How to measure angle of repose?

The angle of repose of a material can be obtained through various methods depending on the ultimate application of the material. The value of the angle of repose is affected by different factors, including particle size distribution, particle shape, and particle surface friction. Fixed funnel, circular platform, tilting box, and revolving cylinder methods are four commonly applied methods to determine the angle of repose.

• Fixed funnel method: The powder is poured through a funnel and placed onto a platform, forming a cone. When the predetermined height or the base predetermined width is reached, the powder pouring is stopped. In that case, the angle between the sloping side of the powder cone and the horizontal plane is the angle of repose. During the measurement, the funnel height increases slowly and stably, gradually reducing the impact of the particle falling on the measurement results.
• Circular platform method: The powder is poured through a funnel and placed onto a circular platform whose diameter is specific. A cone is formed by falling particles. When the powder particles start to fall towards the edge of the circular platform, the angle between the sloping side of the powder cone and the horizontal plane is the angle of repose.
• Tilting plate method: Powder particles are flattened on a flat plate, then one side of the flat plate is lifted upwards. When the powder particles start to slide down along the flat plate, the angle between the flat plate and the horizontal plane is the angle of repose.
• Revolving cylinder: The powder is placed into a transparent cylinder. As the cylinder rotates at a fixed speed, the sloping side of the powder appears. The angle between the sloping side and the horizontal plane is the angle of repose.

In addition to the above methods, the angle of repose is also accessible through alternative measurement techniques, for example, the internal funnel method. The measurement results for the same powder sample vary after applying different measurement methods. Therefore, it is critical to choose an appropriate measurement method for the determination of the angle of repose, depending on the application.