Viscosity Of Feedstocks Research Articles

Copper - nickel electro-explosive powder feedstocks for extrusion-based additive manufacturing

The average sizes of copper and nickel nano- and microparticles formed at exploding wires in the range of inhomogeneous and homogeneous heating have been established. The average size of nanoparticles grows, and that of microparticles decreases when the value of energy input into wires reaching E ≈ 0,5Es (Es - sublimation energy). While E > 0.5Es the dependence of the average sizes of nano- and microparticles is weakly expressed. The viscosity of feedstocks increases as the proportion of nanoparticles in the powder increases and their size decreases. At equal dispersity and mass content of particles in the polymer, the feedstock viscosity has been found to depend on the adsorption behavior of metals. The analysis of temperature dependence of the feedstock viscosity based on copper and nickel powders has shown that the optimum values of E/Es for one-stage production of micro-nanoparticle powders by the exploding wires lie in the range of 0.4 … 0.7.

Rheological Behavior Features of Feedstocks with a Two-Component Wax–Polyolefin Binder Compared to Analogs Based on Polyoxymethylene

Despite the large number of studies devoted to different compositions of polymer binders for PIM technology, the actual task is still a comparative analysis of the properties of different types of binders to determine their advantages and disadvantages and optimize the compositions used. In this regard, this study aims at the identification and comparative analysis of the rheological properties of the most demanded feedstocks with binders based on polyoxymethylene and a wax–polyolefin mixture under the condition of using identical steel powder filler. The rate of change in the volume fraction of the liquid phase of the binder in the compared feedstocks with temperature change was determined by the calculation–experimental method. As shown, the temperature dependence of the viscosity of feedstocks with a binder based on a polymer blend depends on factors with variable power, i.e., the viscosity change with temperature occurs by different mechanisms with their relaxation spectra. Thus, the principle of temperature–time superposition for feedstocks with multicomponent binders is not applicable, and the study of the viscosity of such materials should involve a wide range of shear rates and temperatures using experimental methods. Capillary rheometry was used to measure the flow curves of feedstocks based on polyoxymethylene and wax–polyolefin binders. The analysis of flow curves of feedstocks showed that feedstocks with a binder of solution–thermal type of debinding have significantly lower viscosity, which is an advantage for molding thin-walled products. However, their difference of 1.5 times sensitivity to the shear rate gradient leads to their lower resistance to “jets” and liquation of components because of shear rate gradients when molding products with elements of different cross-sectional areas.

A gravity-driven sintering method to fabricate geometrically complex compact piezoceramics

Highly compact and geometrically complex piezoceramics are required by a variety of electromechanical devices owing to their outstanding piezoelectricity, mechanical stability and extended application scenarios. 3D printing is currently the mainstream technology for fabricating geometrically complex piezoceramic components. However, it is hard to print piezoceramics in a curve shape while also keeping its compactness due to restrictions on the ceramic loading and the viscosity of feedstocks. Here, we report a gravity-driven sintering (GDS) process to directly fabricate curved and compact piezoceramics by exploiting gravitational force and high-temperature viscous behavior of sintering ceramic specimens. The sintered lead zirconate titanate (PZT) ceramics possess curve geometries that can be facilely tuned via the initial mechanical boundary design, and exhibit high piezoelectric properties comparable to those of conventional-sintered compact PZT (d33 = 595 pC/N). In contrast to 3D printing technology, our GDS process is suitable for scale-up production and low-cost production of piezoceramics with diverse curved surfaces. Our GDS strategy is an universal and facile route to fabricate curved piezoceramics and other functional ceramics with no compromise of their functionalities.

Rheological characteristics of polyethylene-nanotube composites by capillary rheometry

Abstract The viscosity and flow rate as rheological characteristics are fundamental in evaluating the nanofillers in processing the polyethylene-nanotube (PE-NT) composite in injecting molding. The purpose of this investigation is to study the rheological conduct of PE-NT composite plastic feedstock through capillary rheometry. For the purpose of obtaining a flawless component, the feedstock is used as a critical parameter, and care must be taken while introducing the raw materials with high solid load and hence perfect flowability. The shear rate viscosity of different feedstocks at an NT ratio extending at 0–3 wt.% has been determined at L/D equal to 10 die and a load extending at 40.0–80.0 KGF at temperatures 140.0, 150.0 and 160.0°C. The three specimens’ viscosity was measured in order to exhibit that the corresponding flow conduct factor varies from 0.40 to 0.70, demonstrating the non-Newtonian behavior of the specimens. The three specimens’ activation energies at the studied temperature degrees were evaluated and turned out to be 36.5–69.88 kJ/mol according to the applied load.

Effects of POE-g-MAH on properties of PP-based binder in metal injection molding

The objective of this study is to explore the effects of maleic anhydride-grafted polyolefin elastomer (POE-g-MAH) on properties of polypropylene (PP)-based binder. The viscosity of feedstocks as well as properties of green parts, brown parts and sintered parts were investigated. Through the analysis of viscosity, the feedstock containing 8 vol% POE-g-MAH in binder was supposed to be more suitable for the injection molding. The impact absorbed energy at break increased with increasing POE-g-MAH content in binder while the bending strength decreased first and then increased. The introduction of POE-g-MAH improve the density distribution and increased the density of green parts. After debinding, most binder components were removed regardless of the POE-g-MAH content in binder. As for the parts after sintering, the carbon content decreased with an increase in POE-g-MAH content. The results suggest that POE-g-MAH act as a toughening agent as well as compatibilizer for PP-based binder/metal powder system. The mechanical properties of the green parts could be enhanced even after multiple injection and in addition the powder-binder separation trend could be decreased.

Ethylene vinyl acetate as a binder for additive manufacturing of tricalcium phosphate bio-ceramics

Tricalcium phosphate (TCP) ceramic scaffolds were made by the fused filament fabrication (FFF) using different grades of Ethylene vinyl acetate (EVA) as a thermoplastic binder. Stearic acid was studied as a processing aid. A wide range of rheological properties, shaping and debinding behavior could be observed with feedstocks made with different EVA grades. The addition of stearic acid affects flexibility of the solid filaments, the viscosity of feedstocks, and causes a pronounced yield stress behavior. These effects are strongly dependent on the molecular weight of the EVA and influence the printing process and shape stability during the debinding process. EVA binder system works well for thin and small parts, made with nozzle sizes below 0.4 mm, whereas samples made by thicker nozzle size form defects during debinding process. TCP scaffold structures with fin struts of 0.27 mm and partition wall thickness of 0.25 mm and a layer thickness of 0.20 mm could be successfully shaped, debinded and sintered. Excellent fusion between the different layers was achieved, since no defects at the interface could be detected.

Experimental study on moldability and segregation of Inconel 718 feedstocks used in low-pressure powder injection molding

Moldability and segregation of feedstock are linked to the rheological behavior of the powder-binder mixture. In this study, the impact of binders on viscosity and segregation of feedstocks was investigated. The experiments were conducted on several feedstocks obtained by mixing Inconel 718 powder with paraffin wax-based binder systems. The viscosity of feedstocks was measured by a rotational rheometer while the segregation within green parts was evaluated using a thermogravimetric analyzer. It was demonstrated that the variation in solid loading within a molded part can be measured with a sensitivity of at least ±0.25 vol% of powder. The results indicated that the predominant powder-binder separation appears clearly at the top and the bottom of the molded part. It was also shown that the viscosity profiles of feedstocks and the intensity of segregation depends significantly on the binder constituents used in feedstock formulation. The mixture containing only paraffin wax produced the best trade-off between high moldability and low segregation for an injection process requiring an extended time range between injection and solidification of the part (e.g. up to 10 min). For a short processing time (e.g. <1 min spent in molten state), the feedstocks containing paraffin wax with stearic acid or small amount of ethylene vinyl acetate can be also considered as good candidates for LPIM process because their viscosity and segregation potential are relatively low.

Screening of biosurfactant producing bacteria for application in microbial enhanced oil recovery

Thermal cracking processes such as visbreaking are used in the petroleum industry to reduce the viscosity of heavy feedstocks, such as atmospheric and vacuum residues, without forming coke or unstable asphaltenes. Thermal cracking offers a potential method to reduce the viscosity of heavy oils and bitumen, enabling their pipeline transportation with less solvent addition. Viscosity is the most important property for transportation of crude oils, but this property also has a highly non-linear dependence on temperature and composition. In this work, we used a lumped-kinetic model, based on boiling point pseudo-components, coupled with a fluid property model, to correlate the viscosity of two heavy oils subjected to thermal cracking reactions at different severities, and assess the impact of the chemical transformations on the behavior of the heaviest fraction. The properties of these pseudo-components were estimated by validated correlations, and tuned with experimental values. By assuming that after the reactions these properties remained invariable in each boiling point pseudo-component, we could estimate the viscosity of the liquid products from the recombination of these individual properties using mixing rules available in literature. The results indicated that the vacuum residue fractions (>524 °C) undergo chemical transformations that alter their fluid properties. By using adjusting factors dependant on conversion, we were able to make estimations of viscosities at different temperatures with absolute average deviations lower than 25%.

A viscosity-conversion model for thermal cracking of heavy oils

Thermal cracking processes such as visbreaking are used in the petroleum industry to reduce the viscosity of heavy feedstocks, such as atmospheric and vacuum residues, without forming coke or unstable asphaltenes. Thermal cracking offers a potential method to reduce the viscosity of heavy oils and bitumen, enabling their pipeline transportation with less solvent addition. Viscosity is the most important property for transportation of crude oils, but this property also has a highly non-linear dependence on temperature and composition. In this work, we used a lumped-kinetic model, based on boiling point pseudo-components, coupled with a fluid property model, to correlate the viscosity of two heavy oils subjected to thermal cracking reactions at different severities, and assess the impact of the chemical transformations on the behavior of the heaviest fraction. The properties of these pseudo-components were estimated by validated correlations, and tuned with experimental values. By assuming that after the reactions these properties remained invariable in each boiling point pseudo-component, we could estimate the viscosity of the liquid products from the recombination of these individual properties using mixing rules available in literature. The results indicated that the vacuum residue fractions (>524°C) undergo chemical transformations that alter their fluid properties. By using adjusting factors dependant on conversion, we were able to make estimations of viscosities at different temperatures with absolute average deviations lower than 25%.

Rheological Properties Analysis of WC-Co Injection Feedstock

In order to produce a defect-free component, the feedstock composition plays as a critical factor. The feedstock needs to meet the following criteria; high solid loading with excellent flowability. The flowability of the feedstock is greatly determined by the rheological response. Therefore, the aim of this paper is to investigate the rheological behaviour of MIM feedstock comprising of WC-Co powder, with a binder system of Palm Stearin (PS) and Polyethylene (PE), by means of a capillary rheometry. The viscosity and shear rate of various feedstocks at powder loading ranging from 59, 61 and 63% were measured at L/D = 10 die. The rheological properties such as flow behaviour index, activation energy and moldability parameter of each feedstock were calculated and from the analysis, it was concluded that they show a good pseudo-plastic behaviour within acceptable ranges in MIM.

Viscosity Measuring Methods for Feedstocks Directly on Injection Molding Machines

There are various methods for testing the viscosity of MIM feedstocks and described in the literature, e.g. melt-indexer, capillary viscosimeter, etc. Typical factors taken into consideration for choosing a proper method for feedstock characterization are the costs and the time needed for measuring. The paper presents three methods which have been developed to check the feedstock consistency directly on the injection molding machine. The first method is based on a slit-die rheometer. The second method considers the energy which is needed for conveying the melt inside of the plastification unit. And the third method is similar to a melt indexer but also in this case the measurement is done directly on the injection molding machine. These novel methods are suitable to detect inconsistencies in feedstock preparation.

Analysis of the rheological behavior and stability of 316L stainless steel–TiC powder injection molding feedstock

An experimental rheological study has been performed to evaluate the influence of TiC addition on the rheological behavior and stability of 316L stainless steel powder injection molding (PIM) feedstock. The effects of TiC concentration, solid loading, shear rate and temperature were investigated via capillary rheometer method. The stability of feedstocks was evaluated quantitatively using “instability index”, which describes the threshold beyond which the variation of viscosity becomes unacceptable for PIM purposes. The results show that the rheological behavior of PIM feedstocks highly depends on the blend composition. The addition of TiC particles to the stainless steel powder increases the viscosity of feedstock at relatively low shear rates, i.e. <500 s −1. Furthermore, the feedstock instability increases, particularly at higher solid loading. Nevertheless, with increasing shear rate and temperature, the viscosity decreases and the instability of feedstock improves. At relatively high shear rates, i.e. >2000 s −1, the viscosity of composite feedstocks was lower than that of the mono-component SS feedstock due to the better particle packing efficiency. This article presents the rheological behavior of bimodal powder mixture of stainless steel and TiC powders prepared for PIM application. The influences of blend composition, i.e. the TiC concentration and solid loading, and the processing parameters, i.e. temperature and shear rate, are addressed.

Effects of PEG molecular weights on rheological behavior of alumina injection molding feedstocks

The rheological behaviors of alumina injection molding feedstocks containing polyethylene glycol (PEG) binders having different molecular weights were analyzed using capillary viscometer. The results indicate that the feedstock containing larger molecular weight PEG shows a higher yield stress and shear stress. The relative viscosity of feedstocks with PEG binder system is small, which show a good fluidity, and the viscosity decreases with increasing both temperature and shear rate. However, when temperature is above 90°C, the fluidity of feedstocks with PEG1K and PEG1.5K is too high to catch powder, which may induce dissociation occurring between the binder and the powder particles.Based on the results, feedstock D containing PEG20K as the binder has the lowest fluidity, however, it possesses viscosities smaller than 103Pas for all working temperatures. The feedstocks all show pseudoplastic behavior with n value in the range 0.41–0.66, which would be accepted for injection molding. In addition, feedstock D with PEG20K shows a lower temperature dependence of viscosity in the temperature range just below the nozzle temperature. It has the best rheological properties and is most suitable for injection molding.

Viscosity and melt rheology of MIM feedstocks : Y.Li et al. (Central South University of Technology, Changsha, China.) Powder Metall., vol 42, no 1, 1999, 86–89

Viscosity and melt rheology of MIM feedstocks : Y.Li et al. (Central South University of Technology, Changsha, China.) Powder Metall., vol 42, no 1, 1999, 86–89

Experimental Study and Neural Network Modeling of the Stability of Powder Injection Molding Feedstocks

Due to their complex rheological behavior, feedstocks for powder injection molding (PIM) may exhibit non-homogeneous flow and separation. This can produce defects of green parts during mold filling, resulting in their cracking and warpage during debinding and sintering, and ultimately in poor physical and mechanical properties of the final part. An experimental rheological study has been performed to evaluate the influence of solids loading, shear rate, and powder particle size on feedstock stability. A micro-rheological explanation is given for the macroscopic effect of separation, and an instability index has been defined to describe quantitatively the threshold beyond which the variation of viscosity becomes unacceptable for PIM purposes. A neural network model has been developed for predicting the viscosity of feedstocks made from binary blends, when the powder characteristics, blend composition, and shear rate are known. The system enables determination of the process parameters for which powder-binder separation occurs in a given feedstock.