Pressure profile in the internal mixer

The net volume of the mixing chamber is 1,690 cm, and the compacted volume of the compound is 1,200 cm. This gives a fill factor of 71%. The material just in front of the rotor is under pressure. At 70% fill factor, a sharp pressure peak of approximately 0.85 MPa at the rotor front has been reported [12]. The ram pressure in the present example is 0.24 MPa. In general, the material in the chamber is under a large and constantly varying pressure gradient. The pressure profile is expected to vary not only in the direction of rotation, but also in the radial and axial directions of the rotors. 

Because in this mixer, the two rotors take different positions with respect to each other for each turn [18] and come back to repeat the same relative position only every eleventh turn, the pressure profile is different for each turn. The pressure profile also depends upon the material properties and is, therefore, expected to change with the progress of mixing. 

Quantitative information on the pressure profile is necessary for the detailed definition of the flow and deformation in the internal mixer. However, it requires extensive instrumentation, which has not been available as yet. For the purpose of the present paper, only a semi-quantitative discussion is given. 

---