Injection unit for injection molding or die-casting

An injection unit for injecting molten material into a cavity, beginning with a pre-filling phase, in which the molten material is shot through an entrance of a cavity, followed by a filling phase, which lasts until the cavity is filled up and the resistance of the material against further injection increases, and thereafter for maintaining the molten material in the cavity under pressure during a squeezing phase, said injection unit comprising;

• injection sleeve means for receiving said molten material;
• injection ram means movable within said injection sleeve means;
• drive cylinder means;
• drive piston means movable within said drive cylinder means and being releasably connected to said injection ram means to form a ram unit;
• control means for controlling the movement of said ram unit during said phases, said control means including
• control valve means connected to said drive cylinder means and assuming a predetermined filling initiating position at the transition from the pre-filling phase to the filling phase, and assuming a predetermined squeeze initiating position at the transition from the filling phase to the squeezing phase to achieve a deceleration of said ram unit of a predetermined deceleration characteristic;
• damping means arranged on said ram unit for absorbing shocks arising from the kinetic energy of masses which are decelerated at least at the transition from the filling phase to the squeezing phase, said damping means allowing a relative movement of said injection ram means with respect to said drive piston means;
• and
• signal transfer means interconnecting said damping means and said control valve means for changing over the latter to one of said initiating positions within a predetermined response time.