|
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 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. 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. |
Sample being tested |
|
The instrument measures 20 parameters relating to the behavior of the sample in the drum including avalanche energy, break energy, surface fractal, sample density, avalanche angle, etc. The standard deviations for all of these measurements is also calculated. Figure A presents the energy level of the powder in the sample drum over time.
|
Figure A - Sample energy versus time |
|
The REVOLUTION Powder Analyzer calculates the power average by measuring the change in the power of the powder for each avalanche. The avalanche spectrum shows graphically the total power amplitude at each avalanche frequency in Figure B.
|
Figure B - Avalanche Spectrum |
|
The cumulative powder spectra provides an excellent tool for comparing the flow properties of different powders (Figure C). The lower the avalanche time and energy, the better the powder flows.
|
Figure C -Cumulative Avalanche Spectrum |
|
The REVOLUTION Powder Analyzer also measures avalanche angle and rest angle of each avalanche. This Angle Graph displayed in Figure D indicates the angles required to start and continue the flow of the powder. The rest angle is typically very close to the angle of repose of the material. The advantage of the RPA is that these measurements can be made hundreds of times providing a repeatable average as well as a range for each parameter measured.
|
Figure D -Avalanche and Rest Angles |
The REVOLUTION Powder Analyzer 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.