Extrusion output

Tube extrusion is quite similar to the wire insulation process. Processing details depend on the size and type of the tube. Tube can be manufactured by both in-line and crosshead dies. FEP tubing can be produced with outside diameters as low as 1 mm to over 20 mm. This range is broken into three processing zones based on the size of the outside diameter small, medium, and large. The sizing die determines the outside diameter of the extrusion output and the line speed determines the inside diameter. Take-up speed and the die gap, and the difference between the inside diameter of the die and the outside diameter of the tip, set the wall thickness. 

Die adjustments do not significantly influence the extrusion rate the lip opening, restrictor bar clearance, die heat, and overall die design have small to moderate effects on the back pressure. However, the extrusion rate is only slightly affected by substantial changes in back pressure. Thus attempts to open the lip or increase the die heat to increase the extrusion output rate can be exercises in futility, as well as the source of many additional problems. 

ECMAE controls the deformation process more effectively and the expected result is attained quicker as compared to ECAE. The ECMAE equipment ensures the increase in manycycle extrusion output, a decrease in single deformation intensities for pol5nners of low plasticity, a possibility of providing a strict alternation of intensity values and shear directions for a guided structure forming. This has... 

Degalan V 26 (Degussa, A.G., B.R.D.). This is a 90/10 (methyl methacrylate)-(butyl acrylate) copolymer. It mixes well with PVC and it does not affect its transparency, water absorption, and electrical properties. It is suitable to modify the rheological properties of impact-PVC. It shortens the plastication time of PVC mixtures and it improves their homogenization and the extrusion output. The addition of Degalan V 26 also improves the heat stability of PVC mixtures and increases the resistance of PVC-based products to heat distortion. 

Extrusion outputs are sometimes limited by flow instabilities producing rough surfaces (shark skin) or periodic fluctuation, but the cooling of thick extrudates is often the major limiting factor because of the low thermal conductivity of PE. 

Increases in extrusion output of over 40% at equivalent die pressure have been observed with some resin ccnnpounds on a laboratory blown film line. 

Tableting, pressing, mol ding, and extrusion operations are commonly used to produce agglomerates of well-defined shape, dimensions, and uniformity in which the properties of each item are important and output is measured in pieces per hour (see Ceramics, ceramics processing Pharmaceuticals Metallurgy, powderp tallurgy Plastics processing).

In addition to elastic turbulence (characterised by helical deformation) another phenomenon known as sharkskin may be observed. This consists of a number of ridges transverse to the extrusion direction which are often just barely discernible to the naked eye. These often appear at lower shear rates than the critical shear rate for elastic turbulence and seem more related to the linear extrudate output rate, suggesting that the phenomenon may be due to some form of slip-stick at the die exit. It appears to be temperature dependent (in a complex manner) and is worse with polymers of narrow molecular weight distribution. 

As plastics can have quite different viscosities, they will tend to behave differently during extrusion. Fig. 4.3 shows some typical outputs possible with different plastics in extruders with a variety of barrel diameters. This diagram is to provide a general idea of the ranking of materials - actual outputs may vary 25% from those shown, depending on temperatures, screw speeds, etc. 

During extrusion blow moulding of 60 nun diameter bottles the extruder output rate is 46 X 10 m /s. If the die diameter is 30 mm and the die gap is 1.5 mm calculate the wall thickness of the bottles which are produced. The flow curves in Fig. 5.3 should be used. 

Kalyan et al. [56] have also studied the effect of alpha-olefin comonomers on the rheological properties and processing of LLDPE. The characteristics of the resins are shown in Table 2. It is found that 1-octene-based LLDPE has the lowest shear viscosity as compared to 1-butene- and 1-hexene-based polymers (Fig. 9). Decrease in power consumption, pressure before the die, temperature in the die, and increase in output has also been found according to shear viscosities of the polymers during tubular film extrusion. 

It can be said that basically the up-stream and down-stream procedures are similar in production lines whether calenders or extruders are used. For a given quantity of output, it is usually necessary to have more extruders than calenders. ITiis situation makes the extrusion fines more flexible and more able to handle relatively short production runs. The extrusion flexibility, when compared to calendering, includes ease of changing product thicknesses, widths, and materials. 

The target output capability for such a multiplex extrusion line is 25,000-30,000 treads per day. This results in a rubber processing capacity of 10,000 kg/h. 

We use profile extrusion to make continuous products that have fixed cross-sectional dimensions, such as pipes, house siding, refrigerator door gaskets, and vindshield wiper blades. During profile extrusion the molten output from an extruder is pumped to a die where it is formed to approximately the desired cross-sectional profile. As the molten polymer leaves the die, we apply the final forming step and simultaneously cool it to yield the product in its solid state. 

Kruder, G. A., Ultra High Output Extrusion on a Commerciai Scaie, SPE ANTEC Tech. Papers, 30, 726 (1972)... 

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