1. Field of the Invention
The invention relates to a process for manufacturing rigid cylindrical cardboard tubes of a certain thickness, whose ends are formed so as to provide ready and efficient closure of the tube, an apparatus for implementing this process and the tubes thus obtained.
2. Description of the Prior Art
It is known from Belgian Pat. No. 435 579 to form paper or flexible cardboard cornets, for example cornets for sweets, whose closure is provided by two facing tongues which are folded back one over the other above the opening of the cornet about a folding line curved towards the point of the cornet. Such cornets are made from a sheet of paper or thin easily deformable cardboard which is cut out when flat and is then shaped so as to form a cornet and is fixed by sticking in this position.
It should be understood that the process of Belgian Pat. No. 435 579 cannot be applied to the formation of a cylindrical rigid cardboard tube of a certain thickness, of the kind of tube for example used for sending documents in roll form by post, for it would not be possible starting with rigid cardboard sheets of a certain thickness, cut out when flat, to deform them so as to obtain cylindrical tubes without considerable risk of breaking the cardboard and without creating an unacceptable bulge in the sticking zone.
The purpose of the present invention is to overcome these drawbacks and for this it provides a process for forming cylindrical tubes from rigid cardboard, comprising opposite tongues cut out so as to form an hermetic closure system, as well as an apparatus for implementing this process.