Method for heating plastic articles

In a method of thermally conditioning an essentially tubular heat degradable thermoplastic pre-form, the steps of:

• (1) horizontally conveying a vertically oriented pre-form in heat exchange proximity to a thermal conditioning means which includes (a) a source of gaseous coolant directed toward the parison and (b) a plurality of elongated, generally horizontal, vertically spaced radiant heating elements interposed between the source of gaseous coolant and the parison;
• (2) rotating the pre-form as it is conveyed past the thermal conditioning means to continuously expose circumferential portions of the pre-form to simultaneous heating and cooling by said thermal conditioning means;
• and,
• (3) thermally conditioning the pre-form during the performance of Steps (1) and (2) to a substantially uniform temperature across the thickness of the pre-form at each radial position by simultaneously (a) penetrating the thickness of that circumferential portion of the pre-form that is exposed to the thermal conditioning means with infra-red rays from said radiant heating elements and (b) flowing gaseous coolant essentially horizontally in a direction generally perpendicular to the direction of parison travel to flow at least a portion of the gaseous coolant directly onto the heating elements to cool the elements and extend their life and then onto the outer surface of the same circumferential pre-form portions that are exposed to said radiant heating elements.

In a method of forming a blown plastic container from an essentially tubular, heat degradable plastic parison consisting essentially of polyethylene terephthalate, the steps of:

• vertically orienting the parison;
• simultaneously moving the parison laterally and rotating the parison about its longitudinal axis adjacent to a thermal conditioning means comprise of (a) a source of air under pressure directed to the parison and (b) a plurality of horizontal, vertically spaced, generally parallel radiant heating elements interposed between the source of air and the parison, each heating element consisting of a tungsten filament encased within a quartz tube to provide radiant waves with a spectral energy peak wave length of about 1.2 micron;
• while the parison is laterally conveyed and rotated adjacent the thermal conditioning means, flowing coolant air from said source generally horizontally in a direction essentially perpendicular to the direction of lateral parison movement, at least a portion of the coolant air impinging directly onto the heating elements to cool the elements and extend their life and then flowing the outer surface of the corresponding parison portions exposed to the heating elements to cool the parison surface to prevent thermal degradation, with the radiant waves from the heating elements penetrating the full wall thickness of the parison to establish a temperature gradiant across the thickness of the parison of no more than about 10.degree. C.;
• displacing the parison from adjacent the thermal conditioning means after the parison has been heated to a blowable temperature;
• and
• closing the sections of a blow mold on the parison and blowing the parison while at a blowable temperature to form a blown plastic container.