Applying advanced powder testing: (1) Screw feeders
Establishing a predictive model for feed rate
Screw feeders are used throughout powder processing industries to dose material accurately and consistently into reaction systems, mixers, and other pieces of processing equipment. However, it can be difficult to predict the rate at which they will deliver any given powder.
A collaborative study with Gericke (Regensdorf, Switzerland), a specialist provider of feeding and mixing equipment, shows how to establish a secure method for predicting feed rate. It illustrates the value of multi-faceted powder characterisation and how equipment selection can be optimised with the right powder testing approach.
Establishing better selection, design or operating protocols for a powder handling process initially requires relevant powder properties to be identified. Many powder testing techniques are critically limited in terms of relevance. If you measure, for example, angle of repose or Hausner Ratio but see no correlation with process performance then that technique provides no value.
To identify properties most relevant to screw feeding, five different powders – Calcium Hydroxide, Maltodextrin, Milk Protein, Cellulose and Calcium Citrate – were characterised in terms of dynamic, shear and bulk powder properties, using an FT4 Powder Rheometer® (Freeman Technology, Tewkesbury, UK).
This instrument evaluates multiple powder properties, using automated, time-efficient measurement protocols. These properties are measured under a range of stress and flow regimes, for example, under consolidation, low stress, or aerating conditions to generate parameters that fully describe the essential characteristics of a given powder.
To identify which properties are most relevant to screw feeding, these parameters were analysed using Multiple Linear Regression with respect to feed rate, as measured for each powder using a full flight single-screw feeder (Tube 3, DIWE-GLD-87 VR, Gericke).
The results show that feed rate with this feeder can be reliably predicted using just two dynamic properties: Flow Rate Index (FRI) and Specific Energy (SE).
The graph illustrates the performance of the resulting model, showing the original data set and two additional powders – cement and lactose – used to validate the relationship. An important point to note is the variation in performance exhibited solely due to differences in powder properties; feed rate varies from ~50 to almost 190 l/hr.
This example demonstrates how an appropriate powder testing regime supports a move from a “trial and error” approach, and a heavy reliance on pilot scale studies, to predictive design employing robust test data. In this particular case, the most relevant variables were dynamic properties, but applying multi-faceted testing maximises the chances of identifying all relevant variables.
This is true whatever the application or equipment of interest. Once the most relevant variables have been identified, testing can be streamlined to maximise long term efficiency.
Find out what happened when the study was repeated with a second feeder here.
Freeman Technology
- +44 (0)1684 851 551
- info@freemantech.co.uk
- https://www.freemantech.co.uk
- 1 Miller Court Severn Drive Tewkesbury Gloucestershire GL20 8DN GB
About us
Freeman Technology specialises in systems for measuring the flow properties of powders and has nearly 20 years' experience in powder flow and powder characterisation.
The company invests significantly in R&D and applications development, and provides detailed know-how to support its range of products. Expert teams guide and support users around the world in addressing their individual powder challenges, focusing on delivering the most relevant information for the process. The result is world-leading solutions for understanding powder behaviour - in development, formulation, scale-up, processing, quality control, or anywhere that powders have a role.
Freeman Technology’s solutions include the FT4 Powder Rheometer®, a uniquely universal powder tester, and the Uniaxial Powder Tester, a complementary tool for quick and robust powder assessment. Systems are installed around the world in the chemical, pharmaceutical, toners, foods, powder coatings, metals, ceramics, cosmetics, and many other industries. They deliver data that maximise process and product understanding, accelerating R&D and formulation towards successful commercialisation, and supporting the long term optimisation of powder processes.
Founded in 1989 as a developer of automated testing systems for materials characterisation, the company has focused exclusively on powders since the late 1990s and in 2018 became part of Micromeritics Instrument Corporation. The company’s R&D, manufacturing and commercial headquarters are in Gloucestershire, UK, with operations and distribution partners in key global territories. In 2007 the company received the Queen’s Award for Enterprise in Innovation and in 2012 the Queen’s Award for Enterprise in International Trade.
Where we supply to
UK Ireland, Europe, Africa, Asia, Australia, South America, North America
Industries we supply to
Chemicals, Food and Beverage, Pharmaceutical Cosmetics Toiletries
