Extrusion head

The first element of the downstream line is the take-off conveyor positioned right where the rubber exits the extrusion head. 

First part Roller train, stainless steel roUs, diameter 50 mm, pneumatical pivoting to get acces to the extrusion head, length approximately 0.7 m... 

The A-A extruders are equipped with a flat perforated plate or screen, combined with two flat extrusion heads. The wet mass is pressed axially through the screen parallel to the feed screws. The extrusion forces are the highest, compared to other low pressure extruders, resulting in a hard and dense extrudate. It is commonly used in the extrusion of food, thermoplastics, and other industries, where a large pellet diameter and thermosetting properties are desired. 

In the A-R type, the feed screws end in blades that rotate along the horizontal axis but force the wet mass through a screen-placed radial or cylindrical around the blades (Fig. 5). The A-R extruders have somewhat conical extrusion heads resulting in an overflow, i.e., a certain amount of feed material is pushed axially between the screen and extrusion head at the front instead of radially through the screen area. A greater open area of screen results in a higher and faster throughput. However, the hardness... 

The dome extruder is a variation of the radial extruder that uses a dome-shaped (hemispherical) screen in combination with dome-shaped extrusion heads, introduced by Fuji Paudal, Inc. in 1992 as the TDG series. This generates lower pressure than the axial and radial extruders, resulting in extrudate with lower density and hardness. The dome extruder has almost no overflow, resulting in higher throughput. 

The pressure exerted by the rotating extrusion heads on the screen as product is being pushed out in an A-R screw extruder (25) is shown in Figure 10. Each spike in the profile represents one revolution of the extrusion head while the frequency represents screw speed. Based on the shear stress developed during extrusion, wet mixtures of MCC-lactose had a lower yield stress in the radial screw extruder (130kN/m ) than in the ram... 

Type and level of binder (e.g., MCC, NaCMC) Rotational speed of extrusion head Temperature... 

In all above- and below-cited publications in this field (e.g. 84 ) the problem was solved in order to calculate the tensors of strain velocity and stress, to prognosticate alteration of longitudinal viscosity, profile of alteration of the thickness of material over the height of the film sleeve (by coordinate on the central line of the sleeve counted from the outlet face of the extrusion head) and configuration of the sleeve ( bubble ) and also to solve thermal problems in order to determine the dependency of melt temperature upon height (or time) and to forecast the position of the crystallization... 

Fig 23. Diagram of molding of molten polymer flat film canvas 1 — flat-slit extrusion head (spinneret) 2 — receiving roller ("drum )... 

Flow through a slit head has been studied also in polymers using the power-function flow principle (Ostwald-de Villes model). Some of the first works in this field were carried out in 1967-1968 by N. V. Tyabin et al.21,22). Tests were arranged with molten polyethylene in an extrusion head having a rotary conic core. The divergence between theory and experiment was comparatively significant which, apparently, is accounted for, primarily, by the basence of a necessary similarity between the conducted experiment and the theoretical description of the flow in a flat slit. 

Fig. 8. Design of angular circular extrusion head with rotating core for manufacturing of tubes and hoses 1 — Single-screw extruder 2 — Adapter 3 — Core holder 4 — Separable core tip 5 — Alignment bolts 6 — Rotating core 7 — Plain bearing 8 — Stop flanging 9 — Head casing 10 — Electric heaters 11 — Place for installation of thermocouples...

Fig. 10. Pressure/flow-rate characteristics ( tentative flow curves ) of angular circular extrusion head (the design is given in Fig. 8) in molding of polypropylene with MFI = 0.5 g/10 min under conditions of core rotation at a speed of, min-1 1 — 0 2 — 10 3 — 20 4 - 30 5 — 40 6 — 50 7 - 60 8 - 70...

High-intensity vibration effect upon dissolved and molten polymers is relatively simple and can be obtained with the help of superimposition of high-frequency ultrasonic (US) vibrations. Periodic (cyclic) shear and volumetric strain of the medium is attained in this case without moving elements and due to elastic oscillations of US-vibrators of various design which function simultaneously as moulding elements (nozzles, cores) of extrusion heads. 

In 77) the authors also give an example of an extrusion head design with acoustic treatment of molten polymer in a circular molding clearance. 

The equipment based on a double-helical machine also comprises a separable extrusion head with a die and a granulator. The screws of the cascade machine are arranged in succession. They turn counter-clockwise and are fitted in one another. Several holes provided in the frame of the machine accommodate flanges adapted to secure metering arrangements. The above holes are also suited to pass through the inhibitors. The screws... 

C.V. Kopp, R.J.W. Streeton and P.S. Khoo, Extrusion Head for Forming Polymeric Hollow Fiber, US Patent 5,318,417 (June, 1994). 

B. P. Stark and A. J. Duke, Extrusion Head ions, Pergamon Press, London, 1967. 

Hose extrusion includes forcing of the polymer melt through the annular slit of the extrusion head, pneumatic blowing of the hose, folding and removal in vertical or horizontal direction. This method produces biaxial films with perfect physical-mechanical characteristics, it is rather simple and economical, and is suitable for the production of laminated film materials by co-extrusion. 

Tdi temperature of Cl destruction initiation Textr the extrusion head die [31]. 

Fig. 2.8. A device for feeding a modifier to the extrusion head mandrel of the hose-film aggregate (1) extrusion head (2) mandrel (3) polymer hose (4, 5) and (24) tube and channels for compressed air (6) channel for inhibitor liquid (7) and (8) liquid levels over extrusion head mandrel and in the feeding chamber, respectively (9) Cl feeding chamber (10) and (12) valves (11) float (13) and (14) mains (15) and (16) magnetic distributors (17) pump (18), (19) and (22) taps (20) and (23) accumulator tanks (21) pressure valve...

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