Continuous Powder Feeding Research Articles

Powder agglomeration in continuous powder feeding by twin-screw feeder

The presence of powder agglomerates results in product with poor content uniformity and intermittent high potency in the processing of pharmaceutical powders.We developed a novel and easy-to-implement methodology, applying image analysis, to quantify the size of powder agglomerates when a powder passes through a screw feeder. Subsequently, agglomeration tendencies of twenty-one pharmaceutical powders were examined and classified. Notably, both the size and endurance of agglomerates were quantified, and our study revealed that the agglomeration tendency of powders can be explained by particle size and compressibility: Powders with small particle size (D50 < 30 μm), and large compressibility (> 35% at 15 kPa normal stress) tend to form large and enduring agglomerates, which can be difficult to eliminate in downstream processes. The study also illustrates how two materials, one that produces enduring and the other unenduring agglomerates, display substantially different content uniformity in the final product after being processed semi-continuously.

In-depth analysis of the long-term processability of materials during continuous feeding

This study determined the feasibility of long-term continuous powder feeding and its effect on the overall process performance. Additionally, quantitative relationships were established between material properties, process settings and screw feeding responses during gravimetric feeding. Twelve divergent raw materials were processed over longer periods using a GEA Compact Feeder integrated in a continuous direct compression line (ConsiGma™ CDC-50). The resulting gravimetric feeding responses were combined with the material properties and process settings into an overall PLS model. The model elucidated the impact of the material descriptors for density; powder flow; particle size; compressibility; permeability and wall friction angle on the feeding process. Furthermore, long-term processing of the materials exhibited challenges related to the processability and refill consistency where a significant impact of the compressibility and cohesive/adhesive properties of the materials was observed. Overall, this approach provided insights into the feasibility of long-term continuous feeding which is not possible through ‘short-term’ feeding trials. Additionally, throughout this study, the need for material-specific adjustments of the feeding and refill equipment was highlighted.

Effects of signal processing on the relative standard deviation in powder feeding characterization for continuous manufacturing

Successful continuous powder feeding is essential for continuous manufacturing and its application in pharmaceutical production. This work focuses on sampling and processing of catch scale (mass) data for the purpose of characterization of continuous powder feeding processes. Specifically, it addresses the sampling frequency and the selection of appropriate filtering (cutoff frequencies) and their effect on statistical measures of catch scale data based on simple test signals representative of continuous feeding. The paper provides suggestions for defining comparability between differently acquired and processed datasets. Specifically, relevant statistical measures which should be reported are mentioned and a reasoning for the appropriate choice of filtering algorithms is provided.

FORMATION OF COMPOSITE METAL-CERAMIC AND METAL-CARBIDE ELECTRIC ARC SPRAYED COATINGS

The paper studies the possibility of forming composite metal-ceramic (Sv-08G2S-О-Al2O3) and metal-carbide (Sv-08G2S-О-TiC) electric arc sprayed coatings using a hardening phase in the form of powder particles in a free form. For this, a modernized cap of the spray head of an EM-14M electric arc spray gun was used, equipped with a unit for continuous powder feed supply. A laboratory batch of samples was obtained in various technological modes of spraying. Microstructures of the deposited coatings are investigated using a scanning electron microscope. It has been established that composite coatings are characterized by a lamellar structure and a rather low porosity from 8 to 12% (depending on the deposition mode and the hardening phase content), and phase particles of different shades are well differentiated in the structure. The phases were identified by their microhardness indicators. It has been established that the microhardness of the metal matrix (Sv-08G2S-О) is 1.88GPa, ceramic Al2O3 particles ‑ 17.1GPa, TiC particles‑ 31GPa. The influence of the technological parameters of spraying, namely: current, voltage and powder consumption on the content of the hardening phase in the structure of the composite electric arc coatings has been investigated. It was found that when using the maximum values of technological parameters (current 160A, voltage 35V and powder consumption 35 g/min), the maximum content of the hardening phase in the coatings is obtained: 10.3% Al2O3 in metal-ceramic and 25.6% TiC in metal-carbide. The significantly higher maximum TiC content in comparison with the Al2O3 content in composite coatings is explained by the high density of carbide and, as a consequence, the increased velocity of these particles in the high-temperature heterophase jet. Experimental studies of the influence of the content of the strengthening phase in composite coatings on their bond strength to the substrate have been carried out. It is shown that the maximum value of the bond strength of metal-ceramic coatings is 30 MPa and corresponds to the Al2O3 content of 8.7%. As for metal-carbide coatings, the maximum bond strength value of 32 MPa was obtained with a carbide phase content of 18.4%. At the same time, the bond strength of the convention coating sprayed of Sv-08G2S-О wire is 26 MPa. An increase in this characteristic for composite coatings is explained by the additional activation of the sprayed surface by unmelted solid particles of Al2O3 and TiC. It is shown that the decrease in bond strength with an increase in Al2O3 content to 10.3%, and TiC to 25.2% is explained by a significant decrease in the actual contact area of the coating with the substrate.

Discrete element modeling for continuous powder feeding operation: Calibration and system analysis.

Research emphases on extensive experimental studies and modeling efforts have been on the rise for the development of accurate predictive models of pharmaceutical unit operations and 'digital-twin' framework for continuous manufacturing lines. These exhaustive studies have been conducted at different process conditions to acquire comprehensive knowledge of effects of process parameters on the overall process dynamics. However, there still lacks a detailed understanding of material property effects of pharmaceutical powders on process operation. To address this issue, a discrete element modeling (DEM) approach combined with material calibration is applied for simulation of feeder unit to obtain particle-level insight into effects of material properties on feeder performance with focus on particle flow and powder mixing within the feeder unit. Bulk calibration is implemented to accurately represent powder material properties within the DEM framework. Different refill situations are simulated using DEM to observe powder mixing, measured at the outlet. Feeder DEM simulations are further applied to understand correlations of material properties on feeder operation. These studies provide a detailed physical insight and particle-scale information into the powder mechanics during powder feeding operation.

Continuous manufacturing of a pharmaceutical cream: Investigating continuous powder dispersing and residence time distribution (RTD)

Recently, an innovative continuous manufacturing technology for a pharmaceutical oral suspension was proposed, based on two consecutive mixing units. A limitation of this technology is the need to dissolve or disperse powder-based raw materials in a liquid via a batch step before continuous manufacturing. Therefore, the aim of the current study was to develop and investigate a method to introduce powders continuously into the existing equipment via the implementation of two upstream continuous unit operations: a powder feeder and powder dispersing unit. A pharmaceutical cream was selected as model formulation to demonstrate the flexibility of the continuous manufacturing technology towards different types of semi-solid and liquid formulations. The ability to continuously feed and disperse active pharmaceutical ingredient (API) using the proposed method was assessed via an experimental design, in which the impact of several process parameters of the powder dispersing unit on the API concentration (relative error (RE) and relative standard deviation (RSD)) was examined. A Raman spectroscopic method was developed to quantify the API concentration in-line after the powder dispersing step. The API concentration was independent of the process parameters and fell within the acceptance limits, except for two experimental runs where a deviating API concentration was observed. These results demonstrate that the continuous powder feeding and dispersing method was suitable, and that a completely continuous manufacturing system was obtained. To achieve raw material traceability and understanding the mixing behavior, the residence time distribution (RTD) of a tracer inside the continuous manufacturing equipment was determined using a colorimetric technique. The time required to remove all tracer from the powder dispersing unit operation was very long (1481 s) and therefore the volume inside this unit operation should be reduced by designing new equipment with smaller dimensions. At the two consecutive mixing units, the peak and mean residence time were influenced by throughput, whereas mixing speed in both mixing units had a significant impact on the degree of axial mixing. Finally, the continuously manufactured cream had a similar rheological behavior as the original batch-wise manufactured cream.

Managing active pharmaceutical ingredient raw material variability during twin-screw blend feeding

Continuous powder feeding is a critical step in continuous manufacturing of solid dosage forms, as this unit operation should ensure the mass flow consistency at the desired powder feed rate to guarantee the process throughput and final product consistency. In this study, twin-screw feeding of a pharmaceutical formulation (i.e., blend) existing of a highly dosed very poorly flowing active pharmaceutical ingredient (API) leading to insufficient feeding capacity was investigated. Furthermore, the API showed very high batch-to-batch variability in raw material properties dominating the formulation blend properties. Formulation changes were evaluated to improve the flowability of the blends and to mitigate the impact of API batch-to-batch variability on the twin-screw feeding. Herewith, feeding evaluation tests and an extensive material characterization of the reformulated blends were performed to assess the impact of the formulation changes upon continuous twin-screw feeding. The transfer of the glidant from extra-granular to intra-granular phase allowed to improve the flowability of the blends. A sufficient feeding capacity for the downstream process and a mitigation of the impact of batch-to-batch variability of the API upon twin-screw feeding of the blends could be achieved. No effect of the formulation or of the API properties on the feeding stability was observed. The material characterization of the blends allowed identifying the material attributes which were critical for continuous twin-screw feeding (i.e., bulk density, mass charge and powder cohesiveness).

Continuous electron beam melting technology of silicon powder by prefabricating a molten silicon pool

We successfully achieved the continuous melting of silicon powder in a vacuum electron beam melting system. The characteristic of electron beam melting of silicon powder was revealed by comparing the three different approaches to prefabricate the molten silicon pool. The application of silicon block can be regarded as the most efficient method to prefabricate a stable molten silicon pool. Afterward, the silicon powder was added into the molten silicon pool at different rates by a spiral silicon powder feeding device. Finally, all of the silicon powder was melted completely. Although the P removal efficiency decreases with increasing powder feeding rate during the powder feeding process, an appropriate increase in the powder feeding rate is not only beneficial to improve the melting efficiency of silicon powder but also conductive to the improvement in uniformity of the obtained silicon ingot. Therefore, the powder feeding rate of 10 g/min was the best option in this study. Compared with the melting of silicon block, which has been wildly applied, this continuous powder feeding process can be beneficial to saving smelting time and the total cost.

Experimental Studies on Melting Behavior of Silicon Powders by In-Flight Plasma Melting Technique

An experimental approach has been used to investigate the charateristics of silicon type powders using heat source of thermal plasma. In this paper, laboratory scale furnace (0.0529m3) using non-transferred hollow thermal plasma torch (150kW) is applied for the rapid melting and the impurities components volatilization. The components and the crystallization behavior of silicon type raw material for complete melting using in-flight melting technique with continuous powder feeding (500~1000 g min-1) into the furnace are investigated by changing the melting atmosphere. The determination of impurities absorption and erodability of the furnace caused by the extremely high localized tempeartures of plasma heat source and molten material is also followed.

Influence of Process Parameters on the Quality of Bionic Non-Smooth Coatings by Laser Cladding

The non-smooth surfaces on 45 steel were prepared by laser cladding with KF-300A alloy powder on the basis of the bionic non-smooth morphology of shark scales. The rib-type coatings were composed of hot-rolled steel 45 and clad layers containing hard phases such as WC/W2C. In this paper, the influence of laser power and defocusing distance on the quality of cladding layer were investigated. The microstructure of the coatings was analyzed by scanning electron microscopy, with attached energy dispersive spectroscopy microprobe, and by X-ray diffraction. SEM inspection of the samples showed that all coatings exhibited similar phases in their microstructure, but the phases presented differ in morphology, size and distribution. Dilution and interaction zone of the coatings were also discussed in this paper. The results showed that the non-smooth coatings were crack-free and had a good metallurgical bonding with 45 steel trenches with a low dilution under the optimum laser conditions (P=700 W, f =14 mm, V=3 mm/s, continuous powder feeding voltage 2.1 V, nitrogen protection).

Growth of Bi12GeO20 Single Crystals by the Pulling-Down Method with a Continuous Powder Feed System.

Transparent and crack-free Bi12GeO20 single crystals have been grown by the pulling-down method with a continuous powder feed system. Bi-rich feed powder having a composition of 14.1mol% GeO2 is favorable to obtain stoichiometric crystals. Striation-free crystals with an increased transmittance are grown under a small temperature gradient. The shape of the solid-liquid interface during the crystal growth is nearly flat, which is advantageous to avoid core formation. Average dislocation density is estimated to be 2×104/cm2, which is comparable to that of Bi12GeO20 crystals grown by the conventional Czochralski method.

Functionally gradient layers of Ti–AI based alloys produced by laser alloying and cladding

AbstractLaser surface alloying and cladding have been used with the aim of producing functionally gradient materials based on the Ti–Al system. A continuous powder feed into a laser generated melt pool produced several fully overlapping layers of increasing Al content. Alloying involved feeding powdered Al onto a near-α Ti alloy substrate. For cladding, powder mixtures of Al and Ti–6Al–4V(wt-%) alloy were used with a Ti substrate of commercial purity. Cladding involving low dilutions provides a better approach to producing several discrete layers of increasing Al content than does alloying which is associated with higher dilutions. Structural and compositional data are reported for samples containing up to four layers having Al contents of up to approximately 34·5 wt-% (48 at.-%).MST/1913

Laser processing of ceramics of the SiO2-Al2O3 system

An investigation has been made of the constitution of laser-processed ceramics from the SiO2-Al2O3 system. Samples were produced in the form of pellets a few millimetres in diameter by pulsed laser melting of mixtures of silica and alumina powders containing 40, 60 and 70 mol % Al2O3. X-ray diffraction identified the main crystalline phases as Al2O3 in the pellets produced from the 70 mol % Al2O3 mixture and mullite from the 60 and 40 mol % Al2O3 mixtures. The proportion of glassy phase present increased with increasing SiO2 content. Microstructural observations on the 60 mol % Al2O3 pellet showed primary mullite crystals and a lamellar structure interpreted as a eutectic of Al2O3 and mullite. Pellets prepared by melting kaolin powder consisted essentially of a glassy phase and much porosity. Cladding of an alumina substrate, carried out using a continuous powder feed into a laser-generated melt pool, was carried out using the same silica-alumina mixtures as those employed for pellet production. A clad layer was also produced by preplacing a kaolin coat on the alumina substrate prior to laser processing. The effects of traverse speed over the range 3.7 to 7.4 mm s−1 inclusive, power density (44.4 and 111 W mm−2) and powder flow rate (0.13 to 0.47 g s−1 inclusive) were investigated. It was found that the phases present in the clad layer depended on the composition of the precursor powder and the processing conditions. Microstructural examination of the clad layers produced from SiO2-60 mol % Al2O3 and kaolin that had completely melted during processing exhibited various growth morphologies.

Laser Cladding with a Ni-Fe-Cr-Al Alloy

ABSTRACTAn investigation is reported of the laser surface.cladding of an alloy of nominal composition Ni-4Fe-30Cr-6A1 (wt%) on a mild steel substrate, using a continuous powder feed of the elemental powder mixture into the melt pool. The effect of laser processing conditions has been investigated in relation to clad dimensions, bonding, dilution level, hardness and microstructural features. A 2 kW CW C02laser was used working at 1.6 kW power and 2.5 mm beam diameter at different traverse speeds ranging from 1.8 to 25 mm/s: clad layers were produced in the range of 0.15-3 mm thick. Fine microstructures were obtained (corresponding to the rapid solidification rates). Good metallurgical bonding was observed between the clad layer and substrate within the range of specific energies, 50-130 J/mm2. For all the conditions studied, no cracking was observed in single tracks; low specific energy conditions gave little porosity.