Vertical extruders

Stoneware pipes produced in the stoneware industry are almost exclusively shaped by way of extrusion, preferably using vertical extruders, but specially for the shaping of pipe bends also horizontal extruders... 

Vertical extruders (suspended extruders). The vertical extruder was very quickly adopted early on for the extrusion of certain products, in particular for stoneware pipes and large size slugs, also for certain shapes of roofing tiles and small items in the advanced ceramic industry. Favoured by the vertical outlet, the column can easily be removed without the risk of being deformed. As the products were extruded in an upright manner the machine was also often incorrectly referred to as an upright extruder. 

One of the most important extruder parameters is that of the extruder barrel diameter. Although there has never been any standardization, certain standard sizes have evolved in the course of time, identical to almost all machine manufacturers. Essentially these standard dimensions are the following 50, 80, 100, 110, 120, 150, 200, 250, 300, 400, 450, 500, 560, 600, 650, 700, 750, 800 and >800 mm 0 (up to approx. 1600mm 0 with vertical extruders for special applications). 

On the other hand the upright extruder with its vertical outlet was beneficial inasmuch as the bricks produced on this machine hardly showed any noticeable laminations created by the auger and the flow movement of the clay. The clay pushed to the bottom was taken along towards the die by the rotating base and was forced to exit laterally. As a result of the change in direction, the previous longitudinal orientation of the clay material was converted to a crosswise orientation. As the clay strings were still turned inside the extruder, any laminations which may have been caused by the flow motion of the material were hardly visible in the extruded column and hence the vertical extruder produced virtually lamination-free bricks. 

In household ceramics for the production of pugs, e.g. roller machines, in structural ceramics for the production of bricks of all types, for the production of lumps for pressing roofing tiles, for the extrusion of tiles and split tiles, for the production of stone-ware pipes with horizontal but usually vertical extruders (Fig. 48) for pelletising expanded clay, in refractory ceramics and in the further field of technical ceramics, for the production of pugs in the manufacture of isolators (Fig. 49) just as for the extrusion of filigree honeycombs for various applications. 

A certain degree of variation in thickness is unavoidable. When caused by the tubular film die, these variations always occur at the same position. A local film excess usually appears as a line. This can be countered if the die head, the haul-off and wind-up gear, or, with a vertical extruder, the extruder barrel is rotated or moved from side to side at regular intervals (Fig. 3-25). 

Vertical extruder n. An extruder arranged so that the barrel is vertical and extrusion is usually downward or upward. 

Viscous Liquids. Fluids with viscosities up to 50.000 centipoise can be processed in a standard thin-layer evaporator. "Zero-clearance" rotors do not exhibit the range of viscosity application that "fixed-clearance" rotors exhibit. Some firms manufacture "thin-film" vertical extruders" for the 50,000 to 20,000,000 centipoise range where fluids cease to flow under the influence of gravity alone. Thin-film evaporators, inherently low-pressure-drop devices, have mechanical turbulence and therefore relatively good heat transfer properties over a wide range of viscosities. 

There are a multitude of commercially available machines that will adequately perform these operations in a variety of ways, e.g. intermittent extrusion, continuous extrusion, horizontal or vertical extruder arrangement. 

Pellet Mills Pellet mills operate on the principle shown in Fig. 20-92. Moist, plastic feed is pushed through holes in dies of various shapes. The friction of the material in the die holes supplies the resistance necessary for compaction. Adjustable knives shear the rodlike extrudates into pellets of the desired length. Although several designs are in use, the most commonly used pellet mills operate by applying power to the die and rotating it around a freely turning roller with Fixed horizontal or vertical axis. 

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. 

In the tubular process a thin tube is extruded (usually in a vertically upward direction) and by blowing air through the die head the tube is inflated into a thin bubble. This is cooled, flattened out and wound up. The ratio of bubble diameter to die diameter is known as the blow-up ratio, the ratio of the haul-off rate to the natural extrusion rate is referred to as the draw-down ratio and the distance between the die and the frost line (when the extrudate becomes solidified and which can often be seen by the appearance of haziness), the freeze-line distance. 

In a typical process a preform billet is produced by compacting a mixture of 83 parts PTFE dispersion polymer and 17 parts of petroleum ether (100-120°C fraction). This is then extmded using a vertical ram extruder. The extrudate is subsequently heated in an oven at about 105°C to remove the lubricant, this being followed by sintering at about 380°C. By this process it is possible to produce thin-walled tube with excellent flexing fatigue resistance and to coat wire with very thin coatings or polymer. 

A mixture of powdered poly(vinyl chloride), cyclohexanone as solvent, silica, and water is extruded and rolled in a calender into a profiled separator material. The solvent is extracted by hot water, which is evaporated in an oven, and a semiflexible, microporous sheet of very high porosity ( 70 percent) is formed [19]. Further developments up to the 75 percent porosity have been reported [85,86], but these materials suffer increasingly from brittleness. The high porosity results in excellent values for acid displacement and electrical resistance. For profiles, the usual vertical or diagonal ribs on the positive side, and as an option low ribs on the negative side, are available [86],... 

The material flow in an internal mixer is oriented vertically. On top of the internal mixer a more or less sophisticated feeding system can be found. Underneath the mixer a downstream device, such as a sheeting extruder with one or two tangential screws, or two roll mills are placed. 

This will be a positive-pressure system, since each dryer will feed 5 extruders. It will be designed to run at the same rate as each dryer, 9,210 lb P.S./hr. The vertical rise is 30 ft and the maximum distance traveled is 130 ft. Because powder is being conveyed a cyclone separator will be specified for each of the extruders. The blowers should be designed to have an LHP of 7.2 and a BHP of 8.4. The power required to operate both is 12.6 kw. 

Figure 11.6 illustrates the general configuration of a film blowing operation. Molten polymer from the extruder is pumped into an annular die, where it is distributed around a tubular melt channel before emerging vertically as a relatively thick-walled molten tube. The top of... 

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... 

A small die of base of approximate dimensions 9/16 in by 1/4 in, having a shape approximately that of a vertical section through a shoe last as per the figure below. It is used in a laboratory extruder to evaluate the extrudability or processibility of a rubber compound. ASTM... 

In the extrusion of rubber tubing, a central core determines the inside diameter. This core is supported by the spider or core-bridge which is itself fitted in the head of the extruder and may be adjusted laterally and vertically to produce a concentric tube. 

Collins et al. (1 3) have suggested that this same concept can be applied to polymer devolatilization processes, except that the HTU might be more appropriately termed the LTU when screw extruders are used since these need not be vertical. By analogy, the following expressions can be written ... 

The goo is then pumped to the top of a vertical, jacketed tower with internal temperature-regulating coils. The vessel is kept full of the styrene/PS mixture. A temperature gradient (change) of 280°F at the top and 400°F at the bottom is maintained. The temperatures are controlled to prevent runaway, but to permit 95% conversion of styrene to PS. As the polystyrene molecules grow, they sink to the bottom of the vessel and can be drawn off The residence time in this vessel is three to four hours. The molten PS is extruded to strands, chopped into pellets, and bagged. 

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