## 3 Design of Internal Meshing Screw Mixer
### Internal Meshing Screw Mixer  
#### 3.2.1 Stator and Rotor Device of the Internal Meshing Screw Mixer  
Most studies focus on extruders in the plastics and rubber industries, where the screw consists of the feed zone, compression zone, melting zone, mixing zone, and extrusion zone. Solid particles are typically fed, so heating devices are generally arranged externally to the stator to provide sufficient temperature to melt the raw material. It is important to emphasize that this study focuses not on an extruder but on a mixing experimental device; therefore, compression, melting, and extrusion zones are not included. Due to the characteristics of the research object (added in gel state, corn syrup), there is no need for a heating device to heat it.  
The stator and rotor device of the internal meshing screw mixer is composed of a sealing section, feeding section, mixing section (including five flat sections and five spiral sections), exhaust section, compaction section, and discharging and sealing section [40], shown in Figure 9a. The sealing section comprises forward threads with gradually increasing pitch. The initial small pitch is designed to facilitate sealing, while the progressively increasing pitch is coordinated with the feed section to facilitate material feeding. The feed section consists of threads with larger pitch, enabling rapid forward propulsion of the material into the mixing section. The mixing section includes multiple straight sections and helical sections. The primary purpose of the straight sections is to stretch and mix the material, while the helical sections provide both mixing forces and forward propulsion. The helical and straight sections are alternately arranged, with the pitch of the helical sections gradually decreasing to enhance mixing forces. Subsequently, the exhaust section follows, characterized by a larger gap between the rotor and stator. Prior to the exhaust section, the material is divided into two portions within the channel to achieve stretching and mixing separately. Increasing the gap in the exhaust section allows the two separated material portions to merge, and by adding a vacuum device, air mixed inside can be removed. Following the exhaust section is the compaction section, where the pitch gradually decreases to compact and convey the mixed material to the discharge outlet for discharge. At the discharge outlet, there are reverse threads at both ends, with the first section having a slightly larger pitch to facilitate discharge, while the other section comprises reverse threads with a smaller pitch for sealing purposes. In order to facilitate the visualization test, the stator is made of transparent material SLA3D printing, and the rotor is made of stainless steel 3D printing, shown in Figure 9b.  
Figure 8: Internal meshing screw mixer drive system. The blue arrow represents the direction of rotation of the gear.  
Figure 10 shows the matching of the rotor and stator at three special positions. Due to the complexity of the rotor profile, the position is marked by the location of the keyway. Position A refers to 0 number of turns in Table 1, position B refers to a 1/4 number of turns, and position C refers to a 1/2 number of turns. It can be seen that the rotor and the stator have a good match, which provides a good basis for mixing.  
Figure 10: Matching of rotor and stator at three special positions: (**a**) Position A; (**b**) Position B; (**c**) Position C.  
Figure 9: Stators and rotors for mixing: (**a**) Rotor diagram and sectorization; (**b**) Rotor and stators of mixer made by 3D printing.