Preform conveyor system provided with means for ejecting badly seized preforms

A conveyor system (10) for an installation for the manufacture of thermoplastic containers by blow molding using preforms (12), of the type comprising a number of transport elements (18) which each have at least one grasping device (26) for carrying a preform (12) so as to convey it, in the vertical position, along a path in the downstream direction, inside the installation, of the type in which each grasping device (26) can move along a vertical axis (A2) relative to the transport element (18) carrying it so as, when it is brought from an upper release position to a lower grasping position, to engage axially in the neck (14) of the preform (12) to be seized, characterized in that each grasping device (26) is linked in terms of upward and downward axial movement to an associated bracket (46) which is mounted so that it can slide axially in one direction (A3) and which bears, at its lower axial end, a cam follower element (58), the bracket (46) being stressed axially downward so that the cam follower element (58) interacts with a surface of a fixed cam (66) provided to bring the grasping device (26) from its upper release position to its lower grasping position, in that the bracket (46) comprises a stud (74) with a bearing surface (76) designed to interact slidingly with a fixed ramp (78) comprising a control surface (86) which is inclined relative to the vertical and oriented generally upward, when the grasping device (26) is in an intermediate axial position between its upper release position and its lower grasping position, this intermediate axial position corresponding to an incorrect positioning of the grasping device (26) in the preform (12), so that the fixed ramp (78) brings the stud (74) upward and causes the grasping device (26) to slide axially into its upper release position so as to eject the associated preform (12), and in that the fixed ramp (78) extends axially at a certain height in such a way that, when the grasping device (26) is in its lower grasping position, the stud (74) can travel under the fixed ramp (78) in a passage (100) provided for this purpose.