Process and apparatus for the production of polyurethane moldings

The invention relates to a process for the production of polyurethane moldings by the reaction-injection-molding process, in which at least one isocyanate component and at least one polyol component are delivered in metered manner into a mixing chamber, are mixed in the mixing chamber to form a polyurethane reaction mixture and the polyurethane reaction mixture is then discharged via a runner into the cavity of a mold, characterized in that a pressure is exerted on the polyurethane reaction mixture in the cavity by means of a pressure medium, which pressure is sufficiently high for defects, which arise by reactive and/or thermal shrinkage, and/or entrapped air pockets to be closed, wherein the pressure medium is introduced into at least one overflow cavity hydraulically connected with the cavity, and/or is introduced into the runner.