Varying Compaction Pressure Research Articles

Effect of Compaction Pressure on the Enzymatic Activity of Pancreatin in Directly Compressible Formulations.

Tableting of biomolecules is a challenging formulation phase due to their sensitivity to various process parameters, such as compression pressure, process dynamics, or the temperature generated. In the present study, pancreatin was employed as a model enzyme mixture, which was formulated in tablet form utilizing the synergistic effects of brittle and plastic excipients (dibasic calcium phosphate and microcrystalline cellulose, respectively). The effect of varying compaction pressure and lubricant concentration on the generated temperature and enzymatic activity was evaluated. The tablets were analyzed for pancreatin content and the activity of two enzymes (protease and amylase) using pharmacopoeial tests. This study indicated that the formulations proposed here allow tableting over a wide range of compaction pressures without adversely affecting pancreatin content and its enzymatic activity.

Investigating the morphology, hardness, and porosity of copper filters produced via Hydraulic Pressing

This paper presents an examination of the production of copper air filters via the Hydraulic Pressing (HP) method. Processing conditions examined included powder particle type (spherical and dendritic), varying compaction pressures (635, 714, and 793 MPa) and different pore forming (polyvinyl alcohol (PVA)) concentrations (1, 2, and 3 wt.%). Following compaction, the samples were thermally sintered in a two stage sintering regime at 200 °C and 750 °C. The morphology, porosity, and mechanical properties of the sintered samples were characterised. Morphological analysis demonstrated better consolidation and overlapping of the copper powder particles in samples with a higher weight percentage of the PVA. Highest porosity was achieved in the sample produced using the dendritic copper powder mixed with highest weight percentage of PVA. As the samples were very porous, the hardness of the samples varied greatly. Samples prepared with spherical powders at high pressure demonstrated the highest hardness. The results in this study show that copper filters with 14%–26% porosity can effectively be produced using spherical and dendritic copper powders by controlling the compaction pressure and PVA concentration.

An investigation of drug compact topography as relates to intrinsic dissolution rates determined by dissolution imaging

The purpose of this study was to characterize compact surfaces (surface roughness) and study its potential importance to the intrinsic dissolution rate (IDR) as determined by dissolution imaging. To this end, the effect of varying compaction pressures and the use of two stainless-steel surfaces with different textures/roughness on the intrinsic dissolution were investigated. Ketoprofen (KET), paracetamol (PAR) and ibuprofen (IBU) were compacted and a focus variation microscope used to determine the surface topology of the compacts. IDR determination was conducted using a surface dissolution imaging apparatus with the flow-through set up in phosphate buffer at pH 7.2 and at 37 °C. The results indicated a general decrease in the surface area of the drug compacts with an increase in compaction force (p values < 0.05 for IBU and PAR but not KET). This change in surface area was measured using the Sdr parameter, which can be defined as the developed interfacial area. The smoother stainless-steel plate insert produced significantly smoother compacts for KET (Sdr decreased from 0.30% to 0.07%). However, PAR and IBU compacts showed an increase in their Sdr values from 3.94% to 17.90% and from 0.60% to 0.83%, respectively, suggesting the changes in surface properties to be drug specific relating to poor compaction properties and elasticity. The dissolution studies suggested that low compaction forces were not suitable for PAR. Overall changes in the surface topology did not have a significant effect on the obtained IDR values.

On the density calculation of fabricated zirconia toughened alumina by unconventional method

Aim of the paper is to fabricate zirconia toughened alumina (ZTA) by varying compaction pressure and sintering temperature from commercially available ZTA powder in the laboratory and postulate an unconventional method for estimating the bulk density in the zirconia toughened alumina (ZTA) apart from conventional Archimedes principle method. The operating parameters have been selected to investigate the void fraction at different sintered conditions. The densities of the as sintered specimens are estimated from the micrograph taken at different positions of the specimens with the help of image processing method using field emission scanning electron microscopy (FESEM). The results are compared with the conventional one and found a deviation of minimum and maximum of ∼ 3.34 and ∼ 5.95 % respectively. The said method can be considered for approximating the voids more precisely since during the conventional Archimedes method, the medium remains unable to reach into the core of each pore completely. At higher temperature the grain growth increases which in turn densifies the overall composite structure and thus leading to the pore reduction.

Modelling the effect of compaction pressure on hysteresis curves of self-developed SMC cores

PurposeThe purpose of this paper is to examine the effect of varying compaction pressure on magnetic properties of self-developed soft magnetic composite (SMC) cores. The change in shape of ferromagnetic hysteresis curves has – in turn – the impact on the values of hysteresis model parameters. The phenomenological GRUCAD model is chosen for description of hysteresis curves.Design/methodology/approachSeveral cylinder-shaped cores have been made from a mixture of iron powder and suspense polyvinyl chloride using a hydraulic press with a form and a band with a thermocouple for controlling heat treatment conditions. The only varying parameter in the study is the compaction pressure. The magnetic properties of developed cores have been measured using a computer-acquisition card and LabView software. The obtained hysteresis curves are fitted to the equations of the phenomenological GRUCAD model. This description is compliant with the laws of irreversible thermodynamics. The variations of model parameters are presented as functions of compacting pressure.FindingsThe compaction pressure has a significant impact on magnetic properties of self-developed SMC cores. The paper provides a number of charts useful for checking how the parameters of the hysteresis model are affected.Research limitations/implicationsThe present paper is limited to modelling symmetrical loops only. Description of more complex magnetization cycles is postponed to another, forthcoming paper.Practical implicationsThe GRUCAD hysteresis model may be a useful tool for the designers of magnetic circuits. Its parameters depend on the processing conditions (in this study – the compaction pressure) of the SMC cores.Originality/valueModelling of magnetic properties of SMC cores has been carried so far using some well-known description like Preisach, Takács and Jiles–Atherton proposals. The GRUCAD model has a number of advantages, and it may be a useful alternative to the latter formalism. So far it has been used for description of hysteresis curves in conventional materials like non-oriented and grain-oriented electrical steels. In the present work, it is applied to novel SMC materials.

Hardness and dry sliding wear behavior of SiC reinforced Al 7150 alloy composite synthesized under the influence of aging, varying compaction pressures, particle size and volume fraction of ceramic particulates by hot compaction technique

The objective of the current investigation is to study the hardness and dry sliding wear behavior of SiC reinforced Al 7150 alloy composite synthesized under the influence of aging, varying compaction pressures, particle size and volume fraction of ceramic particulates by hot uni-axial compaction route. The varying vol% (0, 5, 10 and 15%) of coarse (45 μm) and nano SiC particulates (80 and 27 nm) were blended with the base Al 7150 alloy powders in a planetary ball mill to produce five sets of Al 7150 alloy composite samples via hot uni-axial compaction technique, under different compaction pressures of 400, 450, 500, 550 and 600 MPa. The hot compaction temperature was maintained at 450 °C with varying compaction durations of 30, 45 and 60 min before ejection. The VHN tests showed that the samples synthesized by applying a compaction pressure of 550 MPa produced better microhardness values than the other set of specimens. The hot compacted samples produced by applying a compaction pressure of 550 MPa, were first solutionized followed by artificial aging at 115 °C for durations of 3, 6, 12, 24, 30, 45, 60 and 96 h. The artificially aged samples were tested for VHN hardness and wear resistance using a pin on disc wear tester. The results revealed that the hardness and wear behavior of the samples were influenced not only by the addition of varying volume fraction and particle size of SiC particulates but also due to the occurrence of precipitation hardening. The test samples were characterized using XRD, FESEM and EDS to determine the mechanism of wear.

Mechanical characterization of Al-Cu alloy produced using conventional sintering process

Aluminium Powder Metallurgy (P/M) offers components with exceptional mechanical and fatigue properties, low density, corrosion resistance, high thermal and electrical conductivity, excellent machinability, good response to a variety of finishing processes, and which are competitive on a cost per unit volume basis. In addition, aluminium P/M parts can be further processed to eliminate porosity and improve bonding yielding properties that compare favorably to those of conventional wrought aluminum products. In the Present work Al-4.5 wt.% Cu alloy powder was consolidated using conventional sintering process at a temperature of 500°C for 2 h in a furnace under controlled atmosphere by varying compaction pressures of 200, 280 and 350 MPa and investigated the Microstructure, Physical and Mechanical properties of the conventional sintered Al-4.5 wt.% Cu alloy, also the effect of compaction pressure on the Microstructure, Physical and Mechanical properties has been discussed.

Modelling the compression behavior of ground tire rubber

The purpose of this paper was to study elastomer powder from crushed used tires (CUTs). In particular, the behavior of the green density of elastomeric powder was analyzed by varying compaction pressure. In the Anglo‐saxon bibliography, this powder is known as ground tire rubber: ground tire rubber (GTR). The density of the tyre was made using a hydrostatic balance, the analysis of grain size using cribbing sieves, and the measures of compression parameters by means of a Universal Testing Machine. The main goal was to obtain a behavior model of ground tire rubber along different compaction pressures. This model was used to predict optimum compaction pressures in order to achieve the highest density. This was the first step to obtain recycled products when sintering processes are applied, evidently if thermal compression was used as a manufacturing process. This established model predicted the evolution of green density versus compaction pressures very accurately.

Reciprocating Wear Behavior of Al Alloys: Effect of Porosity and Normal Load

Aluminum alloys are attractive for critical applications such as pistons, clutch housings and liners in automotive industry for their high strength to weight ratio, high corrosion resistance and good heat conductivity. These alloys can be fabricated using casting and powder metallurgy techniques in which porosity is a common feature. The presences of pores adversely affect the mechanical properties and wear resistance of these components. Not only the total area percentage of porosity influences the degradation in properties but also size, shape and interconnectivity of pores play an important role. In this study, aluminum alloys were produced using powder metallurgy technique. The amount of porosity was varied by varying compaction pressure and amount of wax added before compaction. Reciprocating wear tests (ball-on-flat configuration) were performed against AISI 52100 bearing steel ball under both low (1.5- 5N) and high (6-20N) loads. Scanning electron microscopy was employed in order to identify possible wear mechanisms. Both detrimental and beneficial effects of porosity under different loading conditions were observed. An attempt has been made to develop a relationship between pore size and distribution and wear behavior of aluminum alloys.

Role of hybrid reinforcement on microstructural observation, characterization and consolidation behavior of AA 6061 nanocomposite

The present investigation had dealt with the synthesis, characterization and consolidation behavior of AA 6061 nanocomposites reinforced with hybrid (TiC+Al2O3) nanoparticles with varying weight percentages (0.0, 0.5, 1.0, 1.5 and 2.0wt.%) prepared by 30h of mechanical alloying (MA) and compared with 2wt.% of various reinforcements such as titanium carbide (TiC), multi-walled carbon nanotubes (MWCNTs), gamma phase alumina (γ-Al2O3) nanoparticles. The microstructure, grain size, lattice strain and lattice parameter of the above powders were examined using different analysis techniques including X-ray diffraction (XRD) analysis, scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive spectrometry (EDS). The compressibility and sinterability of the prepared nanocomposites at varying sintering temperatures and varying compaction pressures were also studied. Consolidation behavior in terms of particle rearrangement and plastic deformation mechanisms were evaluated by Balshin, Heckel, Panelli and Ambrosio Filho and Ge linear compaction equations. The effect of hybrid and nanolevel reinforcements on mechanical properties such as green compression strength, Vickers hardness and density of nanocomposites were evaluated. Among the above nanolevel reinforcements, hybrid (TiC+Al2O3) and TiC nanoparticles gave maximum green compression strength (211 and 233MPa) and maximum hardness (985 and 1186MPa) for 2wt.% addition to AA 6061 matrix after 30h of MA.

Microstructural observation, consolidation and mechanical behaviour of AA 6061 nanocomposites reinforced by γ-Al2O3 nanoparticles

AA 6061 nanocomposites of nanocrystallite powders reinforced with nano-alumina particles were synthesized and investigated in this study. A uniform distribution of nano γ-Al2O3 in the AA 6061 nanocrystallite matrix was successfully obtained after 30h of mechanical alloying (MA). The compressibility and sinterability of the prepared nanocomposite powders at varying sintering temperatures and varying compaction pressures was also studied. The consolidation behaviour of the AA 6061/γ-Al2O3 nanocomposites was evaluated using the Balshin, Heckel, Panelli and Ambrosio Filho, and Ge linear compaction equations. The compression strength of the green samples and the Vickers hardness of the nanocomposites were also evaluated. A maximum green compression strength of 176MPa and a maximum hardness of 740MPa were obtained for the addition of 2wt.% Al2O3 nanoparticles to the AA 6061 matrix after 30h of MA.

Densification Behaviour in the Fabrication of Al-Fe Metal Matrix Composite Using Powder Metallurgy Route

Densification behaviour of the powder particles in two- and/or multicomponent system is unpredictable. The present work deals with the densification behaviour of Al-Fe powder particles during compaction and sintering in order to fabricate the Al-Fe metal matrix composites by powder metallurgy route. Green compacts of Al-6.23 wt.% Fe powder particles were fabricated under varying compaction pressures, and these fabricated green compacts were sintered over a series of temperatures (430°C–590°C). The sintered products have been characterised with the help of X-ray diffraction (XRD) and scanning electron microscope attached with energy dispersive spectroscopy (EDS). It has been found that the green density of the compacts increases with increase in compaction pressure. The rate of change in green density is found to be lower at higher compaction pressures. Sintered density increases with increasing sintering temperature up to 550°C whereas a drop in sintered density is perceived at 590°C. This decrease in sintered density is considered to occur due to swelling which has been explained on the basis of the Kirkendall effect. The XRD and EDS analyses of sintered products indicated the presence of Al and Fe particles with the trace amount of intermetallics.

Effect of clamping pressure on ohmic resistance and compression of gas diffusion layers for polymer electrolyte fuel cells

This paper describes the use of an in situ analytical technique based on simultaneous displacement and resistance measurement of gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs), when exposed to varying compaction pressure. In terms of the losses within fuel cells, the ohmic loss makes up a significant portion. Of this loss, the contact resistance between the GDL and the bipolar plate (BPP) is an important constituent. By analysing the change in thickness and ohmic resistance of GDLs under compression, important mechanical and electrical properties are obtained. Derived parameters such as the ‘displacement factor’ are used to characterise a representative range of commercial GDLs. Increasing compaction pressure leads to a non-linear decrease in resistance for all GDLs. For Toray paper, compaction becomes more irreversible with pressure with no elastic region observed. Different GDLs have different intrinsic resistance; however, all GDLs of the same class share a common compaction profile (change in resistance with pressure). Cyclic compression of Toray GDL leads to progressive improvement in resistance and reduction in thickness that stabilises after ∼10 cycles.

Mechanistic investigation on pressure dependency of Heckel parameter

This work proposed to study the influence of varying compaction pressure on the plastic energy, elasticity (Young's modulus), particle yield strength, strain hardening, and applied pressures on derived Heckel parameter using material with different densification and deformation mechanisms: ibuprofen (IBN), paracetamol (PCM) (elastic behavior), methyl cellulose (Me-Cel), microcrystalline cellulose (MCC), sodium chloride (NaCl) (plastic behavior), and dicalcium phosphate (DCP) (brittle fracture). Force–displacement data were captured during in-die compaction for all materials having different deformation behavior. The apparent mean yield pressure (Py), plastic energy, Young's moduli, strain hardening parameter and rate of increase in Py were calculated from force–displacement compaction profiles obtained across a pressure range of 65–260 MPa. Materials under confined compression loading showed pressure dependent biphasic behavior in Py upon increasing pressure from 65 MPa to 260 MPa. IBN and PCM showed pressure dependency due to simultaneous elasticity and strain hardening upon increasing applied pressure. Me-Cel, MCC, and NaCl showed lower pressure dependency while DCP showed higher change in Py upon increasing pressure as a result of higher yield strength of DCP particles. Apparent mean yield pressure from Heckel analysis was significantly affected by the applied pressure, viscoelastic behavior, particle yield strength, and strain hardening. The simultaneously occurring events of elastic deformation and strain hardening give a false increase in Py at higher applied pressures.

Variation of part thickness and compaction pressure in vacuum infusion process

In vacuum infusion (VI), it is difficult to manufacture a composite part with small dimensional tolerances, since the thickness of the part changes during resin injection. This change of thickness is due to the effect of varying compaction pressure on the upper mold part, a vacuum bag. In this study, random fabric layers with an embedded core distribution medium is used. The thickness of the composite part and resin pressure are monitored using multiple dial gages and pressure transducers; the results are compared with the model developed by Correia et al. [Correia NC, Robitaille F, Long AC, Rudd CD, Simacek P, Advani SG. Analysis of the vacuum infusion molding process: I. Analytical formulation. Composites Part A: Applied Science and Manufacturing 26, 2005. p. 1645–1656]. To use this model, two material characteristics databases are constructed based on the process parameters: (i) the thickness of a dry/wet fabric preform at different compaction pressures, and (ii) the permeability of the preform at different thicknesses. The dry-compacted preform under vacuum is further compacted due to fiber settling in wet form after resin reaches there; the part thickens afterwards as the resin pressure increases locally. The realistic model solution can be achieved only if the compaction characterization experiments are performed in such a way that the fabric is dry during loading, and wet during unloading, as in the actual resin infusion process. The model results can be used to design the process parameters such as vacuum pressure and locations of injection and ventilation tubes so that the dimensional tolerances can be kept small.

Development of porous ceramics with well-controlled porosities and pore sizes from apatite fibers and their evaluations.

Porous hydroxyapatite (HAp) ceramics possessing well-controlled porosities and pore sizes were developed by firing apatite-fiber compacts mixed with carbon beads and agar. The total porosities could be controlled in the range from 40 to 85% by varying compaction pressure (20-40 MPa), firing temperature (1000-1300 degrees C) and carbon/HAp ratio (0/10-10/10 (w/w)). Most of the pores were regarded as open pores. The pore sizes were mainly affected by the carbon-bead diameter (5, 20 or 150 microm) and partly by the compaction pressure and the firing temperature. The pore sizes of the porous HAp ceramics derived from the carbon beads of 150 microm in diameter were distributed in the two separate ranges of several micrometers and more than 100 microm.

Tuning of the microstructure and electrical properties of SOFC anode via compaction pressure control during forming

We developed an innovative processing technology, liquid condensation process (LCP) to produce thin and large size anode substrate with very high uniformity which allowed easy manipulation of the microstructure and/or pore structure of anode substrate. The anode substrate made with LCP had very homogeneous microstructure, which would be helpful to induce homogenous physico-chemical properties of the anode substrate. Microstructure of anode substrate was critically evaluated in terms of pore structure development by varying compaction pressure. According to electrical and microstructural characterizations of the anode substrate, the physico-chemical properties of the anode substrate including gas permeability and electrical conductivity were closely related with the microstructure and/or pore structure of anode substrate. Proper method to manipulate the processing variables to control the microstructure of anode substrate to achieve superior performance of solid oxide fuel cell was discussed.

Effect of Compaction Pressure on the Microstructure Evolution of Anode Substrate for SOFC Application

Ni/YSZ cermet anode is required to satisfy various properties as a key component of anode-supported type SOFC, since the cell performance is dependent upon anode properties. Ni/YSZ anode, with complicated structural features, consists of three different phases such as metallic Ni, YSZ ceramic and pores. The correlation between those structural features makes it difficult to independently optimize individual function of anode such as gas permeability, electrical conductivity and electrochemical activity. Microstructure of anode substrate was evaluated in terms of pore structure and metallic phase development by varying compaction pressure. The resulting pore structure went through a gradual transition, which was correspondingly reflected in gas permeability and electrical conductivity of anode substrate. An effort to establish structure-property-processing correlation has been made in this study to achieve improved anode performance.

Static pressing of ferrite plates

1. Over the compaction-pressure range investigated the mechanical properties of multihole ferrite plates increase with rising pressure. The best results were recorded at a pressure of 8 tons/cm2. 2. The coercive force of ferrite plates is strongly affected by compaction pressure. At constant chemical composition corresponding to ferrite 2VT it is possible to alter the coercive force from 2.2 to 1.5 Oe by varying compaction pressure. 3. The coefficients of rectangularity and squareness of the hysteresis loop are strongly affected by compaction-pressure variation at low pressures (up to 3.5 tons/mm2, but remain virtually constant at higher pressures.