# Effects of Dry Granulation Operating Parameters on Forming Quality
## 3 Results and Discussion  
### Impact of the Feeding Speed on Table Formation  
To analyze the impact of the feeding speed on tablet formation, the process parameters were set as follows (in Table 4): the roller speed was 2 rad/s; the roller clearance was 4 mm; the friction coefficient between the roller surface and sealing structure was 0.4; and the horizontal feeding speed was 24 mm/s, 30 mm/s, and 36 mm/s, respectively. The corresponding screw speeds were calculated to be 115 r/min, 144 r/min, and 172 r/min, respectively.  
The density clouds and slice diagrams of the tablet at the gap between rollers with the same time step after being solved using the dynamic-explicit solver are shown below in Figure 4.  
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 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, and there is also the influence of the edge effect. The edge effect means that the pressure at the edge of the roller will decrease even if there is an edge seal [11; 13]. This edge effect is reduced due to the increase of pressure generated in the feed powder speed. 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 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.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Screw Speed** & **Axial Velocity** & **Roller Speed** & **Rotational Speed Ratio** \\ \hline
115 r/min & 24 mm/s & 2 rad/s & 6:1 \\
144 r/min & 30 mm/s & 2 rad/s & 7.5:1 \\
172 r/min & 36 mm/s & 2 rad/s & 9:1 \\ \hline \end{tabular}
\end{table}
Table 4: Different combinations of process conditions for the study of feeding speed.