High rotors

For the dispersed phase firm relationships have not been established, but at high rotor speeds, Eq may be 1 to 3 times Ec- In any event, axial mixing for the hquid flowing at the lower rate becomes very severe for extreme flow ratios (>10). 

In most designs, the reaetion of the turbine varies from hub to shroud. The impulse turbine is a reaetion turbine with a reaetion of zero (R = 0). The utilization factor for a fixed nozzle angle will increase as the reaction approaches 100%. For = 1, the utilization factor does not reach unity but reaches some maximum finite value. The 100% reaction turbine is not practical because of the high rotor speed necessary for a good utilization factor. For reaction less than zero, the rotor has a diffusing action. Diffusing action in the rotor is undesirable, since it leads to flow losses. 

Figure 5.123 a and b. Gas-liquid mixing modes a) bubble column behaviour (high gas flow, low rotor speed) b) circulating tank behaviour (high rotor speed, reduced gas flow). 

The viscosity curve of a typical non-Newtonian product such as polystyrene is plotted in Figure 8 as a function of the shear gradient. Because of the small gap between rotor and heating wall, together with the relatively high rotor speed, the thin-film machine works within the limits of shear gradient of 1000 to 10,000 sec 1. 

Excessive terminal voltage from the generator implies that the exciter is being forced to produce a high rotor current in the generator. Consequently both the generator itself and its exciter are being overstressed in terms of current, and therefore may become overheated. 

It may be seen that if this method is used to control the speed of a standard, almost constant-speed type of induction motor, then the actual range of speed control obtained will, in fact, be small before stalling occurs. The situation could be improved by using a motor with a high rotor resistance as shown in Figure 14.2. The rotor resistance at full-load has been increased by a factor of 10 in order to demonstrate the effect on the torque-speed characteristic. 

Start the Banbury at medium to high rotor speed. 

Fig 7. Viscosity versus mixing time for mastication and peptization, (a) High rotor speed, high ram pressure (b) low rotor speed, high ram pressure (c) high rotor speed, low ram pressure (d) low rotor speed, low ram pressure. 

Fig. 9. Viscosity versus peptizer level for in batch peptization using a short, high-rotor-speed, high-ram-pressure mixing cycle. Symbols as in Fig. 8. The top two curves represent the viscosity of the masterbatch stage in each case...

The Banbury mixer is ideally suited to the making of thermoplastic rubbers. Polystyrene/SBR blends can be mixed in 3-4 min and TPEs requiring higher temperatures in 5-6 min. The requirement is to have a mixer with high rotor speeds, e.g. 120 rpm for an 80-litre mixer, discharging into an extruder with an underwater pelletizing head. 

---