Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Controlling heat transfer with molding material
Reexamination Certificate
2001-11-05
2003-11-18
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Controlling heat transfer with molding material
C264S328100, C425S144000, C425S145000
Reexamination Certificate
active
06649095
ABSTRACT:
This invention relates generally to a method and apparatus for controlling molding-process, melt-volume conditions, and more particularly to the control of molding conditions so that molded articles of uniform volumetric consistency and quality are obtained at all times irrespective of fluctuations in melt-flow properties of mold resin in injection molding machines, including injection-molding machines that employ a hot-runner system.
COPYRIGHT NOTICE
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention is directed to the control of mold cavity melt conditions in injection molding systems so that molded articles of uniform consistency and quality are produced at all times irrespective of fluctuations in the flow properties of mold resin. The present invention relies upon novel methods and techniques for sensing and monitoring a temperature profile at one or more locations in a molding system. In one embodiment, the invention contemplates the use of an injection molding support sensor array system (machine & mold) throughout a molding process, including start-up, purge, operation, etc.
Heretofore, a number of patents and publications have disclosed systems and methods for the control of injection-molding equipment, the relevant portions of which are hereby incorporated by reference and which may be briefly summarized as follows:
U.S. Pat. No. 5,419,858 to Hata et al., issued May 30, 1995, discloses a system and method for automating the sensing of flow properties of a resin material and the adjustment of molding conditions (e.g., temperature).
The article “Temperature Control Builds Better Injection Molding, by James R. Koelsch, published in the magazine
Quality
in May 2000, describes the monitoring and control of temperature as a critical parameter in an injection molding process.
The Dynisco Technical Reference, 42
nd
Issue, Section Nine “The Importance of Accurate Melt Temperature Measurements in Extrusion” (ref. Pg. 171) states that the thermal degradation of polymers is a time-temperature degradation. The degradation curves are shown therein. The “Variations In Temperature and Residence Time During Extrusion” are explained. The importance of accurate melt temperature measurements is in relation to the original material and “Regrind” percentage being used. The conclusions are based on a large thermocouple sensor mass that is used at the edge and moved in a melt stream.
In injection-molding machines the cyclic thermal-mechanical operating precision and stability of the equipment has been greatly improved through improvements in the control circuitry used and the use of “real-time” closed-loop machine process control. However, the plastic material or “melt” used to mold a part, in the injection molding industry, is produced by a complicated polymerization reaction. The occurrence of some variance in the “melt” and “flow” properties of the plastic material cannot be avoided due to variances in the raw material and difficulties in controlling the polymerization reaction. In particular, in resin materials produced by the batch method, maintaining the material properties constant from one batch to another is extremely difficult.
For example, the value of the melt-flow index (MFI—determined using a five minute static state and five minute “melt” extruding time test) often fluctuates by approximately 10% with respect to the specified value for a particular material. Furthermore, in the case of a colored material, there is of course a variance in properties from one color to another due to differences in the pigments and the compounding of additives.
Even if the control precision of an injection-molding machine is improved, a disparity of density, and quality, in the molded articles develops because a fluctuation in resin “melt-flow” effects the “shrink” properties. In particular, a fluctuation in the quality (dimension, weight, density, warping etc.) of the molded articles arises when resin “melt-flow” lots are changed over from one to another. Accordingly, a technician must often monitor the molding machine (e.g.,
FIG. 2A
,
198
) and mold temperature at all times and address any fluctuation in resin “meltflow” properties. And the technician must try to adjust for the melt process variance. The molding process is a cyclic sequence starting from an “OPEN” static “free” thermal state, to a dynamic “CLOSE” thermal-mechanical injection state, and then followed by a mold “OPEN” to eject the molded part.
An object of the present invention is to automate the melt to mold exchange by monitoring thermal characteristics using a melt-flow temperature sensor(s). Such sensors may include edge temperature sensor(s) and inner melt-flow temperature sensor(s). As a result of Boyle's law, the resultant pressure-volume temperature “rise” may be used to monitor the molding system, and to control the process in an acceptable [Min-Mean-Max] Range. It is further contemplated that the temperature profiles may be recorded and analyzed with trend averaging and LAST-cycle readout, so as to contrast each melt process cycle relative to a predetermined temperature-time sequence control points (process limits). In a preferred embodiment, such a process will be able to identify possible “reject” parts and divert such parts for further inspection and/or widen the latitude of the process, if the sample is acceptable.
Another object of the present invention is to determine the input material temperature and moisture status after being loaded into the injection system hopper. A hydroscopic material must be properly conditioned by drying, otherwise the process produces parts with moisture “streaking” and “brittleness” and a commensurate reduction in the expected finished product performance.
Another object of the present invention is to stabilize the final melt/mold cavity volume and consistency of each cavity molded article's density by monitoring and controlling fluctuation in resin melt-flow property, through a systematic machine support and melt/mold temperature sensor array system. A system employing aspects of the present invention preferably monitors temperature during each OPEN and CLOSE operation, at one or more locations including: melt source nozzle orifice; mold cavity sprue; runner; gate to vent; and through OPEN mold time to part ejection.
The present invention provides a method of monitoring the indirect process support system and direct machine-to-mold melt temperatures, using inner melt and/or edge temperature sensor(s). In a full system monitoring embodiment, monitoring preferably proceeds from initial machine hopper material conditioning, screw return-melt, and melt-flow injection process, and molding stages of each cavity resin melt-flow. The system may further include processes and controls for independently shutting off gates for each mold cavity (e.g., gating) based upon melt temperature profile for an accepted melt-mold cavity volume.
The inventor has further discovered that temperature change impacts the machine applied mechanical clamp force on the melt/mold cavity volume to establish the molded product final thermal-mechanical “shrink” properties. The machine and mold material mechanical Modulus of Elasticity “E” (Force per unit area) lowers with increasing temperature, while the material thermal coefficient of expansion “e” (change in Length divided by initial Length times temperature change) rate increases with increasing temperature. Therefore, the temperature rise increases the material thermal “strain” (Length increase) and lowers the mechanical modulus (strength decrease).
In a typical molding cycle, molten material (melt-flow) exits a nozzle orifice and enters the mold sprue, the runner, and
Basch Duane C.
Basch & Nickerson LLP
Heitbrink Jill L.
LandOfFree
Method and apparatus for controlling a mold melt-flow... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for controlling a mold melt-flow..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for controlling a mold melt-flow... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3132574