Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With accumulator – trap chamber – or serially arranged valves...
Reexamination Certificate
2000-05-10
2002-02-19
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With accumulator, trap chamber, or serially arranged valves...
C425S561000
Reexamination Certificate
active
06347934
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to the manufacture of molded articles. More particularly, the present invention relates to systems for precisely metering and delivering a desired amount of a moldable composition into a mold, such as aqueous, starch-based compositions.
2. The Relevant Technology
There has been a marked trend in recent years toward finding biodegradable and environmentally friendly alternatives to containers made from polystyrene foam and other plastic materials. The search for environmentally friendly substitutes has been driven by the recognition that polystyrene and other plastics tend to persist in the environment for years, decades, and even centuries before finally breaking down. Some companies, like McDonald's Corporation, have abandoned fast food boxes, cups and other containers made from polystyrene foam and plastic in favor of alternative materials.
More bio-friendly materials, such as starch-based compositions, are of interest in the manufacture of disposable containers and other articles, including cups, clam shell sandwich containers, plates, bowls, boxes and lids. Such compositions may include water, starch and other admixtures to improve processing and final properties. Starch-based plates and other containers manufactured by Biopac Corporation of Sweden were demonstrated at the winter Olympics in Lillihammer, Norway. Such containers were manufactured according to a process described in U.S. Pat. No. 5,376,320 to Tiefenbacher et al. For purposes of disclosing moldable starch-based compositions, the foregoing patent is incorporated herein by reference. Whereas the starch containers developed by Biopac were beneficial from an environmental standpoint, they were expensive to manufacture, both from a materials and processing standpoint.
Improved starch-based compositions that are less expensive to make and to mold into containers have been developed by researchers at E. Khashoggi Industries, LLC and are described in U.S. Pat. Nos. 5,662,731, 5,679,145 and 5,868,824. For purposes of disclosing moldable starch-based compositions, the foregoing patent is incorporated herein by reference.
In general, the manufacture of starch-bound articles having a foamed cellular matrix involves the use of aqueous molding compositions that include water, ungelatinized and pregelatinized starches, fibers, and other desired admixtures. The aqueous starch-based mixtures are introduced into a heated two-part mold in order to (1) gelatinize the ungelatinized starch portion and (2) remove at least a portion of the water by evaporation in order to yield a form stable molded article. The vaporizing water also causes the moldable composition to expand and fill the mold cavity. Venting means such as vent holes allow for escape of water vapor from the mold cavity and associated expansion of the starch-based mixture.
In order to ensure proper formation and density of the molded article, it is necessary to meter and deliver an optimum quantity of the moldable composition into the mold, typically a two-part mold including male and female mold halves. As stated above, the aqueous compositions typically expand to fill the mold cavity. If too little of the composition is introduced into the mold, it may not properly expand and fully fill the mold cavity, thus yielding incompletely formed articles which must be culled and discarded. On the other hand, introducing too much starch-based composition into the mold may result in excessive pressure build-up within the mold cavity, which can also result in improperly formed or damaged articles. In addition, excess mold material expelled through the vent holes typically remains attached to the molded article as unwanted “flashing” that must be removed and which can cause scarring or breakage of the article at the point where the flashing is broken off. In view of this, one would expect the failure rate when molding starch bound articles to be greatly reduced the amount of composition that introduced into the mold each time can be more precisely metered and delivered.
In a typical process the starch-based composition is mixed together batch-wise and then pumped through hoses to the mold site where it is intermittently dropped or expelled into the molds. One system for introducing the starch-based material into the molds consists of an aperture and shutter arrangement. Initially, the shutter covers the aperture and prevents the pressurized starch-based composition from exiting the aperture. When it is desired to introduce a quantity of material into the mold, the shutter is opened for predetermined duration and then closed. In theory, the speed and duration of this opening and closing action can be calibrated in relation to the pressure and rheology of the molding composition in order to introduce a desired amount of the composition into the mold each time. In reality, there are simply too many changing variables for such a system to accurately and precisely deliver the desired quantity of material into the molds during each and every cycle.
The inability of the aperture/shutter valve system to precisely and accurately deliver the same quantity of material during each cycle is due to a number of changeable variables. One variable is the pressure of the starch-based composition being delivered to the mold system. Assuming that the shutter speed and open dwell time are calibrated according to the specific mold requirements and the assumed pressure of the starch-based composition, even slight variations in the actual pressure of the starch-based composition can cause deviations in the amount of material actually delivered. If the pressure is higher than what is assumed, too much of the starch-based composition will be delivered; conversely, if the pressure is lower than what is assumed, too little of the material will be delivered.
Another variable is the rheology of the starch-based composition, including both the viscosity and yield stress of the material. Once again, even slight variations of mixture rheology can affect the flow rate of the material through the aperture. Such discrepancies in flow rate are only exacerbated when multiple valves are used, since it is difficult to ensure that every value experiences the same pressure and associated flow rate. Ensuring an even flow rate throughout all the valves would require a very complicated delivery system.
One way to overcome these problems might be to have a computer monitored system that could continuously monitor the foregoing variables and adjust the individual valve shutter speeds in order to maintain close tolerances of the quantity of material being delivered. In practice such an arrangement would be difficult to implement, particularly because the correction mechanism would only be triggered when deviations were actually detected. Such variations will likely have already resulted in poorly formed containers before corrective measures can be made. Moreover, a highly complicated system of measuring transducers, information relays, computer algorithms, individual speed and timing adjustments to each valve, and other required equipment for such a correction system would be extremely complicated and would tend to further increase the already high initial capital costs of setting up a manufacturing line. Moreover, careful calibration of all the equipment would be necessary from time to time in order to ensure that the information feedback and correction system would actually work as intended.
In view of the foregoing, what is needed are improved methods and systems for metering and delivering a precisely measured quantity of a flowable composition into a mold.
It would be a further improvement in the art to provide methods and systems for metering and delivering a precisely measured quantity of a flowable composition which did not change in response to fluctuations in pressure and rheology of the mold material.
It would also be an improvement in the art to provide methods and systems for metering and delivering a precisely measured q
Andersen Per Just
Dellinger David A.
Laine Matthew E.
Turner Kristopher R.
E. Khashoggi Industries, LLC.
Heitbrink Tim
Workman & Nydegger & Seeley
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