# Study of Refining Effect of Mixed Pulps Using Refiner Plates with Different Bar Patterns
## 2 Experimental
### Manufacturing a Novel Refiner Plate without a Draft Angle  
Refiner plates manufactured using conventional sand casting usually require 2 to 5 degrees of draft angle to prevent damage to the sand mold during the pattern removal step (see Figure 1). If the draft angle can be eliminated, the new plate will have several advantages over trapezoidal bar plates in terms of stock throughput, energy saving, plate life, and bar edge sharpness [20; 21]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \begin{tabular}{c} **Length-Weighted** \\ **Mean Fiber** \\ **Length (mm)** \\ \end{tabular} & \begin{tabular}{c} **Length-** \\ **Weighted Fine** \\ **Contents (\%)** \\ \end{tabular} & \begin{tabular}{c} **Fiber Width** \\ **(um)** \\ \end{tabular} & \
\begin{tabular}{c} **Fiber** \\ **Coarseness** \\ **(mg/m)** \\ \end{tabular} &
\begin{tabular}{c} **Freeness** \\ **(mL CSF)** \\ \end{tabular} \\ \hline Hw-BKP & 0.7 & 9.5 & 20.6 & 0.46 & 640 \\ Sw-BKP & 2.2 & 5.1 & 34.0 & 0.18 & 790 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Fiber properties of raw materials. However, it was not possible to remove the draft angle with the general sand casting method, so a new manufacturing method had to be developed. A stainless alloy plate with excellent wear and corrosion resistance was cut with a laser to about 15 mm high and the desired bar length to manufacture a plate without a draft angle. Each cut bar was heat-treated at about 1500 \({}^{\circ}\)C and then inserted into the pre-made grooves of the metal mold (refer to Figure 2a). The flask was placed in the metal mold with the inserted bars and filled with resin-coated sand. The flask was hardened at 200-500 \({}^{\circ}\)C to make a sand mold. The flask for the base plate was also prepared in a similar way. When the cooled sand-mold flask was lifted, the bars inserted in the metal mold were transferred to the flask and combined with the base-plate flask. After the molten aluminum alloy was placed in the inlet between the flasks and cooled (refer to Figure 2b), the sand mold adhering to the finished plate was removed, followed by post-treatment to adjust the plate base surface and the bar height uniformly. Since the refiner plate is manufactured with laser-cut stainless-steel bars inserted into the plate base, the bar has a rectangular shape in a lateral view without the draft angle, unlike a conventional casting plate (refer to Figure 3). Figure 1: Draft angle for manufacturing a bar plate through the sand casting and breakage of sand mold during removal of the cast pattern. Figure 2: Manufacturing process for the refiner plate without a draft angle: (**a**) Bar insertion process to a metal mold; (**b**) Flask for the casting. Figure 4 shows the two types of novel refiner plates without the draft angle used for this study. The refining effects of the mixed pulps were investigated using these two novel plates with different bar fillings. CELs for the two plates were calculated according to the guidance of ISO/TR 11371 as follows:  
\[SEL\ (\mathrm{J/m})=\frac{P_{t}\ -\ P_{0}}{Z_{r}\times Z_{st}\times I\ \times\ n}\ =\ \frac{P_{t}\ -\ P_{0}}{CLF\ \times\ n}\ =\ \frac{P_{t}\ -\ P_{0}}{CLL} \tag{1}\]  
where \(SEL\) is the Specific Edge Load (SEL, \(\mathrm{J/m}\), \(\mathrm{W\cdot s/m}\)), \(P_{t}\) is the total load power (kW), \(P_{0}\) is the no-load power (kW), and \(n\) is the rotational speed (rev/s). \(Z_{r}\) and \(Z_{st}\) are the total numbers of rotor and stator bars, \(l\) is the bar length (km), \(CLF\) is the cutting length factor (km/rev), and \(CL\) is the cutting edge length (km/s). Table 2 compares the dimensions and CEL of the two plates with different bar fillings. Plate A (PA55) had 67 bars, significantly fewer than Plate B (PB97), with 160 bars, producing a much smaller CEL than PB97. CEL has been regarded as the predominant factor in determining SEL. Low-intensity refining becomes possible with the increased CEL of the refiner plate.