Powder Testing to Improve Product Quality and Manufacturing Efficiency

Interview conducted by Stuart MilneJul 25 2014

 

Jamie Clayton, Operations Director at Freeman Technology, talks to AZoM about using powder testing to improve product quality and manufacturing efficiency.

Freeman Technology focuses exclusively on powder characterisation and how it can be used in process and product development. Can you start by telling us which industries you work with?

We work with customers from any industry that handles powders. This ranges from pharmaceutical, food and powder coatings manufacturers, to those processing ceramics and metal powders.

In terms of the relative size of these markets for Freeman Technology, the pharmaceutical industry is a major, well-established user base. Almost every pharmaceutical product is handled in powder form at some point and extending powder processing capability is a major goal for the industry as it works to improve manufacturing efficiency.

A much newer sector, where we are seeing considerable activity, is additive manufacturing (AM) or 3D printing. Here there is a growing appreciation of the need to optimise the properties of the powders used in AM processes in order to exploit the full potential of this pioneering technology.  

Are there a lot of similarities in the problems that your customers are trying to solve, or do they vary considerably from industry to industry?

In many respects, there is considerable similarity. The customers we talk to are united by the challenge of ensuring that their powders perform consistently and in an optimal way, whether as finished products or during processing, and the fundamental mechanics that dictate this are consistent regardless of the application. However the precise nature of the problems faced varies considerably.

For example, we were approached to help develop a specification for a powder coating used in a fluidised bed. It was proving difficult to set a specification that reliably identified a material that would fluidise well. By using the FT4 Powder Rheometer to characterise a number of potential candidates and correlate the results with in-process performance, a robust specification was established

While this particular example is specific to powder coating, it illustrates a wider issue that we encounter routinely; defining a specification that will accurately and reliably differentiate the performance of a product or raw ingredient. It is not uncommon for poor performance to be detected only when the product or ingredient is in use, an inefficiency that can often be avoided.

Other common goals among our customers include: developing a successful powder formulation for a given application, such as a blend that will tablet efficiently to form a stable product, for example, and optimising processing conditions for a particular product.

How does the challenge of working with powder processing differ from working with gases or liquids?

I think it’s safe to say that powders represent a greater challenge and there are fundamental reasons why this is the case. There is well established understanding of how certain properties of a liquid or gas will influence behaviour in a given process. Furthermore, these properties can be measured, predicted and/or modelled with accuracy.

In contrast, powders exhibit more complex behaviour and as a result they are less well-understood. Powders are bulk assemblies that contain particles, gases - normally in the form of air - and liquid, usually water, on the surface of the particle or within its structure. The properties of each these phases, and the interactions between them, define bulk powder behaviour.

Powder behaviour is therefore influenced by a large number of variables and a vast array of potential interactions. Some of these variables relate to the particles present - size, shape, porosity, hardness, surface charge - others to the process. Process or ‘external’ variables include the amount of air and moisture present, and the degree of consolidation.

Powder properties are therefore challenging to measure and predict, and the way a powder behaves in a process will only be consistent if the many influential variables remain constant. As a result, variability is a common issue in many powder processes.

How easy is it to gather data that will help with understanding how a powder will perform in a process, or as a finished product?

Powder testing is both increasingly automated and based on more closely defined methods. This is helpful in improving the reproducibility of powder characterisation data, and consequently its accuracy and reliability.

However, it’s critical to gather data that are relevant to understanding how a process or product will behave. This is the limitation of many techniques, especially when attempting to rationalise the performance of complex manufacturing processes.

After more than a decade of working with powders, we have identified shear, dynamic and bulk powder properties as the most valuable in solving industrial problems related to powder processing. Powder testers that support all three of these techniques are now commercially available, so accessing appropriate data has become easier.

How has this understanding of powders shaped your company’s development of the FT4 Powder Rheometer, that you manufacture and supply?

The FT4 Powder Rheometer was designed from the outset as an instrument for testing powders in order to solve problems associated with their industrial use. It was developed  in response to a recognised need to reliably measure properties that directly correlate with process and product performance. The instrument introduced a new characterisation method - dynamic powder testing - an intuitive approach based on the measurement of a powder in motion. Complementary measurement of bulk powder properties including permeability, compressibility, and bulk density, was also a feature of the original design.

Dynamic testing has since proven to be most valuable in applications where traditional shear cell analysis is arguably least relevant. With dynamic testing, samples can be characterised in a consolidated, moderately stressed, aerated or even fluidised state. This makes the technique particularly useful for investigating how a powder responds to external stresses and air content. In contrast, shear cell testing only measures powders in a consolidated state, quantifying how a static powder bed transitions into flow under moderate to high stress. Such conditions most notably occur in a hopper, the design of which is directly supported by shear analysis.

The complementary nature of shear, bulk and dynamic testing is reflected in the development of our powder tester, which now enables all three methods.

What are the main benefits this product will offer your customers with regard to powder characterisation?

The ability to apply multiple test methods with a single instrument is perhaps the feature that most clearly sets the FT4 Powder Rheometer apart from other powder testers. This functionality is essential when it comes to measuring powders under conditions that simulate the actual process environment.

The way in which a powder blend performs in a tablet press provides a good example. Performance in this application has been shown to correlate with basic flowability energy (BFE), cohesion and compressibility. These are dynamic, shear and bulk properties respectively demonstrating how a multi-faceted approach is critical in order to optimise this operation.

Beyond the test capabilities themselves, the instrument’s design reflects our understanding that precision and control are crucial in powder testing. A strong focus on product engineering, combined with detailed attention to automated analytical methods, delivers unparalleled reproducibility and sensitivity. This brings valuable benefits when differentiating powders that may be physically and chemically very similar, but perform differently in a given process.

With multiple test methods there must be the potential to generate quite a lot of data. Is all of this information relevant to every application?

The short answer is yes, it is possible to generate a lot of data, and no, not all information is always relevant. This is a critical point.

Using multiple test methods it is possible to measure a number of different powder properties. However, for any given application just a small number will correlate closely with performance. In the previous answer I discussed the parameters that are relevant to tablet manufacture. In contrast, the performance of a dry powder inhaler, a very different drug delivery vehicle, can be predicted from aerated flow energy. This is a dynamic powder property, measured while a powder sample is being aerated.

Our recommendation to customers is to start by measuring all the parameters you can, to get the most comprehensive picture of how a powder behaves. Then correlate the measured parameters with the critical aspects of powder performance, whether fluidisation behaviour in a dryer, discharge from a hopper, or mixing in a blender. This allows for efficient analysis, refined to just a few key properties.

This is clearly a productive approach compared with investing in a powder tester that measures just one variable, and then discovering that this one variable fails to correlate with powder performance. We regularly encounter customers who are investigating a new approach after having already gone down this route.

Can you provide us with a couple of examples of how FT4 Powder Rheometer data have been used to solve industrial problems?

Yes, this first example relates to tableting, a vital process for the pharmaceutical industry. Many pharmaceutical blends are granulated prior to tableting. This helps prevent segregation of the active pharmaceutical ingredient, and delivers material optimised both for high throughput in the tablet press and finished tablet quality.

We have worked recently with GEA Pharma Systems to assess whether measurable granule properties correlate directly with critical quality attributes of the tablets produced, such as hardness. This work has been highly successful with the results demonstrating a strong correlation between tablet hardness and the BFE of the granules at various points during the wet granulation process.

These results are valuable because they suggest that the wet granulation process can be optimised and controlled with reference to BFE data, rather than by working up every batch of granules to determine the quality of tablets they will produce. Potentially this accelerates the development and scale up of wet granulation processes, not least within the context of working towards continuous tableting processes.

In a very different field, FT4 Powder Rheometer data are being used to assess whether metal powders that have already passed once through an AM machine can be re-used without compromising process efficiency or finished product quality. Not all the powder fed into an AM machine is incorporated in the finished product. Re-using residual material is important for cost-efficiency and the long term sustainability of the industry. However, powders can be changed by passage through the process.

Recent research has shown that dynamic powder properties can sensitively differentiate virgin and used powders in ways that relates to how they will process. This means that dynamic testing can be used to support the development of an efficient strategy for metal powder re-use, based on, for example, blending or sieving, to support lifecycle management.

How do you think comprehensive powder testing could deliver more value for powder processors in the future?

Across the industrial sectors we work with it is clear that many powder processors still rely heavily on experience, rather than on a complete understanding of the powders they work with. The impact of losing older, experienced personnel is regularly highlighted as an issue for the processing industries and, generally speaking, this approach is inconsistent with the lean manufacturing environment that now prevails in almost every sector.

Over the last decade or so, powder testing has advanced considerably and we are now able to successfully measure and rationalise powder behaviour. These capabilities

will deliver more value for powder processors when they are effectively exploited to systematically tackle the day-to-day problems that many face. Using modern multi-faceted characterisation to learn as much as possible about the powders being handled is the key to smarter, more knowledgeable powder processing and product development.

About Jamie Clayton

Jamie Clayton is Operations Director at powder characterisation company Freeman Technology, and is based at the company’s headquarters in Tewkesbury, UK. He graduated from University of Sheffield with a degree in Control Engineering and is responsible for all daily activities of the company, including overall management of the administration, production, R&D, sales and customer support teams.  Jamie also works with the company’s clients to provide application based support. [email protected]