1. Field of the Invention
The present invention generally relates to the field of articles that are blow molded from parisons, and more particularly concerns methods and apparatus 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 stretch blow molded articles, such as those articles formed from polymeric resins. 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 with physical dimensions such as material distribution may exist across various production platforms and between production facilities seeking to produce substantially identical stretch blow molded articles. Consistent physical dimensions such as material distribution are very important for end performance characteristics of stretch blow molded articles such as burst strength, deformation, and stress cracking.
Current material distribution analysis techniques directed to already formed stretch 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, overall material distribution of the sections, the section weighing method cannot account for variability within the section, although variability within a section of a stretch blow molded article has been frequently observed in both laboratory and production environments. Further, the section weighing method is necessarily destructive of the article. Therefore, such method may 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.
Consequently, there exists a need in the art for a method and apparatus 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.