Pressurized rheometer

High pressure rheometer (Camargo et al., 2000) Yes P, T, viscosity vs. time Typically 1000 psi Viscosity changes vs. time... 

For tests using a Rheometrics pressure rheometer (RPR), the HPG solution is pumped with a chromatography pump, and the cross-linker is injected into the flowing polymer solution with a syringe pump. The two... 

Elevated Temperature Testing. The tests in the RSIV were conducted only at ambient temperature. Elevated-temperature tests were conducted by using a Fann viscometer, a Rheometrics pressure rheometer (RPR), and a reciprocating capillary viscometer. The basic test procedure used for testing at 80 C with the Fann viscometer and reciprocating capillary viscometer is as follows. 

The second set of experiments is performed under similar operating conditions, but pra-tically without lateral sliding and spin, first, for the lubricants L2, L3 and L4 tested by Bair and Winer on their high pressure rheometers, and second, for two lubricants used in ball bearing applications the silicone oil L5 and the lithiisn grease L6. 

The fH essure dnq>, pr, in the reservoir shows up as a gradually falling pressure in a constant flow rate instrument or as a rising flow rate with a constant pressure rheometer. It may be eliminated by extrr lation to the o nllary entrance, as indicated in Figure 6.2.8. A power law model can be used to get an estinute of pr (Skinner. 1961 Marshall and Riley, 1%2 Metzger and Knox, 19isS)... 

Figure 8.2.15 shows a design for a pressurized rheometer. The key is the thin-walled tube, which acts as a torsion spring and also permits the motion to be transferred out of the chamber. 

Schematic diagram of a torque transducer for a pressurized rheometer. The thin-walled tube twists slightly when torque is exerted by the sample on the inner cylinder. This twist is recorded by the rod and capacitance gage.

In general, the rheological properties in high shear rate region are conducted by capillary rheometers. These rheometers are popular because of their simplicity in design and use. In capillary rheometers, the viscosities are measured by the measurement of the pressure drop of a given flow rate. Capillary rheometers are broadly categorized as constant speed rheometers and constant pressure rheometers. 

Figure 42 Storage and loss inoduluses ((/" and O ") of glutenin (30% moisture content) in a temperature weep test (0,5 K min heating rate 0.5% strain 1 Hz frequency) carried out with a pressure rheometer (modified from [258]).

A pressure rheometer was built to measure rheological properties of polymers at elevated pressures and temperatures. However the viscosity at high deformation rates decreases more than the predicted theoretical value represented by the Cross-WLF model. This paper studies the role of viscous heating in the resulting viscosity deviations by means of simulation nsing the Radial Functions Method (RFM). 

Piston Cylinder (Extrusion). Pressure-driven piston cylinder capillary viscometers, ie, extmsion rheometers (Fig. 25), are used primarily to measure the melt viscosity of polymers and other viscous materials (21,47,49,50). A reservoir is connected to a capillary tube, and molten polymer or another material is extmded through the capillary by means of a piston to which a constant force is appHed. Viscosity can be determined from the volumetric flow rate and the pressure drop along the capillary. The basic method and test conditions for a number of thermoplastics are described in ASTM D1238. Melt viscoelasticity can influence the results (160). 

Another type of rotational viscometer is the hehcal-screw rheometer (176). This iastmment is basically a screw-type metering pump that does not pump. The measure of force is the pressure difference resulting from the rotational motion. It is possible to use a bank of pressure transducers of different sensitivities to measure viscosity over a wide range. The iastmment can be used for high temperature rheometry and to foUow polymerkation, shear and heat degradation, and other developments. 

J The viscosity characteristics of a polymer melt are measured using both a capillary rheometer and a cone and plate viscometer at the same temperature. The capillary is 2.0 mm diameter and 32.0 mm long. For volumetric flow rates of 70 x 10 m /s and 200 x 10 m /s, the pressures measured just before the entry to the capillary are 3.9 MN/m and 5.7 MN/m, respectively. 

A slit die is designed on the assumption that the material is Newtonian, using apparent viscous properties derived from capillary rheometer measurements, at a particular wall shear stress, to calculate the volumetric flow rate through the slit for the same wall shear stress. Using the correction factors already derived, obtain an expression for the error involved in this procedure due to the melt being non-Newtonian. Also obtain an expression for the error in pressure drop calculated on the same basis. What is the magnitude of the error in each case for a typical power law index n = 0.377... 

Over the twentieth century, the mbber industry has developed special rheometers, essentially factory floor instmments either for checking process regularity or for quality control purposes, for instance, the well-known Mooney rheometer (1931), the oscillating disk rheometer (1962), and the rotorless rheometer (1976). All those instmments basically perform simple drag flow measurements but they share a common feature During the test, the sample is maintained in a closed cavity, under pressure, a practice intuitively considered essential for avoiding any wall slip effects. Indeed it has... 

Capillary rheometers are in the form of a barrel where the operator puts the polymer sample. After heating to equilibrate its temperature, the sample is pushed by a piston through a die at chosen rates. Various sizes and shapes of dies are available. Capillary rheometers measure the rheological properties under broad ranges of conditions of temperature, pressure, stress, strain and time, allowing the adoption of parameters near to those for processing. 

Monsanto Automatic Capillary Rheometer gas pressure, pneumatic cylinder B... 

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