The flow properties of granular magnesia

Investigation on side-spray fluidized bed granulation with swirling airflow

Top-spray fluidized bed granulation with axial fluidization airflow from the bottom of the granulator is well-established in the pharmaceutical industry. The application of swirling airflow for fluidized bed granulation was more recently introduced. This study examined the effects of various process parameters on the granules produced by side-spray fluidized bed with swirling airflow using the central composite and Box-Behnken design of experiment. Influence of the amount of binder solution, spray rate, and distance between spray nozzle and powder bed were initially studied to establish operationally viable values for these parameters. This was followed by an in-depth investigation on the effects of inlet airflow rate, atomizing air pressure and distance between spray nozzle and powder bed on granule properties. It was found that the amount of binder solution had a positive correlation with granule size and percentage of lumps but a negative correlation with size distribution and Hausner ratio of the granules. Binder solution spray rate was also found to affect the granules size. High drug content uniformity was observed in all the batches of granules produced. Both inlet airflow rate and atomizing air pressure were found to correlate negatively with granule size and percentage of lumps but correlate positively with the size distribution of the granule produced. Percentage of fines was found to be significantly affected by inlet airflow rate. Distance between spray nozzle and powder bed generally affected the percentage of lumps.

Flow rate and flow equation of pharmaceutical free-flowable powder excipients

Basic aspect of powder handling is powder flow which depends on mechanical properties of the solid material. This experimental work presents the results of flowability testing of the free-flowable particle size fraction of 0.0250-0.0315 cm of five powder excipients. The single-point determination of the mass flow rate from a cylindrical, flat-bottomed hopper was primarily influenced by the diameter of a circular orifice. The significant effect of the orifice height was also noted. Increasing the orifice height, the flow under gravity is directed resulting in the sudden acceleration of the flow rate. The critical zone relates to the orifice diameter. The multi-point determination of flowability employed the actual parameters of the flow equation which allows the prediction of the mass flow rate. The precision of the prediction was the basic criterion in optimization of the orifice geometry. Based on the results, the orifice height of 1.6 cm can be recommended for the correction of faster powder flow. For the slower powder flow, an orifice height of 0.2 cm can be used alternatively. In conclusion, the information about the orifice height used should be referred to whenever test the powder flowability and compare the results.

Some angular properties of magnesia and their relevance to material handling

By measuring the angular characteristics of magnesia over a range of particle sizes from 30–3000 μ, it has been possible to determine the factors which influence the shapes of heaps, cones and wedges of the material, formed under a variety of experimental conditions. The relevance of the measurements to quality control, flow-ability, hopper and chute design and material handling is discussed.

Flow rate of some pharmaceutical diluents through die-orifices relevant to mini-tableting

The effects of cylindrical orifice length and diameter on the flow rate of three commonly used pharmaceutical direct compression diluents (lactose, dibasic calcium phosphate dihydrate and pregelatinised starch) were investigated, besides the powder particle characteristics (particle size, aspect ratio, roundness and convexity) and the packing properties (true, bulk and tapped density). Flow rate was determined for three different sieve fractions through a series of miniature tableting dies of different orifice diameter (0.4, 0.3 and 0.2 cm) and thickness (1.5, 1.0 and 0.5 cm). It was found that flow rate decreased with the increase of the orifice length for the small diameter (0.2 cm) but for the large diameter (0.4 cm) was increased with the orifice length (die thickness). Flow rate changes with the orifice length are attributed to the flow regime (transitional arch formation) and possible alterations in the position of the free flowing zone caused by pressure gradients arising from the flow of self-entrained air, both above the entrance in the die orifice and across it. Modelling by the conventional Jones-Pilpel non-linear equation and by two machine learning algorithms (lazy learning, LL, and feed-forward back-propagation, FBP) was applied and predictive performance of the fitted models was compared. It was found that both FBP and LL algorithms have significantly higher predictive performance than the Jones-Pilpel non-linear equation, because they account both dimensions of the cylindrical die opening (diameter and length). The automatic relevance determination for FBP revealed that orifice length is the third most influential variable after the orifice diameter and particle size, followed by the bulk density, the difference between bulk and tapped densities and the particle convexity.

Artificial neural networks (ANNs) and modeling of powder flow

Effects of micromeritic properties (bulk, tapped and particle density, particle size and shape) on the flow rate through circular orifices are investigated, for three pharmaceutical excipients (Lactose, Emcompress and Starch) separated in four sieve fractions, and are modeled with the help of artificial neural networks (ANNs). Eight variables were selected as inputs and correlated by applying the Spearman product-moment correlation matrix and the visual component planes of trained Self-Organizing Maps (SOMs). Back-propagation feed-forward ANN with six hidden units in a single hidden layer was selected for modeling experimental data and its predictions were compared with those of the flow equation proposed by. It was found that SOMs are efficient for the identification of co-linearity in the input variables and the ANN is superior to the flow equation since it does not require separate regression for each excipient and its predictive ability is higher. Besides the orifice diameter, most influential and important variable was the difference between tapped and bulk density. From the pruned ANN an approximate non-linear model was extracted, which describes powder flow rate in terms of the four network's input variables of the greatest predictive importance or saliency (difference between tapped and bulk density (x(2)), orifice diameter (x(3)), circle equivalent particle diameter (x(4)) and particle density [equation in text].

Cooling as a possible method for increasing the flowability of certain pharmaceutical and other powders

Measurements have been made of the rates of flow under gravity of powdered sugars and of fatty acids through circular orifices at temperatures between -25 and 110 degrees C. The flow rates decrease considerably as the powders are heated; conversely they increase as the powders are cooled from a high ambient temperature of 40 to -25 degrees C. The results are ascribed to changes in the cohesiveness of the powders caused by softening and plastic deformation of particles at elevated temperatures. Lactose, paracetamol and griseofulvin granule formations have been reported to show similar effects and the possibility is discussed of using cooling to increase the flowability of particular powders in pharmaceutical production. The rates of flow of the powders are given by the expression(formula: see text)where W is the flow rate in g min-1, Do is the orifice diameter in cm, rho is the particle density in g cm-3, g is the gravitational constant, and A and n are numerical terms which depend on temperature and particle size.

The flow of granular solids through circular orifices

It has been shown that the use of the bulk density term in place of the particle density, in the equation of flow for granular solids passing through a circular orifice, very largely eliminates differences due to the shape, rugosity, density, porosity and friction of the particles.

The equation

has been tested on seven different materials and has been found to predict the flow of single and binary systems with an overall accuracy of ±5% and ±10% respectively.

The flow of granular magnesia

Investigations of the flow rates of loosely packed magnesia have shown that the general equation developed by Jones & Pilpel (1966)

can be applied to single component and multicomponent mixtures in the size range 0·003 to >0·2 cm. The increase in flow rate caused by mixing coarse and fine particles has been related quantitatively to the size of the particles by the general expression

This can be used to calculate the composition for maximum flow in multicomponent mixtures. The mechanism of action of glidants is discussed in the light of the experimental results and a distinction is made between glidants which improve the flow of granulations and those which improve the flow of cohesive powders.