Mercury Scientific
Revolution

Powder flowability is defined as the ease with which a powder will flow under a specified set of conditions. Some of these conditions include: the pressure on the powder, the humidity of the air around the powder and the equipment the powder is flowing through or from. For some applications, ease of flow is simply defined by whether the powder flows or not, the so called “go no-go” approach. The only question is: Will the powder flow through the system or not? For other applications, the rate and consistency of the powder flow is important.

The following are some process examples where the flow rate and consistency is important: a powder die that must be filled with the same amount of powder each and every time or a consumer product that must flow smoothly out of a small container.

Any device used to test powder flowability must take the application problems and processing conditions into account to supply relevant data to the user. The powder in the test device must be in the same state as it is in the process being studied. This ensures that the flow analysis will be applicable to the problem.

The REVOLUTION Powder Analyser is the perfect powder tester for measuring the following:

• the flowability of powders in low stress situations
• to study how the powder behaves once it is flowing in all applications
• to determine the condition of the powder as it moves through a process.

A flowability method is created by selecting the time and rate of rotation based on evaluated process conditions. 10-500cc’s of sample are placed inside of the measurement drum. The instrument is run for a set number of avalanches or data points.

The REVOLUTION Powder Analyser measures many parameters to help determine the difference between powders and establish parameters for predicting powder performance. These measurements include fractal dimension, powder volume and surface linearity. Once the flowability test has been completed, the software will provide the user with the statistical analysis.

A powder is fluidised when a gas is injected into the powder causing the powder particles to separate and enter a fluid like state. The properties of the powder, as well as the pressure and temperature of the gas, determines the degree of fluidisation. For fine powders, the gas pressure required to fluidise the particles is very low. This low pressure can be created by rotating the powder in a drum. Varying the rate of drum rotation results in changes of the fluidisation pressure. The fluidisation of a fine powder can be studied by measuring the volumetric expansion of the powder in a rotating drum as a function of the rotation rate of the drum.

The following are some process examples where the flow rate and consistency is important: a powder die that must be filled with the same amount of powder each and every time or a consumer product that must flow smoothly out of a small container.

In addition, the rate at which a fluidised fine powder settles to its original state can be measured by stopping the rotation and reducing the fluidisation pressure to zero.

The REVOLUTION Fluidisation Test measures a powder’s volume increase at specified angular velocity intervals in a rotating drum to create a fluidisation function for the powder. During the fluidisation test, the rate of decrease in the powder’s volume is measured to create a settling function for the material. Appropriate powders for the REVOLUTION Fluidisation test include: toners, catalysts, powder coatings, and other powders with low pressure fluidisation potential.

There are four optional process steps to the Fluidisation Analysis: Prep, Settling, Analysis, and Settling. These four steps are discussed below.

• Prep Step

  Within the Prep Step, the user can rotate the powder at a chosen rotation rate and length of time to completely fluidise the material. This step will allow the user establish a repeatable initial fluidised state for this analysis. This prep step can be skipped if the user wishes to study the fluidisation of the material in its original state.

• Settling Step

  If the material has been fluidised in the prep step, the material must return to its un-fluidised state to perform the fluidisation analysis. In this step, the rotation of the drum is stopped for a specific length of time or until the volume of the sample reaches its original state. The rate at which the powder’s volume decreases is measured and is used to create a settling function.

• Fluidisation Analysis Step

  During the analysis, the user sets the start and end drum rotation rate with the desired step rate. REVOLUTION will begin the drum rotation at the specified start rotation rate, stepping up the rate at the desired intervals until the end rotation rate is achieved. The user can chose to ramp up the angular speed at any desired intervals to achieve the equilibrium fluidised state.

After a specified equilibration time has elapsed at the end rotation rate, REVOLUTION will begin computing the statistical measurements described below for this fluidisation analysis step. In Figure A, the statistical analysis shows the operator the rate at which the powder fluidised by the increase in the overall volume. In Figure B, the fluidisation test results are shown for two different powder samples: one sample fluidises at a faster rate than the other.

Powders can behave very differently depending on the amount of energy they are subjected to as they move through handling equipment. One powder may flow more evenly as it is subjected to more mechanical energy while another powder may become more erratic. This behavior can be studied using the REVOLUTION Multi-Flow test method. In the multi-flow method, the sample drum speed is increased gradually over time and the sample powder’s behavior is measured.

The Multi-Flow Analysis studies how a powder or granular material transitions from avalanching to continually flowing as it is subjected to faster speeds. By gradually increasing the rotation speed in the Multi-Flow Analysis, the user can evaluate the speed at which their powder is no longer avalanching in their process but flowing continuously. This data can be used to predict how powders will behave in high speed equipment.

Before analysis, the samples are prepared by rotating the sample drum at a fixed speed for a fixed time. In this case, the preparation consisted of rotating the powder drum at 20 RPM for 30 seconds to aerate the sample. The prep time and rotation speed are user programmable and are selected to best suit the application being studied.

After preparation, the sample drum rotation is started and sample properties are measured. After programmable intervals, the drum speed is increased by fixed intervals and changes in the sample properties are determined.

The Energy Function Graph displays the energy level of the sample powder versus drum rotation rate. This data is used to calculate energy slopes. The gray area presents the standard deviation of the energy level. Figure A shows data for a sample that behaves more erratically as the rotation speed increases while Figure B shows data for a sample that’s behavior improves.

The Packing Analysis studies the powder’s ability to pack or settle after being exposed vibrational energy during transportation and storage.

The following are some process examples where packing and settling are important: a container that must be filled with the same amount of powder each and every time but settles to a different amount during transportation and storage or a powder that packs into a strong cake during handling and storage. An ideal powder has properties that do not change during processing, handling and storage.

Any device used to test the changes in volumetric expansion and compression must take the application problems and processing conditions into account to supply relevant data to the user. The powder in the test device must be in the same state as it is in the process being studied. This ensures that the packing analysis will be applicable to the problem.

The REVOLUTION Packing Test has three process steps: Preparation, Vibration and Analysis.

Sample Preparation

The sample powder is rotated at a chosen rotation rate and length of time to completely aerate the material. This step will allow the user establish a repeatable initial powder state before beginning the packing analysis. After the initial preparation, the RPA measures the powder volume.

Analysis

After the volume measurement, the powder is rotated at a specified speed until the compacted powder breaks (or avalanches). The software calculates the force required to break the powder mass.

Electrical Charge and Material Handling

Powders and granular materials can acquire electrical charge on the surface of their particles due to contact and movement against handling equipment and containers. They can also acquire charge due to contact and movement of particles within the material itself. This process is called tribocharging. Tribocharging is caused by electrons moving from one surface to another when different materials come in contact with each other. One material will become positive and the other will become negative. The amount of charge developed depends on the nature of the materials in contact, the pressure of the contact, the relative velocity of the contact surfaces, and the friction between the contact surfaces.

Measuring the charge acquisition properties of powders and granular materials is important because charge acquisition leads to problems and unstable behavior. Charged materials stick to processing equipment and containers. Charged materials can become airborne more easily. Charge materials flow in different ways than materials with no charge. In fact, many research believe that material electrical properties are the most important contributors to powder flow behavior.

Using the ION Charge Module with the Revolution allows measurement of charge acquisition properties between contact surfaces and test samples while controlling velocity and contact time.

Experimental Data

Charge Versus Particle Size

The data above is for a powder with different particle sizes charged with glass. Typically charge development increases as particle size decreases.

Charge Versus Moisture Content

The data above is for a powder with different moisture content charged with glass. Typically charge development decreases as moisture content increases.

Charge Versus Flow Aid Concentration

The data above is for a powder with different flow aid concentrations charged with polycarbonate. Typically charge development changes as flow aid content changes.

Charge Versus Surface Treatment

The data above is for a powder with different concentrations of surface treatment liquid charged with glass.

The Revolution Temperature Control option can heat samples from room temperature up to 250 degrees Celsius while running flow tests. Samples can be heated moving constantly, moving intermittently or not moving. Tests can be performed before heating and at temperature intervals.

Example Test Data

A polymer was tested at 26C, 110C, and 135C to determine flow changes with temperature between annealed and non-annealed. Increases in temperature caused the powders to flow more poorly and this resulted in a lower powder bed density. In this case the annealed material showed more flow temperature resistance than the non-annealed material.

Each REVOLUTION Powder Analyzer includes:

• One 100mm Large Sample Drum Assembly
• One 100cc Sample Cup
• One Set of Cables
• One Revolution Powder Analyser Software Package

The Following Additional Options are available:

• Ion Static Charge Analysis Module to measure the tribo-charging properties of powders, including charge sensor assembly, polycarbonate drum sides, and de-ionizing blower
• Temperature Control Oven to heat samples to 250 degrees Celsius
• 50mm Small Sample Drum Insert with small sample cup for measuring 25 cm3 of sample.
• An additional 100mm Large Sample Drum Assembly with large sample cup.
• 100m Extra Large Sample Drum Assembly for testing granular material, sample volume 500ccs.
• Packing Analysis with Drum Locking Assembly for high vibrational energy packing test.
• Set of Drum Seals for either small, large or extra large sample drums for making sample drums air and water tight.
• IQ/OQ Certification Package which includes: IQ/OQ Procedure, IQ/OQ Certification Document and Drum Test Standard.