Compensatory expansion bellows and its production

A device for manufacture, by the hydroforming process, of expanding bellows for pipe systems from metal collars, characterised in that it comprises, in combination, a rigid sleeve for placement inside said metal collar and forming an inner annular space therebetween, a fixed ring connected to the outer surface of one end of said sleeve, a displaceable ring mounted concentric to said sleeve and located between said fixed ring and the other end of said sleeve and arranged to slide with a sealing action thereon and contacting an edge of said metal collar, a cylindrical skirt concentric to said sleeve and connected to said displaceable ring and having a length so as to slidably contact said fixed ring with a sealing effect thereby defining a closed variable volume annular chamber, means for admitting under pressure a fluid into the variable volume annular chamber formed between said sleeve and said skirt and bounded by said rings, and means to regulate the inflow and outflow of liquid into and out of the inner annular space between the collar to be shaped and the sleeve, whereby when said fluid is admitted under pressure to said variable volume annular chamber, said displacable ring and said skirt are displaced relative to said fixed ring thereby deforming the collar into a bellows.