A mold clamping unit includes a mold height adjustment
system having a length-adjustable threaded connection, comprised of a threaded spindle and a spindle nut which supports a platen of a molding tool, for
stroke transmission and transmitting a locking force in clamping position. A clamping mechanism, which locks the spindle nut in relation to the threaded spindle and is selectively releasable for length adjustment of the threaded connection, includes a clamping nut, connected in fixed rotative engagement with and coupled for slight
axial displacement in relation to the spindle nut, and an
actuator, switchable between an active position, in which the spindle nut is braced with the clamping nut by a tightening force so that the platen is urged against the spindle nut, and an idle position, in which the
actuator is released and which can be implemented irrespective of a
stroke position of the drive mechanism. The threaded spindle and the platen are coupled to each other directly via the spindle nut for transmitting the clamping and locking forces, and via the
actuator for transmitting an opening force in opposition to the clamping force.