Roll Configuration

Compactor design features have evolved over the years. By the mid-1970s, research revealed a number of roll design improvements that increased compacting efficiency. Three key conditions were identified, at that time, which optimized the roll compact throughput and minimized leakage of noncompacted powder (26)  

Equipment engineers and researchers worked on improving feeding equipment systems and roll designs to satisfy and maximize the above conditions. Some of the key advances are identified in Ref. 21 and are re-emphasized in this chapter. 

Because of powder feed variability at the nip and in the roll gap regions, powder leakage is produced during the compaction process. This situation produces excessive fines and possible undesirable processed material. Usually, this problem is caused by uneven powder fiow and compact formed when the powder is fed toward the middle of the roll width. Granules produced under these conditions are typically not optimal for further pharmaceutical processing. 

Parrott further substantiated the usefulness of the rimmed concavo-convex roller pair to increase the density of several pharmaceutical powders. His work resulted in optimizing a process with an uncompacted leakage rate of 5%. The optimization depended on the physical properties of the powder and the machine operating conditions such as the roller gap, feed screw speed, and roll speed (27). Some of their key design feature findings are summarized  

Jerome et al. in the 1980s studied the effects of compactor adjustments on powder blend properties. His team s research showed that pressure applied by the movable roller is not a predominant factor. They found that the most important variable was the compactor feed screw in relation to the roll speed. More will be said about this 

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Figure 44.20 represents a typical process-roll configuration. The arrows indicate the force vectors generated by the wire, belt, or product wrap around these rolls. The left roll has a force vector at 45° down to the left the right roll has a mirror image force vector and the bottom roll has a vertical vector. 

Figure 44.20 Typical process-roll configuration and wrap-force vectors...

In the roll-to-roll configuration the substrate consists of a continuous roll, e.g. stainless steel [154], Sn02 F-coated aluminum [155], or plastic [156-158], which is pulled through a sequence of deposition chambers. 

Screw/roll configuration Single or twin Single or twin Single or twin Single Dual roothed gears/dual cylinders (one blank and one drilled) Dual solid... 

Fig. E6.1b Alternative design solution of a roll pump from building block 1. On the top we see two two-roll pumps one co-rotating and the other counterrotating. The latter is a toothless gear pump where the pumping mechanism is viscous drag rather than positive displacement. In the middle we have three three-roll configurations, and at the bottom a four-roll pump.

The Li-SOCl2 is produced in the spirally wound, jelly-roll configuration to power high rate applications, such as instrumentation for down-hole oil well logging to determine the characteristics of oil bearing strata. It is also produced in a low surface area, bobbin construction for low drain applications, such as automatic reading of home gas meters. 

It should be noted that in practical batteries such as coin cell (parallel plate configuration) or AA, C, and D (jelly-roll configuration), there is a stack pressure on the electrodes (the Li anodes are pressed by the separator), and the ratio between the solution volume and the electrode s area is usually much lower than in laboratory testing. Both factors may considerably increase the Li cycling efficiency obtained in practical cells, compared with values measured for the same electrolyte solutions in the Li half-cell testing described above. It has already been proven that stack pressure suppresses Li dendrite formation and thus improves the uniformity of Li deposition-dissolution processes [107], The low ratio between the solution volume and the electrode area in practical batteries decreases the detrimental effects of contaminants such as Lewis acids, water, etc., on Li passivation. 

Typical compactor roll configurations are shown in Fig. 8. Most compactors now have one floating roll and one fixed roll each on separate bearing blocks. An illustration of this is shown in Fig. 9. 

Fig. 8 Roll configuration designs. (Courtesy of Alexander-werk Inc.)...

As with other unit operations, the scale-up success for roller compaction is dependent on understanding and identifying the process parameters that will influence the quality of the final product. The typical parameters that can influence compacted ribbon characteristics and the resultant final product qualities are hopper design, feed screw design, and roll configuration. 

Further work is being directed to computer-aided analysis of (1) flow in other roll configurations, especially roll-wall combinations and reverse-roll coating (2) stability of the flow to meniscus nonuniformity — "ribbing," for example and (3) effects of viscoelasticity. 

Figure 7.8 Configurations of corona treatment equipment. (a) Conventional configuration, (b) Bare-roll configuration.

Immobilized-enzyme reactors were considered in Chapter 20. It is easy to extend the concept to immobilization on the walls of a membrane tube. What is even more practical is to immobilize the enzyme in the usual manner on solid particles such as silica and encapsulate the particles in a ribbed sheet of a microporous plastic such as PVC. Then this sheet can be rolled in a jelly-roll configuration inside a spiral reactor (Figure 24.2i). The consequent large surface area of immobilized enzyme available per unit volume of reactor space makes such a spiral reactor an attractive choice. 

Figure 18 Precision corrective leveler corrective roll configuration.

A calender consists of two or more heated rolls with different configurations depending on the product to be manufactured. All different roll configurations (I, L, F, Z, etc. [2]) used for PVC can also be optimized for the processing of PP. The purpose of the heated rolls in the calender is to convert the molten material into a product that has the desired thickness. The thickness decrease is achieved by squeezing the molten plastic through the nips between the heated rolls. The differences in rotation speeds and directions of the rolls drive the molten material to pass the calender [2, 4]. 

Fig. 15. Calendering-roll configurations (a) three-roll superimposed type (b) four-roll inverted-L type (c) four-roll Z type.

Fig. 6.108. Linear elongating dielectric elastomer actuators a tube and b roll configuration...

Details concerning the rolls and roll covers, the roll configuration and other important components of the calenders will be treated below. 

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