Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Measuring a weight or volume
Reexamination Certificate
2000-07-27
2003-09-16
Davis, Robert (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Measuring a weight or volume
C264S040600, C264S521000, C264S532000, C264S535000, C425S140000, C425S143000, C425S169000, C425S215000, C425S526000, C425S529000
Reexamination Certificate
active
06620352
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the field of blow molding articles from plastic parisons, and more particularly concerns methods and systems for producing stretch blow molded articles formed of polymeric resin and having consistent physical dimensions.
2. Description of the Prior Art
Providing consistent physical dimensions, including consistent material distribution, has been a chronic problem in production of blow molded articles, such as those articles formed from polymeric resins such as polyethylene terephthalate (PET). Difficulties in achieving consistent physical dimensions, such as material distribution, has led to problems in assuring acceptably high quality of such articles. In addition, difficulties arising from the lack of uniform physical dimensions can exist across various production platforms and between production facilities seeking to produce substantially identical blow molded articles. Consistent physical dimensions such as material distribution are very important for end performance characteristics of blow molded articles, e.g., stretch blow molded containers, such as burst strength, top load strength, thermal deformation resistance, and stress cracking resistance.
Current material distribution analysis techniques directed to already formed blow molded articles are time consuming, relatively crude in that such techniques provide only gross material distributions, and, in addition, do not lend themselves to automated inspection. One current analysis technique for material distribution is the so-called section weighing method, where, for instance, portions of a stretch blow molded article such as a base, label panel, and shoulder, are cut away from each other and individually weighed to ascertain whether these sections weigh within prescribe tolerances. Despite the availability of the section weighing method, and while this method is adequate for gross determination of overall material distribution of the sections, the section weighing method cannot account for variability within the section, although variability within a section of a blow molded article has been frequently observed in both laboratory and production environments. Further, the section weighing method is necessarily destructive of the article and can only be performed on a very small number of the articles, while most (perhaps as much as 99.9%) of the articles manufactured by a particular line are not inspected at all for material distribution. Therefore, the section weighing method can only be used to indirectly determine whether the material distribution of a stretch blow molded article which has not been cut and weighed but was made using the production parameters of a section weighed article is within acceptable tolerances. Further, there is no easy method of integration of the results of such testing back into the manufacturing process to achieve articles having more uniform or desirable parameters.
Consequently, there exists a need in the art for methods and systems for directly and non-destructively assuring consistent physical dimensions such as material distribution for stretch blow molded articles, in order to produce stretch blow molded articles of consistent quality across various production platforms and between different production facilities. Preferably such systems can be applied to a substantial portion, if not all, of the containers manufactured in a given production line so that product quality can be maintained to better standards.
Our prior patent, namely, U.S. Pat. No. 5,902,526, disclosed a method for inspecting blow molded articles on a continuous or substantially continuous basis, wherein the parisons employed in the blow molding process included a plurality of first markers formed at preselected position on the parison exterior surface. The first markers were generally in the form of light circumferential lines disposed generally planarly and parallel to each other, each line forming a complete outwardly projecting annulus on the exterior surface of the parison. The product is formed by placing such a parison in a blow mold having sections defined generally by smooth interior surfaces, but having a plurality of second differentially dimensioned portions, each second differentially dimensioned portion disposed at a predetermined location on stretch blow mold interior surface. The location of each second differentially dimensioned portion was generally selected to correspond with the optimum location of one of the first markers when the parison was transformed by the blow molding process to conform to the interior of the blow mold. The second differentially dimensioned portions could be disposed on the blow mold interior surface in any of a variety of configurations and orientations, such as where the individual second differentially dimensioned portions are formed of small or large differentially dimensioned segments disposed planarly or non-planarly, or as raised or depressed impressions on the blow mold interior surface, or by modified surface finish of blow mold interior surface.
In a finished article formed in accordance with U.S. Pat. No. 5,902,526, the relative position of first markers with respect to the corresponding, proximately disposed second markers indicates whether at least one dimension is within the preselected range. For example, the thickness dimension of a profile of the article may be determined to be within a preselected range of thicknesses by ascertaining whether the distance between each first marker and a corresponding second marker is less than a preselected distance. The marker can be formed to define tolerance bands or zones. Upon blowing the parison with the first markers within such a mold produces an article having second markers defining a tolerance zone or band, and including a plurality of first markers in close relation to the plurality of corresponding tolerance zones. The relative position of the first markers with respect to corresponding, proximate tolerance zones indicates whether at least one dimension is within a preselected range. Where the first markers lie within corresponding tolerance zones, the at least one dimension will be within a preselected range. However, if a first marker lies outside the corresponding tolerance, then the at least one dimension is not within a preselected range.
Inherent in the process of U.S. Pat. No. 5,902,526 is the need to form both the first marker on the parison and the second marker upon blow molding the finished article, followed by comparing their relative location. While such overlapping or closely proximate markings can be formed in a manner to be detected by individual visual inspection, the use of such a system of markers in connection with any automatic inspection system has proven to be elusive if not impossible. U.S. Pat. No. 4,131,666 also employed a surface grid marking technique followed by visual examination to determine the distribution of plastic in a finished container, but did not suggest any manner of converting the visual inspection to one that might be automated.
The control of variations in dimensions of finished articles through modifications in process parameters is taught generally by U.S. Pat. Nos. 3,934,743 and 4,044,086. Other patents, e.g., U.S. Pat. Nos. 3,956,441; 4,307,137; and 4,564,497, have disclosed structures included on the surface of parisons to achieve decorative effects on the finished articles. Still other patents, e.g., U.S. Pat. Nos. 4,151,249; 4,320,083; 4,359,165; 4,785,950; 4,927,679; 4,997,692; 5,101,990; 5,116,565 and 5,312,572, have disclosed structures included on the surface of parisons to achieve structural effects in the finished articles. U.S. Pat. No. 4,117,050 discloses the longitudinal thermal profiling of a parison to control wall thickness distribution in blow molded articles, but does not discuss any scheme for automated inspection of the resulting articles. U.S. Pat. Nos. 4,571,173 and 5,066,222 disclose schemes by which the temperature of a parison is heated in a no
Davis Craig
Minton Spencer
Roberts Eddy
Ball Corporation
Davis Robert
LandOfFree
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