Issue link: https://www.e-digitaleditions.com/i/1112785
Tablets & Capsules May 2019 23 Figure 13 Typical tablet press feed frame Figure 14 Expected unwanted breakage in a tablet press feed frame during operation 20 18 16 14 12 10 8 6 4 2 0 Total degradation (%) Particle size (microns) 0 100 1,000 Total strain (cm/cm) 200 1,000 Kerry Johanson is chief operational officer of Material Flow Solutions (352 379 8879, www.matflowsol.com). He holds a PhD in chemical engineering from Brigham Young University and has more than 35 years of experience solv- ing bulk powder and granule handling problems. The com- pany specializes in material property testing and analysis and designing or retrofitting material handling systems to optimize production. causing the most stress to minimize breakage. In some cases, the key variable would be the diameter of a ves- sel. In others, high stress conditions may be caused by excessive friction on the walls of a feeder. Sometimes changing the shape of a vessel will reduce stress on the particles and minimize unwanted breakage. In the example of the 10-foot-diameter versus 3-foot-diameter bins, the smaller bin diameter signifi- cantly reduced the expected particle breakage, decreasing fines generation by 43 percent. In the case of the feed frame, strain from the rotating paddles is the process variable causing unwanted breakage. You can control this strain by changing the paddles' rota- tional speed relative to the rotational speed of the tur- ret plate and optimizing the gap spacing in the feed frame to minimize total strain. Conclusion T h i s s c i e n c e - b a s e d a p p r o a c h t o m i t i g a t i n g unwanted particle breakage is applicable to a range of process scenarios and industries, including pharmaceu- ticals, food, consumer goods, ceramics, and mining. You can apply the stress-strain breakage tests to bins, hoppers, pneumatic transport lines, tablet press feed frames, rotary driers, screw conveyors, rotary valves, ribbon blenders, plow blenders, v-blenders, fluid-bed units, fill hoppers with rotary agitators to aid flow, and bin-dumping stations. The approach requires measuring the breakage as a function of stress-strain and impact events, computing the stress-strain and impact conditions in the process of interest, and then incrementally evaluating the pro- cess to determine which unit operation(s) are causing the breakage problem. Understanding the material's sensitivity to stress, strain, or impact events allows you to determine how to modify a unit operation to mini- mize particle breakage, making this approach a power- ful tool for mitigating unwanted breakage issues. T&C