Friction Analysis of Powder Against Wall Material

How a bulk solid slips across a surface is an important parameter for understanding its performance during storage and processing. This is a measurement vital for determining the correct inclination of a container’s wall (e.g. in a silo or hopper) for the required flow characteristic. Such data is also useful for the assessment of a powder’s flow behaviour down chutes and along pipes, and through mixers and screw feeders.

By measuring the friction between a bulk solid and a sample of the material used in the process the user can design the correct angles and surface finish to necessitate the required flow. This type of measurement is also essential for understanding batch and source variation of powders before processing and storage, rather than only discovering some variation in friction coefficient during the processing when it is too late to take steps to avoid costly downtime and loss is final product quality.

An Example:

In a snack food company different flavourings will be used in the manufacture of final products. During the manufacturing process the flavouring in powder form will have to travel across many different materials and down pipes and chutes. In order to maintain as low variable costs as possible, the snack food company’s buyers will buy flavourings from a number of suppliers. However the friction between the new batch of flavouring and the materials used in the processing can vary greatly compared to the friction of the previously used flavouring.

A change in the frictional characteristics can result in less flavouring flowing down the chute into the flavouring drum (resulting in lower amounts of flavouring on the final product and ultimately unsatisfactory product in the hands of the consumer), it can also cause “rat holing” and other forms of reduction in the performance of silos and other containers.

Method of Laboratory Analysis

Using the Powder Flow Analyser from Stable Micro Systems in its Texture Analyser/Materials Tester format, the production team would be able to work with the buyers and the suppliers of flavouring and measure the friction characteristics.

By analysing the powder before processing and storing steps can be taken to ensure adequate flow will occur, this can involve added a liner to the silo or container, altering the surface finish or material in chutes and pipes, or by adding a flow aid, that will reduce the friction, to the flavouring mix.

Such a quality control method or research and development tool is simple to configure on the Stable Micro Systems Powder Analysis system and analysis can be run at the click of a button. Data can be easily interpreted by minimally trained staff and decisions about whether the new batch or same supplier variation will affect the performance of the production line.

Typical Curves:
The above curves if produced by testing before processing or storage of powder B would tell the production team that powder B would be have a higher friction coefficient against the material used in the silo wall or the chute and would be likely to flow less effectively against that material. This reduction in flow would potentially cause loss in productivity and also lower the final product quality.

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