科研之友
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摘要
Ferrosilicon (FeSi) has a fast settling rate in dense suspension, attributed to its very high solids density, coarse particle size, more spherical particle shape and low medium viscosity. The fast-settling nature in dense suspension is a challenge to acquire reliable rheological data. A testing rig was set up to maintain a constant medium density during the rheology measurement by circulating the medium to keep FeSi particles well suspended. A rotational rheometer with a modified concentric bob-cup measuring system was incorporated in the testing rig. Taylor number (T-a) was calculated and a threshold T-a = 41.3 was used to identify the onset of unstable laminar flow owning to the Taylor vortices and turbulence formation in the measuring system. The data with T-a > 41.3 were excluded in the determination of rheological flow curves. Evaluation of the modified measuring system with Newtonian silicone oils of known viscosities confirmed that the system can produce true flow curves over the entire tested shear rate range for a stable laminar flow (T-a < 41.3). This data reduction procedure was applied to the FeSi medium rheology measurement. It demonstrates that FeSi medium exhibits a pseudoplastic trend with a yield stress. The apparent viscosities were calculated at two shear rates, 10 s(-1) that is assumed to be a typical shear rate in dense medium bath separators and 75 s(-1) for dense medium cyclones. A characteristic curve between apparent viscosity and medium density was established, which can be used in FeSi selection for dense medium separation. Medium stability was determined from the FeSi sedimentation rate measurement. It shows that medium stability was closely correlated with medium viscosity. A trade-off between stability and viscosity for optimal dense medium separation should be established.
- 出版日期2016-11
