Slit Die Rheometer

Edi-Soetaredjo, F., Nashed, G., Rutgers, R.P.G., and Torley, P.J. (2003). Numerical analysis on the effect of extrusion conditions on flow in slit die rheometer. Srdint. Conf. On CFD in Minerals and Processing Ind., CSIRO, Melbourne, Australia, pp. 300-302. 

ISO 11443. Determination of the fluidity of plastics using capillary and slit die rheometers, 1995. 

ISO 1133, 1991(E), Plastics—Determination of the melt mass flow rate (MFR) and the melt volume flow rate (MVR) of thermoplastics. BS2782. Part 7. Method 722B. Plastics-Determination of the fluidity of plastics using capillary and slit die rheometers. 1996. 

High density polyethylene CH3CF2CI 200 NR NR Pressure-driven slit die rheometer... 

Reactive viscosity of thermosets Uniaxial extensional viscosity Biaxial extensional viscosity First normal stress difference 6721-10 6721-10 A slit die rheometer according to ISO 11443 can also be used. 

Plastics—Determination of the Fluidity of Plastics Using Capillary and Slit Die Rheometers Plastics—Determination of Fracture Toughness (Gc and Kq). Part 1 Linear Elastic Fracture Mechanics (LEFM) Approach Methods of Test for Volume Resistivity and Surface Resistivity of Solids Electrical Insulating Materials... 

Whenever a process engineer uses flow property data, he should know on what instrument and how these data were determined in order to properly assess the validity of the data. Instruments to determine flow properties are generaliy referred to as rheometers. The rheometers that wiii be briefly described in the next few sections are the capiiiary rheometer, the meit indexer, the cone and plate rheometer, the slit die rheometer, and dynamic mechanicai rheometers. For a more detailed description of these and other rheometers, the reader is referred to the literature [64-66]. A brief but good survey of commerciai rheometers was presented by Dealy [92]. 

A slit die rheometer is an extruder die with a rectangular flow channel with provisions to measure pressures at various axial locations. The slit die is either directly connected to an extruder or to a gear pump, which, in turn, is connected to an extruder. A typical slit die geometry is shown in Fig. 6.22. 

An interesting aspect of the slit die rheometer is the fact that the polymer has a significant temperature and shear history by the time it reaches the slit die. This can affect the rheological properties, as reported by the author [71]. On the other hand, if viscosity data is to be used for die design purposes, the slit die viscometer is most likely to produce pertinent viscosity data. 

Capillary and slit-die rheometers are used to determine the dependency of viscosity on shear rate. Since most molten polymers exhibit non-Newtonian behavior, it is important to be able to characterize this behavior. Measurements are made using a piston-driven cylinder that drives the molten polymer through a die of precise dimensions. The pressure drop across the die is measured, as is the flow rate through the die. Temperature is precisely controlled throughout the measurement. This test yields precise viscosity measurements as a function of temperature and shear rate. However, measurements tend to have artifacts in them, which need to be corrected in order to obtain true viscosity using Bagley and Rabinowitsch corrections. Capillary rheometers are also used to determine the effects of slip, a phenomenon in which the velocity of the melt at the capillary wall is nonzero. Slip has important implications for highly filled materials. 

Lodge and Ko (1989) tested this criteria with Newtonian oils in a miniature slit die rheometer, O.OS x O.S x 2 nun. At the remarkably high shear rate of 5 x 10 s with a 2.5 m Pa-s oil, they reached Na = 1.3 and recorded a 7% error in viscosity. Lodge and Ko (1989) and also Winter (1975, 1977) give detailed analyses of the role of viscous dissipation in slit flow. 

FIGURE 3.23 Slit-die rheometer showing the position of the pressure transducers (Ti). 

Slit-die rheometers (see Fig. 3.23) are useful devices for measuring the viscosity of polymer melts because it is possible to measure the pressure gradient directly. The geometry is that of two flat plates with a rectangular cross section. If the aspect ratio, WIH, is greater than or equal to 10, then there is no side wall effect. The wall shear stress, t, is then... 

The slit-die rheometer also offers the possibility of obtaining values of M at high shear rates (Baird, 2008). The method is based on the measurement of a quantity called the hole pressure, Ph, which is the difference of pressures Pi and P2, where P2 is the pressure measured by transducer T2 mounted... 

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