Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Patent
1998-03-13
1999-09-28
Williams, Hezron
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
137 92, G01N 1104, G05D 1100
Patent
active
059591951
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of determining and evaluating melt flow index values (MFR values) of thermoplastic materials with the aid of a continuously operating on-line capillary rheometer, wherein a pressure difference .DELTA.p is predetermined between an inlet and an outlet of a measuring nozzle of the capillary rheometer.
Based on their wide measuring range and their simple and robust construction, capillary rheometers are rheometer systems most frequently used in the polymer industry.
One possibility of acquiring measurement data with a capillary rheometer consists in measuring the pressure difference between the inlet and the outlet of the measuring nozzle, wherein the volume flow through the measuring nozzle is generally kept constant. However, it is also possible to predetermine a constant pressure difference and to measure the thereby resultant volume flow through the measuring nozzle. In practice, it is common to use round hole nozzles or flat slotted channels as a measuring nozzle. In continuously operating on-line capillary rheometers, the volume flow is metered by means of so-called melt pumps, for example, gear pumps. The adjustable operating range of melt pumps is from 0.5 to 100 rpm. The delivery is normally from 0.6 to 1.3 cm.sup.3 per revolution. As a result, a variable volume flow can be predetermined, which makes it possible to cover the viscosity function of the melt within a specifiable range. On the condition of identical nozzle geometries, identical results are obtained with on-line capillary rheometers and conventional laboratory instruments.
From the viewpoint of the industry, the melt flow index (MFR) represents the most popular parameter for describing the flow behavior of thermoplastics. Even when this value is determined within the scope of a classic one-point measurement, it is often specified by raw material producers for application engineering as the only Theological value for product specification. In this respect, central importance is also attributed to the melt flow index (MFR) in the product-concomitant quality control and quality assurance.
According to DIN, ISO, the melt flow index is determined as the extruded test material in grams, which is extruded in ten minutes from a temperature-controlled channel through a defined nozzle, the test material being weighted, via a piston, by a defined load M.
Since in the case of many polymers, the density .zeta. of the melt does not change significantly, it has been found practical to also standardize the volume index (MVR). In its instance, the extruded material is specified in cubic centimeters. The determination of the volume index (MVR) represents the more common form of determining measurement data.
The measuring nozzle of melt flow indexers as are used in a laboratory has a diameter of 2.1 mm and a length of 8 mm. The load weight is selected from 2.16 kg to 21.6 kg as a function of each polymer being characterized.
Unlike the melt flow indexers used in the laboratory, the measuring nozzles of on-line capillary rheometers have a length to diameter (L/D) ratio greater than 10. This configuration is necessary, for purposes of generating between the inlet and the outlet of the measuring nozzle pressure differences of a magnitude, which can be acquired with the use of commercially available pressure gauges.
The MFR or MVR measurement is in a first approximation a creep test, wherein the shear stress .tau..sub.W that acts upon the melt as a result of the load weight is constant on the wall.
Different nozzle geometries of melt flow indexers used in the laboratory and on-line capillary rheometers, and likewise different flow conditions that are present in each case make it only difficult to draw a comparison between the MFR or MVR values acquired in the laboratory and those acquired on line.
It is therefore the object of the invention to enable a kind of to-scale transfer, so that continuously acquired MFR and MVR values correspond within acceptable limits to MFR or MVR values that are determined under standardized laborat
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patent: 3252320 (1966-05-01), Welty
patent: 3468158 (1969-09-01), Chien
patent: 3908442 (1975-09-01), Chimel
patent: 4449395 (1984-05-01), Kurtz et al.
Gottfert Werkstoff-Prufmaschinen GmbH
Politzer Jay L.
Williams Hezron
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