Pump ratio

Improper pump ratio for a two-stage screw Flow of resin out the vent opening 13.1... 

Eor PA/ABS blends, e.g., Alphaloy MPA, Elemid , Diaaloy N, Kane ace MUH, Malecca S, Maxloy A, Monkalloy N, N5, Novaloy -A, Stapron N, SX, Techniace TA, Toyolac Adloy, Triax 1000, Ultramid ), single or twin screw extruders are suitable. However, the latter are preferred. Typical ABS extrusion procedure should be followed. Eor two-stage screws, a first stage compression ratio of 25-2.1 and pump ratio 1.5-2 are recommended. 

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The ratio of depth in the pump section to depth in the metering section is often referred to as pump ratio Xp. The optimum pump ratio H according to Eq. 8.83 is only a function of the power law index this is shown in Eig. 8.38. 

Optimum pump ratio versus power law index... 

The pump ratio should increase when the power law index decreases. The practical lower limit is 1.5 and should be used for polymers with almost Newtonian flow characteristics. The upper limit of the pump ratio is 2.0 and should be used for polymers with very strong pseudo-plastic flow behavior. 

Strictly speaking, one cannot insert a power law melt viscosity in the Newtonian throughput-pressure reiationship, as discussed earlier in Section 8.2.1. Thus, Eqs. 8.81 and 8.83 are not 100% accurate. However, they are much more accurate than predictions based on pure Newtonian behavior, because the latter can cause substantial errors see, for instance. Figs. 7.62 through 7.66. The dimensionless maximum pressure is shown as a function of the pump ratio Xp in Fig. 8.39. 

Figure 8.39 Dimensionless maximum pressure versus pump ratio...

Dimensionless pressure versus pump ratio for n = 0.5 and various shear rates... 

As discussed in Section 8.5.1, the optimum pump ratio ranges from 1.5 to 2.0. In practice, the pump ratio is often selected in the range from 1.2 to 1.4. However, these lower pump ratios make the extruder more susceptible to vent flow. Sometimes vent flow is avoided by starve feeding the extruder. However, if starve feeding... 

They offer a range of pumps. For adhesives, driving air motor pumps are used an air motor is used to drive the fluid pump reciprocating motion to feed material. The area of the air motor piston versus the area of the pump piston creates the theoretical pump ratio. 

The pump pressure ratio multiplied by the air pressure gives the stalled fluid outlet pressure for instance, a pump ratio of 20, multiplied with an air pressure of 4 bars, will give 80 bars fluid pressure. 

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