Low Compaction Pressure Research Articles

Balanced die method for metal powder compaction

AbstractDramatic reduction of ejection forces in a metal powder compaction process has been achieved using a balanced die method. The approach uses a toolset consisting of a thin walled die in a fairly rigid metal, with a rubber sleeve capable of transmitting high radial pressure. By maintaining a pressure balance between internal compaction pressure and external ‘bolstering’ pressure across the thin wall die, the ejection forces were reduced to almost zero. With limited equipment available, the compaction process was carried out in incremental stages to produce cylindrical metal billets of 32 mm diameter by 20 mm height. Green densities of 6·49 Mg m−3 were achieved for NC100 iron powder supplied by Hoganas at much lower compaction pressure than those reported elsewhere. PM/0711

Characterization of Compressibility and Compactibility of Poly(ethylene oxide) Polymers for Modified Release Application by Compaction Simulator

Poly(ethylene oxide) polymers (PEO) appear to have great potential for controlled release applications. These polymers are hydrophilic with good water solubility, low toxicity, and high swelling capacity. As part of formulation optimization for a large-scale solid dosage form production, physicomechanical characterization of PEO was undertaken using a compaction simulator. Heckel plots for all PEOs were constructed, and yield pressures (Py) at different punch velocities were calculated from the linear portion of the plots. Low Py values, increase of Py with increasing punch speed, upward curvature of the plot, and strain rate sensitivity values indicate that the densification process and consolidation mechanism for PEOs of various molecular weights (0.2 × 106 to 7 × 106) are identical and follow plastic deformation. PEOs have a high degree of crystallinity (57–85%) and show significant axial recovery (15–25%) upon decompression and ejection. The low Py values (58–78 MPa) and low mean compaction pressures demonstrate that volume reduction (compressibility) under pressure is excellent. However, due to viscoelastic behavior and large axial expansion, tablets of relatively low tensile strength are produced. These observations suggest the need to blend PEO with highly compactible excipients in order to produce tablets on a high-speed production press.

The surface topography of compacted agglomerates; a means to optimize compaction conditions

The measurement and quantification of the surface topography of single-ended die-pressed cylindrical compacts, prepared using agglomerated alumina powders at various values of compaction pressure and cylinder aspect ratio, are described and a means to study the deformation and breakdown of the agglomerates at the die walls is evaluated. A specially constructed non-contacting laser scanning profilometer, with associated hardware and software, is described and has been used to obtain the surface topographical profiles of the green alumina compacts. Selected data are reported and interpreted using conventional roughness parameters, autocorrelation functions, and bearing area curves. These computed parameters are used to elucidate the deformation characteristics of the agglomerates within the compacts. The deformation of the alumina agglomerates, at the planar (upper and lower) surfaces of the compacts, commences at very low compaction pressures and the inter-agglomerates surface pores are eventually annihilated at relatively high compaction pressures. The optimum normal pressure for the elimination of these inter-agglomerate surface pores, in the present alumina system, was determined as 74 MPa. The results obtained from the curved surface profiles of the compacts, as a function of the distance from the compression sourc,, show that the wall normal pressure distribution, along the height of the compact, decreases exponentially as a function of the height of the compact (from top to bottom).

Influence of pore structure in green compacts on the densification of SiCAl 2O 3Y 2O 3

Pore size, pore size distribution (PSD), and the resultant densification behavior of α-SiC granular compacts, which were shaped under the uniaxial compaction pressure of 6.8–154 MPa, were investigated. Three kinds of SiC granules were used, namely Powder R (as-received spray-dried granules), Powder C (after classification of the Powder R), and Powder G (after grinding of the Powder R). Experimental results showed that at low compaction pressures, the green compacts derived from Powder R and Powder C exhibit a bimodal PSD, which is primarily caused by the presence of intergranular porosity. At relatively high compaction pressures, all of the green compacts display a roughly similarly unimodal PSD and exhibit a similar densification behaviour regardless of the starting granule characteristics. The green compacts with a narrow and unimodal PSD can be easily densified to a high-density sintered body and this behaviour was particularly pronounced for the green compacts derived from the ground granules even when the applied compaction pressure is relatively low.

Balanced Die Method for Metal Powder Compaction

Dramatic reduction of ejection forces in a metal powder compaction process has been achieved using a balanced die method. The approach uses a toolset consisting of a thin walled die in a fairly rigid metal, with a rubber sleeve capable of transmitting high radial pressure. By maintaining a pressure balance between internal compaction pressure and external ‘bolstering’ pressure across the thin wall die, the ejection forces were reduced to almost zero. With limited equipment available, the compaction process was carried out in incremental stages to produce cylindrical metal billets of 32 mm diameter by 20 mm height. Green densities of 6·49 Mg m−3 were achieved for NC100 iron powder supplied by Höganäs at much lower compaction pressure than those reported elsewhere. PM/0711

3-D profiles and surface topography of alumina compacts

A non-contacting laser scanning profilometer, with associated hardware and software, is used for the determination of the overall shape and surface topography of cylindrical alumina compacts. The change in the shape distortion of the cylinder, defined as (R max-R min)/R min (R is the radius of the compact), was monitored, as a function of the ambient temperature, during sintering.During sintering, an increase in the diameteral distortion values were observed. Certain surface topographic characteristics , also obtained by the laser scanning of the surfaces of the green compacts, were used to characterise the agglomerate deformation and breakdown. The deformation of agglomerates starts at very low compaction pressures. However, the inter-agglomerate pores are not eliminated until a compaction pressure of 37 MPa.

衝突，圧縮，粉砕に伴う三酸化二アンチモン粒子の性状変化

The morphological changes of particles through three different processes (impaction, compaction and grinding) were investigated experimentally. This was done using two types of antimony trioxide (Sb2O3)-fine particles which have almost the same particle size distributions but different surface properties. One has the sulfate group (-SO4) on the surface; the other does not.It is found that the diameter of the Sb2O3 particles having -SO4 begins to increase at lower impaction velocity or at lower compaction pressure than those having no -SO4 does. Estimation of the load applied on a single particle through these two processes reveals that the threshold of the load inducing the particle enlargement is almost the same for impaction and compaction.The tendency for the diameter to change through grinding is opposite to that through impaction or compaction. However, the Sb2O3 particles having -SO4 keep higher crystallinity than those having no -SO4 among these three processes.

The effect of the compaction pressure on the microwave surface resistance of the Pb doped BSCCO system

Microwave surface resistance is analyzed in Bi-based sample superconductors prepared under different compaction pressures (250 to 1500 MPa). The measurement is performed with the help of a new automatic measuring system based on a resonant cavity. It was found that the best results are obtained for samples initially sintered at low compaction pressure, then crushed and resintered for a short time at larger pressure.

アルミナ粉末の造粒とプレス成型

In general manufacturing process of ceramics with dry compaction, quantitative analysis of each element of the process and of whole process is necessary. In this study, it is clearified that the diameter of spray-dried granulated Al2O3 particle can be controled effectively by choosing rotation rate of atomizer. We showed that apparentdensity of green-compact is greatly influenced by apparent density of granulated Al2O3 particle, especially at low compaction pressure. Both granulated Al2O3 particle and the green-compact have higher density, if concentration of slurry is relative high. And then, only density of sintered Al2O3 jumps up at about 57 wt%. So. we decide that the optimum concentration is 57.0 wt%, where there is no problem on this condition.

Compression characteristics of granulated materials II. Evaluation of granule fragmentation during compression by tablet permeability and porosity measurements

Lactose was granulated with 5% (w/w) polyvinylpyrrolidone as a binder with a wet massing-screening procedure. Fourteen granulations were produced by using different amounts and types of solvent for the binder during the agglomeration procedure. After the granulation, the size fraction 500–710 μm was separated from each granulation for investigation. The granules were characterised on water and binder content, and granule porosity and friability. Both the porosity and friability of the granules were affected by the process conditions. However, there was no correlation between these parameters, which indicates that one surface property of the granule i.e., the ability to withstand attrition, can be different from the overall granule strength. The volume reduction behaviour during compaction was evaluated by measuring tablet permeability and tablet porosity as a function of compaction pressure. The results indicate that the granules became denser at low compaction pressures. It is therefore difficult to use the changes in porosity with compaction pressure as a measure of the degree of granule fragmentation during compression. The tablet permeability as a function of compaction pressure varied among the granulations which indicates that the ability to break down during compression, i.e., the granule fragmentation, varied. It is suggested that changes in tablet permeability with compaction pressure can be used as a measure of this property. The difficulty of defining the intergranular pore space in the tablet will affect the calculation of the tablet surface area. However, the results indicate that in the pressure range used for the permeametry measurements, the total porosity is probably fairly close to the intergranular pore space. Thus, it is suggested that surface area—compaction pressure profiles give a reasonable estimate of the degree of granule fragmentation during compression.

Investigation des mécanismes de liaison impliqués dans la cohésion des compacts a usage cosmétique

Synopsis In cosmetology eye shadows are often presented as pressed powders. The pressed powder studied contains about 80% of lamellar substances such as talc and titanised mica, pigments, preservatives and a liquid binder which is a mixture of lipophilic substances. Usually cohesion in compacts is obtained by establishing bonds between dry particles; on the contrary in the case of pressed powder in the presence of a liquid binder one can suppose that all particles are covered before compaction with a thin layer of liquid, so that the binding mechanism must be different to that for dry compacts. The aim of this study is to verify this hypothesis using (i) investigation of the energy of compaction by measuring the total energy balance during compaction; (ii) a resistance evaluation by a drop test; (iii) indentation hardness measurements. Among the different energy terms the network of compaction is representative of the formation of the bonds between particles and also of particle fragmentation or deformation occurring during compression. The results show that the network of compaction is influenced by the binder level, but the resistance is not proportional to the network. This indicates that the network of compaction, as it has been measured or calculated, is not able to predict the resistance of the compacts. However, a direct relation, independent of the binding level, has been found between network of compaction and indentation hardness. It means that indentation hardness is rather more indicative of the compact deformation under a low loading rate than of the resistance to rupture, which implies a high loading rate. However, the binder level is of paramount importance: the rupture resistance increases when the quantity of binder is increased. The rheological properties of the liquid binder are also important. The effect of a variation of the binder viscosity upon the compact cohesion is important, especially at low compaction pressures (<8 MPa); at higher pressures the viscosity influence is less drastic, suggesting a change of the banding mechanism. However, viscosity is only one aspect of the medogid properties of the binder. The rheological behaviwr is shown to be thixotropic so that shearing time aid relaxation time become an importnnt parameter for cohesion and resistance. This conclusion is of importance for the formulation. Those two facts throw light on the cohesion mechanism of pressed powder. The banding of the particles seems to be essentially due to the presence of the liquid binder. Capillarity forces or viscosity forces, depending on the binder rheology, am responsible for the properties exhibited by pressed powder. Finally, one can conclude that the pressed powders form damp powder-eompacted systems whose binding mechanism is very different from those involved in pharmaceutical compact cohesion, so that a good formulation must involve a complete study of the rheological properties of the binder.

Studies of smectite membrane behavior: Temperature dependence, 20–180°C

A brine 5.0 molal in NaCl and 0.45 molal in CaCl 2 was forced through random-fabric clay cakes, 1.0 to 1.6 cm thick, prepared from the 0.25–2.7 μm diameter size fraction of Cheto montmorillonite from Chambers, Arizona. Runs were made at 20°, 95°, 140° and 180°C using a compaction pressure of 34.5 MPa (5000 psi), an upstream fluid pressure of 22.8 MPa (3300 psi), and a downstream fluid pressure of 8.96 MPa (1300 psi). An additional run was made at 140°C, a compaction pressure of 68.9 MPa (10,000 psi), an upstream fluid pressure of 39.0 MPa (5650 psi), and a downstream fluid pressure of 25.3 MPa (3650 psi). At constant fluid flow rate, the molal filtration efficiencies of both Na + and Ca 2+ increase with temperature, the latter more rapidly. The effect of compaction pressure is shown by comparing the two runs at 140°C: the filtration efficiency for Ca 2+ at the higher compaction pressure was twice that at the lower compaction pressure; for Na +, it was 60% greater. At the slower flow rates found in nature, it appears that Ca 2+ must be retained preferentially relative to Na + in virtually all sedimentary environments, with the Ca 2+ preference increasing with increasing temperature. The apparent membrane enrichment for the heavy oxygen isotopes of throughput water molecules observed at 140°C is 0.15%. and that at 180°C is 0.05%., values that are opposite in sign to those reported in the literature for 20°C. This apparent shift in enrichment with temperature is 4 to 5 times the room-temperature salinity correction, but the reliability of the shift value is reduced by the possibility in the high-temperature runs of exchange between brine and clay, which would also make the brine isotopically heavier. Observed changes in filtration efficiency of Ca 2+ and Na + with temperature and fluid velocity can be explained qualitatively using arguments involving fluid viscosity and hydraulic drag. The newly-designed membrane press used in the study performed adequately at temperatures up to 180°C, but failed in several respects at 220°C.

The consolidation kinetics of amorphous Ni 80P 20 powder under warm pressing

The kinetics of the consolidation by warm pressing of amorphous powders of composition Ni 80P 20 has been studied from room temperature to 250°C and for compaction pressures ranging from 0.1 to 0.8 GPa. The kinetics are described in terms of an effective viscosity that varies with T according to an Arrhenius law. The powder shows a non-newtonian behaviour even for low compaction pressures. The dependence of the Vickers hardness and density on pressure and temperature is reported.

Investigation of the hydraulicked layer of a high-grade loess soil fill

1. The hydraulic fill layer of loess soil in its central section is characterized by the following features: a) It possesses complete water saturation over the whole depth; b) with increasing depth, the density of the poured soil increases and, accordingly, the moisture content diminishes; each depth has its corresponding density and moisture content; c) the top 3-m of the layer takes the form of a soil mass with moisture contents above the yield point (W=34–60%), being a small layer of poured soil with a low compaction pressure. This layer must be artificially dewatered if the hydraulic-fill structure has to be brought quickly into service. 2. The density and moisture content of the soil through the depth of the hydraulic-fill layer in its central section, starting from 3 m and lower, can be determined from the data of compression tests on the soil mass, assuming a depth of hydraulic fill numerically equal to the compaction pressure in accordance with Eqs. (9) and (10). 3. Prolonged stoppage of hydraulicking has an unfavorable effect on compaction of freshly poured layers and continuous pouring over the height favors more solid placing of the soil in the structure. 4. Stability of the outer slopes of the hydraulic fill during construction, starting from a depth of 3–4 m from the hydraulic-fill surface and lower, should be carried out by the usual methods of soil mechanics, disregarding fluidity of the core and pore pressure. For the layer from the hydraulic-fill surface to a depth of 4–5 m, where the freshly poured soil is unstable and presses on the side shells like a heavy liquid, the strength calculation has to be carried out for the dry embankments.

Densification behavior of Fe, Co, and Ni powders with additions of zirconium, niobium, and molybdenum carbide powders

1. The densification behavior of Fe-ZrC, Fe-NbC, Fe-Mo2C, Ni-ZrC, Ni-NbC,Ni-Mo2C,Co-ZrC, Co-NbC, and Co-Mo2C mixtures was investigated. It was observed that increasing the carbide content of mixtures intended for pressing raises their porosity at pressures above 10–15 kg/m2 and lowers it at lower compaction pressures. 2. The dependence of the density of compacts on compaction pressure and carbide content was established. It was found that the magnitude n, which appears in Eq. (1), is a linear function of the amount of the second component over a wide range of carbide contents of a mixture. The magnitudes n0 and K0 in Eq. (4) are determined by the physicomechanical properties of the mixture components. 3. It was demonstrated that the presence of a lubricant (solution of synthetic rubber in benzine) exerts no significant influence on the value of n and on its rate of variation, i.e., on the value of K0. 4. The effects of compaction pressure and the amount of a second component on compact porosity was studied. A hypothesis is advanced postulating that the same mechanism controls the deformation of sintered metal-powder materials and the deformation of powders subjected to densification in a closed die in the second stage of compaction.

Investigation of lateral pressure at small compaction forces

1. An installation has been developed for measuring the lateral pressure of powders at small compaction pressures. It was established that, at low compaction pressures (2–42.5 daN/cm2), the coefficient of lateral pressure is constant and practically independent of powder particle size. 2. The coefficients of lateral pressure were determined for powders of Kh17N2, Kh18N15, and 1Kh18N9T stainless steels, copper, tin, tungsten, molybdenum, chromium, aluminum, iron, and titanium, as well as for hydrate, carbonyl, and electrolytic nickel powders. The highest value of the coefficients of lateral pressure (0.39) is exhibited by tungsten, molybdenum, and tin powders, and the least value (0.33) by Kh18N15 stainless steel powder. 3. In spite of the pronounced porosity of powders in this range of compaction pressures, the values of the coefficients of lateral pressure are high. For instance, for the iron powder produced by the Sulinsk Factory the mean value of ɛ is 0.35, which is very close to the values obtained in measurements of the lateral pressure of iron powder at high compaction pressures [1, 2]. Equation (3) may be employed for the approximate determination of the coefficient of lateral pressure at small compaction forces.