Slit viscometers

Paar HVA 6 Automated Capillary/Slit Viscometer gas pressure ... 

The calculation of surface viscosity by this method had a maximum sensitivity and precision of 3 X 10 5 and 1 X 10 4 surface poise, respectively, in the low viscosity range, and 1 X 10 3 and 1 X 10 - surface poise, respectively, in the high viscosity region. The method offers extreme simplicity in construction and operation, and is more adaptable to high viscosity films (greater than 10 2 surface poise) than the canal or slit viscometer. Recent work (31) with the canal viscometer indicates an inability to measure film viscosities of palmitic and stearic acid mono-layers over pH 9.0 to 9.5 KOH substrates. 

HVA 6 Automated CapiUary/Sht Viscometer MFM Melt Flow Rheometer Automatic Melt Flow Indexer AK Continuous Capillary Rheometer Han Slit Rheometer... 

A number of instruments are based on the extmsion principle, including slit flow and normal capillary flow (Table 6). These instruments are useful when large numbers of quality control or other melt viscosity test measurements are needed for batches of a single material or similar materials. When melt viscosities of a wide range of materials must be measured, rotational viscometers are preferable. Extmsion rheometers have been applied to other materials with some success with adhesives and coatings (10,161). 

Capillary Viscometer. The end products from the liquid mixtures are usually obtained by extruding the liquid mass through narrow tubes or slits (e.g., spinning of fibers, injection molding, or film extrusion). Therefore, the pressure flow through a capillary is of technological interest. Hence, we analyzed the flow of a liquid mixture through a capillary with circular cross-section and compared the results of theory and measurement. 

Viscometers can be divided into rotational instruments and axial flow instruments. Rotational instruments include concentric cylinder (cup and bob), cone and plate and parallel disc viscometers, while axial flow instruments include capillary, slit and extrusion rheometers. 

In axial-flow viscometers, the sample is made to flow through a duct of regular cross-section. Capillary (circular cross-section) and slit (rectangular cross-section) viscometers are controlled stress instruments a known pressure difference (which causes shear stress in the sample) is applied over the duct length, and the resulting volumetric flow rate measured. In the extrusion viscometer, a controlled shear rate instrument, the sample is extruded through a capillary tube by the action of a constant speed piston, acting on the sample in a cylindrical reservoir to which the capillary is attached. The pressure difference between the ends of the capillary is measured. 

Senouci, A. and Smith, AC. 1988. An experimental study of food melt rheology. I. Shear viscosity using a slit die viscometer and a capillary rheometer. Rheol. Acta 27 546-554. 

Indirect measurements. Indirect methods for determining the interfacial shear viscosity include procedures in which the liquid underneath, together with the monolayer are brought into motion and the ensuing dissipation consists of a bulk and interfacial contribution. Theory is required to compute these two contributions and to subtract the former. An old method for determining the interfacial shear viscosity is the canal surface viscometer. It is based on the determination of the flow rate of a film through a narrow canal or slit under eui applied two-dimen-... 

Surface viscosity can be measured with a canal viscometer or with a torsion viscometer. The former instrument measures the flow of the film through a slit in a beurier on a film balance the latter, the damping caused by the presence of a film on a body moving in the surface of the liquid. Interpretation of measurements on films with a constant viscosity is difficult and would be more so in the presence of viscosity changes caused by reaction. 

Rotation Viscometers. In rotation viscometers, a rotor moves against a stator (see Figure 9-23). The Epprecht viscometer is particularly suitable for measurements on highly viscous solutions. Here, the angle of rotation of a torsion wire on which the stator is suspended is a measure of the torque produced by the rotating rotor on the liquid. Since all the other quantities (cylinder radius, width of the slit, gap between rotor and stator, number of rotations in unit time) are kept constant, the viscosity is easily calculated. 

Pressure-driven devices include capillary viscometers and slit-die viscometers, in both of which the flow is driven by pressure. In the case of the capillary viscometer the pressure is generated by an upstream piston, and in the case of the slit-die viscometer flow is generated by an extruder. In both cases, measurements of pressure drop and flow rate are used to determine the viscosity. Both techniques have the inherent problem of pressure drop, which may result in phase separation. For this reason, the techniques are suitable for low-pressure measurements, which may mean that the polymer has not reached equilibrated CO2 concentrations. 

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. 

X2.2.3 A convenient holder can be made by drilling two holes, 22 and 8 mm in diameter, respectively, through a No. 11 rubber stopper. The center-to-center distance between holes should be 25 mm. Slit through the rubber stopper between the holes and also between the 8-mm hole and edge of the stopper. When placed in a 2-in. (51-mm) diameter hole in the bath cover, the stopper holds the viscometer in place. Such holders are commercially available. 

The need to measure fluid properties at shear rates higher than those accessible with rotational viscometers arises because deformation rates can easily reach 10 -10 sec in polymer processing operations. To attain these high shear rates, we use flow through capillaries or slits and calculate the viscometric functions from a knowledge of the pressure drop-versus-flow rate relationship. 

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