Method improvements for controlling parison length

In a method of blow molding hollow articles which includes:

• continuously forming a freely pendant hollow thermoplastic parison in the outlet of an extruder head;
• moving a carrier in synchronism with formation of said parison to consecutively position molds supported on said carrier beneath the head to receive portions of said parison for blow molding into said articles in cavity sections therein;
• sensing the length of a parison section protruding beyond the cavity of successively presented molds;
• and
• generating a control signal in response to said sensing, to regulate and thereby reduce the variability in the amount of said length;
• the improvement in said method whereby the amount of such length is regulated without causing a related change in the rheological properties of the thermoplastic forming the parison, which improvement comprises, in combination, the step of:
• varying the speed of movement of said carrier in response to said signal to vary the rate at which said molds receive consecutive parison portions and therefore regulate the amount of the length of each parison portion protruding beyond the cavity portions thereof.