Flight radii

Figure 5.27 The effect of flight radii size on solids conveying rates for a barrel temperature of 75 °C, a screw temperature of 50 °C, and a screw speed of 50 rpm...

Spalding, M. A., Dooley, J., and Hyun, K. S., The Effect of Flight Radii Size on the Performance of Single-Screw Extruders, SPEANTEC Tech. Papers, 45, 190 (1999)... 

The size of flight radii on the screw channel is important for the proper performance of a single-screw extruder. The specifications of the flight radii are commonly made using a combination of personal experience and guidelines [16] from the Society of the Plastics Industry, Inc. (SPl). These guidelines state unless otherwise specified the root radius will not be less than one-half of the flight depth up to... 

Figure 11.14 Flight radii and tangent points in a screw channel. The pushing flight R, in this case is estimated at 0.5 the depth of the channel (H) while the radius R2 at the trailing side of the channel is estimated at 1.5 times the channel depth...

Table 11.3 Flight Radii Recommendations to Minimize Resin Degradation at the Channel Edges [20]...

Screw Section Flight Radii to Channel Depth Ratio... 

The lead length was 120 mm for the main flight of the screw. The main flight width and clearance were 13 and 0.12 mm, respectively, in all sections of the screw. The compression ratio was 1.5 and the compression rate was 0.0013. The ratio of the flight radii in the meter section to the meter depth was 0.2. The specific rotational rate was calculated at 9.3 kg/(h rpm). ... 

The injection-molding press was producing a part and runner system that had a mass of 2.15 kg. The mass was plasticated using a 120 mm diameter, 8L/D screw. The screw used for the process had a barrier melting section that extended to the end of the screw, as shown by the specifications in Table 11.9. That is, the screw did not have a metering channel. Instead, the last sections of the barrier section were required to produce the pressure that was needed to flow the resin through the nonreturn valve and into the front of the screw. The specific rotational flow rate for the screw for the IRPS resin was calculated at 9.3 kg/(h-rpm) based on the depth of the channel at the end of the transition section. The screw was built with an extremely low compression ratio and compression rate of 1.5 and 0.0013, respectively. For IRPS resins and other PS resins, screws with low compression ratios and compression rates tend to operate partially filled. The compression ratio and compression rate for the screw are preferred to be around 3.0 and 0.0035, respectively. The flight radii on the screw were extremely small at about 0.2 times the channel depth. For IRPS resin, the ratio of the radii to the channel depth should be about 1. 

A high-performance screw was designed for the injection-molding press. This screw was designed with a much higher compression ratio and with large flight radii in all sections of the screw. The details of the screw are provided in Table 11.14. 

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