Speed, extrusion

The potential volume involved and our assessment of the property benefit of Celcon in the application were sufficient to justify a lab program whose objective was to develop a polymer or modify the extrusion process so that Celcon would extrude at comparable or faster speeds than the material being used. After some nine months of effort an extrusion die was designed that permitted extrusion speeds of 450 feet per minute while making tubing with the tolerance specifications established by the customer. The foregoing is an example of a type of process development work described in the preceding paper. 

Even though these obstacles are far away from the die lip region, the polymer melt, at normal extrusion speeds, is unable to heal completely. That is, the macromolecules comprising the two layers that were split by the spider legs do not establish the entanglement level characteristic of the bulk at the prevailing shear rate and temperature. 

The processing window for the first four HOPE materials was wider in terms of extrusion speed, stress, and temperature. The last four HDPE materials were closer to melt fracture and the resulting sharkskin, roughness, tearing, and rupture of the extruded shape. The corresponding composite materials formulated with the last four resins had a lower throughput. 

One can see that the first four HDPE samples that ran well in the extrusion of the GeoDeck composition have a higher critical shear stress and higher critical shear rate. Their critical shear rate was in the range of 500-600 s . The extrusion window for them was wider in terms of extrusion speed, stress, and temperature. 

Resin Type Reduction Ratio Lubricant Content Lubricant Type Die Cone Angle Die Land Length Extrusion Speed Temperature... 

Fixed scrapers clean the body of the rollers and bars by momentarily turning the latter ones. After cleaning, the bars return immediately to their basic position. Very high pressures can be produced with this press. The compression ratio and the extrusion speed are adjustable and can be varied infinitely. 

The above indicates that, while a feed mill may be equipped with one or more pellet mills that are selected to handle the production capacity with the most common feed type, conditioning, die design, extrusion speed, and, potentially, post-treatment must be variable. This is accomplished by controls, variable speed drives, the availability of various dies, and an adaptable flowchart with diverters (circles in Fig. 6.5-6) for different process path selections. Installation of redundant equipment helps to chose the most effective system and maintaining production during machine modifications and maintenance. 

No. Y2 4 23 5 13 Spher. time min Spher. speed rpm Extrus. speed rpm Spher. load kg Extrus. screen mm Yield pellets %... 

Without further analysis, these results add little to what we have already seen. Nevertheless, we notice that the estimates of the effects are of the same order, with three important exceptions, the inversion of the coefficient supposed to represent the effect of the extrusion speed, considerable changes in the mixed interaction effect fe 14.25, and also a difference in the constant term b g (figure 3.15). 

Spheronization time Spheronization speed Extrusion speed Spheronization load -Extrusion screen -... 

Spheronization time 1 Spheronization speed 2 Extrusion speed Spheronization load Extrusion screen 12+45 14+25 15+24 13 23... 

Sharkskin occurs at a lower shear rate than melt fracture, but the term melt fracture is often applied to all regular flow defects including sharkskin. Sharkskin occurs at a critical linear extrusion speed that can be raised by increasing melt temperature. Melt fracture starts at a critical shear stress and can be reduced significantly by reducing the die inlet angle, but, like sharkskin, it is also reduced by raising melt temperature. Linear low-density polyethylene is particularly prone to these defects, but they are minimized by the addition of special additives or blends with other polymers. 

The pressure is determined at two extrusion speeds, using a capillary rheometer fitted with an extrusion die and a pipe with fixed dimensions. The determinations are carried out one hour after the ceramic mass has been prepared, and again 24 hours later. The figures obtained, and the factors Ha (ageing factor) and Ks (increase factor), provide useful information on the characteristics of the ceramic compounds. The principle of the method is illustrated in Fig. 4. 

At the same speed, identical nozzle and identical mass, the extrusion speed was increased by factor 2.7 and the torque reduced by 25%. 

Water cooling and adjustment of the extrusion speed to 5.5 cm/min (0.18 ft/min) resulted in a 20.3-cm (8-in.)-diameter billet at a reduction ratio of at least 9.9, as opposed to a reduction of 4.8 under adiabatic conditions. The increase in the reduction ratio, however, was achieved at the expense of increasing the extrusion cycle time for a 1.27-m (50-in.)-long billet from about 3 min to 23 min. The practical... 

When desigtung a new product, a design team begins by specifying the desired optical properties. Then, it designs a stack of on the order of 100-1,000 layers of polymer films. Next, it designs extrusion devices to properly blend the polymer, and feed-block-splitters that divide the flow into 100-1,(K)0 thin films. The effluent films from these splitters are stacked at high extrusion speeds. 

Monofilament Extruder-melt pump-spinneret-quench-stretch- heat-set -wind. For Newtonian fluids the critical draw-down ratio is about 20 (take up velocity/ die exit velocity). Extrusion speeds 1 to 8 m/s. Feed must be dry. 20 to 200 filaments per spinneret. Operating limit is linear speed filaments can be drawn. 

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