Powder Handling – A Beginners Guide
What is Powder handling?
Powder handling is the term given to the engineering of equipment specifically aimed at the processing and dosing of Dry Bulk Solids.
The products that are to be “handled” range from food, drinks, confectionery, dairy products, pharmaceuticals, chemicals, plastics, environmental services, and nonwovens, just to name a few.
Powders are dry, bulk solids consisting of extremely fine particles that may flow freely when shaken or tilted. But not everything is that simple…
What are some of the key differences between material/powder types? And why might are others harder to handle than others?
Powders can exhibit many different characteristics. Even between batches, consistencies can vary, even if the material is from the same manufacturer. Combined with changes in environmental conditions (i.e. humidity) and the processing of a particular powder can then become considerably challenging.
Several key factors will help define the characteristics of a bulk solid. These are:
- Bulk density – The dry weight of product per unit volume. Both solids and pore space are considered, not to be confused with ‘particle density’.
- Temperature – Certain products may be more sensitive to temperature changes than others, and others can be sensitive at a constant temperature. In turn, the temperature can also affect moisture rates (see next).
- Moisture/humidity – Moisture can cause some powders to become ‘sticky’, and in turn, they can become trickier to dispense without the use of agitation. Flour is known to commonly suffer from such properties.
- Particle size and shape – Larger particles flow with more ease than many powders as they are not as prone to “bridging” or “rat holing”.
- Material form – Type of material e.g. powders, granules, flakes, pills, chips, etc.
- Time resting/storing – Materials left in storage stations, such as a Bulk Bin or Hopper, can become more cohesive, and become difficult to handle, whether from a chemical reaction, adhesive bonding, or even due to crystallisation.
- Cohesive strength – The bonding between particles.
- Chemical structure – Chemical structure and thermodynamic properties provide indicate if a material tends to be thermochemically unstable.
- Static charge – Is the material likely to create an electrostatic charge? Is the powder explosive?
Granular materials come in all different shapes and sizes, and their physical properties play a huge role in the flow of your product. Not all granular solids are the same. Here are a few examples:
Material scientist Patrick Richard was quoted stating: “Granular materials are ubiquitous in nature and are the second-most manipulated material in industry (the first one is water).”
A powder flow and characteristics can vary massively. It is essential that both the materials physical properties and the equipment used are taken into consideration. Both factors will play a big part in processing your product. Even a Hopper can affect the flow, if not steep enough in angle, and can help the powder to pass through, or cause bridging.
In addition, the terms ‘powder flow’ and ‘powder flow properties’ are entirely different, and should not be confused.
Powder Flow – Describes how the material will ‘flow’ – the research!
Powder Flow Properties – The results, after testing has taken place. I.e. Testing 25kg of sugar to determine the average weight of powder ‘handled’ per minute and the results.
What issues might be experienced when dosing or conveying your materials?
Powders in bulk form will typically be passed through the following process stages:
- Storage – Often kept in bulk storage sacks to be emptied using a Sack Tip Station or FIBC Discharger.
- Transportation – The movement of bulk solids from storage containers to the manufacturing process. A Flexible Screw Conveyor, or perhaps an Aero Mechanical Conveyor may be used.
- Processing – The handling, batching or dosing of the materials. Metering Screw Feeders or Belt Feeders might be used, for example.
Gravity plays an important part in the Bulk Solids Handling process. Products can start to become difficult to process if large quantities of material have become compacted together, which can be caused by the overfilling of machinery.
Powders can be susceptible of ‘bridging’, or ‘arching’, and may require additional equipment features such as an Agitator to be in place. Another issue that manufacturers experience is ‘rat-holing’. Before going further, let’s touch up on what these terms mean:
- Bridging/Arching – Caused when forces acting upon the particles at the walls of the Hopper (or Sack Tip/FIBC Discharger) is equal to the internal stress of bulk powder particles. It is more common amongst powders that have tendencies to ‘cake’ and ‘pack’. The term ‘bridging’, or ‘arching’, is given due to the shape in which the product forms, and is the result of when a powder becomes difficult to pass through the equipment used.
- Rat-holing – Caused when the flow takes place within a small channel above the outlet/inlet, with material above having enough cohesive strength to hold so that the now-stationary material cannot resume flow. The term ‘rat-holing’ is given due to the burrow-like hole that appears from the top of the material, through to the bottom of the Hopper/Feeder.
Unless proper agitation takes place, bridging and rat-holing will continue to be a problem and is required for preventing material build-up in the Hopper, or Feeder Conditioning Zone.
An Agitator is usually a specially designed blade, both in shape and purpose, however, vibratory Agitators are available, along with many other different incarnations.
How does Trantec the Powder Handling Industry? How are you different from other machinery suppliers?
Not all machines are the same. Some may measure and distribute materials at much higher accuracies than others due to different reasons, whether it be poor machine quality, or the parts used to manufacture it.
Trantec has been a leading manufacturing of Powder Handling Equipment and Bulk Solids Solutions for over twenty years and we pride ourselves on quality products, robust machinery, keen pricing, and second-to-none Customer Services.
Trantec’s aim is to innovate today’s Materials Handling Equipment, adding a fresh perspective on the capabilities of current technology. Our machinery is in operation worldwide and spans process plants of universities, blue-chip firms, multinationals, and many household brands that you would find in your own kitchen.
With our brand-new Modular Range of Metering Screw Feeders, in addition to Auger Conveyors, Flexible Screw Conveyors, Spares & Replacement Service (Augers, Spiral, UHMWPE Tubing, Seals, etc.), and various types of Ancillary Equipment (such as FIBC Dischargers, Sack Tip Stations, Hoppers), we can find the perfect solution for your application.
For further details concerning our products, or to discuss your Powder Handling Process in further detail, get in touch today on 01282 777566.
Alternatively, you can email us directly by completing the contact form at the bottom of our homepage, or by visiting our Contact Us page.