Homogeneity Of Feedstock Research Articles

Buckwheat waste depolymerization using a subcritical ethanol solution for extraction of bioactive components: from the laboratory to pilot scale

Buckwheat waste (BW) is rich in bioactive components such as antioxidants and saccharides. To effectively extract these compounds, subcritical ethanol solution treatment (SEST) was conducted from laboratory to pilot scale. Extraction at 80 °C with hot water and ethanol solutions, and at 120 °C with subcritical water and subcritical ethanol solutions were evaluated in laboratory scale. Then, the SEST was scaled up to the pilot level using a batch reactor with a volume scale factor of 1000. Degradation of lignin and dissolution of extractives increased the total phenolics yield. The increase in the temperature led to the degradation of some flavonoid components. Reducing sugars were mainly present as polysaccharides because of the low extraction temperature. Water and ethanol exhibited synergistic effects under subcritical conditions, which resulted in degradation of more lignin and extraction of more bioactive components than hydrothermal extraction, while retaining cellulose and hemicellulose. In the pilot-scale experiment, the total yields of phenolics, flavonoids, and reducing sugars were 29.8 ± 0.1, 13.9 ± 0.5, and 33.9 ± 0.5 g/kg, respectively. The turbidity and Brix values of the liquid samples obtained by SEST were high because of breakdown of the structure of the BW and the dissolution of the bioactive components. Additionally, compared with the laboratory scale, better results were obtained on the pilot scale because of greater feedstock homogeneity and equipment parameters. SEST is a promising approach that could be used on the pilot scale to depolymerize BW and extract bioactive components.

A new model for predicting the flow properties of Ti-6Al-4V-MIM feedstocks

Titanium and its alloys have high specific strength and high resistance to corrosion but are expensive to manufacture. Manufacturing cost can be reduced by using metal injection moulding (MIM) to produce near-net shaped intricate parts. Feedstock rheology affects feedstock homogeneity, injection moulding and quality of the MIM parts. Methods to quickly obtain these rheological parameters will help optimise processing conditions and hence decrease manufacturing cost. Feedstocks were produced from hydride-dehydride titanium alloy powder and binder containing polyethylene glycol, polyvinyl butyral and stearic acid using a four-stage mixing process. Feedstock rheology and morphology were investigated using a capillary rheometer and a scanning electron microscope. A new model, which incorporates a newly defined parameter, feedstock flow index (p), was developed for predicting the rheological properties of titanium-based feedstocks using shear stress and melt flow rate. The MRF value, obtained from these low-cost rheological tests predicted HDH Ti-6Al-4V-MIM feedstock flow properties well.

The effect of debinding and sintering parameters on the mechanical and microstructural properties of Fe-2Ni metal injection molded compacts

This paper investigates the effect of debinding and sintering parameters on the density, ultimate tensile strength (UTS), hardness and grain size of the Fe-2Ni MIM compact. For this purpose, a wax-based binder system containing PE, PP, PW and SA was adopted for developing the feedstock. After optimizing the feedstock powder loading based on the critical solids loading and studying the homogeneity of feedstock, green parts were injected. The samples were then immersed in the n-hexane solution for different times to investigate the effect of debinding time on the weight loss of binder system. After observing the samples shrinkage behavior, sintering temperatures were selected and the samples were sintered at temperatures of 1050, 1125, 1200, 1275 and 1350 °C. Finally, the microstructure, density and hardness of the sintered samples were evaluated and the UTS of the samples was measured using the DIC technique. The results showed that immersion of samples for 12 h in n-hexane with 50 °C temperature applied as optimum parameters for solvent debinding. In addition, appropriate thermal debinding cycle was designed through the TGA analysis to produce flawless samples. It was observed that the density increases with the sintering temperature increasing, until where in the temperature of 1350 °C the relative density was 97.2%. UTS and hardness values of the sintered samples increased to (∼548 MPa) and (∼144 HV) for the sintered specimen at 1275 °C and decreased at higher temperature. This phenomenon relates to the substantial grain growth in the sintered sample at 1350 °C, as proved by the results of EBSD analysis. Finally, proper sintering condition for Fe-2Ni samples derived through the density, UTS, hardness and microstructural evaluations, so that sintering of the samples at 1275 °C under hydrogen atmosphere showed the optimum condition due to an excellent balance between the mechanical properties and grain size in the samples.

Fabrication and properties of Si3N4 based ceramics using combustion synthesized powders

Silicon nitride (Si3N4) based ceramics were fabricated with β-SiAlON and Si3N4 powders synthesized by combustion synthesis method via power injection molding (PIM). In the PIM process, the solids loading for each material was first determined from the results of the torque rheometer experiment. The mixing process was repeated to produce the homogeneous feedstock, and homogeneity of feedstocks was evaluated by observing the shear viscosity with time at a constant shear rate. The rheological behavior of feedstocks was investigated using capillary rheometer. It found that both feedstocks have no problem in injection molding. The binder decomposition behavior was also investigated, and a wax-polymer binder system was nearly removed by the optimized solvent and thermal debinding processes. Thereafter, the debound samples were sintered at 1750 and 1800 °C for 4 h in nitrogen atmosphere. Regardless of sintering temperature, the relative density of higher than about 96% was achieved. When comparing mechanical properties including bending strength, Vickers hardness and fracture toughness, Si3N4 with 2 wt% Y2O3 and 5 wt% Al2O3 (Si3N4+2Y5A) had higher values than β-SiAlON with 4 wt% Y2O3 (β-SiAlON+4Y) regardless of sintering temperature. It was supported by observing the microstructures of the plasma-etched samples.

Effect of nanoparticles in bimodal powder on physical and mechanical properties of powder injection molded parts

This paper presents investigation of how nanoparticles in bimodal powder that contains both nanoparticles and microparticles affect the physical and mechanical properties of injection-molded parts. As the starting materials, a pure-micropowder, and three different nano/micro-bimodal powders were prepared and mixed with a wax-based binder system. Addition of nanoparticles slightly decreased the critical solids loading and the feedstock homogeneity, and significantly increased the flexural strength and strain of green bodies. Addition of nanoparticles increased the density, decreased the grain size and provided superior surface finish of the sintered samples, and thereby improved their mechanical properties. The Vickers hardness of the samples increased as the nanoparticles content increased. Tensile strength was also improved by addition of small amounts of nanoparticles. However, the large passivation area of the nanoparticles raised the oxide content in the bimodal powder samples and degraded the strength and elongation. As a result, tensile strength was the highest in the sample fabricated from the bimodal powder that contained 12% nanoparticles.

Influence of nano powder on rheological behavior of bimodal feedstock in powder injection molding

Rheological behavior of feedstock, which highly affects the condition of green body, is substantial issue in powder injection molding process. In this paper, the influence of nano powder contents in bimodal feedstock on solids loading and rheological behavior has been investigated. The bimodal powders were fabricated with 100nm and 4μm sized 316L stainless steel powders, and mixed with wax-based binder system. The critical solids loading for each powder was measured by torque rheometer. In order to analyze net effect of nano powder ratio, all feedstocks were formulated as solids loading of 42vol.%. Feedstock homogeneity was evaluated by rotational rheometer. Capillary rheometer test was conducted to measure the viscosity of feedstock with different temperatures, shear rates and nano powder ratios. Rheological parameters, like flow index, flow activation energy and moldability index, were calculated based on the capillary rheometer test. The results indicated the critical solids loading and feedstock homogeneity decreased as nano power ratio increased in bimodal feedstock. Rheological parameters were also affected by nano powder ratio, and the optimal mixing ratio of nano powder for moldability index was investigated as 12vol.%.

Effect of a mild torrefaction for production of eucalypt wood briquettes under different compression pressures

The heat treatment of wood (i.e. torrefaction) followed by densification of wood particles (e.g. by briquetting) may be used as a process to improve homogeneity and energy properties of wood for use as a solid fuel. The wood of Eucalyptus grandis and Eucalyptus spp. were treated at 180, 200 and 220 °C for 60 min under a nitrogen atmosphere. Briquettes were produced with untreated and heat-treated wood particles using 120 °C, for 7 min pressing and 6 min cooling time, under pressures of 6.9, 10.3 and 13.8 MPa. The briquetting compacting pressure showed no significant influence on the briquettes properties. Briquettes density was similar for all cases presenting 1.14 g cm−3 for Eucalyptus spp. and 1.06 g cm−3 for Eucalyptus grandis wood. A mild torrefaction of the wood at 200–220 °C increased the potential energy of the particles and briquettes, showing an improvement in their density, dimensional stability and hygroscopicity. Briquettes produced from heat-treated Eucalyptus spp. wood presented higher energy density (24.79 GJ m−3) at 200°C-treatment when compared with untreated wood (20.76 GJ m−3). Regarding E. grandis, briquettes produced with heat-treated (200 °C) particles showed only a marginal higher energy content than with untreated wood, 21.70 GJ m−3 and 21.38 GJ m−3, respectively. The two eucalypt woods showed differences regarding the heat treatment and briquetting, pointing out that the optimization of these processes should be specific for each species. However, a mild torrefaction of the wood particles decreased the differences between materials which might be useful as a process to increase feedstock homogeneity when using mixed raw-materials.

Effects of process parameters on quality of ultrafine WC/12Co injection molded compacts

Abstract The effects of process parameters for ultrafine WC/12Co cemented carbide powder injection molding (PIM) on quality of molded compacts were investigated in this study. The quality characteristics are divided into compacts' appearance, flexural strength and density. The Taguchi method and ANOVA were taken to optimize the process parameters and to identify the most significant factors. The experimental results revealed that the flexural strength of injection molded compacts is significantly affected by all of chosen injection parameters. The sensitivity of flexural strength is closely related to the characteristics of binder. The density of compacts is mostly affected by injection pressure. The stability of density is attributed to the homogeneity of feedstock and the wettability between organic binder and WC/12Co powder mixture. It is found that, in a certain degree, the flexural strength of compacts is higher with the density increasing. Thus, the flexural strength is chosen as the main quality characteristic of injection molded compacts. It is proved by the confirmation experiments that the statistical model used to predict the value of flexural strength of compacts is reliable.

Fabrication of zirconia-toughened alumina parts by powder injection molding process: Optimized processing parameters

Abstract Zirconia-toughened alumina (ZTA) parts were fabricated by using a powder injection molding process that utilizes a multi-component binder system based on high-density polyethylene, paraffin wax, and stearic acid. The entire aspect of the manufacturing process, which includes mixing, injection molding, debinding, and sintering, were optimized in this study. ZTA powder was mixed with binders at powder loading ranging from 53 vol% to 59 vol%. The optimum powder loading was determined by analyzing the rheological properties and homogeneity of feedstocks. During injection molding, the temperature and injection pressure parameters were manipulated to obtain optimum density results. A two-stage debinding process (solvent and thermal) was used to remove binders in green parts. Debound parts were sintered at temperatures ranging from 1400 °C to 1600 °C for 2 h. The shrinkage, density, and hardness of the sintered parts were measured. Results show that with homogeneous mixing, the feedstocks were transformed into pseudoplastic in less than 30 min. Powder loading of 57 vol% is the most optimal case for injection molding according to the power law index and flow activation energy values. The theoretical relative density reached 90.27% with defect-free parts under optimum injection temperature and pressure. The weights of the parts decreased by 82.26% during solvent debinding at 60 °C, whereas the binders were completely degraded at approximately 550 °C during thermal debinding. Experimental results also indicate that the shrinkage, density, and hardness reached their maximum values at a sintering temperature of 1600 °C. The sintered parts were densified with approximately 98% theoretical density, hardness of 1582.4 HV, and 15% shrinkage value.

Powder extrusion moulding of 430L stainless steel thin tubes for porous metal supported SOFCs

Thin and thick walled tubes made of 430L stainless steel for porous metal supported solid oxide fuel cells (SOFCs) were prepared by powder extrusion moulding (PEM). A gas atomised metal powder and a binder composed by 50 vol.‐% high density polyethylene and 50 vol.‐% paraffin wax were chosen. The most suitable powder loading for feedstock (68 vol.‐%) was determined by means of torque experiments and rheological measurements. Mixing temperature was selected taking into account the results from differential scanning calorimetry. The extrusion of tubes was carried out in a single screw extruder and two kinds of tubes with two different wall thicknesses were obtained. In order to investigate the homogeneity of feedstock, microstructure of green tubes was evaluated by SEM. Thermal debinding was performed on the basis of thermogravimetric analysis results. After sintering, tubes with good dimensional stability and without defects were obtained. Different wall thicknesses extruded were 150 and 500 μm.

Binder System for Coarse Powders Processed by Metal Injection Molding (MIM)

Research on determined alloys produced by metal injection molding has been done for cost reduction purposes through the use of powders with bigger particle size. However, regarding feedstock homogeneity, certain limitations are presented when coarse particles are used. For instance, homogeneity strongly influences rheological behavior of the feedstock and dimensional control of the sintered part. Therefore, the purpose of this work was to evaluate effectiveness of a modified binder system with the addition of a surfactant polymer which makes the feedstock more homogeneous. This study was carried out on a FeNiP alloy currently processed by MIM, where 50%wt of the iron powder was replaced with course powder having a particle size distribution of D90 less than 47 ,m. Effectiveness of binder systems using a Melt Flow Index (MFI) and the behavior of dimensional accuracy at sintered part were analyzed. Results showed more feedstock homogeneity and less dimensional deviation when a surfactant agent was used.

Production of alumina parts by powder injection molding with a binder system based on high density polyethylene

In this experimental work, injection molding of alumina parts was performed with a developed binder system based on high density polyethylene (HDPE), paraffin wax (PW) and stearic acid. Firstly, the optimum binder composition was determined by torque measurements and rheology. Alumina feedstocks with powder loadings between 50 and 60% in volume were prepared with the developed binder system. A suitable formulation for powder injection molding was chosen based on torque measurements, rheological behaviour and homogeneity of feedstocks. All the feedstocks studied exhibited a pseudoplastic behaviour with flow behaviour index n < 1. Feedstock with 58 vol.% solid loading exhibited the most suitable behaviour for ceramic injection molding and was chosen to perform the complete process. Debinding cycle was designed based on thermogravimetrical analysis and differential scanning calorimetry. The best results were found using solvent debinding followed by thermal debinding. Final parts had densities close to 99% after sintering at 1600 °C during 2 h.

Analysis and evaluation of effects of processing steps on dimensional tolerance of PIM parts

The factors affecting the dimensional tolerance of powder injection molding (PIM), such as the selection of the powder and binder, the feedstock homogeneity, the feedstock thermal properties, the feedstock rheologic behavior, the debinding schedule and atmosphere and sintering temperature gradient were discussed. An attempt was made to develop a model to estimate the influence of important variables. The results show that a better understanding of these factors can provide some useful theoretical instructions for large scale production.

De‐Agglomeration Kinetics of Feedstocks with Granule Tetragonal Zirconia Polycrystalline Powder

This study establishes the relationship between homogeneity of tetragonal zirconia polycrystalline (TZP) feedstocks and the kneading time in order to understand the kneading energy adsorption during the de‐agglomeration period of pre‐existing ceramic granules. Two spray‐dried Y‐TZP powders with different compress strengths were investigated using torque rheometer and transmission optical microscopy. Several properties, kneading torque (T), Casson viscosity (μ), Reynolds number (Re), and dispersive index (Ds) of the feedstocks were introduced, and monitored as a function of kneading time. Optimal processing windows were identified from the dependence of dispersive index with a power number (Np). The best shear‐kneading procedure was proposed in consideration of best feedstock homogeneity and shortest kneading time. One homogenous feedstock and two comparable cases were prepared for subsequent injection molding, debinding, sintering, and mechanical testing. The fracture strength of sintering parts by a partially homogeneous feedstock can be improved from 520 to 680 MPa by a homogeneous feedstock.

Mixing and characterisation of 316L stainless steel feedstock for micro powder injection molding

In recent years, micro powder injection molding (μPIM) is being explored as an economical fabrication method for microcomponents. μPIM, adapted from powder injection molding (PIM), has the same four main processing steps as PIM: mixing of powder and binder system to form the feedstock, injection molding, debinding and sintering. Unlike PIM, the feedstock for μPIM requires more stringent characteristics. Thus, commercial feedstock may not be suitable especially for microstructures with high aspect ratio. In this paper, the mixing, characterisation and feasibility of an in-house feedstock for the injection molding of microstructures, each of ϕ100 μm×height 200 μm, is reported. The feedstock comprises 316L stainless steel and a multi-component binder system. The effects of powder loading and extrusion on mixing and feedstock homogeneity were investigated. The rheological and thermal characteristics of the feedstock were determined and used in subsequent processing steps. The results show that the feedstock can be used for the fabrication of the microstructures with good shape retention.

Kneading behaviour and homogeneity of zirconia feedstocks for micro-injection molding

This study used capillary rheometer, transmission optic microscopy (TOM) and torque rheometer to quantitatively analyze the homogeneity of zirconia feedstock and presents the report of the relationship between homogeneity and kneading parameters. The rheological indexes ( α stv, H a and H z) of four feedstocks were determined by the capillary rheometer showing consistent results. The results of torque and kneading power input of the feedstocks showed consistent behavior with the microstructural parameter (dispersive index, D s). This indicated that the D s (=1− φ a) could be used as a parameter for the improvement of the homogenous property of the feedstocks. The power consumption diagram (kneading power–Reynolds number, N p– Re′) calculated by several torque parameters reveals the critical issues related to the homogeneity of the feedstocks.

Torque evolution and effects on alumina feedstocks prepared by various kneading sequences

The effects of different kneading sequences on the homogeneity, strength and Weibull modulus of green density and sintered parts were studied. Polypropylene (PP), paraffin wax (PW) and stearic acid (SA) in a mass ratio of 25:70:5 mass% were mixed with Al 2O 3 to produce feedstocks. Five different kneading sequences were implemented and analyzed using several techniques, including capillary and torque rheometries, Fourier transformed infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and pycnometry to reveal the properties of the feedstocks. Subsequently, the properties of injection molded samples subjected to the same solvent and thermal debinding conditions were observed. After sintering, the results of the fracture strength and Weibull modulus of Al 2O 3 strongly suggest that the kneading process closely control the homogeneity of feedstocks. The p3 process (kneading sequence, Al 2O 3->PP->SA->PW) could produce the largest torque and homogeneous feedstock. The produced specimens showed the greatest average strength (371 MPa) and Weibull modulus (8.1).

Homogeneity of feedstock in powder injection moulding: R.M. German et al (Pennsylvania State University, Pennsylvania, USA).

Homogeneity of feedstock in powder injection moulding: R.M. German et al (Pennsylvania State University, Pennsylvania, USA).