Resins stagnation

Material Flow Shorter hold-up times. Less resin stagnation in the barrel. EfScient pressure transmission to the melt. EfScient mold filling. 

Resin stagnation may be avoided by the use of a slightly conical or rounded nose screw tip. The type of the screw tip depends on whether a breaker plate is installed in the extruder. Although fluoropolymer extrusion does not require breaker plates, their installation can increase the backpressure for additional mixing. Breaker plates should be streamlined to avoid melt holdup and stagnation. Fluoropolymer screws do not need internal cooling. A screenpack consisting of one 120 mesh and two 80 mesh screens can be installed to filter contaminants out of the melt. 

Figure 11.11 Schematic of two transfer line elbows a) a properly designed elbow made by cutting half channels into two metal blocks using a ball end mill, b) a top view of an improperly designed elbow where a single block of metal was drilled from both corners, and c) oblique view of the improperly designed block. Resin degradation products are likely to form in the stagnation positions shown in b)...

The entrance and exit regions in the spiral dam were also modified to eliminate the stagnant sections of the channel. The modification Is shown In Fig. 11.40. This modification allowed a relatively small amount of resin to flow Into the smaller channel at the entry such that stagnation of the resin cannot occur. A similar modification was made at the exit to allow a small amount of resin to flow out of the smaller channel into the main flow channel. To eliminate the unmelted particles or the particles that appeared to be more viscous because they were at a lower temperature, the clearance to the spiral dam was decreased from 0.76 to 0.25 mm. Since the meter channel depth was unchanged, the specific rotational flow rate for the modified screw was unchanged at 0.94 kg/(h-rpm). 

Stagnate for several minutes in the temperature zone of more than 200 °C. As a result, NF is degraded by heat and the strength of the fiber is reduced. Moreover, the impregnation of resin to the inside of the NF bundle of cotton yarn becomes difficult in the conventional system currendy used in the manufacture of GF, LFP, of CF. Therefore, the pellet for injection molding with the configuration of an LFP, using cotton yarn as the reinforcement fiber has not been manufactured. 

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