A mould closing unit for an injection moulding machine for processing plastics and other plasticisable materials, comprising - a stationary platen, - a platen (11, 11') which is movable in relation to the stationary platen and which forms a mould clamping space between it and the stationary platen for the purpose of receiving injection moulds, and which is movable along a closing direction (s-s), for the purpose of closing and opening the injection mould, - a mould moving device (13, 13') for the purpose of moving the movable platen (11, 11') into and out of mould closure of the parts of an injection mould which are received between the platens (10, 11; 11'), - at least one force transmitting element, which is connected to one of the platens (11, 11'; 10) and, at its end spaced from the one of the platens (11, 11'; 10), has a portion that is associated with the other of the platens (10; 11, 11') and is actuable for an operative engagement, - at least one locking device that is associated with the other platen (10; 11, 11') and is movable into positive operative connection with the actuable portion when the parts of the injection mould are in the mould closure position, for the purpose of applying a closing force, - wherein the locking device comprises at least one floating collet chuck (16, 116) that is movable into positive operative connection with the actuable portion for the purpose of locking the force transmitting element and the other of the platens (10; 11, 11') during mould closure, and at the same time is connected to at least one piston (18, 118) of a piston-cylinder unit for the purpose of applying the closing force, characterised in that the locking device comprises at least one unlocking element that is arranged in the collet chuck and a cylindrical chamber (48, 148) that is configured to put the unlocking element (55, 155) under load for the purpose of opening the collet chuck (16, 116), and in that when the unlocking element (55, 155) abuts by its end face against a tie bar configured as high-pressure opening of the injection mould is configured to be generated from this cylindrical chamber (48, 148). - a stationary platen, - a platen (11, 11') which is movable in relation to the stationary platen and which forms a mould clamping space between it and the stationary platen for the purpose of receiving injection moulds, and which is movable along a closing direction (s-s), for the purpose of closing and opening the injection mould, - a mould moving device (13, 13') for the purpose of moving the movable platen (11, 11') into and out of mould closure of the parts of an injection mould which are received between the platens (10, 11; 11'), - at least one force transmitting element, which is connected to one of the platens (11, 11'; 10) and, at its end spaced from the one of the platens (11, 11'; 10), has a portion that is associated with the other of the platens (10; 11, 11') and is actuable for an operative engagement, - at least one locking device that is associated with the other platen (10; 11, 11') and is movable into positive operative connection with the actuable portion when the parts of the injection mould are in the mould closure position, for the purpose of applying a closing force, - wherein the locking device comprises at least one floating collet chuck (16, 116) that is movable into positive operative connection with the actuable portion for the purpose of locking the force transmitting element and the other of the platens (10; 11, 11') during mould closure, and at the same time is connected to at least one piston (18, 118) of a piston-cylinder unit for the purpose of applying the closing force,