Laboratory extruders

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... 

Table 9.1 Baseline Performance for the 40 mm Diameter Laboratory Extruder...

As pointed out at the beginning of the chapter, when designing a new polymer processing operation to produce a product or to blend or compound a new material, it is often desirable or necessary to work on a smaller scale such as a laboratory extruder, internal batch mixer, stirring tank, etc. The evolving model must then be scaled up or down to the actual operation. 

Tests are usually carried out on a smaller scale before an extruder is built or configured on a production scale. Here again, modeling helps to support the process. A scale-down is used first in order to decide at what scale the miniature trials should be carried out. If only a small amount of resin is available, it might be practical to carry out initial tests with a small laboratory extruder to produce a sample quantity. These tests therefore tend to be used for product development. Once this is done the question is What will the production screw for the manufacture of the product look like For this purpose it may be necessary to carry out... 

A constant average shear rate ensures that the product treatment is comparable if the fill rate of the screw elements is similar. With an identical diameter ratio D0/D( the screw speed of the laboratory extruder is the same as the production extruder. If the diameter ratios differ, the speed must be adjusted. 

The specific heating and cooling power is an often-underestimated source of error. It is physically possible for a large production extruder to require less heating and/or cooling power than a small laboratory extruder in terms of drive power (Fig. 11.15). Therefore, laboratory extruders are often operated adiabatically or only moderately heated in order to ensure comparability with a large extruder. 

For example, if a process is developed on a laboratory extruder, the power required from a production extruder can be calculated using specific energy. 

The apparatus used for the first tests included a 3/4-inch diameter, 20 1 L/D laboratory extruder. The second series of evaluations was run on a Brabender torque rheometer equipped with mixing head. The third tests utilized large scale processing equipment including a two-roll,... 

Repeated Extrusions. 0.25% Tris(nonylphenyl) phosphite and 0.25% polymeric phenolic phosphite were added to unstabilized polypropylene, and the resins were run through the laboratory extruder four times. The barrel temperature was 450°F., and the stock temperature of the extrudate was approximately 500°F. Melt flow rate of samples taken after each pass was measured according to ASTM 1238-62T. 

Extruded compounded pellets were converted into strips (1 in. X 0.05 in.) using a % in. Brabender laboratory extruder. ASTM-D 638 Type I 0.05 0.005 in. tensile specimens were tensile cut from the extruded strips. Extrusion conditions used were typical for this class of materials. Extrusion take-off rates were controlled to minimize orientation in the extruded strips. Annealing experiments showed shrinkage to be approximately 2% in the longitudinal direction. 

The dried components were melt mixed in a single-screw laboratory extruder. The extruded strands were regranulated and the extrusion cycle was repeated up to five times. After every cycle, samples were taken for the investigations. By the repeated extrusion, different degrees of dispersion were realized. 

TABLE 3.10 Effect of rice hulls on the oxidative induction time (the OIT) of an HDPE, processed on the Brahender laboratory extruder... 

The composites were processed on the Brabender laboratory extruder. The OIT was measured at 190°C. The OIT values show the resistance of the material to oxidation The higher the OIT, the higher the resistance. The amount of Biodac was 28% in all cases. The amount of rice hulls and sawdust was 32% in all the cases. The amount of HDPE was 40% in all the cases. 

TABLE 15.17 Effect of colorants and fillers on OIT (at 190°C) of an HOPE, processed on the Brabender laboratory extruder... 

To develop reactive compatibilization, the laboratory extruder should match the production unit. Thus, a TSE, either CORI or ICRR, with segmented barrel and screw should be used. 

Measurements using a laboratory extruder are possible. The rapid cooling of an extruder and removal of the screw followed by examination of material removed from... 

Gonzales RJ, Torres RL, De Greef DM (2001) Application of an ideal model to the scaling up of a laboratory extruder. J Journal of Food Engineering 48 45-51... 

A laboratory extruder of 1.5 inch in diameter is used at a speed of 100 rpm. What will be the ratio of output, pressure and power when an industrial extruder of 4 inch diameter is applied (both in geometrical similarity), working at 150 rpm. Assume no change in melt temperatures. 

The polymorphic composition of extruded p-nucleated iPP products depends significantly on the cooling conditions and on the take-off speed. Sheets of almost pure p-iPP were successfully produced by means of a laboratory extruder (Viskosystem) with wide-gap die and equipped with a calendering unit composed of three superimposed, thermo-regulated compression rollers. The temperature of the first two compression rollers should be set between 105-110°C, i.e. in the temperature range between T( p) and T(pa) where the formation of pure p-iPP is... 

Goodhart FW, Draper JR, Niger FC. Design and use of a laboratory extruder for pharmaceutical granulations. J Pharm Sci 1973 62 133-136. 

Polymers with low viscosity melts require a shallow channel of low depth in the metering section to generate sufficient pressure for efficient pumping to the exit die. Helix configuration may also be a consideration. In a small-scale laboratory extruder with L/D = 24/1 and screw diameter 0.6 cm (output between 0.2 to 2 g), the screw, in most cases, rotates at a speed between 30 and 90 rpm, corresponding to shear rate of 1368 sec to 408 sec (see above), and experiences pressures from 500 psi up to 2000 psi. 

As it is very costly to run commercial scale equipment, initially the effects of a newly developed lubricant system on the properties of a rPVC compound are measured using laboratory scale equipment such as rheometers, dynamic two-roll mills and small scale molders and extruders. An example of the effect of various lubricants on output in a laboratory extruder is shown in Figure 2. 

Polycaprolactone, which is widely used in medical applications, can be blended with a number of polymers such as styrene-acrylonitrile (SAN), PVC, and polycarbonate. In this example a polymer blend of polycaprolactone with a high nitrile SAN was expected to give a transparent extruded sheet which was thermoformable in hot water. Suitable thermoforming properties and adequate transparency had been achieved with 35 wt% polycaprolactone blended with 65 wt% SAN using small laboratory samples prepared in a torque rheometer. Unfortunately, strips extruded from a pellet blend using a 25 mm laboratory extruder were white, cloudy and not transparent. 

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