Method and apparatus for determining the environmental stress crack resistance of plastic articles

A method for testing the environmental stress cracking resistance of a thin-walled, hollow plastic container having an interior chamber, which container comprises a neck having a mouth for filling the interior chamber of the container, a generally cylindrical midsection, and a rounded base at the end of the container opposite the neck, which base has a plurality of feet for supporting the container on a supporting surface in an upright position, and an inverted center radially inwardly of the feet and adjoining said interior chamber, which center is spaced by a base clearance in the lengthwise direction of the container from an imaginary plane passing through toes of each of the feet, which toes contact the supporting surface, which method comprises:

• (a) measuring the base clearance of the container;
• (b) pressurizing the interior chamber of said container;
• (c) remeasuring the base clearance of the container;
• and
• (d) comparing the resulting change in base clearance with a standard to determine the susceptibility of said container to environmental stress cracking.

An apparatus for measuring a base clearance of a thin-walled, hollow plastic container having an interior chamber, which container comprises a neck having a mouth for filling the interior chamber of the container, a generally cylindrical midsection, and a rounded base at the end of the container opposite the neck, which base has a plurality of feet for supporting the container on a supporting surface in an upright position, and an inverted center radially inwardly of the feet and adjoining said interior chamber, which center is spaced by the base clearance in the lengthwise direction of the container from an imaginary plane passing through toes of each of the feet, which toes contact the supporting surface, which apparatus comprises:

• a housing having an upper opening for closely receiving the base of the container;
• a measuring probe extending into said housing through a lower opening therein, such that, when said measuring device is placed in mating juxtaposition with the base of the container in engagement with its inverted center, the depth of the inverted center is measured by the extent of downward displacement of said measuring probe;
• and
• an indicator connected to said measuring probe for displaying the extent of such downward movement.

Apparatus for testing the environmental stress crack resistance of a hollow plastic article having an internal chamber, a mouth for filling and emptying said chamber, a base, and a sidewall spanning said mouth and said base, comprising:

• means for sealing said mouth;
• means for supplying a pressurized gas into said chamber through said mouth;
• means for exposing said article to an environmental stress cracking agent;
• and
• means for detecting crazing of said article.