The invention relates to a blow mold (100) comprising a mold base (101) having a cavity (102) as the mold cavity, the cavity (102) having a bottom region (1), a center region (2) and a top region (3). When the blow mold (100) is closed, the center region (2) can be moved relative to the top region (1) and/or relative to the bottom region (3).

When a preform having been molded while released from a mold at an earlier timing in an injection stretch blow molding machine is stretched and blow molded, the bottom of the preform is prevented from rupturing and the bottom of a hollow molded article is prevented from being uneven in wall thickness to produce such a hollow molded article without defect bottom by the injection stretch blow molding machine. An injection molding process of injection molding a preform; and a blow molding process of blow molding the preform to obtain a hollow molded article. The blow molding process allows a tip of a stretching rod cooled to a temperature between 50° C. and 90° C. to be brought into contact with the bottom of the preform in a softened state, and to press down the bottom of the preform while the bottom is cooled.

A preform configured to form a container by stretch blow molding. The preform includes a finish portion and a tip portion. The finish portion is at a first end of the preform and is a container finish of the container. The tip portion is at a second end of the preform opposite to the first end. The tip portion is configured to form a container base and a container heel of the container. An outer surface of the tip portion includes a flat surface, a first radius on a first side of the flat surface, a second radius between the first radius and the flat surface, a third radius extending from the flat surface on a second side of the flat surface, and a fourth radius extending from the third radius towards the second end of the preform through which a longitudinal axis of the preform extends.

A preform configured to form a container by stretch blow molding. The preform includes a finish portion and a tip portion. The finish portion is at a first end of the preform and is a container finish of the container. The tip portion is at a second end of the preform opposite to the first end. The tip portion is configured to form a container base and a container heel of the container. An outer surface of the tip portion includes a flat surface, a first radius on a first side of the flat surface, a second radius between the first radius and the flat surface, a third radius extending from the flat surface on a second side of the flat surface, and a fourth radius extending from the third radius towards the second end of the preform through which a longitudinal axis of the preform extends.

Described is a method for producing thermoplastic material containers by blow-molding or stretch-blow-molding a hollow body previously heated in an oven and placed in a mold. The method includes a preliminary calibration step of: producing containers on the basis of first control parameters; measuring the wall thickness on extraction from the mold at two or more different heights; storing a reference thickness in a memory unit; modifying at least one control parameter; measuring the wall thickness at two or more different heights after the modification of each control parameter; storing the thicknesses; comparing said stored measured thicknesses with theoretical thicknesses that would have been obtained after modification of the control parameter(s) according to predetermined correction coefficients; and modifying the predetermined correction coefficients so that the thicknesses measured after modification of the control parameter(s) correspond to the theoretical thicknesses that would have been obtained with the aforementioned predetermined coefficients.