Maddock Solidification Experiment

Figure 4.1 Density of the solid bed from a Maddock solidification experiment running PVDC resin [2]. The extruder was 63.5 mm in diameter and had an L/D of 21...

The melting process is the primary mode for mixing in single-screw machines. This concept can be observed from Maddock solidification experiments. Melting as a method for mixing is presented in Section 8.4. 

Figure 6.2 Photograph of resin solidified in the transition section after a Maddock solidification experiment for an ABS resin. The pushing flight is on the left side of the photograph...

The melting process for a resin is complex and depends on many parameters, including screw speed, screw geometry, barrel temperatures, and channel pressures. Moreover, the compression ratio and compression rate also affect the pressure in the channel. The melting flux is known to increase with increasing pressure in the channel [1,12]. A series of Maddock solidification experiments were performed at... 

The locally high pressure underneath the solid bed and the positive dP/dx in Film D causes some flow of resin from Film D to the melt pool. Thus, for a local Az increment for Film D, there is material entering the element from the melting process and from the drag motion of the screw core, and there is material leaving the increment from the motion of the screw core and from the flow of material into the melt pool due to a positive dP/dx. These complex flows are consistent with observations from Maddock solidification experiments. This flow is shown in detail for the Maddock experiment shown in Fig. 6.35. 

At the start of the melting process, the pressure in the channel is relatively low and the solid bed may not be fully compacted. In this case, molten resin from all films has the ability to flow into the voids between the individual pellets. This process is often referred to as melt infiltration. A photograph of a cross section of a Maddock solidification experiment at the start of the melting process is shown by Fig. 6.21. For this figure, the molten material prior to the solidification was black. Melt infiltration is shown by the black resin that has flowed from the films and in between the pellets. The flow of resin into the solid bed will likely cause the pressure in the films to decrease. 

Figure 6.21 Photograph of a cross section from a Maddock solidification experiment at the start of the melting process. The black material shows the melt films and the regions where the melt infiltrated the loosely packed solid bed...

Figure 6.37 Photograph of a segment from a Maddock solidification experiment for a PVDC resin extrusion. The dark band is resin degraded due to a long residence time at the location...

Figure 10.2 Photograph of a Maddock solidification experiment a) the screw is being pushed out of the barrel with the solidified resin, b) the screw with resin solidified in the channels, and c) a cross-sectional view parallel to the screw axis in the melting section...

Figure 10.23 Select barrel (Z2 and Z3) and screw temperatures as a function of cooling time during a Maddock solidification experiment...

Figure 14.10 Cross-sectional views for a Maddock solidification experiment for the ET screw at a letdown ratio of 220 1 white-pigmented ABS resin to a black color concentrate [29]. The A and B channels are labeled along with the axial positions in diameters. The views were for a screw speed of 66 rpm and a rate of 70 kg/h using a 63.5 mm diameter extruder...

A Maddock solidification experiment was performed using ABS resin at a screw speed of 60 rpm [30]. Like the solidification experiment for the ET screw of Section 14.2.2, the feedstock resin contained 2% Ti02 compounded into the pellets, and a black-colored masterbatch was added at a letdown ratio of about 220 1. The cross-sectional views of the resin solidified in the channels are shown by Eig. 14.15. The white pellets and unmixed resin are visible in the views as white regions. The regions that are well mixed are an evenly colored dark or black color. 

Figure 14.23 Photographs of cross-sectional views of resin removed from a Maddock solidification experiment for a Stratablend screw. The labels are the axial positions of the views in diameters...

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