Roller compaction roll speed

Figure 3 Plot of d90 and d50 values for the 10% tolmetin granules versus the slope of best-fit line showing good agreement between the values from the compacts prepared under two different sets of roller compactor roll/HFS/VFS speed settings.

Different spectral preprocessing and transformations available in SIMCA P-p (version 10.0, Umetrics, Sweden) were evaluated and the best approach for data handling and manipulation was determined. Data collected on the surrogate tablets were divided into a training set to generate the PLS models, and prediction set to test the PLS models. MCC powder, equilibrated at different RH, was also roller compacted at different roll speeds on a Fitzpatrick IR220 roller compactor fitted with smooth rolls. Powder feed rate and roll pressure were kept constant for all experiments. The key sample attributes measured on the surrogate tablets were also measured for the samples prepared by roller compaction. 

The 10% w/w APAP powder blend was roller compacted. Different moisture contents were achieved by equilibrating and roller compacting the above powder blend under 24, 45, and 65% RH conditions, representing 3.3, 5.0, and 6.3% w/w moisture content, respectively. Compacts were prepared at 5.0, 6.0, and 7.2 rpm roll speeds with the powder feed rate and roll pressure kept constant. Compaction run time was four minutes at each roll speed. Samples were also collected for off-line measurements of... 

Figure 8 PLS predicted values of LOD from the NIR data collected during realtime monitoring of roller compaction at different RH. Key Diamonds, 24% RH squares, 45% RH triangles, 65% RH. Four minutes each at 7.2, 6.0, and 5.0 rpm roll speeds, respectively.

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. 

Dehont et al. provided a simplified approach to roller compaction theory. They described that powder granules move through stages in the feed area. The material is drawn into the gap by rubbing against the roll surfaces. The densification that occurs in this area is particle rearrangement. At this stage, the speed of the powder is slower than the peripheral speed of the rollers. Fig. 1 represents compactor rolls in the horizontal plane powder is pushed vertically downward into the compaction area. 

Roll speed For most considerations and approximations it is assumed that the peripheral speed of the rollers and the speed of the particulate matter are identical in the entire compaction zone. In reality this is not true throughput does not increase proportionately with roll speed. The maximum speed is determined by two effects starved conditions in the compaction zone develop if ... 

PVP Concentration. The effect of binder concentration on the properties of granules and tablets prepared by roller compaction is dependent on other processing parameters including feed rate, roll pressure, and speed. Increasing the binder level increases tablet hardness and decreases their friability due to the... 

Powder compaction may also be achieved in roll processes, including briquetting, in which compression takes place between two rollers rotating at the same speed—that is without producing any shearing action. In pellet mills, a moist feed is forced through die holes where the resistance force is attributable to the friction between the powder and the walls of the dies. 

Figure 4 Comparison of the offline slope values (filled circles) with the real-time slope values (open triangles) for the 10% tolmetin compacts prepared at different roller compactor settings. Values on top are the roll, HFS, and VFS speeds, respectively.

Dehont et al. assumed that the material in the compaction area remains horizontal and moves at the peripheral speed of the rollers. They also considered that the angle a is independent of the roller diameter size and noted that the flake thickness ei depends on the roller speed, the roller surface, and the compaction pressure. All these parameters influence the density of the flake, d. Dehont et al. concluded that if the same flake thickness was obtained with different roller diameters, the flake density would be greater with larger diameter rollers. This is due to the greater nip angle formed, with the larger rolls allowing more material to be compacted. 

Roll gap is defined the narrowest distance between the two rolls. At any given compaction pressure, a specific roller gap will yield a corresponding fixed flake thickness (allowing for some product expansion). A fixed feed rate for a fixed roller speed and compaction pressure maintains the flake thickness. Rollers get too close if the material feed is too low and vice versa. Therefore, in principle, acceleration or deceleration of product delivery system can cause variations in the ribbon thickness and density. By monitoring the roll gap in a feedback loop, a constant material feed can be achieved. 

Figure 227 shows a smooth face roller press. The feed zone is defined by the two angles and In the feed zone, the material is pulled into the nip by friction on the roller surface. Densification is solely due to rearrangement of particles (Figure 181A). The density of the feed is characterized by the bulk density 70 and reaches the tap density 7t at the point . The peripheral speed w of the rolls is higher in this zone than the velocity u of the material to be compacted, ocq is the so-called angle of delivery which is defined by the width /Zo of the feed opening above the rollers as well as the material (flowability)...

Theory of rolling The basic principle of compaction of particulate solids between two counter-currently rotating rollers (Figure 230) is similar to that used in calenders for plastic foils or in rolling mills for metals. The first can be adjusted to extremely narrow gap tolerances across press rollers with face widths of up to 2 meters and production speeds of approximately lOOm/min in the latter enormous pressing forces can handle ingots of more than 35 tons weight. 

Expansion of the strip after pressure release is influenced by the physical characteristics of the material to be compacted (plasticity, brittleness, particle size and distribution, particle shape, etc.), the roll diameter, the speed of rotation, and the surface configuration of the rollers. With increasing roll diameter and/or decreasing speed the expansion of compacted material is reduced due to better deaeration during densification and a more complete conversion of elastic into permanent, plastic deformation. 

A product as described under operation 1 is most easily obtained with a small roller diameter or narrow roll gap (small sheet thickness) and low circumferential speed (both resulting in small capacity) as well as little compaction ratio. Then, only a relatively small amount of air is expelled which can escape partly to the top and partly to the sides of the rollers. 

Roll drive arrangement In most cases, a high torque is necessary on the rollers. The drive torque should be divided equally between the two rollers and both rolls should (in the case of briquetting, must) rotate with exactly the same speed. Also in the case of smooth rollers and compaction of a sheet, even minute... 

In machines with fixed rolls the optimum compaction force is obtained by adjusting the feed rate and density to the nip. Roller diameter, speed, and gap, as well as characteristics of the raw feed such as friction between material and rolls and particulate size, shape, and brittleness, all greatly influence the respective operating conditions. 

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