Continuous movement brazing process

Abstract

An improved process for brazing a sleeve within a tube is disclosed herein. In the first step of the process, a radial expansion is induced in the tube in a first longitudinal section which does not include the ring of brazing alloy which circumscribes the sleeve. In the second step of the process, the heat source which applies the heat to the tube is gradually translated from a position adjacent to the first longitudinal section of the tube, to a position adjacent to the ring of brazing alloy which circumscribes the sleeve. The resulting thermal expansion which is induced in the length of the tube between the first longitudinal section where the heat source is initially placed, and the ring of brazing alloy avoids the creation of gaps in the resulting braze joint by producing a tapered, stress-absorbing expansion in the tube having a minimum profile in the region where the brazed joint is formed. In the preferred embodiment, the sleeve is circumscribed by a ring of a ceramic stop-off material in order to prevent the melted brazing alloy from spreading itself too thinly along the length of the tube. This process is particularly useful in creating high-quality braze joints in sleeving operations in nuclear steam generators, where the heat exchange tubes which need to be sleeved may be partially or completely prevented from expanding in the longitudinal direction due to sludge deposits within the generator.