## 4 Test Results and Analysis
### Significance Analysis
The quadratic polynomial regression model derived from the regression coefficients calculated by Design-Expert software is as follows:  
\[ \begin{cases}\begin{array}{c}PLR=1.07-0.18A+0.26B+0.15\text{C}-0.028 AB+0.09 AC+ \\ 0.095 BC+0.14A^{2}+0.37B^{2}+0.11\text{C}^{2}\\ PLR=1.07-0.18A+0.26B+0.15\text{C}-0.028 AB+0.09 AC+\\ 0.095 BC+0.14A^{2}+0.37B^{2}+0.11\text{C}^{2}\\ PBR=0.7+0.37A+0.12B-0.18C-0.018 AB-0.08 AC+\\ 0.1 BC+0.29A^{2}+0.28B^{2}+0.051\text{C}^{2}\end{array}\end{cases}  \tag{8}\]  
The \(p\) values for each factor listed in Table 4 show that \(A\), \(B\), \(C\), \(A^{2}\), and \(B^{2}\) had a significant effect on the _PLR_ (\(p\) < 0.01); \(BC\) and \(C^{2}\) had a significant effect on the _PLR_ (\(p\) < 0.05); and \(AB\) and \(AC\) had no significant effect on the _PLR_ (\(p\) > 0.05). For the _PIR_, the effects of \(A\), \(B\), \(C\), and \(B^{2}\) were very significant (\(p\) < 0.01), and those of \(AB\), \(A^{2}\), and \(C^{2}\) were significant (\(p\) < 0.05), whereas those of \(BC\) and \(AC\) were not significant (\(p\) > 0.05). For the _PBR_, the effects of \(A\), \(B\), \(C\), \(A^{2}\), and \(B^{2}\) were very significant (\(p\) < 0.01); those of \(AC\) and \(BC\) were significant (\(p\) < 0.05); whereas those of \(AB\) and \(C^{2}\) were not significant (\(p\) > 0.05). The F-value of each influencing factor in Table 4 was analyzed; the larger the F-value, the greater the influence on the response index. Therefore, the order of single factor effect on _PLR_ is as follows: operating speed \(>\) drum rotation speed \(>\) spiral angle of straw guide board; the order of single factor effect on _PIR_ is as follows: drum rotation speed \(>\) operating speed \(>\) spiral angle of straw guide board; and the order of single factor effect on _PBR_ was as follows: drum rotation speed \(>\) spiral angle of straw guide board \(>\) operating speed. For the _PLR_ interaction terms, the order of influence is operating speed \(\times\) spiral angle of straw guide board \(>\) drum rotation speed \(\times\) spiral angle of straw guide board \(>\) drum rotation speed \(\times\) operating speed. For the _PIR_ interaction terms, the order of influence is drum rotation speed \(\times\) operating speed \(>\) operating speed \(\times\) spiral angle of straw \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Indicator** & **Source** & \
\begin{tabular}{c} **Sum of** \\ **Squares** \\ \end{tabular} & **df** &
\begin{tabular}{c} **Mean** \\ **Squares** \\ \end{tabular} & **F-Value** & \(p\)**-Value** & **Significance** \\ \hline \multirow{8}{*}{_PBR_} & Model & 2.29 & 9 & 0.25 & 71.44 & \textless{}0.0001 & ** \\  & \(A\) & 1.10 & 1 & 1.10 & 309.91 & \textless{}0.0001 & ** \\  & \(B\) & 0.11 & 1 & 0.11 & 31.04 & 0.0008 & ** \\  & \(C\) & 0.26 & 1 & 0.26 & 71.84 & \textless{}0.0001 & ** \\  & \(AB\) & \(1.225\times 10^{-3}\) & 1 & \(1.225\times 10^{-3}\) & 0.34 & 0.5758 & \\  & \(AC\) & 0.026 & 1 & 0.026 & 7.20 & 0.0314 & * \\  & \(BC\) & 0.042 & 1 & 0.042 & 11.81 & 0.0109 & * \\  & \(A^{2}\) & 0.36 & 1 & 0.36 & 100.22 & \textless{}0.0001 & ** \\  & \(B^{2}\) & 0.33 & 1 & 0.33 & 91.79 & \textless{}0.0001 & ** \\  & \(C^{2}\) & 0.011 & 1 & 0.011 & 3.08 & 0.1228 & \\  & Residual & 0.025 & 7 & \(3.558\times 10^{-3}\) & & & \\  & Lack of Fit & 0.016 & 3 & \(5.108\times 10^{-3}\) & 1.43 & 0.1993 & \\  & Pure Error & \(8.68\times 10^{-3}\) & 4 & \(2.17\times 10^{-3}\) & & & \\  & Cor Total & 2.31 & 16 & & & & \\  & \(\text{R}^{2}\) & 0.9892 & & & & & \\  & Adj R\({}^{2}\) & 0.9754 & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._  
Figure 7 shows the response surface and contour plot for the _PLR_. As can be seen from from Figure 7a,b, the _PLR_ tends to decrease with increasing drum rotation speed (\(A\)). This is because as \(A\) increases, the impact force of threshing teeth on the straw increases, the probability of impact per unit of time also increases, the grain on the straw is easier to be depurated, and the entrainment loss decreases.