Fluidized Bed Jet Mill Research Articles

Influence of process parameters on the characteristics of TiAl alloyed powders by fluidized bed jet milling

Micro-fine high Nb containing TiAl alloyed powders were prepared by using fluidized bed jet milling from the pre-crushed Ti–45Al–8.5Nb–0.2W–0.2B–0.02Y(at.%) ingot. The effects of process parameters on the powder characteristics were investigated. The results show that the particle characteristics are mainly determined by classifier frequency. At or above 5600rpm, the ground powders are composed of coarse block-shaped particles and finer flaky debris, with particle number-average diameter lower than 18μm. With the increase of classifier frequency and the decrease of grinding gas pressure, the amount of flaky debris formed under abrasion mechanism gradually increases, which causes the obvious decrease of the powder number-average diameter, distribution uniformity, and sphericity degree. With the classifier frequency of 8400rpm and grinding gas pressure of 0.55MPa, the obtained powders possess the minimum particle size of 5.32μm, with a uniformity level of 0.38 and a Wadell's sphericity factor of 0.820.

Cut Size Determination of Centrifugal Classifier with Fluidized Bed / Wyznaczanie Ziarna Granicznego Klasyfikatora Odśrodkowego Z Warstwą Fluidalną

Abstract The cut size determination on the basis of proposed matrix model of classification process in a centrifugal air flow classifier with a fluidized bed is presented using matrix model. The presented methodology of cut size determination is based on the precise measurement of the total mass of fed material and coarse product in experimental tests. Knowledge of the feed particle size distribution is also required. Considered classifier is a part of the fluidized bed jet mill. The presented cut size determination will allow to optimize mill work and prediction of particle size distribution of the classification products.

A Novel Process for Making Spherical Powders of High Nb Containing TiAl Alloys

A novel process was developed to make micro-fine spherical high Nb containing TiAl alloyed powders in quantity. Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y(at%) ingot prepared by vacuum induction melting was heat-treated for homogenization, and then machined with a crusher. The chippings were refined by fluidized bed jet milling, and subsequently spheroidized with radio frequency (RF) argon plasma. The effects of processing parameters on powder characteristics were studied. By fluidized bed jet milling, the particle size and distribution uniformity both decline with the rise of classifier frequency. Above 5800rpm, the number-average diameter is lower than 20μm with a bimodal particle size distribution. The powders consist of coarse plate-shaped particles and some finer flaky debris, and with the further rise of the frequency, the amount of debris gradually increases. The plasma-spheroidized powders are found to possess good sphericity and composition homogeneity with phase dominated by supersaturated α2-Ti3Al. The granulometric characteristics of the spherical powders strongly depend on those of the feed powders. For the jet milled powders below 5800rpm, due to the relatively lower size distribution uniformity, the fine particle fraction reduces after spheroidization, which causes an obvious improvement of distribution uniformity and the corresponding increase of number-average diameter

Fabrication of micro-fine high Nb-containing TiAl alloyed powders by fluidized bed jet milling

A fluidized bed jet milling process was used to make micro-fine high Nb-containing TiAl alloyed powders from the chippings obtained by crushing the Ti-45Al-8.5Nb-(W,B,Y) ingot. The influences of classifier frequency on powder characteristics were investigated. The results show that the powders with controlled average particle size can be prepared on a large scale. The powders with different sizes are all dominated by γ with a minor amount of α2-Ti3Al. The particle size significantly decreases with the classifier frequency increasing. At a classifier frequency higher than 38 Hz, the average particle size of the ground powders is lower than 25 μm. The powders are composed of two different sizes of particles: shaped particles and some clastic particles, and both particle sizes meet the log-normal distribution. With the classifier frequency increasing, the both sizes decrease; meanwhile, the proportion of the clastic particles gradually increases, and the size distribution span value of the ground powders increases correspondingly.

Environmental Benefits and Energy Efficiency of Superheated Steam as Media in Processing Ultra-Fine Fly Ash Technology

With superheated steam from thermal power plants for medium, the fluidized bed jet mill which had improved vertical turbine classifier was used to study Superheated steam as media in processing ultra-fine fly ash technology. Experiment tested the energy consumption of processing fly ash with superheated steam, which was converted into standard coal compared with the air jet mill technology to prove the environment and energy saving advantages in superheated steam-gas processing ultra-fine fly ash. Experimental results showed that this technology has low energy consumption, high grinding force, and its grinding, grading, collection process is completely in dry method, so this technology is an ideal method for processing ultra-fine fly ash by low-cost and large-scale. At the same time, this paper assessed the environmental benefits of some environmental indicators. Finally, the applications of this technology are summarized.

Batch grinding kinetics of Ethenzamide particles by fluidized-bed jet-milling

Ethenzamide solids as a representative active pharmaceutical ingredient (API) were batch-ground by means of a fluidized-bed jet-mill which is a relatively new equipment and promising for production in the pharmaceutical field. Thus, the characteristic grinding mechanism was investigated. As a result, the variation of the residual ratio with grinding time after milling was expressed simply by a mathematical model using only the first Kapur function, and it was consistent with experimental data satisfactorily. As the shape of the function was much different from that of inorganic compound and peculiar to API, a cubic function with respect to particle diameter was defined newly and well fitted to the experimental data. The function was also found to be affected by the operating parameters as the grinding gas pressure, the charge weight of raw material and the linear velocity at the grinding nozzle. According to the assessments of the breakage and the selection functions derived from the first Kapur function, it was found that the grinding mechanism of Ethenzamide particles was related with particle attrition mainly.

Continuous Grinding Kinetics of Ethenzamide Particles by Fluidized-Bed Jet-Milling

ABSTRACTContinuous grinding kinetics of Ethenzamide powder, as a model active pharmaceutical ingredient (API) was investigated by fluidized-bed jet-milling. Because the oversize fractions after the classification were well fitted by a modified Rosin-Rammler distribution function, an equation of grade efficiency curve was obtained, which was also characteristic of API. A continuous grinding model was developed on the basis of a batch model by using 1st Kapur function relating grinding rate, the grade efficiency curve, and the overall process flow model consisting of grinding, classification, and mixing zones. The residual ratio obtained was well fitted to the experimental results except for the particle size range smaller than 4 μm and larger than 100 μm. Furthermore, because the volume of the active grinding zone adopted as the fitting parameter was found to be 5 cm3 in all experiments and the value was considered to be appropriate dimensionally, this result supports the reliability of the model.

Variation in Particle Shape of Active Pharmaceutical Ingredients Prepared by Fluidized-bed Jet-milling

In pharmaceutical industries, most active pharmaceutical ingredients are poorly water soluble, and therefore milling processes are important to obtain fine particles that can be easily dissolved in the body. However, the main purpose of milling is micronization of particles. From the viewpoint of fine particle preparation in the formulation process, milling has not been investigated sufficiently. In this paper, ethenzamide was milled under various operating conditions using a fluidized-bed jet-mill. It was found that not only the particle size but also the particle shape varied with the milling conditions. The relationship between particle shape and milling conditions has been obtained experimentally.

Effect of Particle Shape of Active Pharmaceutical Ingredients Prepared by Fluidized-Bed Jet-Milling on Cohesiveness

Milling is a common procedure to improve bioavailability of many active pharmaceutical ingredients (APIs), which typically have low solubility in water. But such micronization can yield an increase in the cohesiveness of particles. Although particle cohesiveness is desirable for tablet strength in the subsequent formulation process, increased particle cohesiveness can lead to operational difficulties in a milling equipment due to compaction of particles inside. In this article, the impact of milling via a fluidized-bed jet-mill on the cohesive strength and interparticle force was studied using Ethenzamide as a pharmaceutical model compound. As a result, the particle shape was found to affect both the tensile strength of powder bed and the interparticle cohesive force. A powder bed, having relatively high void fraction by direct tensile test, shows a positive correlation between the cohesive force and the particle sphericity, while powders with low void fraction by diametral compression test show a positive correlation between the cohesive force and the angularity of the particle. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association

A model for performance of the centrifugal countercurrent air classifier

Based on the pneumatic mechanics and the gas-solid two-phase fluid theory, a model of gas-solid two-phase flow speed field was set up for horizontal turbines during the classifying process, and the formula of classified particle cut size in irregular speed fields was deduced. In order to evaluate the model, a number of experiments were carried out in a fluidized-bed jet-mill using samples such as calcium carbonate, carbon silicon, alumina, etc. It was found that the formula of classified particle cut size agreed with the experimental results very well. Furthermore, the relationship between the structural parameters of turbine and the classifying results was discussed, and the turbine structure was optimized according to the formula of classified particle cut size.

Performance of a fluidized bed jet mill as a function of operating parameters

Fluidized bed jet mills are used for the dry comminution in the μm range. The application of the jet mill ranges from deagglomeration purposes to grinding of hard materials. This indicates the wide field for the usage of this grinding technique. The comminution effect is based on particle-particle impact in expanding gas streams. A dynamic classifier is integrated in the fluidized bed jet mill. There are two parameters which can be used to control the performance of the fluidized bed jet mill: the speed of the classifier rotor and the pressure of the gas used for grinding. As a characteristic value the “spin-number” was defined. The “spin-number” is given as the ratio of the circumferential speed of the classifier rotor and the flow-through velocity of the classifying gas in radial direction. Results of limestone grinding were presented. The comminution of limestone represents a grinding process, not just a deagglomeration step. The fineness achieved, expressed by the mean particle diameter, can be modelled as a function of the “spin-number” and the pressure of the gas used for grinding. A similar dependency was found for the parameters of the RRSB-distribution, describing the shape and the position of the distribution. The dependencies could be backed-up with experiments performed with an easily grindable rubber chemical. A few experiments performed at the base-points of the working range of the fluidized bed jet mill enable to establish a characteristic field of performance for a given product. The knowledge of this characteristic field simplifies the selection of the optimum operation conditions of the fluidized bed jet mill for a given grinding task. Moreover it enables to include milling processes in more advanced process control systems.