# Effects of Dry Granulation Operating Parameters on Forming Quality
## 3 Results and Discussion
### Impact of the Roller Speed on Tablet Formation  
The quality parameters of the tablet formed after rolling are evaluated via the density distribution, and the rollers and sealing structures are hidden during the analysis. A monitoring surface was established in the width direction of the tablet at the gap between the rollers, and the density on the path was extracted and used to solve for the average density. By comparing the simulation results of the model at different feeding speeds, it can be found that the tablet has the maximum density at the gap between the rollers, mainly concentrated in the middle, and decreases approximately in a circular manner towards both sides. This is mainly because the powder expands towards both sides under the pressure. The powder is more concentrated in the middle, and the actual screw feed shows uneven material in the space. The filling rate of the powder in the middle is higher, leading to a greater contact pressure. The analysis of the slice diagram of the tablet shows that with the increase of the feeding speed, the area of the maximum density of the tablet in the center increases towards both sides, and the average density increases from 0.49 g/cm\({}^{3}\) to 0.58 g/cm\({}^{3}\), which makes the tablet thicker and is conducive to increasing the efficiency of  
Figure 4: The density distribution of the sheet under different feeding speeds: (**a**) Sheet forming with a feeding speed of 24 mm/s, with a maximum density of 0.603 g/cm\({}^{3}\) and an average density of 0.49 g/cm\({}^{3}\). (**b**) Sheet forming with a feeding speed of 30 mm/s, with a maximum density of 0.628 g/cm\({}^{3}\) and an average density of 0.51 g/cm\({}^{3}\). (**c**) Sheet forming with a feeding speed of 36 mm/s, with a maximum density of 0.739 g/cm\({}^{3}\) and an average density of 0.58 g/cm\({}^{3}\). the tablet formation. As shown in Figure 4c, there is an expansion at the tail of the powder, mainly because when the feeding speed is too high and the roller speed is constant, the amount of feeding is increased, and the powder accumulates near the sealing plates. There are some burrs or distorted grids on both sides of the tablet, which is due to the rolling effect of the small gap, causing some of the meshes to extend to both sides and interact with the sealing plate, thereby causing curling towards the gap between the sealing plate and the roller. This is consistent with the actual leakage of the powder, but the finite element method cannot show the volume reduction caused by the leakage of the powder. To analyze the impact of the roller speed on tablet formation, the friction coefficient between the roller surface and the sealing structure was set to 0.4, the horizontal feeding speed was set to 25 mm/s, and the roller clearance was set to 4 mm. As shown in Table 5, the roller speeds of 1.5 rad/s, 2.5 rad/s, and 3.5 rad/s were taken as three variable parameters. The density cloud and the slice diagram of the tablet after solving are shown in Figure 5.  
By comparing the simulation models at different roller speeds, it can be seen from Figure 5 that the area of the highest tablet density is concentrated at the gap, which is consistent with the simulation results in the previous section. When the speed of the feeding powder remains constant, increasing the roller speed accelerates the roll pressure on the tablets. The maximum tablet density decreased from 0. 64 g/cm\({}^{3}\) to 0.52 g/cm\({}^{3}\) because the increased linear speed of the roller surface drove a large amount of powder, while the time the formed tablets stayed at the gap between rollers was reduced. The pressure time applied by the rollers at the gap decreased, and the average density of the powder decreased. As the roller speed increased, the maximum density of the powder density shifted from the edge to the center of the powder, and the density around the center was relatively low, which indicates that the tablet forming quality was poor, and the surface of the tablet was soft.