Locking device for an injection molding machine

In combination, first and second platens of an injection molding machine, a tie bar extending from the second platen to the first platen, and a locking device for releasably securing together the tie bar and the first platen, the locking device comprising:

• a) a housing extending along an axis coaxial with the tie bar and including a first bearing surface affixed to the first platen;
• b) a lock nut received in the housing and rotatable within the housing about the axis between locked and unlocked positions, the lock nut comprising:
• i) an inner bore with radially inwardly projecting engagement elements that engage the tie bar when in the locked position to transfer an axial clamp load from the tie bar to the lock nut, the radially inwardly projecting engagement elements provided along a first axial extent of the lock nut and defining a tie bar engagement portion;
• ii) an outer surface with at least a first step face retained in abutting relation against the first bearing surface to transfer the axial clamp load from the lock nut to the first platen, the first step face having a first radially outer extent;
• and,
• iii) the lock nut including a narrowing section having a second axial extent bounded by a first position proximate the first step face and a second position spaced axially from the first step face in a direction towards the second platen,
• wherein the outer surface has a first diameter at the first position and a second diameter at the second position, the first diameter being less than the first radially outer extent and greater than the second diameter, and
• wherein the lock nut further comprises a major load portion having a third axial extent bounded by the first step face and a first one of the plurality of radially inwardly projecting engagement elements, the first one of the radially inwardly projecting engagement elements being axially nearest the second platen;
• and
• wherein the outer surface of the lock nut along the narrowing section is defined by a tapered surface that starts at the first position and ends at the second position;
• and
• wherein the second axial extent of the narrowing section is at least as great as the third axial extent of the major load portion.