Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Reexamination Certificate
1999-09-11
2002-06-18
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
C425S115000
Reexamination Certificate
active
06405579
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the measurement of process characteristics of melted materials and pertains, more specifically, to the on-line measurement of such characteristics as the viscosity of polymer melts for purposes of monitoring and controlling of manufacturing processes involving molten plastics.
2. Description of the Prior Art
Rheological testing equipment has been available for a very long time in conducting laboratory measurements of certain important characteristics of polymer melts used in various manufacturing processes. Thus, such properties as viscosity and melt flow index are being measured in the laboratory with increasing accuracy. More recently, efforts have been directed toward the measurement of these characteristics on-line, during the manufacturing process itself, in order to provide constant, closer control over the quality of the melt utilized in the process. On-line measurement requires equipment which not only is relatively easy to use and maintain, but which is rugged enough to withstand the operating conditions to which the equipment will be exposed. In order to be effective, the equipment must be responsive, and must avoid disturbing the manufacturing process being monitored.
Among the more successful on-line rheometers available currently are capillary rheometers which divert a portion of the polymer melt from the main stream of molten plastic, conduct measurements on the diverted melt, and then simply purge the melt out to the atmosphere, hence called A on-line rheometer. Also, rheometers have been developed in which the diverted melt is returned to the main stream, hence called A at(or in)-line) rheometer, thereby eliminating additional steps associated with the purge stream. Both on-line and in-line rheometers usually employ a first metering pump, such as a gear pump, to feed a capillary passage with a controlled flow of the diverted melt, and in case of in-line, a second metering pump to return the diverted melt to the main stream. Pressure drop along the capillary passage is measured and the temperature of the diverted melt is closely controlled with an independent heating or cooling arrangement in order to measure viscosity, as a function of the measure of the pressure drop, to gain the information necessary to control the process.
For a more complete understanding of the state of the technology with respect to rheological testing, consider some instances of known methods and apparatus as reflected by the patent literature. U.S. Pat. No. 4,817,416 to Blanch et al. discloses a system for making in-line rheological measurements utilizing a rheometer of the type in which a first metering pump delivers diverted melt from a process main stream to a capillary passage and a second metering pump returns the diverted melt from the capillary passage to the process main stream and the viscosity of the diverted melt is measured by controlling the rate of flow of the melt to maintain constant the pressure drop between spaced apart locations along the capillary passage and measuring the temperature of the melt in the capillary passage. The measurements may be made while controlling the speed of the second metering pump independent of the speed of the first metering pump to maintain the pressure at the exit of the capillary passage essentially constant. The capillary passage is placed in close proximity to the process main stream for maintaining a relatively short residence time during which the diverted melt resides outside the process main stream so as to attain a relatively quick response to changes in the measured viscosity.
U.S. Pat. No. 4,449,395 to Kurtz et al. discloses a system for testing thermoplastic material according to which a fractional, continuous, molten and flowable sample of the material is passed as a stream to and successively through each of either a controllable pumping zone maintained at constant temperature and pressure or controllable pressure zone maintained at constant flow rate and temperature, and a die zone to form a continuous strand of the material. The viscosity of the material in the pumping and die zones is measured. A measurement of elasticity is provided by obtaining a measurement of percentage of cross-section area swell in the strand in passage from the die zone over a constant length distance downstream of a point of mark sensing. The viscosity measurement is combined with the elasticity measurement to provide fuller Theological characterization data for the material.
U.S. Pat. No. 4,403,502 to Lindt discloses a motionless viscometer and associated method for resinous materials including polymeric foams and non-resinous materials includes a reservoir section, a receiver section and an interposed tube. As the foam is expanded, the axial pressure within the connecting tube is measured as is the rate of rise of the foam within the receiver element. Shear viscosity and density as functions of time may be determined.
It was with knowledge of the foregoing that the present invention has been conceived and is now reduced to practice.
SUMMARY OF THE INVENTION
A system for providing process control information concerning a polymer melt comprises: means containing a polymer melt under pressure; means for diverting a stream of said polymer melt directly from said containing means to and through an orifice of predetermined cross sectional area wherein the flow of said diverted portion to and through said orifice is unobstructed and directly dependent on the pressure of said main polymer melt, said cross sectional area being sized to permit the flow of said diverted melt polymer therethrough absence additional independent means acting on said diverted melt polymer for increasing flow through said orifice; temperature sensing means for measuring the temperature of the diverted melt stream and producing a resultant temperature signal; pressure sensing means for measuring the pressure of the diverted melt stream and producing a resultant pressure signal, said pressure signal being directly dependent on the pressure of polymer in said main polymer melt and the predetermined size of said orifice; means of measuring the production rate of the extruder; and manufacturing control system, such as a Programmable Logic Controller (PLC), means responsive to the temperature, pressure and production rate signals for determining process characteristics of the main polymer melt.
In the present invention, the flow of the diverted steam is unobstructed and characterized by the absence of pumps or other pressure enhancing devices which might be employed to increase the pressure in the diverted stream. The orifice is sized to provide for substantially continuous flow of polymer melt therethrough with the pressure differential provided by the pressure in the main polymer melt and the pressure at the orifice outlet which is typically atmospheric pressure. Preferably the orifice opening has a diameter of about 0.05 to about 0.15 inch or if the opening is non-circular an equivalent cross-seasonal area. The means containing the polymer melt is preferably an extruder. A single Screw or twin screw extruder having a Length to Diameter ratio from bout 5 to about 60, and preferably from about 20 to about 40, a pressure in the extruder of polymer melt is greater than about 20 pounds per square inch and is typically within the range of about 600 to about 2000 pounds per square inch, more typically within the 800 to 1400 range, and an extruder diameter of about ¾ to 16, preferably about 1 to about 8 inches are preferred features.
With the above system a passage extends between an inlet communicating with the main polymer melt and the outlet at the orifice. In the most preferred embodiment, the passage comprises a barrel member extending between inlet and outlet ends selectively attached at said inlet to said main polymer melt. The orifice comprises an insert mounted internal to the outlet end of the barrel. A heater means may be provided for maintaining substantially constant temper
Fischer George F.
Georgieva Galina D.
Haraburda Scott S.
Janssen Joseph M. H.
Lin Ye-Gang
Larkin Daniel S.
Politzer J L
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