Roll force

FIG. 20-91 Roll-force factor as a fimction of compressibility K and dimensionless gap distance d + h)/D. [Vietsch (ed.). Roll Pressing, Fowder Advisoiy Centre, London (1987).]... 

The rolling force F must cause the metal to yield over the length I and width w (normal to Fig. 12.6). Thus... 

The TF-Mini and TF-156 compactors (Vector Corporation, Marion, Iowa, U.S.A.) were equipped with concavo-convex rolls and single flight screws. The roll speed of the TF-156 was scaled to achieve the same linear velocity 74.2 in./min as the TF-Mini model. This setting maintained a comparable dwell time for material in the compaction zone. The TF-156 roll force was scaled to 5.6 ton, which equaled a force per linear-inch approximately equal to the TF-Mini 3.1 ton/in. roll width. The authors established a feed screw speed to roll speed ratio of 1.3 1 for the trials. Table 7 gives the compactor equipment settings. 

The major disadvantages of dry granulation are the reduction in tablet compressibility, formulation-dependent process optimization, and inconsistency of equipment types with respect to the process parameters being measured (e.g., roll force vs roll pressure), thus complicating transfer between equipment types. In spite of these... 

The compaction system consists of two, counter-rotating rolls at equivalent speeds. One roll is normally fixed while the other is allowed to float. The floating roll was implemented to control the roll gap. The roll force is applied to the floating roll by hydraulic pressure, which is counteracted by the normal force of the fixed rolls. This force is subsequently applied to the blend in the gap. A schematic of three typical roller compaction system arrangements with a feed screw can be found in Fig. 6.1. 

In contrast, increasing the gap width between the dry granulator rollers decreases the density of the compacted ribbon or briquette (also possible when other factors, such as feed rate or roll force, are changed). This reduced densification process results in a weaker binding of API to carrier excipients, and reduced overall granulation particle size distribution and increased bypass. 

A granulation optimization study on model Drug A targeted the least variability in sieve cut potency.35 The highest percentage bypass levels were concentrated in the region of minimal roll force values and maximal gap width values. 

The variability of sieve cut potencies for Drugs A and B as a function of various roll force levels and dry granulation equipment manufacturers is tabulated in Table 6.14. The change in equipment type had no significant affect on sieve cut potency variability for Drug B. The increased roll force using the same equipment type did impact the variability of sieve cut potencies for Drug A in terms of RSD. 

TABLE 6.14 Variability in Sieve Cut Potency as a Function of Roll Force... 

Sample Batch 1 Batch 2 5 kN Roll Force 9 kN Roll Force Batch 1... 

TABLE 6.19 Effect of the Roll Force, Roll Gap, and Mill Screen Size on Main Compression Force at Target Tablet Hardness ... 

Roll Force (kN) Gap Width (mm) Sieve Size (mm) Compression Force at 7 kPa Crushing Strength... 

Fig. 5.9. Johanson s theoretical roll press design roll-force factor (F) versus (d + S)/D [13].

Tension Control Roil These type rolls provide the important function of material tension control. There is a proportional relationship between winding tension and lay-on-roll forces (eliminating areas were bumps, valleys, unwanted stretch, etc. develop). There are various tension control techniques available. The proper selection involves decisions on how to produce the tension, how to sense the tension, and how to control the tension. For instance, if the material has a very low tension requirement and if exact control is required, then perhaps, using a magnetic particle brake with an electrical transducer roll with appropriate electronic control is best. However, if the material is on large diameter rolls and moves at slow speed, then a roll follower system can be used effectively. 

The appropriate roll force then scales as follows ... 

Figure 221. Double roll pressing geometry, angles, and roll force. Compaction of particulate matter in the nip of a smooth roll press...

Roll pressure and torque After determining roller diameter, width, and gap or briquette size and shape as well as roller speed, using throughput capacity and product density as input, roll force and torque as well as feed pressure must be determined. The requirements on these design parameters of a roll-type press are ... 

The press must be capable of safely supporting the roll force and sustaining the torque necessary to make a good sheet or briquette. 

These relate to the flow properties of the solid to be compacted. if the pressure distribution between the rolls is known (see, for example. Figures 232 and 233), the roll force can be calculated " " from (see Figure 227)... 

Reductions in the roll force and diameter accompanying the increase in precompaction pressure lower the size, weight, and cost of roller presses. In contrast, roll drive requirements remain almost unchanged " if the production rate is kept constant. This is due to increases in the roll torque factor T in the roll drive power equation (106). 

Roll or compaction force. The roll force results from the compaction of... 

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