Extruder section

To increase the extremely poor efficiency in co-rotating extruders, special screw elements have been developed. These include the gear element , which allows the pressure generating benefits of gear pumps to be used in co-rotating extruders. A gear element for co-rotating extruders will be available from CWP in future. 

The equations given in Fig. 6.5a and/or 6.5b can also be applied to an extruder section. In general, however, we do not know the power input to the shafts for an extruder section or, therefore, the specific energy input for this section. The pumping efficiency can be of use here it is determined in advance for the screw geometry in question (measurements taken with a model fluid are adequate, see Section 6.7) or determined by 3-dimensional calculations (as shown in Fig. 6.7). 

The specific energy input can be cancelled out by the pumping efficiency in the equation for the temperature increase in the back-pressure zone ATS, Fig. 6.8 a. The overall temperature increase is therefore obtained together with the temperature increase at the nozzle ATd- 

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Figure 31.15 Forming a conductor or enclosure from the available extruded sections...

The cross-sections of the conductor and the enclosure arc then checked for their adequacy to dissipate the heat generated. The cross-section is then adjusted suitably by permuialions and combinations to arrive at the most appropriate size, keeping in mind the available extruded sections, accounting for all such factors that may affect the rating or the fatilt level of the enclosure and the conductor, such as tap-offs, which are subjected to a cumulative faull level, openings in the conductor for heat dissipation or the enclosure for inspection windows that can infhience their ratings. A calculation in Example 31.1 will clarify the procedure to establish the size of the... 

This dissipation of heat will not be applicable when the circular section is made of circular extruded sections which have no surface openings. 

Once the required sizes of the conductor and the enclosure are established, one can choose the nearest economical sizes of the extruded sections available in the market, or have them specially manufactured if possible. 

A design engineer will be the best judge of the best and the most economical design and extruded sections. 

Series major additives Al + 0.5 Mg 0.5 Si Moderate-strength age-hardening alloy anodised extruded sections, e.g. window frames. 

With most homopolymers and copolymers the apparent viscosity is less dependent on temperature and shear stress (up to 10 dyn/cm ) than that of the polyolefins, thus simplifying die design. On the other hand the melt has a low elasticity and strength and this requires that extruded sections be... 

A solid circular extruded section of mbber compound generally of small diameter used as blanks in moulding O-rings and similar products. 

The increase in dimensions of an extruded section as it leaves the die the swell is mainly due to elastic recovery. 

A continuous process for the vulcanisation of extruded sections. The heating medium is a bed of tiny glass spheres fluidised by steam or hot air. Fluidisation... 

The technique of passing a gas into a solid which is in the form of tiny granules and thus making the solid behave as if it were a dense, viscous liquid. Fluidised materials may be easily piped from place to place, but a particular application in the rubber industry is the vulcanisation of extruded sections. See Fluid Bed Vulcanisation. Fluorinated Elastomers... 

Change in dimensions of an unvulcanised rubber (calendered sheet or extruded section) on cooling from the processing temperature. Also the volume contraction of a moulded rubber product on cooling from vulcanising temperature. See Coefficient of Thermal Expansion (Volumej. Shrinking... 

A compounding ingredient used to reduce the plasticity (increase the stiffness) of rubber compound and thus enable, e.g., an extruded section, to retain its shape or to reduce air trapping in moulding soft rubbers. 

Applied at present mainly in the vulcanisation of cables, and in fluid bed vulcanisation of extruded sections. 

The advantage of screw machines is that work done by the screw heats and plasticises the mix, under conditions which can be carefully regulated by jacket temperature, screw speed and back pressure. A natural rubber mix leaves the extruder section of the machine 20-30 °C higher than the jacket control temperature. 

The retreading compound is in the form of an extruded section. It can be supplied at a width to cover the whole area to be retreaded, when it is called Camelback , or it may be in a narrower strip for winding. The extruded material is then vulcanised to the casing in a patterned mould. 

The barrel floats" on the screw, rather than being permanently affixed to the frame of the device itself. This facillitates the measurements of barrel torques and thrusts as a function of operating conditions and the type of polymer being conveyed. Fig. 5.9 schematically details the extruder section of the solids conveying device and the instrumentation location [10]. Dark red arrows indicate force measurements, and light yellow rectangles represent temperature and heat flux measurements. A total of five force devices allowed the measurement of the screw... 

Single screw extruder. Let us take the case of a single screw extruder section that works well when dispersing a liquid additive within a polymer matrix. The single screw extruder was already discussed in the previous section. However, the effect of surface tension, which is important in dispersive mixing, was not included in that analysis. Hence, if we also add surface tension as a relevant physical quantity, it would add one more column on the dimensional matrix. To find the additional dimensionless group associated with surface tension, as, and size of the dispersed phase, R, two new columns to the matrix in eqn. (4.32) must be added resulting in ... 

Most models may be described as partially empirical . For instance, we know that the dimensionless pressure in an extruder section L is... 

We have therefore a rigorous model for pressure build-up in an extruder section. However, we also need dimensionless parameters A, and A2 for the screw geometry used (for full details see Section 6.7.1 and Chapter 7). These are either measured beforehand (Fig. 2.24, Chapter 2) and/or, if possible, calculated by means of a comprehensive flow simulation (Section 6.8.3). Thus, all three aspects of Fig. 6.2 contribute towards the description of the... 

As indicated by the arrow in Fig. 6.3, the model depth increases as the model dimensions increase. However, the possibility of actually performing the description decreases with increasing model dimension. This is shown in more detail in Fig. 6.4. In this case, a yes (colored green) indicates the strengths of a model with respect to its usefulness in describing the complete extruder , extruder section or the extruder cross-section . 

FIGURE 2.31 Relationships between extruder die orifice and extruded section. 

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