Method of controlling mandrel in a tube-extruding press

A method of operating a tube-extrusion press having

• a die having a cavity;
• a holder for pressing a billet forward through the die;
• a mandrel shiftable forward and backward and having a front end positionable in the die, whereby the billet pressed into the die around the mandrel is deformed into a tube;
• a hydraulic cylinder having a piston connected to the mandrel and shiftable therewith, the cylinder defining a front ring compartment between the piston and the die and a rear compartment;
• a pump for supplying pressure to the cylinder;
• and
• a tank connectable to the cylinder, the method comprising the steps of:
• operating the pump such that it supplies a pressure in excess of what is needed to prevent forward movement of the mandrel into the die during extrusion;
• and
• bleeding pressure from the front compartment through a control valve to a tank to control the position of the mandrel relative to the die.