Friction properties of fertilizers and methods of analysis
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Swedish Institute of Agricultural Engineering, P.O. Box 7033, S-750 07 Uppsala, Sweden
Publication date: 2021-06-28
Int. Agrophys. 1994, 1(8): 53–57
In many cases the angle of internal friction of fertilizers is substituted by the angle of repose. Theoretically, this is considered correct but there is a risk that other factors such as particle size, shape and surface texture might interfere with the friction properties. For this reason, another method to measure the dynamic angle of internal friction has been developed. The origin is an apparatus made by Brübach (1973) that has been modified for granular fertilizers. The equipment is a shearing apparatus that brings a layer of the test material to slide against another layer. For different normal forces (N) on the layers, different shearing forces (F) is required. The linear relationship between shearing and normal forces gives the angle of friction (Φ) from a well known formula: tan Φ = F/N. For comparisons a box for measuring the dynamic angle of repose also has been developed. The shearing method gives an angle of internal dynamic friction that for each fertilizer is 7°-9° lower than the angle of repose, and 0°-5° lower than the angle of internal static friction. The apparatus developed can also be used to determine the angle of external friction between fertilizer and other materials such as steel, plastic or wood.