Slope angle

If a bulk material flows downwards from a nozzle in free fall, a powder heap is formed. If the heap forms on a horizontal plane, a more or less symmetrical cone of debris is created. This is also known as the "slope cone". From the slope inclination, initial conclusions can be drawn about the internal friction of the bulk material. The slope angle is measured from the horizontal.

The stronger the particles adhere to each other, the steeper the slope cone becomes. The internal friction of the bulk material is then high. If the powder is free-flowing, the internal friction of the powder is lower. A fairly symmetrical, compact cone of debris is formed. If a dry powder consists of very small particles, it can fluidise during flow. In this case, the internal friction of the powder is almost zero. Such a powder would spread out in the plane in a similar way to water and would not form a cone of debris.

Slope cones also form when large mixers are filled with powder. It is advisable to turn the mixing tool half a turn intermittently during the filling process in order to achieve an even fill level.

The better a bulk material flows, the better it can be

• dose
• promote
• fill
• store
• automate

Very small quantities of so-called anti-caking agents can significantly improve the flowability of bulk materials if they are mixed in accurately and gently.

The subject of segregation:

Powder mixtures that flow well segregate more easily than those that flow poorly. Distinct bulk cones can also contribute to segregation. Larger particles roll to the edge of the bulk cone, while fine particles collect in the centre. For this reason, pouring cones should be avoided.