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20 May 2019 Tablets & Capsules given size when the same example material with a maximum particle size of 320 microns is subjected to repeated impact events at prescribed velocities. These tests are relatively simple to do and provide engineers with the data needed to quantify the particle breakage caused by stress-strain and impact events in most process conditions. Quantifying particle breakage in process equipment Any process or handling step induces a combination of stress, strain, and impact events. In many instances, it's possible to quantify or estimate the stress, strain, and impact velocities generated by the process. Characteriz- ing your processing and handling steps in this manner and coupling these characterizations with the breakage tests discussed in the previous section can help to deter- mine the expected particle breakage during your particu- lar processing and handling operations. The following examples demonstrate how to use breakage testing to characterize process behavior. Because this approach is general to all processes that handle powders or granular materials, the examples come from a variety of industries. Consider the simple process of filling and emptying a bin, which is a very common operation in many manufacturing processes. In the pharmaceutical indus- try, a newly blended material may be transferred to a small surge bin one meter in diameter and held for a period of time before packaging or tableting, at which time the bin is fully emptied. In the consumer market, a bin or silo may be filled, and then the material is dis- charged over time in smaller amounts. While the con- sumer bin may be much larger than the one used in the pharmaceutical industry, the approach is the same. Both impact and stress-strain breakage tests can be used to estimate the expected unwanted breakage in these process conditions. The filling process causes stress from impact events but very little strain as parti- cles free fall into the bin and subsequently rebound down the material pile. The emptying process similarly causes impact stress on the material, but the particle motion during emptying also induces significant strain. Differences in bin size can greatly influence the expected amount of particle breakage. In the food or consumer industry, a typical bin may be about 10 feet in diameter. The bin is filled initially, then the process continuously uses the material while maintaining the bin fill level at some constant value. Using the stress- strain data from the same example material used in the previous section, you can calculate the stress, strain, and percentage increase in particles smaller than 160 microns as shown in Figures 7 through 9. This results in an increase in particles smaller than 160 microns of about 4.98 percent, with most of the particle breakage resulting from strain caused by material flow. Compare those results with those of a typical surge bin for a pharmaceutical application, which may be only 3 feet in diameter. Using the stress-strain data for Impact breakage. You can measure breakage due to impact events by placing a sample in a test cell and shaking the test cell back and forth, causing the mate- rial to impact the cell walls at a prescribed velocity, as illustrated in Figure 4. Figures 5 and 6 show the expected increase in the percentage of particles of a Figure 4 Movement of material in a cylinder test cell during impact testing Figure 6 Expected increase in particles of a given size when a granular material with a maximum particle size of 320 microns is exposed to 300 repeated impact events as a function of impact velocity 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 Percentage increase Velocity (ft/sec) 0 5 10 15 20 Particle size (microns) 130 160 180 Figure 5 Expected increase in particles of a given size when a granular material with a maximum particle size of 320 microns is exposed to 300 repeated impact events as a function of particle size for various velocities 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 Percentage increase Particle size (microns) 10 100 1000 Velocity (ft/s) 17.8 14.8 11.8 5.9