The invention relates to a pressurized-fluid workhead for permanent bell-forming of tracts of ends of plastic pipes, comprising: a die exhibiting a cavity for receiving a thermally plasticized end tract of a pipe, being provided with flow conduits for a pressurized fluid; a forming buffer, insertable into the end tract of the pipe and further exhibiting flow pipes for a pressurized fluid; a flange mounted coaxially and slidably with respect to the buffer and die, and having a striking surface which is associable to an edge of the end tract of the pipe. The die, the buffer, the flange and the pipe define a first and a second pressure chamber of a fluid; the pressure chambers being fed by the conduits to dilate and contract the end tract of the pipe, to produce a ribbing of the pipe.
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