Powder Flow Research Articles

The effect of material properties and process parameters on die filling at varying throughputs: A PLS-model-based analysis

When tablets are manufactured on a rotary tablet press and the throughput is increased, it leads to changes in powder dynamics during die filling due to formulation characteristics and changing powder flow in the feed frame. This may result, a.o. in increased tablet weight variability, poorer content uniformity, capping and lamination. This research focuses on explaining the die filling performance depending on material properties and process settings, including throughput for small and large tablets. It was concluded that throughput had a negative impact on die filling variability, which is related to reduced residence time and lower fill fraction of the feed frame and dies. Furthermore, the die filling mechanism was inherently different for large tablets in comparison to small tablets. Higher die filling consistency was observed for dense, less porous, less compressible and better flowing powders. As a result of this work, a model was developed to predict the impact of formulation properties and process settings on die filling variability and its dependency on changes in throughput. This model will benefit formulation development at an early stage when active ingredient availability may be challenging as it will avoid the need to conduct experiments at high throughputs.

Optimizing large porous mannitol-leucine microparticles via spray drying technique

The development of large porous microparticles (LPPs) has gained attention for dry powder in-halation (DPI) formulations due to their potential to enhance the efficiency of drug delivery into the lungs. In this work, large porous mannitol-leucine microparticles (MALs) were developed using a spray drying technique. Mannitol was co-spray dried with ammonium bicarbonate (0–50 % w/w) and leucine (1–20 % w/w). The morphology of MAL particles was spherical hollow with corrugated surface. The MAL with 10 % leucine (MAL-10) showed the lowest bulk density (0.08 g/cm3) with the highest surface area (7.85 m2/g), while the aerodynamic diameter (Daer) was within 1–5 μm, indicating the suitability to penetrate the lung. The DSC and XRD results indicated that the MALs exhibited a mixture of β- and α-polymorphs, while the FT-IR spectra con-firmed that no chemical interaction during co-processing. The leucine co-processing significantly improved powder flowability of the MAL-10 (28.33° for angle of repose). In addition, the co-processing with high leucine concentration (10–20 %) significantly reduced moisture sorption, while the polymorph of MALs did not change after 30 days of hygroscopicity study that indicated good stability. According to all results, the MALs could potentially be applied as drug carriers for DPI formulations.

Dynamic evolution of temperature field, flow field, and solidification behavior during multilayer multitrack laser cladding

During multilayer multitrack laser cladding, secondary melting and solidification in the interlayer lap zone have a significant impact on the mechanical properties of cladding coatings. However, mathematical modeling of the melt flow and solidification behavior of multilayer, multitrack laser cladding interlayer lap zones is lacking. In this paper, a 3D finite element model was established to investigate the mass and heat transfer processes in both lap and non-lap zones during the laser cladding of multilayer multitrack Fe-Cr-based alloys on 45# steel surface. A dynamic grid is used to track the free surface of the melt pool, while the enthalpy method is used to simulate the solid-liquid phase transition. The change in thermophysical properties with temperature, as well as the change in laser energy and alloy powder flow density in the lap zone, were taken into consideration. The influence of the number of cladding layers on the heat and mass transfer in the molten pool, remelting, and solidification in the lap zone was investigated, along with its intrinsic mechanism. The results show that the model can accurately predict the size and microstructural change law of coating layers, including the grain size of the lap region between layers. The melt pool temperature and grain size increase with the number of cladding layers, while the convection and cooling velocities decrease. In addition, the grain size in the lap zone of the cladding is larger than that in the nearby non-lap zone. Using solidification parameters extracted from the solidification front of the molten pool, changes in grain size and morphology were predicted for both the interlayer lap and non-lap zones. The numerical calculation results were consistent with the experimental measurements.

High‑silicon electrical steel powders aimed for additive manufacturing

The Fe6.5Si soft magnetic alloy exhibits promising magnetic properties for energy applications, including near-zero magnetostriction, low magnetocrystalline anisotropy, and higher electrical resistivity than conventional electrical steels. However, its brittleness impedes industrial use. Recent advances in powder-based additive manufacturing show potential for processing high‑silicon electrical steels. This study focuses on the production cycle and properties of feedstock powder, which are crucial for such applications. Fe6.5Si alloy powders were produced via closed-coupled gas atomization. Comprehensive analysis covered mass balance, particle size distribution, powder flow, morphology, density, rheological properties, and thermal and magnetic behavior. Results suggest the feasibility of producing suitable Fe6.5Si alloy powder via gas atomization, enabling additive manufacturing of the next generation of medium/high-frequency electrical motors. The powder exhibited desirable characteristics within the size ranges applicable to laser powder bed fusion (20–75 μm) and direct energy deposition (75–106 μm), showing excellent flow behavior and morphological suitability for additive manufacturing.

Numerical study of dense powder flow in a rotating drum: Comparison of CFD to experimental measurements

Designing chemical reactor equipment requires a thorough understanding of powder flow. Solid rheology modelling offers various models for this purpose. A comparative study of two different CFD models, the Kinetic Theory of Granular Flow (KTGF) and the dense granular flow (μI law), is proposed. Both models were confronted with experimental results obtained on a rotating drum for different rotation speeds and powder flowabilities. Image processing was used to compare the experimental gas/solid interfaces with those obtained from CFD. The KTGF model did not represent the powder rheology at low rotation speeds, regardless of the powder, whereas it was closer to experiments at higher speeds. The dense granular flow model was more appropriate for this system as it described the powder shape inside a rotating drum relatively well for each experiment. The latter model is recommended for modelling dense granular flows, while the KTGF is better suited to gas-solid flows.

The potential of sonocrystallization in crystal habit modification for improving micromeritic and physicochemical properties of Dapagliflozin

Dapagliflozin propanediol monohydrate (DAPA), an antidiabetic drug owing to its needle-shaped crystals exhibits poor micromeritic and physicochemical properties. Crystal habit modification by conventional and sonocrystallization approaches was employed to improve its manufacturability. SEM analysis of sonocrystallized DAPA in acetonitrile (DAPA_SNC3) revealed a rod habit with lower aspect ratio (3.56±0.91) and narrow size distribution (span value-1.37). In case of DAPA_EH and DAPA_CS (solvent evaporation in ethanol:n-hexane, and chloroform, respectively), rod and plate-shaped crystals were obtained with aspect ratios 6.98±5.84 and 6.03±4.21, respectively. All three samples showed significantly improved powder flowability (p<0.0001) compared to DAPA. Further solid-state characterization by FTIR, TGA, DSC, and PXRD showed no polymorphic changes in recrystallized samples. The contact angle studies in water revealed wetting tendency in the following order: SONO_SNC3>SONO_EH>SONO_CS>DAPA. Polar energies of DAPA_SNC3 and DAPA_CS were significantly higher (p<0.01 & p<0.001, respectively) when compared with DAPA. The XPS studies showed increased hydrophilic elements on the surfaces of DAPA_SNC3 crystals which resulted in improved wettability. DAPA_SNC3 among all samples showed highest tensile strength at 200 MPa compression force because of its shape. DAPA_EH showed no significant improvement in IDR profile, while DAPA_CS and DAPA_SNC3 showed significantly faster IDR because of prominent polar functionality (p<0.05 and p<0.0001, respectively).

Wet chemical surface functionalization of AA2017 powders for additive manufacturing

Laser Powder Bed Fusion (L-PBF) is an important route for processing aluminum alloys, nevertheless, the high laser reflectivity and thermal conductivity and lower powder flowability of the aluminum alloys remain a challenge for their processing. Aiming to overcome these issues, AA2017 powders were surface-functionalized using chemical etchings. The powders' physical and rheological characterization revealed a decrease in the laser reflectance and an improvement in the flowability of the surface-functionalized powders, when compared to the gas-atomized powder. The higher amount of keyhole porosity in the as-printed L-PBF samples using the surface-functionalized powders also suggests an improvement in the laser absorption of these powders. However, the formation of a thick oxide layer on the surface-functionalized powders led to oxidation porosity in the as-printed samples. Therefore, the chemical etching should be improved to avoid the formation of a thick oxide layer on the powder surface and oxidation porosity in the as-printed L-PBF samples.

Mannitol-coated hydroxypropyl methylcellulose as an alternative directly compressible controlled release excipient

One of the most common forms of controlled release technology for oral drug delivery comprises an active ingredient dispersed in a hydrophilic matrix forming polymer such as hydroxypropyl methylcellulose (HPMC), which is tableted via direct compression. However, HPMC may pose problems in direct compression due to its poor flowability. Hence, mannitol syrup was spray-coated over fluidized HPMC particles to produce co-processed HPMC–mannitol at ratios of 20:80, 50:50, and 70:30. Particles of pure HPMC, co-processed HPMC–mannitol, and their respective physical mixtures were evaluated for powder flowability, compression profiles, and controlled release performance. It was found that co-processed HPMC–mannitol consisted of particles with improved flow compared to pure HPMC particles. Sufficiently strong tablets of >2 MPa could be produced at moderate to high compression forces of 150–200 MPa. The dissolution profile could be tuned to obtain desired release profiles by altering HPMC–mannitol ratios. Co-processed HPMC–mannitol offers an interesting addition to the formulator’s toolbox in the design of controlled release formulations for direct compression.

Process Simulation of Twin-Screw Granulation: A Review.

Twin-screw granulation has emerged as a key process in powder processing industries and in the pharmaceutical sector to produce granules with controlled properties. This comprehensive review provides an overview of the simulation techniques and approaches that have been employed in the study of twin-screw granulation processes. This review discusses the major aspects of the twin-screw granulation process which include the fundamental principles of twin-screw granulation, equipment design, process parameters, and simulation methodologies. It highlights the importance of operating conditions and formulation designs in powder flow dynamics, mixing behaviour, and particle interactions within the twin-screw granulator for enhancing product quality and process efficiency. Simulation techniques such as the population balance model (PBM), computational fluid dynamics (CFD), the discrete element method (DEM), process modelling software (PMS), and other coupled techniques are critically discussed with a focus on simulating twin-screw granulation processes. This paper examines the challenges and limitations associated with each simulation approach and provides insights into future research directions. Overall, this article serves as a valuable resource for researchers who intend to develop their understanding of twin-screw granulation and provides insights into the various techniques and approaches available for simulating the twin-screw granulation process.

Characterization of the powder flow behavior of cooked Adzuki bean using image analysis and grinding models

The study employed thin-layer models and sigmoid model to analyze the drying behavior and grinding kinetics of the Adzuki bean (AB) powder, respectively. Particle size distributions were determined using conventional sieving and a vibrator with image analysis, providing accurate measurements within a narrower size range (0.1 mm–3.0 mm) in the sample. The flow properties were evaluated across different particle sizes ranging from 0.25 mm to 2.00 mm. These flow characteristics were then utilized for designing a hopper. The study revealed that the smallest particle size (0.25 mm) exhibited the lowest flowability (1.7873 and 1.4384 for 10% and 15% moisture content (MC), respectively). Additionally, the internal friction angle varied significantly for particle sizes between 0.60 and 1.70 mm at 10% MC, while at 15% MC, a greater effect of friction due to moisture was observed. Furthermore, the study highlighted the need for a larger hopper angle and opening for the smallest particle sizes.

β-Modification in heterogeneous polypropylene for laser-based powder bed fusion of polymers

Currently, polyamides serve as the primary material used in laser-based powder bed fusion of polymers (PBF-LB/P), which prevents the components from exhibiting the mechanical characteristics of traditional manufacturing techniques. As a result, highly ductile and chemical-resistant materials are needed to cover more potential application areas. The preferred material is polypropylene (PP) with various structures and settings. A common practice in conventional manufacturing processes is adjusting the morphology of the component, but studies examining this type of influence in PBF-LB/P are scarce. In addition to examining important PBF-LB/P process characteristics like thermal properties and powder flow behavior, this work first presents potential nucleation agents and then manufactures components to assess the impact of the structure. It was concluded that processing the material is possible despite significantly higher crystallization kinetics. A parameter study was conducted to evaluate the initial PBF-LB/P processability by building single and triple layers. These results led to the creation of mechanical specimens that showed the material system’s processability. For the first time, it was possible to process β-nucleated PP, which displays increased elongation at break for higher β-content.

Effect of process parameter on the flowability of nanocrystalline CoNiCrAlY powder synthesized by mechanical milling

The present study concerns understanding the effect of process parameters on the characteristics and flowability of nanocrystalline CoNiCrAlY powder synthesized by mechanical milling. Mechanical milling has been conducted in a planetary ball mill with tungsten carbide (WC) ball, with ball to powder ratio of 10:1 at 300 rpm speed, using 1% stearic acid and toluene as process control agent (PCA) with time varying from 10 h to 36 h. The synthesized nanocrystalline powder were characterized by Scanning Electron Microscopy, X-ray Diffraction technique, X-ray Photoelectron Spectroscopy, and Differential Scanning Calorimetry. Subsequently, flowability in terms of Hausner ratio was assessed by Tap Density Tester. Average particle size of the powder was found to decrease from 33 μm to 22 μm after 10 h of milling and further increases to 43 μm and 38 μm after 25 and 36 h of milling, respectively, in stearic acid medium. However, in toluene medium particle size continuously decreases from 33 μm to 9.7 μm with increasing milling time. The particle morphology changes from spherical to platelet shape at low milling hours in both of the media. After 25 h of milling, the shape of the particles is nearly spherical for stearic acid and irregular for toluene used as a PCA. Crystallize size was found to decrease with increasing milling time from 147 nm to 7.7 nm and to 6.4 nm in stearic acid and toluene media, respectively. There was presence of γ, γʹ, β, hcp-Co, Al2O3 and AlOOH phases on the powder particles milled in both the medium. The measured Hausner ratio of the powders was found to vary from 1.18 to 1.32 in stearic acid medium, and was found to increase with increasing milling time. On the other hand, in toluene media flowability decreases (Hausner ratio increases from 1.33 to 1.44) with increasing milling time.

The effect of glidant on the tabletting behavior of common pharmaceutical excipients

Glidant used for the purpose of powder flowability enhancement is well known within the pharmaceutical industry to improve tablet manufacturing. Despite the widespread use of glidant for this purpose, the effect of glidant on the effect of tableting behavior is not well studied. To address this deficiency, the effect on glidant on the tabletting behavior of seven common excipients was investigated. Tabletability, compressibility, compactability, and tablet expansion were studied. It was shown that glidant increased the tabletability for excipients known to exhibit plastic behavior. Based on compressibility and compactability, it was inferred that an increase in total bonding strength due to the presence of glidant was responsible for the improvement in tabletability. Results suggest this may be due to an increase in inter-particle bonding area. Conversely, glidants did not affect the tabletability of brittle excipients. The effect of glidant on die-fill bulk density was also studied to examine the impact associated with air entrapment and tablet expansion. While glidant significantly increased the die-fill powder density, this did not have an observable effect on tablet expansion or any other tabletting behavior examined.

In-situ monitoring of sintering and analytical modeling of densification and shrinkage in binder jetted 316 L stainless steel

In binder jetting, shrinkage and deformation occur during the sintering step, both of which are affected by the green density of the binder jetted materials. The study innovatively introduces a cost-effective, practical, and in-process monitoring system for visualizing shrinkage and deformation on larger samples than conventionally observed using small-scale specimens in dillatometry equipment. The powder characteristics and binder jet printing process itself influence the initial green density. The comprehensive analysis of powder flowability and packing density, densification behavior, and shrinkage reveals that the consolidated parts using virgin powder (with a green density of 55 %) can achieve a relative density above 99.9 % with an anisotropic shrinkage in the Z > X > Y direction. In contrast, the used or recycled powder exhibits a lower green density of ∼48 %, higher shrinkage rate in all three dimensions, and a decreased degree of anisotropy. Using in-process imaging and experimental data on the grain size attained through optical microscopy and electron backscatered diffraction imaging, the material's shear and bulk viscosities were determined. The formation of delta-ferrite and its impact on densification were discussed in the context of solid-state and supersolidus liquid phase sintering. The model relied on the continuum sintering theory formulated by Skorohod and Olevsky. The strain evolution from the in-situ imaging of sintering process is correlated with porosity based on the used feedstock and applied sintering temperatures. The outcomes of this study offer valuable perspectives on anisotropic sintering mechanisms, bridging the knowledge gap regarding the relationships between structures produced through binder jetting and subsequent sintering of materials.

Reduction in Powder Wall Friction by an a-C:H:Si Film

The wall friction angle is an important parameter in powder flow. In a recent study for various powders, a reduction in the wall friction angle for steel was demonstrated by the application of an a-C:H:Si film on the steel surface. This work presents the results of a study of this effect in more detail regarding the influence of the powder material, the wall normal stress and the particle size of the powder for mass median diameters from 4 µm to approximately 150 µm. The wall friction angles were measured using a Schulze ring shear tester for three different powder materials: aluminum oxide, calcium carbonate and silicon carbide. The results showed little difference with respect to powder chemistry. For the coarser powders, the reduction in the wall friction angle due to the a-C:H:Si coating was highest (10° to 12°) and rather stress-independent, while for the fine and medium-size powders the reduction was lower and stress-dependent. With increasing wall normal stress, the reduction in the wall friction angle increased. These results can be explained by the friction reduction mechanism of a-C:H:Si, which requires a certain contact pressure for superficial graphitization.

Effects of the demineralisation degree on physicochemical, functional, microstructural and powder flow properties of whey powder

This study aimed to investigate the effects of the demineralisation process on powder flow, physicochemical, functional, and microstructural properties of whey powders (WP). WP samples were produced from 50, 70 and 90% demineralised sweet whey concentrates. Although the salt, ash, and lactic acid content of the powders decreased with increasing demineralisation, pH increased. D [3,2] (surface area mean diameter) value of WP samples ranged from 28.2 to 60.9 μm, in which demineralisation increased the particle size. The colour values showed increased darkness and yellowness, attributed to the higher demineralisation process. Demineralisation improved solubility and foaming characteristics, whereas it decreased the wettability and dispersibility of samples. The caking and cohesion characteristics of WP were significantly decreased by demineralisation. Demineralisation significantly improved the powder flow characteristics of samples. The cohesion index decreased depending on the demineralisation degree increased. Also, demineralisation decreased the cake strength and compaction coefficient of samples. Mineral content decreased with increasing demineralisation, with some minerals showing more sensitivity to demineralisation than others. Scanning Electron Microscope images showed reduced caking and clustering in samples with higher degrees of demineralisation. The results highlighted the importance of demineralisation as an effective parameter to control the properties of WP. In conclusion, this study demonstrated that the degree of demineralisation had a substantial impact on the physical and functional properties of WP.

Numerical study of powder flow characteristics of coaxial nozzle direct energy deposition at different operating and design conditions

Numerical study of powder flow characteristics of coaxial nozzle direct energy deposition at different operating and design conditions

Recovery of residual polyamide (PA12) from polymer powder bed fusion additive manufacturing process through a binder jetting process

PurposeThis study aims to propose the reuse of PA12 (powder) in another AM process, binder jettiinng, which is less sensitive to the chemical and mechanical degradation of the powder after multiple cycles in the laser system.Design/methodology/approachThe experimental process for evaluating the reuse of SLS powders in a subsequent binder jetting process consists of four phases: powder characterization, bonding analysis, mixture testing and mixture characteristics. Analyses were carried out using techniques such as Fourier Transform Infrared Spectroscopy, scanning electron microscopy, thermogravimetric analysis and stress–strain tests for tension and compression. The surface roughness, color, hardness and density of the new mixture were also determined to find physical characteristics. A Taguchi design L8 was used to search for a mixture with the best mechanical strength.FindingsThe results indicated that the integration of waste powder PA12 with calcium sulfate hemihydrate (CSH) generates appropriate particle distribution with rounded particles of PA12 that improve powder flowability. The micropores observed with less than 60 µm, facilitated binder and infiltrant penetration on 3D parts. The 60/40 (CSH-PA12) mixture with epoxy resin postprocessing was found to be the best-bonded mixture in mechanical testing, rugosity and hardness results. The new CSH-PA12 mixture resulted lighter and stronger than the CSH powder commonly used in binder jetting technology.Originality/valueThis study adds value to the polymer powder bed fusion process by using its waste in a circular process. The novel reuse of PA12 waste in an established process was achieved in an accessible and economical manner.

Study on shallow configuration preparation and macroscopic and microscopic properties of cemented carbide surface

This study aimed to reduce surface configuration defects and improve the service performance of the configuration surface. The configuration was prepared using the principle of preset powder feeding laser cladding. Macroscopic and microscopic properties of the shallow configuration were tested to understand the mechanism behind the preset cladding material's ability to repair defects and improve surface hardness, and the preparation process of the shallow configuration was obtained. Finally, the method's potential for improving the wear resistance of the configuration surface was evaluated through friction and wear tests. The results indicate that the flow of molten preset powder can fill in pores, leading to the formation of a dense cladding layer on the configuration surface. This process also minimizes the generation of defects and holes. The incorporation of hard phases, such as TiN, Ti2N, and the solid solution (Ti, W)C1-X, positively influences the improvement of surface hardness and wear resistance of shallow configuration. When the average laser energy density ranges from 70 to 120 W·cm−2, the average microhardness of the shallow configuration surface is elevated by 13.4% compared to that of the conventional configuration surface. The friction force on the shallow configuration surface is 13.1% lower than that on the conventional configuration surface when the laser power is set to 80%, the scanning speed is maintained at 1500 mm/s, the scanning passes are 9, the spacing between configurations is 130 μm, and the configuration diameter is 50 μm. This technique presents a novel approach to producing configuration surfaces with enhanced quality.

The effect of powder recycling on the mechanical performance of laser powder bed fused stainless steel 316L

Powder recycling refers to the reuse of unused powder feedstock in the laser powder bed fusion (PBF-LB/M) process. This approach is crucial for the economic viability and sustainability of PBF-LB/M, as powder accounts for a large proportion of the total production cost. However, through powder recycling, the physical and chemical properties of powder are liable to change. This variation in powder properties can subsequently lead to knock-on effects on the mechanical properties of a fully built component.This research has investigated the changes that occur to stainless steel 316L (SS316L) powder as a result of recycling. This includes changes to powder size distribution (PSD), flowability, chemistry and phase composition. Likewise, the impact that these changes have will also be assessed in PBF-LB/M SS316L components manufactured from powders after different levels of recycling and subjected to alternative post processing routes such as hot isostatic pressing (HIP). This comprehensive investigation involves a thorough examination of both macro- and microstructures, encompassing detailed analyses of chemical composition, microstructural features, and defects. The study aims to elucidate differences in mechanical behaviour through a series of experiments, including uniaxial tensile tests, Charpy impact assessments, and low cycle fatigue (LCF) experiments. Additionally, the investigation will be complemented by pitting potential tests, providing a holistic understanding of the material's performance and characteristics.Although moderate changes to powder were observed for both PSD and chemistry, this was found to be negligible and not enough to result in any adverse changes to part performance. In addition, the microstructure of SS316L remained stable across differing levels of powder recycling. Whereas the porosity content increased marginally as the fine particle content of powder was reduced, this was not found to be sufficient to affect the LCF performance of the material. After powder recycling, increases in ductility and Young’s modulus were attributed to a reduction in oxides present in the microstructure, which were sources of localised damage and deformation.