Safety system for hydraulic vertical press

Abstract

A system for preventing the free fall of the platen of a vertical molding machine in the event of failure of the connection between the drive rod and the platen. A hydraulic network is employed to enable the movement of the platen. The network employs a counterbalancing circuit to permit raising the rod and platen and for preventing the gravitational fall of the rod and platen. The operation of this hydraulic circuit is controlled by valves which transfer the hydraulic fluid between the two ends of the respective cylinders, and a storage tank (to store the difference in volume between the rod end and cap end of the respective cylinders). With fluid flowing from the cap end of cylinders to the rod end of said cylinders, the platen may descend. With fluid remaining in the cylinders, the piston and platen cannot descend without the fluid being transferred back to the other end of said cylinder by operation of an electrically controlled valving arrangement. A normally open (held closed by presence of the rod) switch is connected into the operating path of the valving network. The switch control mechanism senses the continued engagement of the rod and platen and opens on the release of this engagement to open the valve operating circuit and prevent descent of the ram and platen.