PTFE Expansion Bellows

To guarantee the highest quality from the beginning of the production process, CRP manufactures paste extruded or multi-ply PTFE tubes.

Our unique convolution process is undertaken at very high temperatures and combined with additional material to compensate for transitional change from straight tube to to convoluted bellows, providing a uniform PTFE wall thickness and a stress-free material in a thermally locked bellows shape.  This process significantly impacts on product lifetime performance.

There are a lot of ways to produce PTFE expansion bellows, but only a few offer the best solutions. Occasionally bellows are produced with sets of rotating rollers that are cold forming the PTFE tube into the convolutions. This can lead to a lot of residual stresses as the PTFE tube retains its plastic memory and will over time try to return to the initial shape. 

Others can be produced by blowing a PTFE tube using high pressure into a mould which has the shape of the bellows convolutions. With this method the PTFE is stretched into this shape with localised thinning of the material producing poor pressure performance for users. 

Another production method is through isostatic moulding techniques where the bellows are produced from PTFE powder formed into the shape of the convolutions in a mould and sintered. Here the wall thicknesses cannot be regulated and the bellows are very susceptible to permeation.

When CRP manufacture our FluoroFlow bellows we compress the bellows into shape and remove all stresses with the PTFE tube by soaking the bellows in manufacture at 572° F. The bellows assembly is then rapidly cooled and retains the bellow shape. The original tube has lost is ‘plastic memory’ and will retain its bellows shape indefinitely.

All our bellows are subjected to a 1.5 x pressure test with manufacture, independent tests have been conducted by TÜV to confirm the pressure ratings we present in our catalogues alongside our own extensive burst pressure tests.