Extruder vertical

Many articles, bottles and containers in particular, are made by blow moulding techniques of which there are many variations. In one typical process a hollow tube is extruded vertically downwards on to a spigot. Two mould halves close on to the extrudate (known in this context as the parison ) and air is blown through the spigot to inflate the parison so that it takes up the shape of the mould. As in injection moulding, polymers of low, intermediate and high density each find use according to the flexibility required of the finished product. 

Figure 14.1 illustrates the general principles of extrusion blow molding. A molten tube of polymer, known as a parison, is extruded vertically downwards from an extrusion die, as shown in Fig. 14.1 a). The two halves of the blow mold surround and then close on the... 

Coring Strategy. Sediment cores were collected with a thin-walled polycarbonate tube fitted with a piston and operated from the lake surface by rigid drive rods (30). This device recovers the very loose uncompacted sediment surface as well as deeper strata without disturbance or displacement (core-shortening, cf. refs. 31 and 32). Core sections were extruded vertically from the top of the tube into polypropylene collection jars, transported on ice to the laboratory, and stored at 4 °C until analysis. 

Blown film is usually extruded vertically upward through a circular die. This forms a tube that is then blown into a bubble that thins or draws down to the required final gauge. Orientation takes place in two directions horizontally (transverse direction/TV) as the bubble is formed, and in the machine direction (MD) as controlled by adjustable-speed haul-off nip rolls. 

Blown film extrusion is perhaps the most widely used extrusion technique, by production volume. Billions of pounds of polyethylene are processed annually by this method to make products such as grocery sacks and trash can liners. In a blown film system (Figure 14-30), the melt is generally extruded vertically upward through an annular die. The thin tube is filled with air as it travels up to a collapsing frame that flattens it before it enters the nip rollers, which pull the film away from the die. The flattened tube then travels over a series of idle rollers to a slitter,... 

In a typical arrangement for producing juice bottles, the tube is extruded vertically downward to some predefined length, as shown in Figure 14-59. This tube is commonly called the parison, from the Latin word for wall. 

Another approach to increase production is to use one parison extra long to cover two or more cavities located vertically in the mold. In fact, one parison can extend the multiparison with two or more vertical cavities. AH that is required is a machine with the capacity to handle the output from the extruder to the clamping capability. See blow molding, extruder horizontal rotary-wheel blow molding, extruder vertical rotary-wheel clamping platen, rotary clamping platen, shuttle mold cavity. 

Another simple technique involves a hquid which is slowly extruded vertically downward through a capillary into another immiscible fluid of lower density (the submerged pendant drop technique). The heavier ejeeted fluid forms a sphere at the nozzle tip, and grows until the drop is no longer supported by surface tension. The drop then falls and stretches the ligament which connects the drop to the nozzle [Matta, 1984]. 

Film blowing (blown-film extrusion). The process of forming thermoplastic film wherein an extruded plastic tube is continuously inflated by internal air pressure, cooled, collapsed by rolls, and subsequently wound into rolls on thick cardboard cores. The tube is usually extruded vertically upward, and air is admitted through a passage in the center of the die as the molten tube emerges from the die. An air... 

Blown Film Linos. A blown film line is quite different from a flat film line. In a blown film line, a tubular film is extruded vertically upwards as shown in Figure 28. Air is introduced to the inside of the tube as a result, the tube expands to a bubble with a diameter larger than the diameter of the die. The ratio of the bubble diameter to the die diameter is called the blow-up ratio. T5q>ical blow-up ratios used in LDPE film extrusion for packaging are in the range of 2.0-2.5 l. 

Polymer melt spinning is one of the major processes for the manufacture of synthetic fibers. Typically, a polymer melt is extruded vertically downward through a spinneret or die, which may have hundreds of openings. The resulting filaments are simultaneously cooled by crossflow air and are stretched by the action of rollers. On solidification, the yam is wound onto a bobbin. Different aspects of this operation have been described in the literature.(, 59-63) When the fiber-spinning process is used as an extensional viscometer, the setup is simplified and only a single filament of circular cross section is employed. This is shown schematically in Fig 6. Also, the operation is run in an isothermal manner by spinning into an isothermal oven. 

The design of the tools in the base of the container is illustrated in Fig. 9. The tin is extruded vertically to the center-line of the container. 

Chill RolL In the chill roll cast film process, a plasties web is extruded from a slit die (Fig. 8.6) against the surfaee of a water-cooled chill roll. The die is arranged to extrude vertically or obliquely downwards so that the film web is delivered approximately tangentially to the roll surface. The die is similar in principle to a sheet die but will usually not inelude a restrictor bar. Film thickness is partially regulated by the gap between the die lips but also by the rotational speed of the chill roll which is arranged so as to drawdown and thin the melt web. Consequently, the die gap... 

The fiber was extruded vertically downward to a nylon guide wheel (8) located about 30 cm below the die, by which point the fiber had been solidified. This guide was mounted on a force transducer to allow measurement of the tension on the fiber. The fiber was wrapped 180° around this guide wheel and directed to a second guide wheel (9) on its way to a pair of take-up rolls (10 and 11). The fiber was wound once around the take-up rolls and was next taken up by a wind-up roll (12). These rolls were 5 cm in diameter and were made of aluminum covered with tape to enhance their grip on the fiber. Only two rolls (10 and 12) were motor-driven having a maximum speed of3,600 rpm, while one roll (11) was free spinning. The maximum take-up speed was therefore about 600 m/min. The motor speed was controlled by a variable transformer (14). 

The most commonly used of these techniques is extrusion blow molding, where the parison is a hollow, thick-wallcd tube of melt that is extruded vertically from a crosshead die. (A schematic diagram is shown in Fig. 19.39.) The parison then is surrounded by a split, cooled mold of the desired shape. One end of the parison is damped around a blow pin, which incorporates an inlet for compressed air that expands the parison to make it contact the mold wall. The molded object is ejected when solidified, and excess material is trimmed from the ends and recycled. Containers in the range of 0.25 to 5000 liters are made this way, and integral handles as well as special shapes can easily be designed in. 

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