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Compaction Pressure (compaction + pressure)
Selected AbstractsStudy on Crack-like Pores of Al Foams Made via the Powder-Metallurgy Route,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2010Lei Wang Mechanisms for the formation and disappearance of the crack-like pores generated during the early stage of Al foaming are investigated. A model for their disappearance process is proposed for the first time. The stress, perpendicular to the compaction direction in uniaxial cold compaction, is caused by the interaction of the Al powder under a high compaction pressure and is the main reason for the formation of the crack-like pores. The results of the model analysis and theoretical calculations suggest that the pressure difference ,P between the initial, round bubbles and the crack-like pores is the driving force for their disappearance. The rapid reduction of ,P is attributed to the decomposition characteristics of the TiH2 powder. [source] Transforming powder mechanical properties by core/shell structure: Compressible sandJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2010Limin Shi Abstract Some active pharmaceutical ingredients possess poor mechanical properties and are not suitable for tableting. Using fine sand (silicon dioxide), we show that a core/shell structure, where a core particle (sand) is coated with a thin layer of polyvinylpyrrolidone (PVP), can profoundly improve powder compaction properties. Sand coated with 5% PVP could be compressed into intact tablets. Under a given compaction pressure, tablet tensile strength increases dramatically with the amount of coating. This is in sharp contrast to poor compaction properties of physical mixtures, where intact tablets cannot be made when PVP content is 20% or less. The profoundly improved tabletability of core/shell particles is attributed to the formation of a continuous three-dimensional bonding network in the tablet. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4458,4462, 2010 [source] Influence of crystal structure on the tableting properties of n -alkyl 4-hydroxybenzoate esters (parabens)JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2007Yushi Feng Abstract Certain crystallographic features, such as the existence of slip planes, can greatly facilitate the ability of crystals to deform plastically. An investigation of the relationship between the slip planes and the tableting performance of the crystals of methyl, ethyl, n -propyl, and n -butyl 4-hydroxybenzoate (parabens) was conducted. The absence of slip planes in methyl paraben crystal structure results in significantly poorer tableting performance than the other three parabens. While slip planes are present in the crystal structures of ethyl, propyl, and butyl parabens, they exhibited different plasticity as confirmed by crystal free volume analysis, crystal nano-indentation hardness, and Heckel analysis. Sieved fraction, 150,250 µm, of each paraben powder was compressed into tablets under different conditions. Tablet tensile strength, porosity, and Indices of tableting performance (ITP) were obtained. Under the same compaction pressure, tablet tensile strength was higher for crystals with higher plasticity. Tableting performance, assessed using the ITP, also improved with increasing crystal plasticity. The results confirm that high levels of plasticity, which can result from the presence of slip planes in crystal lattice, plays a critical role in the formation of strong and intact tablets by means of powder compaction. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 3324,3333, 2007 [source] Differential Sintering by Improper Selection of Sintering Parameters during Pulse Electric Current SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2004D. Doni Jayaseelan Recently, we reported on the retention of fine-grained micro-structure in Al2O3/3 vol% 3Y-ZrO2 composites using the pulse electric current sintering (PECS) technique. It was demonstrated that a high heating rate is beneficial for the retention of fine grains and homogeneous microstructure. As there are few reports on microstructural inhomogeneity and excessive grain growth in compacts densified by the PECS technique, we carried out a series of experiments on monolithic alumina by varying the sintering parameters and discussed the characteristic results. All specimens that were densified under selective sintering conditions attained high density (,99% of the theoretical density) at 1250°3C in > 5 min. The average fracture strength of monolithic alumina was observed to be 741 ± 25 MPa and the fracture toughness was 2.2 MPa.m <1/2, and these were reasoned out to small grains. However, compacts sintered under very low compaction pressure attained ,92%-93% of the theoretical density, and these specimens had undesirable microstructural inhomogeneity owing to differential sintering. Hence, in the present study, we address the problem of differential sintering. [source] Modeling and analysis of thickness gradient and variations in vacuum-assisted resin transfer molding processPOLYMER COMPOSITES, Issue 5 2008Jing Li As vacuum-assisted resin transfer molding (VARTM) is being increasingly used in aerospace applications, the thickness gradient and variation issues are gaining more attention. Typically, thickness gradient and variations result from the infusion pressure gradient during the process and material variations. Pressure gradient is the driving force for resin flow and the main source of thickness variation. After infusion, an amount of pressure gradient is frozen into the preform, which primarily contributes to the thickness variation. This study investigates the mechanism of the thickness variation dynamic change during the infusion and relaxing/curing processes. A numerical model was developed to track the thickness change of the bagging film free surface. A time-dependent permeability model as a function of compaction pressure was incorporated into an existing resin transfer molding (RTM) code for obtaining the initial conditions for relaxing/curing process. Control volume (CV) and volume of fluid (VOF) methods were combined to solve the free surface problem. Experiments were conducted to verify the simulation results. The proposed model was illustrated with a relatively complex part. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source] Compaction of fiber reinforcementsPOLYMER COMPOSITES, Issue 3 2002Gibson L. Batch In resin transfer molding, dry fiber reinforcements are compacted as the mold closes before injection of a curable resin matrix. This paper presents experimental data of compaction pressure as a function of fiber volume fraction. Data are presented for woven roving mats, random fiber mats, loose fiber rovings for pultrusion, and uniaxial or biaxial roving mats. These data are fit to a mathematical model derived in an Appendix. Experimental data are also given for six combinations of reinforcements. We use the compaction model of each constituent layer to predict the average volume fraction assuming that fiber layers do not interact. However, we see that most combinations of reinforcements have fiber volume fractions greater than expected at pressures under 50 psi, indicating a synergistic packing between the layers of different composition. [source] Effect of Externally Applied Plasticizer on Compaction Behavior of Spray-Dried PowdersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Sreeram Balasubramanian The effects of an externally applied plasticizer on compaction behavior and green microstructure quality of spray-dried powders was investigated. The plasticizer was applied to the external surfaces of already spray-dried powders by spraying it on tumbling spray-dried granules. The apparent yield point of the spray-dried powder was reduced when the plasticizer was added. Microstructures of compacts made from these granules (with and without the externally applied plasticizer) were compared at different compaction pressures. Better knitting across granule interfaces and fewer defects were obtained for the granules with the externally applied plasticizer. [source] Effect of Internal Lubricants on Defects in Compacts Made from Spray-Dried PowdersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002Sreeram Balasubramanian The role of internal lubricants in the closure of large intergranular pores during dry-pressing was investigated. Alumina was spray-dried with and without an internal lubricant to yield granules with similar characteristics other than lubricant effects. Green and sintered microstructures were evaluated at different compaction pressures. The defects were quantified by evaluating the fracture surface of ,90% dense sintered compacts. The samples that contained an internal lubricant had higher green densities and fewer defects at comparable compaction pressures. The internal lubricant did not cause any significant reduction in green strength or increase in springback. [source] | ||||||||||