Barrel surface

The drag flow is most easily visualized by unwrapping the screw and dragging a flattened barrel surface diagonally across the channel (Fig. 3). 

Maddock s and Street s famous solidification experiments revealed that melting in many situations takes place in a specific order. The experiments showed that after melting began, there was a continuous solid bed and a melt film over the inner barrel surface. Later the solid bed was completely surrounded by melt. Farther downstream, a melt pool developed between the pushing flight and the solid bed. The... 

Figure 6.33 Simulation results for melting only from the barrel surface, that is, one-dimensional melting. About 75% of the resin was melted at the end of the transition seotion. The bed height Y in this ease decreases essentially at the same rate that the channel depth decreases...

The dissipation is calculated for barrel rotation in the screw pump device in a similar manner. For this case, the velocities Vozl, and are used for the calculations, and they are provided by Eqs. 7.21,7.23, and 7.27, respectively. The rate of work input for barrel rotation tv, is obtained by multiplying the normal shear stress for the barrel surface by the velocity of the barrel surface integrated over the barrel surface area. The traditional method for calculation of dissipation for barrel rotation is as follows ... 

The stress at the interface was measured as a function of temperature and sliding velocity for the resin using the equipment shown in Fig. 4.11, and the data are shown in Fig. 12.33. The stress curve had two maximums the first peak was at the Tg of the resin at 150 °C, and the second peak occurred at a temperature of about 240 °C. In order to maximize solids conveying while maintaining a viable process, the optimal forwarding forces would occur at a barrel surface temperature near 240 °C, and the retarding forces at the screw surfaces would be minimized at temperatures less than about 120 °C. In order to maintain the high rate of this line and the inside barrel wall at a temperature near 240 °C, the first zone of the extruder needed to be maintained at a temperature of 310 °C. 

Unfortunately, cannot be easily determined analytically, and is often either estimated using methods from the field of soil mechanics (from the normal stress ratio, K, or simply adjusted to a value which produces good fits for the experimental data. The forwarding force f, at the barrel wall is positioned in the plane of the barrel surface. This force is adjusted using as found in Eq. A5.1 and results in Eq. A5.2. This is because is the local pressure in the channel. Referring to Fig. A5.4, the forces are defined as follow ... 

Equation A6.15 represents the temperature profile in Film C. The temperature appears to decrease as the square of the distance (y ) away from the barrel surface assumes that Tf, > To visualize this see Fig. 5.29 in Tadmor and Klein [1]. Now the heat flow per unit area, or the heat flux into the interface, is obtained by differentiating Eq. A6.15 and multiplying by /c as follows ... 

The viscous energy dissipation is calculated by multiplying the normal shear stress for the barrel surface by the velocity of the barrel surface integrated over the barrel surface area. The traditional method for calculation of dissipation for barrel rotation is as follows ... 

It is important to understand the flow characteristics of the polymer inside the screw. If we unwind the screw channel, as illustrated in Figure 7.59, we see that the polymer is conveyed to the die through nothing more than a square channel formed between the screw and the barrel surface. For the purposes of this development, we will assume that the channel has a constant channel depth, H (at least in the metering... 

Calculation with the barrel surface/liter (Table II) shows that for each millimeter that wine penetrates into the side of the barrel, it would extract about 16.4 grams wood/liter wine in a 20-liter, 12.7 in 50-liter, 9.6 in 100-liter, 7.6 in 200-liter, and 5.6 in a 500-liter barrel. These data mean that the typical oak barrel near 200 liters in size can contribute 3800 mg wood for extraction at a depth of penetration of 0.5 mm or in about two months for a new barrel. Based on the tasting results this is about three to 10 times the amount necessary to produce a tastable difference in wine. We have measured the depth to which wine has visibly penetrated into staves from used wine barrels and found that 6-mm penetration is not unusual. This could represent extraction of 45.6 grams wood/liter wine in a... 

This paper was originally presented at the Third International Oenological Symposium in Cape Town, South Africa, March 6-10, 1972. The Cape Wine and Spirit Institute, Stellenbosch, South Africa is thanked for permission to publish the paper in this volume. The California Wine Advisory Board is gratefully thanked for funds supporting the research. C. Kramer, D. Draper, and K. Singleton are thanked for assistance. E. B. Roessler is thanked for advice in calculation of barrel surfaces. 

The unit can be fed polymer in the particulate solids form or as strips, as in the case of rubber extrusion. The solids (usually in pellet or powder form) in the hopper flow by gravity into the screw channel, where they are conveyed through the solids conveying section. They are compressed by a drag-induced mechanism in the transition section. In other words, melting is accomplished by heat transfer from the heated barrel surface and by mechanical shear heating. 

The solids conveying zone. The task of the solids conveying zone is to move the polymer pellets or powders from the hopper to the screw channel. Once the material is in the screw channel, it is compacted and transported down the channel. The process to compact the pellets and to move them can only be accomplished if the friction at the barrel surface exceeds the friction at the screw surface. This can be visualized if one assumes the material inside the screw channel to be a nut sitting on a screw. As we rotate the screw without applying outside friction, the nut (polymer pellets) rotates with the screw without moving in the axial direction. As we apply outside forces (barrel friction), the rotational speed of the nut is less than the speed of the screw, causing it to slide in the axial direction. Virtually, the solid polymer is then "unscrewed" from the screw. To maintain a... 

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