## 3 Results and Discussion
### Study of the Degree of Grinding and Screw Rotation Speed on the Oil Mass Flow Rate  
The mass yield of oil was the primary outcome measure to assess the efficiency of the pressing machine under different conditions. At a screw rotation speed of 30 rpm, the results indicated that without pre-grinding, the oil output was 10.8 g/s. However, as the grinding degree increased, the oil yield also increased (\(p<0.05\)), reaching 12.6 g/s when ground to 5 mm and 15.3 g/s when ground to 4 mm. Further reduction in grinding size to 3 mm resulted in a decreased oil output of 8.4 g/s, while grinding to 2 mm led to a further decrease to 6.9 g/s (\(p<0.05\)). The same trends were observed when the screw rotation speed was increased to 60, 120, and 250 rpm (Figure 13).  
Figure 11: Pressed granulated seed cake.  
Figure 12: The oil separated from the cake.  
The findings from this study provide valuable insights into the optimal conditions for sunflower oil pressing. The results indicate that a grinding degree of 4 mm consistently yielded higher oil outputs across different screw rotation speeds. Additionally, a lower screw rotation speed of 60 rpm appeared to be optimal for achieving higher oil yields, as it consistently outperformed the higher speeds of 120 rpm and 250 rpm.  
As can be seen from Figure 13, the most optimal degree of grinding is the use of the plate with a hole diameter of 4 mm and a screw rotation speed of 60 rpm. At these parameters, the highest oil yield (15.6 g/s) was registered. Increasing the rotational speed leads to an insufficient pressing duration, i.e., to incomplete oil extraction from sunflower seeds and to an increase in the power required for pressing.  
[PERSON] et al. (2011) investigated the pressing of black seeds using a KOMET Screw Oil Expeller with a shaft screw diameter of 11 mm and nozzle sizes of 6 and 10 mm. They achieved the highest oil yield of 65% under these specific conditions [27]. It is worth noting that their study involved a different seed type and equipment specifications compared to our research. [PERSON] et al. (2009) studied Jatropha seeds pressing with a screw press and found that the highest oil yield was obtained at a rotational speed of 45 rpm and nozzle size of 6 mm [28]. Although they worked with a different seed type, rotational  
Figure 13: Dependence of oil mass flow rate on the degree of sunflower seed grinding and screw rotation speed (different letters above the lines indicate significant differences between samples, \(p<0.05\)).  
speed, and nozzle size, their findings align with our observations that adjusting operational parameters can influence the oil yield. [PERSON] et al. (2023) investigated the pressing of safflower seeds using a RAWMID Dream Modern oil press. They reported the highest oil yield at a diaphragm gap of \(\delta=0.1\) mm and a screw rotation speed of \(\omega=6.2\) rad/s (372 rpm) [29]. Their research, focusing on safflower seeds and a specific oil press model, reinforces the notion that optimizing operational parameters can enhance oil yield.  
In line with [PERSON] et al. (2018), our results also support the idea that increasing the rotation speed of the screw press can enhance its capacity and decrease the passage time [30]. However, it is important to note that higher rotation speeds may result in a reduced extraction yield and specific energy consumption, implying the need for a careful balance between efficiency and oil yield.  
Overall, comparing our findings with other research results showcases the significance of adjusting pressing parameters to achieve optimal oil yield. The specific characteristics of the seeds, equipment, and experimental conditions in each study contribute to variations in the outcomes. Our research provides valuable insights into the pressing of sunflower seeds, demonstrating the influence of the grinding size and screw rotation speed on the oil yield. Future investigations exploring additional parameter combinations to optimize the oil extraction process for sunflower seeds can further build on these findings.