Extruder compression ratio

The copolymers are used in the manufacture of filaments. These may be extruded from steam-heated extruders with a screw compression ratio of 5 1 and a length/diameter of 10 1. The filaments are extruded downwards (about 40 at a time) into a quench bath and then round drawing rollers which cause a three- to four-fold extension of the filaments and an increase in strength from about 10000 to 36 000 Ibf/in (70-250 MPa). The filaments are used for deck chair fabrics, car... 

Compression of the rubber compound as it travels up the barrel is developed in the extruder by either decreasing the thread pitch but maintaining a constant root diameter, or alternatively by increasing root diameter whilst maintaining constant thread pitch. Each of these situations increases the pressure as the rubber compound travels up the barrel. The last portion of the screw prior to the die entry, however, is maintained at a constant pitch or root diameter to enable stock to stabilise in characteristics just prior to entering the die head, to ensure uniformity for extrusion through the die. Conventional extruder screws achieve a compression ratio of 2.5 1. 

Flight width and flight clearance were 13.5 and 0.12 mm, respectively, in all sections of the screw. The extruder had a smooth-bore feed section. Three rings of pin mixers were evenly positioned in the middle portion of the metering section of the screw. All pins in a single ring had the same axial position as the type shown by Fig. 8.25. The specific rotational flow rate for the metering section was calculated at 5.0 kg/(h rpm). The compression ratio was 2.7. 

Extrusion accounts for about 30% of nylon produced and is used in various processes (24). Nylons can be extruded on conventional equipment having the following characteristics. The extruder drive should be capable of continuous variation over a range of screw speeds. Nylon often requires a high torque at low screw speeds typical power requirements would be a 7.5-kW motor for a 30-mm machine or 25-kW for 60-mm. A nylon screw is necessary and should not be cooled. Recommended compression ratios are between 3.5 1 and 4 1 for nylon-6,6 and nylon-6 between 3 1 and 3.5 1 for nylon-11 and nylon-12. The length-to-diameter ratio, L D should be greater than 15 1 at least 20 1 is recommended for nylon-6,6, and 25 1 for nylon-12. 

Fig. 11.28 The number average fiber length at various axial positions of an injection molding screw. DuPont Alathon 2010 pellets preblended with 3.2 mm chopped fibers and extruded in a 0.75 in diameter, 20.1 L/D, with 3 1 compression ratio extruder. [Reprinted by permission from R. von Turkovich and L. Erwin, Fiber Fracture in Reinforced Thermoplastic Processing, Polym. Eng. Sci., 23, 743 (1983).]... 

Single screw extruders develop more frictional heat and rely more on back pressure from the die to improve homogeneity. Screw design involves higher compression ratios, e.g., 2 1, which means the volume occupied between two fights at the start of the screw is twice that occupied between two consecutive flights at the end of the screw. 

The vent in the extruder used in the HIPS extrusion process allows the removal of volatiles from the melt. The classical vented screw extruder optimized for HIPS has a length-to-diameter ratio of 36 and a compression ratio of 2-2.5. 

Extruder Diameter, mm Length to Diameter Ratio (L/D) Compression Ratio Polymer Film Thickness, fxm... 

PPIEPDM blends (Santoprene , Sarlink ) show a co-continuous morphology. The melt has high viscosity, but all the grades are easily extruded. The recommended extruder should have L/D s 24 and the screw a moderate compression ratio, e.g., 2.5 to 3.5 (similar to those used for PVC or PE extrusion). Temperature settings... 

Eor PA/ABS blends, e.g., Alphaloy MPA, Elemid , Diaaloy N, Kane ace MUH, Malecca S, Maxloy A, Monkalloy N, N5, Novaloy -A, Stapron N, SX, Techniace TA, Toyolac Adloy, Triax 1000, Ultramid ), single or twin screw extruders are suitable. However, the latter are preferred. Typical ABS extrusion procedure should be followed. Eor two-stage screws, a first stage compression ratio of 25-2.1 and pump ratio 1.5-2 are recommended. 

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