Temperature settings, extruder

The response of the RTDs and the temperature of the screw were tested with the screw not rotating. For this experiment, the temperatures were first measured with the extruder at ambient conditions. Next, the barrel temperature set points were increased to 200, 220, and 240 °C for Zones 1, 2, and 3, respectively. The downstream die system was heated at the same time as the barrel and at a set point temperature equal to Zone 3 (240 °C). The temperature profile of the screw as a function of axial length is shown in Fig. 10.19 for select heating times. For heating... 

During the sintering, the powder is heated by conduction. Thus, the time needed to heat it to the sintering temperature depends on the size and shape of the extrudate as well as on its heat transfer properties. Temperature settings in the sintering zone are from 380°C to 400°C (716°E to 752°E), although for large-diameter rods, where... 

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... 

After the reader has started the extruder screw with a valid temperature profile, extrudate begins to flow from the top of the die (Fig. A.6). The molten, high melt-strength polymer can then be dragged up the tower to the nip rollers. Dropping the melt onto the nip rollers will string the bubble, if the nip rollers have been turned on and set to a speed... 

Reinforced PPS compounds may be extruded into profile shapes or sheets under carefully controlled processing conditions using a 24 1 to 28 1 LID standard metering screw with 3 1 compression ratio and a heated die clamp. Typical barrel temperature set points are about 285 to 310°C (545 to 590°F). Some extruded rods and sheets of reinforced PPS compounds are used as stock for machining small quantities of parts, as is compression-molded stock. Thermoforming of extruded sheet may be performed using conventional techniques at temperatures above the crystalline melting point of PPS of 285°C (545°F) [133]. 

A second consideration in scaling down a reactive extrusion process concerns the axial temperature profile. Because of the different volume to surface ratio between large-scale and small-scale equipment the cooling capacity of the latter will be far better than in production size machines. To obtain similar axial temperature profiles, the temperature settings of the barrel wall in the small-size extruder should be different from those in the large-size machine. The most convenient situation is, of course, if a reliable mathematical model of the reactive extrusion process is available. An alternative is the use of an approximating heat balance over the extruder ... 

Rauwendaal [152] conducted a study using thermochromic powders used commercially in thermochromic paints to study melt temperature in extruders. The study involved a small laboratory twin screw extruder processing a highly filled HDPE. It was found that the material degraded inside the extruder even though the barrel temperatures and exit melt temperature were quite reasonable. The barrel temperatures were set a 200°C and the exit melt temperature was measured at about 215 to 220°C. 

Fig. 7.4 N-Q operating diagram for a 27-mm twin-screw extruder (TSE) with adiabatic barrel temperature settings...

Terblend can be extruded on the same machines as SAN and ABS resins. Sheets and fQms with a good, somewhat dull, finish can be produced with stock temperatures of about 250-280°C. Under no circumstances shordd the chill roll temperature be higher than 5°C below the Vicat temperature settings of 70-110°C are standard practice. Extruded sheet intended for thermoforming should be prevented from moisture pick up. The stock temperature for the extrusion of sections shordd be set to a lower value than that for sheet. 

The recommended L/D ratio of the extruder is at least 24 1. The preferred screw design should have compression ratio of 3 1 and should feature a long, gradual transition zone and a long metering zone. Temperature setting should be between 200 and 230 C. 

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