Method for heating a preform and corresponding method for forming a container

A method for manufacturing a container, using a preform comprising an open neck portion at a first end, a closed base portion at a second end, and a body portion extending along a longitudinal axis between the neck portion and the base portion, the preform being made in a thermoplastic material configured to withstand less than 5 Mpa at a stretch ratio above 250% while elongated under a strain rate of 16/s, the method for manufacturing comprising the following steps:

• heating the preform comprising an open neck portion at a first end, a closed base portion at a second end, and a body portion extending along a longitudinal axis between the neck portion and the base portion, the preform being made in a thermoplastic material having no strain hardening properties or low strain hardening properties, the method comprising the following steps:
• introducing the preform into a heating apparatus comprising an array of infrared emitters arranged in a plurality of columns and a plurality of rows, the preform and the array of infrared emitters being disposed such that the longitudinal axis and the columns of the array of infrared emitters are parallel or directed obliquely with respect to each other;
• orienting angularly the preform at an input angular position by rotating the preform around the longitudinal axis;
• setting power levels of the array of infrared emitters so as to divide the array of infrared emitters into subsets of the plurality of columns, each subset of the plurality of columns generating heat at a different power level from an adjacent subset of the plurality of columns;
• heating the preform with the array of infrared emitters while translating the preform in a direction parallel to the rows of the array of infrared emitters at a translation speed, and simultaneously rotating the preform around its longitudinal axis in front of the array of infrared emitters at a rotation speed,
• the rotation speed, the translation speed, the input angular position and the power levels of the array of infrared emitters being set so that the power levels of the subsets of the plurality of columns facing at least three zones of the body portion extending longitudinally are different from the power levels of the subsets of the plurality of columns facing the rest of the body portion, the zones of the body portion extending relative to one another in a polygonal array, the power levels of the subsets of columns facing the zones of the body portion being set higher than the power levels of the subsets of the plurality of columns facing the rest of the body portion if and only if the zones of the body portion have a greater thickness than the thickness of the rest of the body portion;
• transferring the heated preform into a container-shaped mold;
• stretching the preform along the longitudinal axis by means of a longitudinal rod;
• and
• blow-molding the preform by injecting air in two steps so as to make the heated preform stretch and take the shape of the container-shaped mold, the air being injected at a first pressure then at a second pressure higher than the first pressure.