Rheometer circular orifice

Coimnercially available instruments such as tire Monsanto Automatic Rheometer and the Instron Capillary Rheometer are examples of equipment which extrude the polymer through a capillary with a circular orifice using a pltmger at constant speeds. The principal features of this rheometer are shown schematically in Figure 3.3. 

Constant Plunger Speed Circular Orifice Capiiiary Rheometer... 

Figure 3.3 Schematic diagram of a constant plunger speed circular orifice capillary rheometer.

Constant Pressure Circular Orifice Capillary Rheometer (Melt Flow Indexer)... 

The apparatus for determining MFI is basically a circular orifice rheometer. By its very definition, MFI represents a point at specific shear rate and shear stress values on the viscosity versus shear rate curve. The expressions for shear stress T and shear rate y in the melt-flow apparatus are given by the well-known conventional forms discussed in Sec. 3.2.1 as follows ... 

Orifice 6r-9-f9s, ar- [ME, fr. ME, fr. LL orificium, fr. L or-, os mouth - - facere to make, do] (15c) n. (1) A small, usually cylindrical passage in a die, as in a strand die or an orifice-type rheometer. (2) A beveled, sharp-edged, usually circular hold in a thin metal plate that is inserted between flanges in a pipeline. By measuring the fluid pressure up- and downstream near the plate, one can calculate the rate of flow of the fluid. The method has long been used with simple gasses and liquids and is useful for dilute polymer solutions, but not for melts. 

This rheometer is similar in all respects to that discussed in section 3.2.1 except for the fact that it has a slit orifice cross-section rather than a circular one. The major credit for the development of the concept and use of this rheometer goes to Han [69,71,72] though others [73] have also used it for polymer melt studies. The instrument makes use of a series of flush mounted transducers located along the flow channel wall which measure the pressure gradients along the flow direction. These are then converted into wall shear stress values [69] as follows ... 

These capillary rheometers are principally the same as those described in Sections 3.2.1 and 3.2.2 except for the melt transport system which is of the screw extrusion type rather than the plunger type discussed earlier. A schematic diagram of an extrusion capillary rheometer is shown in Fig. 3.5. Commercially available extrusion capillary rheometers are the Haake Rheocord (Haake Buchler Instruments, Inc., Saddle Brook, NJ) and the Brabender Plasticorder (Brabender, Duisburg, Germany). The rheological property measurements can be done using a circular or slit orifice, as these are separate attachments for the miniaturized single screw extruder. 

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