Papers by Keyword: Rheological Behavior

Abstract: 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).

Abstract: In this investigation, waste printed circuit board resin powder (WPCBRP) was used to replace 0-30% of the fine aggregate in controlled low-strength materials (CLSM), to explore their rheological behavior, mechanical behavior, and durability. The results thus obtained demonstrate that when 10% of the fine aggregate was replaced by WPCBRP, the adjusted slump flow, setting time, and compressive strength could all met the standards at the ages of 12 hours and 28 days, with a high impedance of 1.54-1.63 kΩcm. CLSM with WPCBRP has a similar water permeability, of between 10-8 and 10-9 cm/s, to that of compacted clay. Therefore, this form of CLSM is impervious, and has a lower compacted settlement when compared with clay.

Abstract: The optimum powder loading of feedstock based on an alumina–zirconia powder was investigated. The optimum powder loading were important to avoid any problems that may arise during the ceramic injection molding (CIM) process. The optimum powder loading is determined based on the critical powder loading and the characterization of the material rheological properties. The critical powder loading was determined using an oil absorption method, and the rheological studies were conducted using a capillary rheometer machine. The results showed that a 57 vol.% powder loading is the most suitable and optimal for the CIM process.

Abstract: The effects of gellan gum and calcium ions concentration on gelation characteristics and rheological behavior were investigated using TA(texture analysis)and mechanical rheometer which monitored respectively press strength and the evolution of G′. At a premium gellan gum content of 0.02g in 100ml buffer solution, increasing calcium ions concentration led to an increase in the gelation strength, but when calcium ions content reached a critical concentration values range from 0.015% to 0.02%, gelation strength begin to decrease. While in the same content of calcium ions, calcium lactate exhibits grater effects on gelation strength than calcium chloride. The temperature at the onset of gelation and the gelation rates showed an increase with the increasing of gellen and calcium ions content. At the same calcium ions concentration, the evolution of modulus storage (G′), gel temperature and rate are higher with the addition of calcium lactate than using calcium chloride. Our study indicated exponential relationship between gelling temperature (gelling rate) and calcium concentration.

Abstract: The rheological behavior of polyamide-66 (PA66)/liquid crystal polymer (LCP) blends and the effect of liquid crystal polymer on melt flow rate were studied. A torque rheometer was used to investigate the rheological behavior of the PA66/LCP blends, and the effects of mass fraction of LCP, compatibilizer (PS-g-MAH), blending temperature and rotor speed on the rheological behavior of the blends were analyzed by an orthogonal experiment method. The results showed the above factors’ effects on the equilibrium torque of the blends were different individually, and the rheological behavior of the blend strongly depended on the LCP content. The melt flow rate was enhanced by a small content of LCP, and decreased with increasing LCP content.

Abstract: A series of loading - unloading consolidation creep experiments had been carried out on Nanning unsaturated expansive soils. Lots of loading - unloading creep curves under different stress levels were obtained. Through the various stages of creep deformation analyzed, it was concluded that the creep deformation of expansive soil contained elastic deformation, viscoelastic deformation and plastic deformation of components. Then model components in constitutive model of expansive soils were discussed. The rheological model of the seven components was proposed, which can describe unsaturated expansive soil elastic - viscous - plastic behavior. According to the experimental datum, all parameters of this model under different stresses were determined by the inverse analysis method. It is showed that the values of numerical calculated using this model agree well with those obtained by the creep tests. The conclusions provide a reliable theoretical basis for the rheological model of expansive soils to further study.

Abstract: The PLA/tourmaline composites were prepared by co-extrusion of PLA chips and tourmaline fillers. Rheological behavior of PLA chips and PLA/tourmaline composites were analyzed using a capillary rheometer. Experimental results showed that the rheological curves complex viscosity of the PLA chips exhibited a non-Newtonian flow behaviour. Complex viscosity of the PLA chips decreased with the temperature increasing. A non-Newtonian flow behaviour was observed in all the PLA/tourmaline composites samples at lower shear rate. The complex viscosity of PLA blends increased with the input of tourmaline. The viscous flow activation energy of PLA/tourmaline blend melts decreased compared with that of neat PLA chips. Keyword: Rheological behavior; poly(lactic acid); tourmaline; meltblowing

Abstract: 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.

Abstract: The rheological behavior of semi-solid tool steel is investigated using a conventional rheometer under cooling rate and shear rate. The processing of steels in semi-solid state is still at development stage due to the high processing temperature involved. The candidate grades of steel for thixoforming are high speed, high carbon, stainless steel and ductile iron. TheHS6-5-2 tool steel has a wide semi-solid range of over 200 C and the required spheroidal microstructure achieved by partial re-melting from as supplied state without any mechanical agitation, indicated the potential of this grade to be investigated in semi-solid processing. For non-isothermal processing an increase of solid fraction related to solidification due to thermal exchanges is observed. In the first series of experiment after melting the feed stock in an alumina cup, the alloy is sheared continuously by a rotating rod with a constant shear rate under three different cooling rates to the 55% corresponding liquid fraction. In the second series of experiment three different shear rates were applied under a constant cooling rate. The apparent viscosity of the slurry as a function of cooling rate and solid fraction is calculated from the applied torque to the outer cylinder. The results show that the slurry viscosity decreases with increasing shear rate and increases with increasing cooling rate and solid fraction. Additionally for a given solid fraction, shear thinning behavior is observed.

Abstract: The use of a specially designed hypoeutectic cast iron as a potential raw material for the thixoforming process is described in this paper. Thixoforming technology normally uses aluminum-silicon alloys such A356 and A357 as raw materials. Iron-based alloys are less common, despite the lower cost of the raw material. The paper describes the semi-solid behavior and corresponding final microstructure of a hypoeutectic gray cast iron after thixoforming tests. The Fe-2.6wt%C-1.5wt%Si alloy was prepared via conventional casting in sand molds. Samples were heated to the semi-solid state at 1160 and 1180oC and held at these temperatures for 0, 30, 90 and 120s, and then subjected to compression tests. Two-platen compression tests were carried out in an instrumented eccentric press in order to determine the semi-solid behavior. The holding time in the semi-solid range simulates the industrial heating process that is time-controlled rather than temperature-controlled. The semi-solid behavior indicated that the semi-solid cast iron behaves like aluminum-silicon alloys, presenting a stress of up to 24MPa under 80% strain and a corresponding apparent viscosity of up to 1.5*105 Pa.s at 1180oC. The final microstructure after compression testing was essential in determining the material’s morphological evolution. Tests revealed that heating up to the semi-solid range followed by thixoforming changes the material’s graphite morphology from type A to B (or E), but does not significantly affect the interdendritic arm spacing between graphite lamellae. The resulting structure is composed of fine graphite and pearlite.