GB941845A - Heat treatment of metals - Google Patents

Abstract

<PICT:0941845/C3/1> Welds and the like are annealed by placing, in contact with the welded article but spaced from the actual weld zone, one or more blocks of exothermic material, surrounding the weld with a heat insulating material which is either in contact with the weld or spaced from it by an air gap, firing the exothermic composition and allowing it to cool in situ. The location is such that the weld zone is heated by conduction through the article and by radiation from the fired composition when an air gap is provided. A typical composition used is as follows in percentage by weight:- .aluminium.20 - 80 .sodium or potassium nitrate. .or chlorate.0 - 10 .manganese dioxide and/or. .iron oxide.5 - 20 .fluoride.0.5- 20 .binder.0 - 5 .filler.remainder Silica and siliceous materials which form silicate slags and restrict access of air preferably do not exceed 5%, non-slagging fillers such as alumina being used. Preferably also the exothermic mixture is backed with a layer of heat insulating material, the latter being vented to allow free access of air. The exothermic mass itself may be well vented, e.g. by using fillers such as foamed polystyrene. In the particular embodiment illustrated, pipe 1 has a weld area at 2. Preformed collars 3 of exothermic material are arranged as shown and are backed by sleeve 4 of heat-insulating material, which is itself backed by further heat-insulating sleeve 5, to ensure slow cooling of the heated region. A suitable insulating material consists of .Low density furnace aggregate -.55% .Mixture of paper pulp and wood. .chippings - - - -.40% .Asbestos fibre - - - -.5% the mixture bound with gum arabic or sulphite lyeALSO:<PICT:0941845/C3/1> Welds and the like structures are annealed by placing, in contact with the article but spaced from the weld zone, one or more blocks of exothermic material, surrounding the weld with a heat insulating material which is either in contact with the weld or spaced from it by an air gap, firing the exothermic composition and allowing it to cool in situ. The location is such that the weld zone is heated by conduction through the articles and by radiation from the fired composition when an air gap is provided. As illustrated, pipe 1 has a weld area at 2. Preformed collars of exothermic materials are arranged as shown and are backed by sleeve 4 of heat insulating material, which is itself backed by a further heat-insulating sleeve 5.