Rotational moulding of polymer liners for composite overwrapped pressure vessels in cryogenic fuel storage applications

A modified rotational moulding process is presented for polymer liner production in composite overwrapped pressure vessel design. This modified process uses electrically heated mould tooling integrated within the rotating axes to produce polymer liner components. The integrally heated tooling provides improved control of heating parameters, thus increasing the dimensional accuracy of the part and reducing energy consumption. Microscopy, in conjunction with image processing software, has been used to characterise void densities in liner samples. High percentage air void densities in polymer materials have been shown to increase permeability as they act as leakage paths for permeation; therefore reducing air void densities for liner applications is of paramount importance. Results show that increased hold temperatures reduce void density percentages but increase void sizes. Other processing parameters such as mould wall thickness variations and cooling rates are analysed for this novel process of liner manufacture.