Powder Rheometer for Dynamic Angle of Repose Measurements – GranuDrum

The GranuDrum instrument is an automated powder flowability measurement technique predicated on the rotating drum principle. The drum is a horizontal cylindrical with transparent sidewalls and it is half-filled with the powder sample.

The drum rotates about its axis at an angular velocity varying from 2 to 70 rpm. For each angular velocity, a CCD camera captures a number of snapshots. Consequently, for each rotating speed, the dynamic cohesive index is measured from the interface fluctuations, and the flowing angle, also called “dynamic angle of repose” in the literature, is calculated from the average interface position. A low value of the flowing angle corresponds to excellent flowability.

Principle

A broad set of parameters, such as the cohesive forces (electrostatic, capillary, and Van der Waals forces) between the grains, the shape of the grains, and the friction between the grains, influences the flowing angle. The dynamic cohesive index is only associated with the cohesive forces between the grains. A non-cohesive powder leads to a regular flow, while a cohesive powder leads to an intermitted flow. Thus, a dynamic cohesive index around zero corresponds to a non-cohesive powder. Consequently, the cohesive index increases when there is an increase in the cohesiveness of powder. Therefore, the spreadability of powders can also be quantified by the cohesive index.

Key Benefits

  • The cleaning and filling of the cell is rapid and simple
  • Measurement is intuitive, simple, rapid, and easy to interpret
  • Before it is safely transferred to the instrument, the cell can be handled in a hood, a glove box, or confined enclosure
  • The chemically-coated GranuDrum cell can handle powder from numerous dimensions
  • Supplied with intuitive software, both variance and average can be accessed easily and enables the comparison of results. All data and images are automatically collected and stored for post-processing. Data can be easily transferred and reports can be automatically generated.
  • Recorded standard operating procedures improve the repeatability of measurements

Differentiators

  • Use of fluctuations for quantifying the cohesive forces of powders
  • Dynamical angle of repose at both high and low speeds (1 rpm to 70 rpm, that is, from 4 mm/second to 290 mm/second)
  • Cell can be conditioned through a glove box under a certain atmosphere like humidity, inert gas, and temperature
  • Cohesion of powders may differ while handling, and this property known as “powder thixotropy” can be accessed with the GranuDrum
  • Simple data interpretation and physical principle
  • High measurements reproducibility (for instance, with low-density materials like excipients = 4.2%, or high-density materials like stainless steel = 1.8%)
  • A smart design assures long lifetime and high robustness

Applications

  • Ideally suited for geometries involving low pressure and high shear like pharmacy pneumatic conveying and additive manufacturing spreadability
  • Classification of powders flowability for a broad array of applications
  • Predictions of the flowing behavior of powders at the time of a pneumatic conveying process; detection of complex samples before introducing them inside the process
  • Ideal tool for quantifying the spreadability of powders and for optimizing speed (because of its original cohesive index analysis) at the time of a recoater process in additive manufacturing

Powder Rheometer for Dynamic Angle of Repose and Cohesive Index Measurements – GranuDrum

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