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MERCURY Scientific Inc

 

REVOLUTION Powder Analyzer 

 

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FLOWABILITY Testing with the REVOLUTION Powder Analyzer

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.

Flowability Process

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 Analyzer is the perfect powder tester for measuring the following: a.) the flowability of powders in low stress situations b.) to study how the powder behaves once it is flowing in all applications c.) 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.  A 125cc of powder is placed inside of the measurement drum.  The instrument is run for a set number of avalanches or data points.  The instrument calculates the power of each avalanche as seen in Figure A. 

The user can create a flowability method link where multiple methods will run consecutively on the same sample.  This method link allows the user to measure any changes in the powder as a result of rotation speed.

The REVOLUTION Powder Analyzer calculates the power average by measuring the change in the power of the powder for each avalanche. The power spectrum shows graphically the total power amplitude at each avalanche frequency in Figure B. 

A spectrum analysis is also performed by Fast Fourier Transform (FFT).  The FFT power average is calculated as the square root of the sum of the squares of the coefficients of the sine and cosine components. 

The cumulative powder spectra provides an excellent tool for comparing the flowability of different powders (Figure C). The lower the avalanche time and power, the better the powder flows.  This analysis allows the user to evaluate the power and frequency of their powder's avalanches.  

One can evaluate the powder's power changes over time by reviewing the surface slope.  The surface slope indicates if the powder avalanche size has changed over time. The REVOLUTION Powder Analyzer also measures avalanche angle and rest angle of each avalanche.  This Angle Graph displayed in Figure D will indicate the average angle required to start and continue the flow of the powder.  For example, let's say the powder has to flow freely and smoothly from a small container.  The Angle Graph will determine the required average angle to start and maintain the flow of the powder. 

In addition to avalanches, the REVOLUTION Powder Analyzer measures many additional parameters to help determine the differences between powders and establish parameters for predicting powder flowability performance.  These measurements include fractal dimension (Figure E), powder volume (Figure F) and surface linearity.

 

Figure A - Powder Power Graph - X Axis is Time - Y Axis is Powder Power (the height of  the powder in the rotating drum)

Figure B - Power Spectrum Graph - Avalanche Time vs. Power

Figure C - Cumulative Power Spectrum - Avalanche Time vs. Power - The avalanche cycles for the Red Sample are longer and stronger than the avalanche cycles of the Blue Sample. This analysis indicates that the Blue Sample will flow easier and smoother than the Red Sample.

Figure D - Angle Graph - Angle (Degrees) vs. Occurrences - The Blue Sample has lower avalanche angles than the Red Sample indicating better flowability performance.

Figure E - Surface Fractal Dimension - Fractal Dimension vs. Avalanche Number - The Red Sample forms a rougher surface than the Blue Sample. This analysis  indicates that the Red Sample will fill molds more unevenly than the Blue Sample.

Figure F - Powder Volume - Time vs. Powder Volume - The volume of a powder was measured over several rotation sequences and the volume decreased.

Once the flowability test has been completed, the software will provide the user with the following statistical analysis.   Please double click on any of the parameters for a brief measurement description.

 

Copyright of Mercury Scientific Inc      Revised March 2008     All rights reserved.