Patent ID: 8074816

Claim:
A mechanism for slewing a rotating part of a tower crane, with a device for placing the tower crane in weathervaning mode, the mechanism comprising: at least one slewing geared motor unit with a motor and reduction gear, and with an internal main brake which is deactivated when the crane is placed out of service, and also additional braking means which can be activated when the crane is placed out of service in order to exert on the rotating part of the crane a braking torque which avoids uncontrolled rotation of said rotating part when placed in weathervaning mode, wherein the additional braking means are incorporated in the geared motor unit or in one of the geared motor units in the form of an internal auxiliary brake interposed between the motor and the reduction gear; wherein the internal auxiliary brake, interposed between the motor and the reduction gear, is a single disk brake controlled by an electromagnet, this brake being supplied electrically so as not to brake the rotation of the rotating part of the crane when the crane is in service, but exerting a braking torque by way of a spring means when it is not supplied electrically, thereby avoiding uncontrolled rotation of the rotating part of the crane when it is placed in weathervaning mode; wherein, with the auxiliary brake being a brake controlled by the electromagnet and urged in a direction of braking by spring means, these means take the form of compression springs acting axially on an armature disk, the compression of the springs adjustable by screwing an adjusting ring.