Angle of Repose:
Typically, the angle of repose is determined by pouring a powder or granule onto a flat surface and noting the angle produced by the pile's top surface and the horizontal surface. The angle can be determined using the following formula:
Angle of Repose (degrees) = arctan (h/r)
Where:
h is the height of the pile r is the radius of the base of the pile
It is important to remember that the angle of repose for a given material is not a fixed value, but can vary depending on factors such as particle size and shape, humidity, and the method used to pour the material.
Powders and granules with low angles of repose are often chosen in the pharmaceutical business because they are easier to handle and process. On the other hand, powders and granules with high angles of repose are employed in some applications, such as tablet manufacture, where a stronger compression force is required.
The calculated results can be compared to the table below to establish its relative ability to flow the powder.
| Angle Of Repose (degrees) | Expected Flow |
|---|---|
| 25-30 | Excellent |
| 31-35 | Good |
| 36-40 | Fair - aid not needed |
| 41-45 | Passable - may hang up |
| 46-55 | Poor - must agitate or vibrate |
If your powder has an angle of repose greater than 45°, it is unlikely to be acceptable for tablet pressing.
Furthermore, the Angle of Repose is linked to different powder flow parameters like as bulk density, tapped density, compressibility, and Hausner ratio.
The angle of repose of powders and granules is an important feature in the pharmaceutical industry since it influences their flowability and handling. Powders and granules with low angles of repose flow effectively and are easy to handle, which is critical for manufacturing and packaging processes. Powders and granules with a low angle of repose can be readily loaded into capsules, vials, and containers. They are easily transportable, can be mixed with other substances, and can be poured into die cavity.
On the other hand, powders and granules with high angles of repose may not flow easily and may cause challenges in processing and packing. They can make filling capsules, bottles, and containers difficult, and they can create bridging and rat-holing in hoppers and bins. They may also be challenging to mix and blend with other ingredients, resulting in unequal active ingredient distribution in tablets.
In summary, the angle of repose of powders and granules is an important parameter in tablet manufacturing because it impacts the flow properties and the needed compression force to form tablets, which can affect the weight, hardness, and overall quality of the tablets.