Protective frame for mounting casings of the type used in construction for the subsequent installation of metal doors in general and fire doors, essentially characterised in that the pre-formed metal casing is internally fitted with a protective frame which provides it with the necessary stiffness for handling during transport and subsequent mounting when being embedded in external or internal walls of buildings. Once the casing setting time has elapsed, the protective frame is removed and the casing is ready for the installation of the door when needed, thereby avoiding any damage to the paint on the door owing to impacts, scratches or marks.
The invention presented offers the main advantages of providing greater ease and precision in mounting, given that it can be carried out by just one worker, considerably reducing labour whilst at the same time avoiding any damage to the door leaf.