PURPOSE: To reduce expenditure from an aspect of equipment by moving at least one mold half toward a base plate, to which the mold half is related, against a preloaded spring element when a clamping unit device is closed.

CONSTITUTION: A spring element 8 is formed as a coil spring and, as a result, a gap (h) is formed between a base plate 2 and an attaching plate 7 when there is no internal molding pressure in a cavity. The width (h) of the gap corresponds to the max. raising distance capable of raising a top mold plate 6 against the preloaded spring element 8 in relation to a bottom mold half 5 by the production of internal molding pressure. The parting surface 11 between the bottom mold half 5 and a top mold half 6 is formed as an insert edge 10.