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

A method for heating a preform for manufacturing a polygonal bottle from the preform, 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 method for manufacturing comprising the following steps:

• introducing the preform into a heating apparatus comprising an array of infrared emitters arranged in multiple columns and multiple rows, the preform and the array 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 infrared emitters so as to divide the array of infrared emitters into subsets of columns, each subset of columns generating heat at a different power level from an adjacent subset 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 at a translation speed, and simultaneously rotating the preform around a longitudinal axis in front of the infrared emitters at a rotation speed, and
• the rotation speed, the translation speed, the input angular position and the power levels of the infrared emitters being set so that the power levels of the subsets of columns facing at least three zones of the body portion extending longitudinally are different from the power levels of the subsets of columns facing the rest of the body portion, the at least three zones of the body portion extending relative to one another in a polygonal array, the power levels of the subsets of columns facing the at least three zones of the body portion being set higher than the power levels of the subsets of columns facing the rest of the body portion if and only if the at least three zones of the body portion have a greater thickness than the thickness of the rest of the body portion, and the at least three zones of the body portion corresponding to the corners of the polygonal bottle;
• transferring the heated preform into a container-shaped mould and orienting the heated preform in the mould such that each zone of the body portion extending longitudinally and relative to one another in the polygonal array faces a corner of an inner wall of the mould;
• and
• blow-moulding the heated preform in a mould having a shape of a polygonal bottle, by injecting air so as to make the heated preform stretch and take the shape of the mould.