The air-jet texturing process for synthetic continuous multi-filament yarns is more versatile than any other texturing process and provides the most effective simulation of natural staple spun yarns. The process itself is inadequately understood, and the ultimate goal of the work is to achieve a better understanding of the mechanism of the texturing process and to make suggestions for more efficient nozzle designs in order to increase productivity and thereby reduce production costs.

Two completely different approaches have been used to study the mechanism of the air-jet method of bulking filament yarns. Part A is an aerodynamic study of the nature of the air flow and of its characteristics, and of the yarn's behaviour during the bulking process. The experimentation involves the use of scaled-up models of the du Pant type 9 commercial Taslan air-jet and of a typically used parent yarn. The study is extended to include a modification of the jet suggested by earlier workers. The results of these investigations provide new evidence regarding the mechanism of the process and the construction of bulked yarns of this type. It is also concluded that the commercially used air-jet on which the model study has been based, is not ideally designed from the stand-point of efficiency, stability and ease of operation. In Part B, a suggested mechanism of the air-jet bulking action is simulated by a purely mechanical means. The simulation of the process has been so effective that yarns of the air-jet bulked type are produced by a method not requiring any compressed air. The preliminary work leading to the design of an experimental apparatus is briefly reported. Theoretical and experimental investigations of the process are made, and the bulked yarn properties for various parent yarn particulars and processing conditions are measured and assessed. An economic evaluation of the process has been attempted, based on a comparison with the limited cost figures available for Taslan processing. - The individual nature of each of the two main investigations has necessitated that the results should be separately discussed in the ultimate Chapter of each Part of the thesis. Suggestions for further work are also made for each of the two techniques.