Nitrogen die cylinder

Claim 1

In combination, a pressurized nitrogen manifold for applying a biasing force to a die member that is axially displaceable in response to reciprocation of a ram of a press in which the die is mounted, a cylinder unit comprising a cylinder having a bore and an externally threaded open end sealingly connected with a threaded port on the manifold, a piston slideable axially in said bore, said piston having a rod on one end thereof extending axially outwardly through the opposite end of the cylinder, the free end of the rod being adapted to abut said die member, said rod having a diameter smaller than the diameter of the cylinder bore to thereby form an annular chamber between the rod and the bore, said piston having a central chamber therein in free communication with said annular chamber, said piston having an annular seal thereon slideably engaging the bore, said cylinder having an annular seal therein adjacent said opposite end thereof slideably engaging the outer periphery of the rod, said cylinder unit being arranged so that, as a result of the manifold pressure applied to the opposite end of the piston through said port, the rod is biased outwardly of the cylinder to apply said biasing force on the die member and in response to movement of the press ram to a bottom dead center position at a lower end of each normal stroke, the piston is displaced in a direction inwardly of the cylinder against the bias of the manifold pressure to a predetermined partially retracted position, said piston also being movable to a fully retracted position inwardly beyond said predetermined position when the pressure in said annular chamber exceeds the pressure in the manifold and passageway means in the cylinder extending from said bore to the open end of said cylinder, one end of said passageway means intersecting said bore at a point on the rod side of the first-mentioned seal when the piston is in said fully retracted position and on the axially opposite side of said first-mentioned seal when the piston is in said partially retracted position, the opposite end of said passageway means communicating with the manifold through the threaded port thereon, whereby during normal operation of the ram, said passageway means is not effective to establish communication between said annular chamber and the manifold, but is effective to establish such communication when the manifold pressure is reduced to atmospheric.