Abstract
This paper describes tests which have been made to study the influence of the design of tube expanders on the characteristics of rolled joints. Of the various features of the propulsive type tool, that of the number of rollers was chosen as the point from which to start such an investigation. Three expanders, otherwise identical in all particulars but with three, five, and seven rollers were used and a series of tests were carried out with each tool to varying degrees of expanding.
Comparisons are made of the values of push-out load, extrusion of the tube away from the front and back faces of the plate, mean seat pressure and hardness distributions in the tube plates. The results show that, judged on the maximum push-out strength, a three-roller expander makes the best joint, the strength falling as the number of rollers increases but there is no difference in the maximum value of mean seat pressure in joints rolled with the different expanders. The number of rollers also has a marked effect on the extrusion of the tube and on the extent of the plastic zones in the tube plates. Care is therefore necessary in selecting the appropriate criterion for optimum joint strength.
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