Rheological Properties Of Feedstock Research Articles

Tuning the rheological properties of paraffin-wax ceramic feedstocks for deposition with thermoplastic 3D printing

Droplet deposition with material-jetting methods such as thermoplastic 3D printing (T3DP) depends greatly on the rheological properties of the feedstocks. This study investigated the effect of particle interactions and the degree of weak flocculation on the shear thinning behaviour, the yield stress and the storage/loss moduli of paraffin-wax-based feedstocks containing 40 vol% of zirconia (3Y-TZP) micron-sized powder. Steric stabilization of the feedstocks was provided by varying the ratios of the surfactants with different chain lengths, i.e., stearic acid (2.4 nm) and Solsperse 3000® (10 nm), which in turn affected the dynamics of the droplet formation and the quality of the layers when jetting non-Newtonian, thermoplastic ceramic feedstocks. The results of the study extend the guidelines for the processing of printable feedstocks used in T3DP additive manufacturing.

Optimization of Rheology Parameters for Feedstock by Powder Injection Molding (PIM) Via Taguchi Analysis

The most critical process in the powder injection molding method is determining the powder/binder rate and its properties. The most important feature that distinguishes the powder injection molding method from other powder metallurgy production methods is its advantage in producing high raw density and complex shaped parts. However, providing these advantages includes a multi-parameter process that directly affects the injection molding parameters and the final part's mechanical properties. In addition, the difficulty of experimental studies causes energy, time, and cost losses in determining the powder/binder rate and rheological properties of the feedstock so that the advantages of the method turn into a manageable disadvantage. This study performed rheology studies for three different feedstocks (PW/CW/SA, PW/PE/SA, and PEG8000/PP/SA). In this context, this paper determined the rheological properties of different feedstocks to take advantage of the Taguchi analysis. Flow behavior index, viscosity and optimum loading rates were determined separately for all feedstocks. The results exhibited the injection molding can be done with the determined best (58% steatite+PEG8000/PP/SA) F3 feedstock by volume. Based on it was found that viscosity and melt flow index were not a problem for injection molding in three different feedstocks used in the result, advantages and disadvantages were observed.

Characterization of nano / micro bimodal 316L SS powder obtained by electrical explosion of wire for feedstock application in powder injection molding

Bimodal nano / micro powders are in demand in powder injection molding (PIM) and additive manufacturing (AM) technologies. Feedstocks with bimodal powder have a higher flowability, and the resulting products have a higher density.In this work, a bimodal 316L steel powder obtained by the electric explosion of a wire (EEW) was investigated. The bimodal powder is formed directly during the explosion and does not require a mixing step. The powder was obtained at different explosion energy densities. A feedstock was obtained with a powder content of 94 wt%.The powders have a different micro: nano ratio depending on the energy density. Feedstocks with these powders have different rheological behavior. The morphology and chemical composition of the powders and the homogeneity and rheological properties of feedstock with bimodal powder were studied and discussed. A comparison of feedstock properties with bimodal and micron powder is carried out.

Fabrication of TiAl alloys turbocharger turbine wheel for engines by metal injection molding

The TiAl turbine wheels possess high acceleration responsiveness and low energy consumption due to its low density, high specific strength and excellent oxidation resistance. However, the mechanical properties of the turbine wheels fabricated by conventional casting can't be fully utilized resulted from inherent defects and compositional segregation. Herein, we used a near-net shaping MIM technology to fabricate this alloy and firstly produced a TiAl alloy turbocharger turbine. The rheological properties of feedstocks, microstructure and mechanical properties were systematically studied. Results indicate that the Feedstock F3 has better rheological properties and no powder-binder separation during injecting using numerical simulation. The microstructure is homogenous and fine-grained fully α2/γ lamellar structure with average size of 111.7 μm. The HIPed TiAl alloy displays excellent mechanical properties which are higher than that of the equivalent casting TiAl alloys. This work presents a valuable method for fabricating complex-shaped TiAl alloy turbine wheels.

Powder injection moulding of Inconel 713C alloy

ABSTRACTTo find a proper super alloy applied to gasoline engine turbochargers which demand a high operating temperature over 950°C, the IN713C super alloy was investigated in this study. The rheological properties of feedstock, density, microstructure and mechanical properties were measured. The proper powder loading was 61 vol.-%. Through the analysis of viscosity, 160°C was supposed to be more suitable for the injection. After debinding, most binder components were removed. A reasonable debinding process was formulated. Two pre-sintering temperature (850, 950°C) were investigated, then 850°C was considered to be more proper relatively. The samples were sintered at different temperatures for various time. The best properties of sintered parts were obtained when sintered at 1300°C for 3 h, the density of sintered parts was 7.83 g cm−3 while the hardness was 43.6 HRC and tensile strength was 1216.9 MPa.

Influence of segregation on rheological properties of wax-based feedstocks

The rheological behavior of wax-based feedstocks has a direct impact on successful mold filling for parts produced by low-pressure powder injection molding. During a rheological test, segregation may occur within low-viscosity feedstocks, leading to errors in results, and to an improper evaluation of the flowability of powder-binder mixtures. The segregation occurring during rheological tests is not generally considered when measuring the viscosity profiles of such mixtures. In this study, the impact of testing time, testing protocol (increasing or decreasing shear rate), polymer degradation, powder deagglomeration, and temperature on the rheological properties of feedstocks was investigated. The segregation occurring during rheological testing produces a meaningful effect in low-viscosity feedstocks. Because the segregation is driven by the time spent in the molten state, the effects of segregation on viscosity were visible, particularly at the end of a long rheological test. During a short rheological test, the pseudoplastic effect occurring in wax-based feedstocks was only attributable to the binder molecules' orientation with respect to the flow. In this respect, and contrary to the information reported in literature, it was demonstrated that the dilatant effect observed was in fact more likely due to segregation occurring during the rheological test, rather than as a result of the elimination of the preferential layer formed during the pseudoplastic regime. Because the rheological properties of low-viscosity feedstocks were significantly influenced by the test duration, a rheological test duration of a few minutes must be used to precisely quantify the flowability of such feedstocks.

Reološke lastnosti mešanic in struktura vbrizganih rezkarjev za sintrane kompozitne orodne materiale na osnovi MMCS

Reološke lastnosti mešanic in struktura vbrizganih rezkarjev za sintrane kompozitne orodne materiale na osnovi MMCS

Influence of binder system and temperature on rheological properties of water atomized 316L powder injection moulding feedstocks

In order to obtain a proper powder injection molding the rheological behavior of feedstocks should be known. To determine the binder effect on the rheological behavior of 316L stainless steel powders feedstock two different feedstock were prepared. In the current experiments water atomized 316L stainless steel powders (-20 µm) were used. Two types of binders, one of which is mainly paraffin wax can be dissolved in heptane and the other Polietilenglikol (PEG) based and can be dissolved in water, were used. Polypropylene was used as binder and steric acid was used as lubricant for both binder systems as skeleton binder. Dry binder system were mixed for 30 min in a three dimensional Turbola. Capillary rheometer was used to characterize the rheological properties of feed stocks at 150-200 °C and a pressures of 0.165-2.069 MPa. Powder loading capacity of PEG and PW based feed stocks were found to be %55 and %61 respectively. The lowest viscosity of PEG and PW based feed stocks were found to be 304.707 Pa.s and 48.857 Pa.s respectively. Keywords: PIM, Binder, Rheological properties

Molding Properties of Inconel 718 Feedstocks Used in Low-Pressure Powder Injection Molding

The impact of binders and temperature on the rheological properties of feedstocks used in low-pressure powder injection molding was investigated. Experiments were conducted on different feedstock formulations obtained by mixing Inconel 718 powder with wax-based binder systems. The shear rate sensitivity index and the activation energy were used to study the degree of dependence of shear rate and temperature on the viscosity of the feedstocks. The injection performance of feedstocks was then evaluated using an analytical moldability model. The results indicated that the viscosity profiles of feedstocks depend significantly on the binder constituents, and the secondary binder constituents play an important role in the rheological behavior (pseudoplastic or near-Newtonian) exhibited by the feedstock formulations. Viscosity values as low as 0.06 to 2.9 Pa·s were measured at high shear rates and high temperatures. The results indicate that a feedstock containing a surfactant agent exhibits the best moldability characteristics.

Impact of binders on viscosity of low-pressure powder injection molded Inconel 718 superalloy

Rheological behavior of powder-binder mixture has a direct impact on the successful mold filling for parts obtained from powder injection molding. In this study, the impact of binders on rheological properties of feedstocks was investigated. The experiments were conducted on several feedstocks obtained by mixing of Inconel 718 powder with wax-based binder systems. Their rheological and thermal properties were investigated using rotational rheometry and differential scanning calorimetry techniques, respectively. It was demonstrated that a large amount of ethylene vinyl acetate (EVA) should be added to paraffin wax (PW) to produce a thickening effect of the mixture. At low shear rate, the mixing of high-viscosity paraffin waxes with a low-viscosity PW produces a similar thickening effect denoted with the EVA. In addition, the feedstocks containing only PW demonstrate a pseudoplastic behavior. It was also shown that an addition of only 1 vol% of stearic acid (SA) in PW generates an important decrease in viscosity, and further increases of this constituent induce no effect on rheological behavior. From a rheological perspective, the best candidate feedstocks are the mixtures containing PW and SA while feedstocks based on PW, beeswax or containing a small amount of EVA could be also considered as good.

Effect of PEG molecular weight on rheological properties of Ti-MIM feedstocks and water debinding behaviour

Polyethylene glycol (PEG) based binder systems are garnering increasing attention because of the environmentally friendly nature of the water-soluble PEG. Rheological properties of the feedstock are essential to metal injection moulding (MIM). Intriguingly the effect of PEG molecular weight on rheological properties of the feedstock and its water debinding behaviour has not been well investigated. In this work, four molecular weights of PEG, i.e. 1500, 4000, 10,000 and 20,000g/mol were selected and PEG/polymethyl methacrylate (PMMA) based feedstocks were formulated with titanium metal powder. We reported a systematic investigation of the rheological properties of the prepared feedstocks with capillary rheometry and the study of the effects of shear rate and temperature on viscosity. The water debinding behaviour of each feedstock was also investigated in terms of debinding temperature and PEG molecular weight.

HA/Ti6Al4V Powder with Palm Stearin Binder System - Feedstock Characterization

Metal Injection Molding (MIM) is widely known as net shape process to mass production for complex shape. In this study polyethylene and palm stearin was used as binder system for composite HA and Ti6Al4V. Ti6Al4V has spherical shape with particle size 25 μm and Hydroxyapatite has particle size 5 μm. Brabender® was used to mix HA and Ti6Al4V powder and binder for making feedstock, rheological properties of feedstock was examined by capillary rheometer. Effects of temperature, viscosity, shear rate and activation energy were discussed in this paper. Binder was removed by thermal debinding. Rheological test showed feedstock of composite HA and Ti6Al4V shows pseudoplastic behavior. Sintering was conducted on 1200°C by argon with holding time 2 hour.

Rheological Properties of Urea-CaLS Mixture for Urea Fertilizer Granulation

The rheological properties of feedstock for granulation process are important in controlling the parameters throughout the process. This study identifies the type of fluid that mixtures of Urea and Calcium Lignosulfonates (CaLS) possessed through the viscosity profiles using a parallel plate rheometer. The viscosity behavior of mixtures with varied weight percentages (wt %) of CaLS in urea solution were analysed. Results identified that the mixtures show shear thickening behavior of non-Newtonian fluid. It is also observed that the increases of CaLS content increase the viscosity of the mixtures. Moreover, the mixture with 50 % CaLS addition is found not suitable for further investigation as its viscosity is too high (3.450-6.773 Pa.s at zero shear rate) compared to molten urea (0.002 Pa.s).

Rheological Properties of Zirconia Toughened Alumina Powder for Ceramic Injection Molding

The rheological properties of feedstock are critical element to the success of the ceramic injection molding (CIM) process. The suitability of the developed feedstock can be reducing the problems that may arise during injection molding, debinding, and sintering. This study identifies suitable powder loading based on the rheological properties of materials by using a capillary rheometer machine. The feedstock used is a combination of zirconia toughened alumina powder with a binder that consists of high density polyethylene, paraffin wax, and stearic acid. Experimental results showed that all of the feedstocks are suitable for injection molding because of their pseudoplastic nature and low viscosity. However, the low power law index and low activation energy flow of the 57 vol.% powder loading make it most suitable for the CIM process.

Influence of powder particle size distribution on rheological properties of 316 L powder injection moulding feedstocks

The rheological behaviour of highly filled polymer systems used in powder injection moulding (PIM) technology influences strongly the final properties of the products. The study of the influence of particle size distribution on the rheological properties of 316 L stainless steel feedstocks is presented. Two kinds of gas-atomized powders were employed with d 90 of 8 and 26 μm of particle size. Five feedstocks were prepared at powder loadings of 50, 55, 60 and 65 vol.%, employing both starting powders and their own mixtures in volume ratios 25/75, 50/50 and 75/25. The binder was composed by 50 vol.% of high density polyethylene and 50 vol.% of paraffin wax. Feedstocks were prepared in a torque rheometer with a pair of roller rotor blades and rheological measurements were performed in a capillary rheometer. The effects of the powder loading and different particle size distributions on the rheological properties of feedstocks were investigated. Different rheological parameters, like melt viscosity, power flow index and activation energy were determined. A relationship between powder characteristics and rheological behaviour was established.

Optimization of feedstock properties for reaction-bonded net-shape zircon ceramics by design of experiments

For the manufacturing of reaction-bonded ceramic microparts by low-pressure injection moulding, feedstocks with an optimized rheological behaviour are required. In order to evaluate the main influences on the rheological properties of feedstocks and their possible interactions, various compositions were systematically tested in the frame of design of experiments (DoE). For this purpose, ZrSi 2, ZrO 2, Al 2O 3, and MgO, and two different paraffins were used as starting materials. The influences of powder volume content, Zr/Si ratio, binder composition and processing temperature on the flowability of the feedstocks were observed in this line of experiments. A four-factorial fully fractional CCC-model was used. Finally the reliability of the computed statistical model was experimentally verified by means of two compositions, whose rheological behaviour has been predicted by the software.

Rheological properties of alumina feedstocks for the low-pressure injection moulding process

The low-pressure injection moulding process (LPIM) allows near-net shape manufacturing of ceramic microcomponents. Feedstocks used in this process have to fulfil different requirements. They have to show good flowability for the machining but they also need to have high solids content to reduce shrinkage during sintering. This work focuses on the flow behaviour of alumina feedstocks with high solids content, based on two different binder systems and two different alumina powders. By varying particle size, organic binder system, and solids content, the rheological properties of the feedstocks were modified significantly. The material parameters such as viscosity, the derived relative viscosity, and yield stress were investigated systematically. The Herschel–Bulkley model turned out to be suitable for the description of the rheological behaviour of these ceramic feedstocks. The dependency of the relative viscosity on solids content could be well described by models like Krieger–Dougherty, the Eilers, and the Quemada models, while the best results for the maximum packing factors were obtained with the Janardhana Reddy et al. model.

Effect of SiC Powder Characteristic on the Rheological Properties of Feedstock

In this study, the effect of SiC powder characteristic on the rheological properties of the feedstock was investigated. It was found that the viscosity of the feedstock decreased with the increase of the particle size. For the binary powder mixtures, the viscosity of the feedstock decreased with the increase of the particle size ratio of the larger particle to finer particle, which is attributed to the increase of the tap density of the powder.

Development of poly(2-ethyl-2-oxaline) based water-soluble binder for injection molding of stainless steel powder

The successful use of new binder system for the injection molding of stainless steel powder as a test material is described. The binder system comprises a major fraction of poly(2-ethyl-2-oxaline) of various molecular weights and a minor fraction of polypropylene (PP). The weight fraction of poly(2-ethyl-2-oxaline) in the binder was maintained to be 77 wt%. The rheological properties of feedstock were investigated systematically. The binder system used provides satisfactory mixture stability, excellent moldability and reasonably fast water leaching and thermal debinding rates. Poly(2-ethyl-2-oxaline) was removed by leaching in water at 65 °C for 6.5 h. The remaining binders were bourn out by thermally at 600 °C for an hour. Brown parts were sintered at 1350 °C for an hour in pure H 2. Debinded and sintered samples were examined by SEM and optical microscopy.

Rheological properties of feedstocks prepared with steatite powder and polyethylene-based thermoplastic binders

In this study, rheological properties and behaviors of binder formulations and powder injection molding (PIM) feedstocks, used in the ceramic industry, were investigated. For this purpose, various binder formulations and PIM feedstocks were prepared. In these formulations, polyethylene (PE) and three waxes (carnauba, bees wax and paraffin) were used with steatite powder loading. A 50% (v/v) fraction of feedstocks was steatite powder with 8.15 μm average particle size. Steatite powder and binder formulations were mixed as dry in a Turbula shaker/mixer for 30 min. To achieve a good disperse mixing, twin screw extruder was also used. The rheological properties of the resulting binder formulations and feedstocks were characterized by a capillary rheometer. In the rheometer, temperature was varied from 120 to 180 °C and pressure was varied from 12.3 to 124.7 kPa. From the capillary rheometer flow curves, the flow behavior index ( n ) parameters for the binder formulations and PIM feedstocks were determined to be less than 1. The apparent shear rates ( γ ̇ a ) of binder formulations and PIM feedstocks were determined to be in the range of 22.6–1005 s −1 . For the above apparent shear rates and shear stresses, the apparent viscosities ( η a ) were calculated as in the range of 23.8–1105.2 Pa s. The melt flow indexes (MFI) were determined under various shear stresses ( τ w =12.3–124.7 kPa) and found to be in the range of 4–231 g per 10 min. Effect of temperature onto apparent viscosities ( η a ) of feedstocks were also studied, and flow activation energies under various shear stresses were determined to be within the range of 59–182 and 25–99 kJ/mol, for the binder formulations and feedstocks, respectively. Further, the thermal behavior and removal of binders from the feedstocks were determined by DTA–TG analysis, and the removal the binders from feedstocks by thermal treatments were achieved.