Patent ID: 8357326
Filing Date: 2013-01-22
Classification: B29B,B29C,B29L,F16J

Abstract:
1. A method for producing a tubular preform from thermoplastic material for a blow-molding process in which a bellows is produced from the preform by means of a device, said device comprising: a die with a die land and a die body which form, between them, an annular die opening, the die body being movable relative to the die land in order to alter the cross-sectional surface of the die opening; an extrusion device with a plunger which during its movement extrudes a specific quantity of plasticized plastic material determined by the plunger path through the die in order to produce the tubular plastic preform; a withdrawal unit which is movable from an initial position adjacent to the die in the direction away from the die, in order to guide the tubular plastic preform emerging from the die, during the extrusion process, the path of the withdrawal unit determining the length of the tubular plastic preform; and wherein the method includes the steps of: determining path signals of the withdrawal unit, the die body and the plunger, respectively, using path sensors; providing said path signals of said path sensors to a control unit, and determining actual values of a velocity of said plunger and said withdrawal unit, respectively, as well as a position of said die body from the path signals of said path sensors; wherein said control unit serves for controlling the movements of the die body, the plunger and the withdrawal unit, according to a predeterminable program for the purpose of adjusting the wall thickness of the tubular plastic preform over its length, said method including the additional steps of: individually adapting reference value curves for the movements of the withdrawal unit, the plunger and the die body respectively; storing said individually adapted reference value curves in said control unit, wherein the reference curve of the movement of the withdrawal unit is a freely adjustable velocity profile of the withdrawal unit over the path of the withdrawal unit, the reference curve of the movement of the plunger is a freely adjustable velocity profile of the plunger over the path of the plunger, wherein said velocity profiles of said withdrawal unit and said plunger are adjustable independently of each other, and wherein said reference curve of the movement of the die body is a position profile of the die body over the path of the withdrawal unit or the path of the plunger, determining control signals of said plunger, said die body and said withdrawal unit based on the derived actual values and the stored reference curves, and controlling drives of said plunger, said die body, and said withdrawal unit, respectively, by means of the determined control signals, so that the movement of said withdrawal unit is carried out according to said freely adjustable velocity profile over the path of said withdrawal unit and the movement of said plunger is carried out according to said freely adjustable velocity profile over the path of said plunger, and the movement of the die body is carried out according to said freely adjustable position profile over the path of the withdrawal unit or the path of the plunger, so that the movement of the die body is carried out for the same duration as the movement of the withdrawal unit or the plunger, said method including the additional step of fixing the position profile for the die body over the path of only one of the withdrawal unit and the plunger such that the movement of the die body follows the withdrawal unit or the plunger as a “slave”.