About Measuring Powder Flow Properties & Powder Flowability

Unlike liquids and gases, powders have an inherent problem in flowing smoothly and consistently. However, many industries and daily-life applications require them to flow in an uninterrupted, even manner. These industries and applications include agricultural, pharmaceutical, cosmetics, food, packaging, construction/building, etc industries and daily-life applications include food products, cosmetics, blending and mixing materials etc. In all these, it's vital for the manufacturer to know powder flow properties and the variations according to type, texture, density and viscosity of the powder.

What Are Powders?

In general, any particulate matter can be classified as a group of solids which ranges in size from sub-micronic to large sized rocks, minerals etc. The bulk solid materials that have a particle size of 1mm or less can be classified as powders.

Liquids are subject to gravity and they tend to have a horizontal surface, whereas powders have a different structure. They form angles/slopes because of the internal friction and interaction between individual particles. So they tend to flow less easily especially when pressure is applied. The study of flow of matter (both liquids and solids) is known as "rheology" which deals with deformation of materials under pressure. This can be measured with a powder rheometer.

The Problem With Powders

Powders fail to discharge or flow smoothly from silos, bins, chutes, hoppers etc and this result in unpredictable or poor flow. In industrial applications, this behavior or powders can result in interruptions in the production cycle, leading to plant shutdowns, variations in packaging/weight, mixtures and the correct blending of powdered products.

Raw materials come in various forms and consistencies from different suppliers. When they finally have to be processed, it can lead to huge anomalies in terms of moisture content, particle size and distribution. For instance in the food industry, blending and powder measurement of spices, salt, flour, milk solids etc has to be accurate and smooth, otherwise the resultant product will be rejected at quality.

Hence, various methods of ensuring smooth flow have to be put into place. The powder handling equipment should be regularly tested, using powder rheometers that give information on powder flow properties. Filling packages correctly using tapped density properties of powders can be achieved through this.

Testing Flow Properties of Powders

The above-mentioned problems can be eliminated using flow function tests which analyze powders for their flow behavior. Flow properties to be tested include:

• Cohesive strength
• Angle and slope of chute/orifice to ensure smooth flow
• Internal friction in the powders during flow
• Pressure and compressibility of powders (to avoid caking/granulation)
• Permeability and interaction with gases or liquids

Based on the test results, the technicians can suitably adjust their machines.

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