required. These powders can be produced in impact mills with internal classifier. The top size and size distribution of particles are controlled by variation of impact speed, and by the circumferential velocity of the impeller wheel classifier. Possibilities for minimization of the amount of fines are discussed. However, the production of a certain amount of fines is unavoidable. The physical limit of produced fines depends on the material properties and the parameters governing the impact of particles. The amount of unavoidable fines can be evaluated by means of single impact experiments, in which the particles are stressed with well-defined impact speed and angle of impact.     

Driver irritation and aggressive behaviour

A sample of 98 drivers responded to a Swedish version of the UK Driving Anger Scale [UK DAS; [Lajunen, T., Parker, D., Stradling, S.G., 1998. Dimensions of driver anger, aggressive and highway code violations and their mediation by safety orientation in UK drivers. Transport. Res. Part F 1, 107–121]. The results indicated that the Swedish version, like the British original, measures three sources of driver irritation: “progress impeded”, “reckless driving”, and “direct hostility”. Structural equation modelling was used to investigate the relationships between the three sources of self-reported driver irritation, aggressive actions, speed, sex, age, and annual mileage. The models suggested a positive relationship between the amount of driver irritation and frequency of aggressive actions for all three sources of irritation. Female drivers tended to become more irritated than male drivers, while the male drivers tended to act aggressively more often. Surprisingly, drivers who reported that they enjoy fast speeds did not become more irritated than slower drivers when obstructed. The important conclusions are that experienced irritation often leads to openly aggressively actions, and that expression of aggressive behaviours may be a cause of other drivers’ feeling of irritation.     

A study of the Mechanisms of Wet Spherical Agglomeration of Pharmaceutical Powders

Spherical agglomeration of a number of chemical and pharmaceutical powders was effected in a stirred liquid mixture using the novel technique developed by Kawashima and Capes, with modifications. The compounds were first classified into four groups on the basis of their solubilities in the liquid systems employed and, accordingly, agglomerated using appropriately developed methods. Each powdered material was first suspended in a liquid medium (external phase) and agglomeration was achieved by addition of a relatively small amount of “bridging” liquid (internal phase) which was immiscible with the (external) dispersion medium. The resulting spherical agglomerates were examined for size, binding strength, and surface topography. It appeared that a considerable number of the suspended particles initially underwent partial dissolution in the bridging liquid. The dissolved portion then collected the undissolved powder into spherical agglomerates under the influence of continuous stirring. Based on the trials and observations on a number of materials ranging from inorganics to organics, the general guidelines for spherical agglomeration of pharmaceutical powders were established. It is hoped that these guidelines will aid the application of this technique in the pharmaceutical and allied industries.     

Irrotational axisymmetric flow about a prolate spheroid in cylindrical duct

Summary A solution to the problem of potential flow about a prolate spheroid placed axially symmetric in a circular duct has been derived. The solution is in the form of a distribution of vortex rings over the surface of the spheroid. The vortex strength is expressed in terms of an infinite series of Legendre polynomials and the analysis yields an infinite set of equations for determining the coefficients of this series. An expression for the velocity distribution on the surface of the spheroid as well as the longitudinal added mass coefficients of the spheroid are derived in terms of the coefficients of the Neumann series expansion of the vortex sheet strength. Numerical results are presented for various spheroids and different blockages. Also given is a comparison between the present method and few available approximate methods.