Experimental Study of Some Variables of the Tube-Expanding Process

Abstract

This paper deals with certain aspects of the tube-expanding process, which have been investigated using the test rig previously developed as part of a research sponsored by the British Shipbuilding Research Association.

The factors investigated are (1) retubing, (2) the starting position of the roller cage within the tube, and (3) the initial clearance between tube and seat. A few tests are also reported on the relaxation of the joint with time.

In the retubing tests, further tubes were expanded into seat plates used in previous tests, from which the original tube had been removed. The main conclusion was that seat pressures can approach the theoretical maximum in retubing, and that if an extra pass is made to take advantage of the work-hardened seat, a stronger joint than in a first expanding results.

To study the effect of the starting position of the rollers within the joint, four complete tests were made. The results show conclusively that a much stronger joint is obtained with less work, if the rollers start with their front ends almost at the back of the joint.

Tests to study the effect of the initial clearance between tube and seat showed that clearance is not a major factor in joint strength.