Reconstructed rheometer for direct monitoring of dewatering performance and torque in tailings thickening process

To further clarify the dewatering performance and torque evolution during the tailings thickening process,a self-made rake was connected to a rheometer to monitor the shear stress and torque.The dewatering performance of the total tailings was greatly improved to a solid mass fraction of 75.33%in 240 min.The dewatering process could be divided into three stages:the rapid torque growth period,damping torque growth period,and constant torque thickening zone.The machine restart was found to have a significant effect on the rake torque;it could result in rake blockage.Furthermore,the simultaneous evolution of the torque and solid mass fraction of thickened tailings was analyzed.A relationship between the torque and the solid mass fraction was established,which followed a power function.Both the experimental and theoretical results provide a reference for the deep cone thickener design and operation to enhance the dewatering performance.

Development of rheometer for semi-solid high-melting point alloys

A rheometer for semi-solid high-melting point alloys was developed based on the principle of a double-bucket rheometer, with which the solidifying of semi-solid high-melting point alloy melt could be effectively controlled by the control of temperature and the outer force-field; and different microstructures have also been obtained. This rheometer can be used to investigate the rheological behavior under different conditions by changing the Theological parameters. By way of full-duplex communication between the computer and each sensor, automatic control of the test equipment and real- time measurement of rheological parameters were realized. Finally, the influencing factors on torque are also quantitatively analyzed .

Wall slip behavior of polymer melts on capillary rheometer

Wall slip behavior of three commercial polymer melts polypropylene(iPP),low-density polyethylene(LDPE)(branched chains) and high-density polyethylene(HDPE)(linear chains) were studied by using a capillary rheometer with twin bores at different temperatures.The results show that a sudden first-stick-then-slip transition was observed for HDPE and a first-slip-then-stick transition was observed for LDPE and iPP as the shear rate sweep was done in an increased order,which shows that the chain structure has an obvious effect on the wall slip behavior of polymers.The critical shear stress for the onset of stick-slip transition increases linearly with temperature for HDPE,which accords with the disentanglement mechanism proposed by Brochard and de Gennes.While the extrapolation length used to quantify the magnitude of the transition remains about 0.05-0.09 mm for HDPE at 150-230 ℃.Also the relationship between the critical shear stress for the onset of wall slip and the molecular mass for polymer samples agrees with the disentanglement model of Brochard and de Gennes.The onset of slip-stick transition for LDPE and iPP at a critical shear stress may be interpreted as the shear thinning of the polymer chains at high shear rates,preventing further development of wall slip behavior.

Autoregressive bispectrum characteristics of magneto-rheometer

The operating principle of measuring rheological properties of magnetorheological(MR) fluid was expounded by means of a new rheometer with double driving discs rotating at the same speed in the opposite directions.The constitutive equation of MR fluid was established with theoretical analysis from experimental data.The conventional power spectrum approach was unable to detect the existence of quadratic phase coupling for dynamic rheological measurement.Bispectrum analysis is emerging as a new powerful technique in signal processing,which can describe nonlinear coupling,restrain Gaussian noise and reserve phase component.An autoregressive(AR) model of the third order cumulant,the bispectra and bispectral contours were utilized for analyzing the dynamic characteristics of the MR rheometer by merely using the sampled output torque signals when a zero mean non-Gaussian white noise interferes with the rotary disc system.The measurement and analysis process based on virtual instruments were automatically controlled by computer in this paper.The experimental and theoretical results show that rheological properties and dynamic characteristics of MR fluid can be measured with this double disc rheometer.

INERTIA EFFECTS OF THE FLUID AND CYLINDER IN COAXIAL CYLINDRICAL RHEOMETER

The inertias of the fluid and the inner cylinder in coaxial cylinder rheometer (CACR) have great influence on the unsteady flow of non-Newtonian fluid. Even for the Newtonian fluid there exist the so called stress overshoot phenomenon. This phenomenon was studied and a method correcting the measured results for an unsteady flow in the rheometer was proposed. It is found that the inertia effect of the fluid can be ignored when the gap between cylinders is small. (Edited author abstract) 11 Refs.

Analysis of general second-order fluid flow in double cylinder rheometer

The fractional calculus approach in the constitutive relationship model of second-order fluid is introduced and the flow characteristics of the viscoelastic fluid in double cylinder rheometer are studied. First, the analytical solution of which the derivative order is 1/2 is derived with the analytical solution and the reliability of Laplace numerical inversion based on Crump algorithm for the problem is verified, then the characteristics of second-order fluid flow in the rheometer by using Crump method is analyzed. The results indicate that the more obvious the viscoelastic properties of fluid are, the more sensitive the dependence of velocity and stress on fractional derivative order is.

An analytic solution and investigation of character of viscoelastic fluids in double-gap concentric cylinder rheometer

An analytical solution to annular pipe flow of the second fluid and Maxwell fluid is given using Weber integral transform. The formulas can be used to analyse the behavior of unsteady flow of viscoelastic fluid in annular pipe, especially to analyse the flow character of double-gap concentric cylinder rheometer. It is found by computation that when the outer cylinder is in simple periodic motion, there are step junctions along the history curve of Maxwell fluid’s velocity and shear stress, and at step junctions both amplitude and phase of oscillatory wave vary sharply; when the outer cylinder makes uniform rotation, the velocity and shear stress of Maxwell fluid exhibit rhombic wave oscillation, and its period is in close parabolic relation with material constant H.

Effect of asphalt thin beams mixed with three nominal maximum aggregate sizes in the bending beam rheometer on the prediction of thermal properties of bituminous material

The objective of this research is to evaluate an impact of asphalt mixture beams with varying sizes of aggregate in the Bending Beam Rheometer （BBR） for testing/predicting thermal cracking properties of asphalt pavements. The BBR test has following benefits： the equipment is cheaper, it uses smaller specimens, faster conditioning, easier availability for quality control, easier to manage, etc. However some concerns have been raised： some consider that the size of the aggregate may affect the test＇s results; the other concern is that such small beams cannot represent the whole properties of the asphalt pavement. To address these criticisms, imaging techniques, statistical analysis, and viscoelastic modeling are used. Asphalt thin beams prepared with three different nominal maximum aggregate size （NMAS） （12.5mm, 9.5 mm, and 4.75 mm） were tested at three different temperatures （-18℃, -24℃, and -30℃）. Based on results from statistical analyses and viscoelasticity, the ratio of asphalt binders and voids and stiffness differences among the three NMAS specimens are not significant, meaning that the impact of asphalt thin beams prepared with the three NMAS on the prediction of thermal cracking is minimal and can be neglected.

Pumpability of Manufactured Sand Self-compacting Concrete

By the addition of superplasticizer and air entraining agent,manufactured sand selfcompacting concrete(MS SCC)with slump flow varying from 500 to 700 mm and air content varying from 2.0%to 9.0%were prepared and the pumpability of MS SCC was studied by a sliding pipe rheometer(Sliper).According to the Kaplan’s model,the initial pump pressure and the pump resistance of MS SCC were obtained.Meanwhile,rheological properties including the yield stress and the plastic viscosity of MS SCC were measured by a rheometer.The experimental results show that the increase of slump flow contributes to a higher pumpability and a proper air content,i e,6%is beneficial for the pumpability of MS SCC.Due to the existence of stone powder and stronger angularity of MS,the initial pump pressure of MS SCC is only about 60%-88%that of river sand(RS)SCC with the same slump flow and air content,indicating that MS SCC possesses a higher pumpability than RS SCC.

Rheological properties of warm mix asphalt binder by DSR test at medium temperature

The rheological properties including the complex modulus G＊ and the phase angle δof matrix and warm mix asphalt （WMA）binders were measured by using the dynamic shear rheometer （DSR ） test at the medium temperature ranging from 16 to 40 ℃,and the relationships between the fatigue factor G＊ sinδand the matrix binder property,WMA additive and test temperature were established.It is found that G＊ decreases with the increasing temperature while δincreases inversely,and G＊ of the asphalt binder with high WMA additive dosage is large,and δis small.G＊sinδexponentially decreases with the increasing temperature and linearly increases with the increase in additive dosage,and the amplitudes of variation are large at low temperatures and high additive dosages.The effect of WMA additive on the rheological property is more remarkable for the matrix asphalt binder with low G＊.Besides,aging has a great effect on the property of matrix asphalt binder,and a slight effect on the interaction between asphalt and additive.The high additive dosage can increase the fatigue cracking potential of the asphalt binder.

基于DSR的改性沥青及混合料动态黏弹性能

为了在相似加载条件下比较改性沥青及混合料的动态黏弹性能,选择4种不同特点的改性沥青,成型了混合料小梁试件.应用动态剪切流变仪(DSR)分别进行了不同温度下的频率扫描试验,根据时间-温度等效原理构建了改性沥青及混合料的流变主曲线,对主曲线形态和流变模型拟合结果进行了对比分析.研究表明:改性沥青及混合料的复数剪切模量主曲线形态相似,采用改进型CAM模型进行拟合的效果很好,相关系数在0.996以上;平衡复数剪切模量G*e可用来区分不同类型改性沥青及其混合料的高温性能;高强改性沥青的高温抗车辙性能明显优于其他改性沥青,但软化点和60℃动力黏度不适用于评价高强改性沥青.改性沥青的动态力学响应能够反映其混合料的黏弹性能.

Road Performances of Mesoporous Nano-silica Modified Asphalt Binders

The objective of this paper was to find new modifier to improve the aging resistance and low temperature cracking resistance of asphalt. To investigate the aging resistance of modified asphalt binders, mesoporous nano-silica（doping Ti^（4＋）） was used as a asphalt modifier. Some physical properties including penetration, ductility, and softening point of asphalt were analyzed with RTFO（Rotating thin film oven） aging and ultraviolet aging. Moreover, the performances of high and low temperature of modified asphalt binders with pressure aging were tested by dynamic shear rheometer（DSR） test and bending beam rheometer（BBR） test. These results showed that the penetration decreased, low temperature ductility, and softening point increased when adding mesoporous nano-silica to base asphalt. After ultraviolet radiation aging, the penetration loss and ductility loss of modified asphalt decreased than that of original asphalt, the increase of softening point was also significantly reduced than that of base asphalt. Furthermore, The test results of DSR and BBR showed that the G＊sinδ and creep modulus‘s＇ of pressure aged asphalt decreased, but the creep rate ‘m＇ increased. It can be concluded that the aging resistance and cracking resistance of modified asphalt are improved by adding mesoporous nano-silica, especially the doping of Ti^（4＋） could improve the aging resistance obviously.

Evaluation of reclaimed asphalt pavement binder stiffness without extraction and recovery

A new testing procedure to estimate the low-temperature stiffness of the reclaimed asphalt pavement （RAP） binder was developed. In the testing procedure, the SuperpaveTM Bending Beam Rheometer （BBR） with special modifications and binder blending charts by Asphalt Institute were utilized. Modifications involved the development of a new kind of sample mold and different testing parameters were made to BBR testing procedure to capture the theological properties of bitumen mortars produced by mixing fresh binder with fine RAP materials or RAP aggregate. The stiffness relationship between binder and bitumen mortar was established based on the BBR test results. The blended binder stiffness in bitumen RAP mortar was estimated from the RAP mortar stiffness based on the binder-mortar relationship. And finally, the RAP binder stiffness was estimated from the blended binder and fresh binder stiffness based on the blending charts by Asphalt Institute. The results indicate that the new procedure can capture the rheological properties of bitumen mortar and can be used to estimate the low temperature stiffness of RAP binder without binder extraction and/or any chemical treatments.

Comparison of Rheometric Devices for Measuring the Rheological Parameters of Debris Flow Slurry

Soil samples with clay content ranging from 15% to 31%, were taken from three debris flow gullies in Southwest China. Three debris flow slurry samples were prepared and tested with four measuring systems of an Anton Paar Physica MCR301 rheometer, including the concentric cylinder system,the parallel-plate system, the vane geometry, and the ball measuring system. All systems were smoothwalled. Flow curves were plotted and yield stress was determined using the Herschel-Bulkley model,showing differences among the different systems.Flow curves from the concentric cylinder and parallelplate systems involved two distinct regions, the low shear and the high shear regions. Yield stresses determined by data fitting in the low shear region were significantly lower than the values from the inclined channel test which is a practical method for determining yield stress. Flow curves in the high shear region are close to those from the vane geometry and the ball measuring system. The fitted values of yield stress are comparable to the values from the inclined channel test. The differences are caused by wall-slip effects in the low shear region.Vane geometry can capture the stress overshoot phenomenon caused by the destruction of slurry structure, whereas end effects should be considered in the determination of yield stress. The ball measuring system can give reasonable results, and it is applicable for rheological testing of debris flow slurries.

RHEOLOGICAL BEHAVIOR OF POLYPHENYLENE SULFIDE/POLYAMIDE-66 BLENDS

Blends of polyphenylene sulfide (PPS) containing trace amounts of branching and/or cross-linking in chain and Polyamide-66 (PA-66) have been prepared by melt blending. The rheological behavior of PPS/PA-66 blends has been studied by means of capillary rheometer, and compared with PPS. The effects of shear rate, shear stress and temperature on the how of PPS/PA-66 blends and PPS are discussed. The non-Newtonian indexes and the activation energies of viscous how are obtained. The results show that the apparent viscosity of PPS/PA-66 blends is not sensitive to shear rate and stress, but decreases with the elevation of temperature. On the contrary, the apparent viscosity of the PPS decreases obviously with the increasing of shear rate and shear stress, but it is increased by the elevation of temperature.

Comparison of the rheological properties of four root canal sealers

The flowability of a root canal sealer is clinically important because it improves the penetration of the sealer into the complex root canal system. The purpose of this study was to compare the flowabilities of four root canal sealers, measured using the simple press method （ISO 6876）, and their viscosities, measured using a strain-controlled rheometer. A newly developed, calcium phosphate-based root canal sealer （Capseal） and three commercial root canal sealers （AH Plus, Sealapex and Pulp Canal Sealer EWT） were used in this study. The flowabilities of the four root canal sealers were measured using the simple press method （n= 5） and their viscosities were measured using a strain-controlled rheometer （n=5）. The correlation between these two values was statistically analysed using Spearman＇s correlation test. The flow diameters and the viscosities of the root canal sealers were strongly negatively correlated （p= -0.8618）. The viscosity of Pulp Canal Sealer EWT was the lowest and increased in the following order： AH Plus〈Sealapex〈Capseal （P〈0.05）. All of the tested root canal sealers showed characteristic time- and temperature-dependent changes in their rheological properties. The viscosities measured using the strain-controlled rheometer were more precise than the flowabilities measured using the simple press method, suggesting that the rheometer can accurately measure the rheological properties of root canal sealers.

A Perspective on Rheological Studies of Gas Hydrate Slurry Properties

Gas hydrates are solid inclusion compounds that are composed of a three-dimensional hydrogen-bonded network of water cages that can trap small gas molecules, such as methane and carbon dioxide. Understanding the rheological properties of gas hydrate crystals in solution can he critical in a number of energy applications, including the transportation of natural gas in suhsea and onshore operations, as well as technological applications for gas separation, desalination, or sequestration. A number of exper- imental and modeling studies have been done on hydrate slurry rheology; however, the link between theory and experiment is not well-defined. This article provides a review on the current state of the art of hydrate slurry viscosity measurements from high- and low-pressure rheometer studies and high-pressure flowloops over a range of different sub-cooling （ATsub = TequiI Texp） and fluid conditions, including for water and oil continuous systems. The theoretical models that have been developed to describe the gas hydrate slurry relative viscosity are also reviewed. Perspectives＇ linkage between the experiments and theory is also discussed.

RHEOLOGICAL STUDIES ON REACTION INJECTION MOLDING PROCESS WITH A SLIT MEASURING SYSTEM

A non-reacting system and a reacting system are run with an on-line slit rheometer devel-oped by the authors.It is found that the polyurethane-urea system behaves slightly elastic and theZaremba-Fromm-Dewitt model may be employed to describe its rheological behaviors.After the geltime,the inside pressure of the testing materials varies dramatically.Reports in this respect have notbeen found in literature,as yet its mechanism warrants further studies.

AN EXPERIMENTAL STUDY OF HOLE PRESSURES FOR POLYMER MELTS

A slit die apparatus is used to measure hole pressures for two polymer melts.Hole pressures up to 110kPa are determined and shear rates reach 200 s-1.Viscosity data obtained from the same apparatus agreewell with the values obtained from a cone-and-plate rheometer or a capillary rheometer.The hole pressuresobtained by direct measurements are all positive and increase with increasing shear stress.The values of the firstnormal stress difference obtained from hole pressures according to the Higashitani-Pritchard（HP）theory are ofthe right order of magnitude,but appear to be on the low side when compared with values obtained from a cone-and-plate rheometer or with values obtained via exit pressures.It is believed that the hole pressure is a measureof fluid elasticity,but cannot yield accurate values of the first normal stress difference according to the HP theory.

Experiments and analysis for rheological properties of MRF

The work principle of flat-plate structure under shearing mode is expounded based on a vertical type rheometer for MRF which combined data acquisition with treatment and result display.The formula to calculate shearing stress is deduced.Based on different recipe for MRF,experiments under different working gap length were done by altering the intensity of magnetic field.The rheological model for MRF was established and the relationships between shearing stress,viscosity and magnetic field intensity were deduced.Experiments indicate that MRF has the flowing characters:with an increase of the magnetic induction and the nominal shear rate,the shear stress of MRF increases.However,as the working gap decreases,the shear stress increases.MRF has shear thinning property under magnetic field.