The invention relates to a process for the production of coupling pieces which possess an undercut annular groove optionally provided with a sealing ring, in which process a sleeve, having an internal diameter which increases in steps towards the open end, is initially preformed, the terminal part of the sleeve is postformed in order to form the annular groove, after having optionally introduced a sealing ring into the preformed sleeve, and, during preforming, only the terminal part of the preformed sleeve is kept at the deformation temperature and the remainder of the preformed sleeve is cooled, the terminal part of the preformed sleeve being cooled after postforming. The device according to the invention comprises a forming mandrel, the front part of which possesses a cooling chamber and the rear part of which possesses heating means, a postforming ring, which can move radially and axially and is equipped with a cooling chamber, and optionally a moulding sheath, a closing ring, which is equipped with heating means, and a member for introducing the sealing ring, which member can move radially and axially.

Process and device for the forming, on the end of a pipe made of a thermoplastic, of a coupling piece possessing an undercut annular groove intended for receiving an annular seal, according to which process and device the coupling piece is initially preformed by means of a forming core which possesses an annular rib for forming the annular groove, the core then being withdrawn from the partially cooled coupling piece by virtue of an elastic deformation of the part possessing the groove, by means of the rib of the forming core, and this part being kept at the elastic deformation temperature, and according to which this part is subjected to a postforming operation, before it has completely cooled, by means of a postforming ring.

In order to improve the introduction or uptake of force in a hollow section (1), in particular a tube, of long fibre reinforced plastic having an integrated force induction element (2) and to simplify its manufacture, a radial enlargement (4) is pressed into the hollow section (1) by means of a moulding body before the plastic matrix has hardened, which radial enlargement tapers into a narrow section (6) towards its free end (5), the jacket (3) which is formed in the process later enclosing an expansion element (9) with a clamping member (10) which merges into a tie rod (11), the expansion element (9) lying in a form-fitting manner against the interior of the enlargement (4,47) over the length of said enlargement.