Development of an On-line Flow Rheometer for Mineral Slurries

Abstract

This paper reports on the development of an on-line flow rheometer for characterising the rheological behaviour of settling mineral slurries. The instrument is a modified concentric cylinder viscometer in which the slurry is continuously circulated to keep the particles in suspension. The rheometer is designed based on the fundamentals of helical flow, which is the combination of tangential Couette and axial annular flows, and thus satisfies both the basic requirements of viscometric principles and the restrictions caused by the heterogeneous nature of the material. A strong emphasis is placed on developing a correct and accurate method for extracting fundamental rheological properties from the experimental data, without relying on any empirical calibrations or corrections. The data reduction procedure developed is firmly based on the theory of helical flow and has been extensively tested and validated with model fluids of different rheological behaviour. Testing of the flow rheometer and the data reduction method is still progressing with real slurries, but the results obtained so far have strongly indicated the practical usefulness of the instrument for continuous on-line measurements of the flow properties of settling slurries.     

Measurement of Workability of Fresh Concrete Using a Mixing Truck

The main objective of this study is to evaluate the workability of fresh portland cement concrete while it is still in the mixing truck by determining fundamental rheological parameters (plastic viscosity and yield stress). Nine concrete mixtures with different values of yield stress and plastic viscosity were tested in a concrete truck. The measurements made with the truck were based on the typical method of determining the flow behavior in a traditional fluid rheometer; that is, the shear rate in the mixing truck was swept from high to low by varying the rotation speed of the drum. The results of these experiments are discussed and compared with data provided by the ICAR rheometer, a portable rheometer designed for measuring concrete rheology. The test results indicate that the mixing truck equipment is sufficiently sensitive to detect differences in yield stress, slump, and plastic viscosity. However, the plastic viscosity determined by the truck measurement did not correlate with plastic viscosity as measured by the ICAR rheometer, while the yield stress determined by the truck measurement did correlate well with the measured slump and the ICAR rheometer resultsSuggestions are given on how to improve the mixing truck for better use as a rheometer.     

聚碳酸酯透明板材的高温力学行为实验研究

在温度为175～200℃、应变率为0.001～0.1s-1的范围内通过Meissner新型拉伸流变仪对聚碳酸酯进行了恒应变率下的高温单轴拉伸实验.结果表明:聚碳酸酯的高温力学行为具有明显的温度效应和应变率效应,其真应力-真应变曲线存在明显的非线性.     

氯化原位接枝改性CPVC流变行为的研究

采用氯化原位接枝技术制备了苯乙烯(St)、甲基丙烯酸甲酯(MMA)、丙烯酸-2-羟基乙酯(HEA)、丙烯酸-2-羟基丙酯(HPA)和丙烯酸丁酯(BA)等五种单体改性的CPVC.用毛细管流变仪测定了它们的流变行为.讨论了CPVC和改性CPVC的熔体粘度与剪切速率、剪切应力以及温度的关系.结果表明:CPVC和改性CPVC熔体均为假塑性流体,改性CPVC的假塑性增强,熔体表观粘度低于CPVC的熔体表观粘度.在190～205℃温度范围,两者的对数表观粘度与1/T呈非线性关系.CPVC-g-PMMA对温度和剪切应力更加敏感,CPVC-g-PHEA熔体的流动性明显高于CPVC及其他四种单体改性的CPVC.     

限定几何构型茂金属催化聚烯烃弹性体EPDM Nordel IP的高速流变性能

采用恒速型双毛细管流变仪研究了由限定几何构型催化剂和INSITE工艺开发的三元乙丙橡胶EPDM Nordel IP（3745P和3722P）高速挤出时的流动规律及挤出畸变特征。结果表明,EPDM Nordel IP为典型假塑性流体;Nordel IP 3722P与Nordel IP 3745P相比较,前者的粘温依赖性较大且挤出物外观明显好于后者,挤出胀大比和入口压力降也较小。而后者的粘切依赖性较大,说明前者的塑料特性较明显,而后者的弹性体行为更加显著;Nordel IP 3745P在高速挤出时发生挤出压力振荡现象,此时流动曲线出现断裂,这与其门尼粘度较大、相对分子质量分布窄有关。     

Effect of moisture content on flow behaviour of molten soy-protein isolate under an elevated temperature

The flow behaviour of molten soy-protein isolate (SPI) with moisture content ranging from 17 to 41% was measured with a capillary rheometer under an elevated temperature of 140°C. The flow-starting temperature of SPI under 90 MPa pressure was inversely proportional to the moisture content. The relationship between flow rate and pressure drop for a molten SPI with 17-35% moisture was non-linear on a log-log scale, while it was linear for a molten SPI with 41% moisture. Based on these results, the shear characteristic of a molten SPI with 41% moisture can be classified as a power-law fluid with a flow behaviour index of 0.3. However, a molten SPI with 17-35% moisture may be classified as an unknown type of non-Bingham plastic.     

聚碳酸亚丙酯(PPC)加工热稳定性研究

可降解聚碳酸亚丙酯(PPC)加工热稳定性较差。采用高压毛细管流变仪、傅里叶红外光谱仪(FT-IR)、热失重仪(TG)、拉力机和色差仪对工业级PPC的加工热稳定性进行了系统测试和分析。结果表明,使用高压毛细管流变仪可以较好地评估PPC的加工热稳定性。热失重法可以评估PPC的加工热稳定性,但评估不同加工条件下或不同加工配方的PPC热稳定性灵敏度不高。其它方法均不适宜于评估该材料。本研究对PPC的加工有一定的指导作用,并为今后提高PPC加工热稳定性的研究提供技术支持。     

To prepare and characterize microcrystalline cellulose granules using water and isopropyl alcohol as granulating agents and determine its end-point by thermal and rheological tools

Microcrystalline cellulose (MCC-102) is one of the most commonly used excipient in the pharmaceutical industry. For this research purpose, authors have developed a different technique to determine the end point for MCC-102 using water and isopropyl alcohol 70% (IPA) as granulating agent. Wet and dry granules obtained were characterized for their flow properties using the powder rheometer and thermal analysis. Powder rheometer was used to measure basic flowability energy (BFE), specific energy (SE), percentage compressibility, permeability and aeration. Thermal analysis includes effusivity and differential scanning calorimetry (DSC) measurements. BFE and SE results showed water granules requires high energy as compared to IPA granules. Permeability and compressibility results suggest IPA forms more porous granules and have better compressibility as compared to water granules. Hardness data reveals interesting phenomena in which as the amount of water increases, hardness decreases and vice-versa for IPA. Optimal granules were obtained in the range of 45–55% w/w. DSC data supported the formation of optimal granules. Empirical measurements like angle of repose did not reveal any significant differences between powder flow among various granules. In this paper, with the help of thermal effusivity and powder rheology we were able to differentiate between various powder flows and determine the optimal range for granule formation.     

Experimental Determination of Shear‐Thinning Behaviour During Extrusion of Rubber Blends

Abstract: In this contribution, the influence of an extrusion process on the viscosity function of rubber blends is identified. This knowledge is required for realistic numerical simulations of injection heads and extrusion tools used for the fabrication of rubber profiles. The experimental basis of this investigation is tests with both, capillary and extrusion rheometer. The latter is a combination of an industrial extruder and an extrusion tool with a circular cross‐section, allowing application of material characterisation methods used for capillary experiments. Thus, the determination of the viscosity function of extruded rubber blends is possible. Additional capillary experiments enable the determination of the influence of an extrusion on the viscosity of rubber blends. For the identification of material parameters, a non‐linear iteration scheme is used, which is proven to be applicable for rubber compounds and rubber blends. The validation of the extrusion rheometer tests is performed by means of numerical back‐calculation of the corresponding pressure measurements.