GB732101A - Improvements in methods of and means for the heat treatment of solid bodies - Google Patents

Abstract

A solid body, e.g. of metal or glass, is heat treated by immersion in a fluidized powdered or granular material containing a source at a different temperature from that of the body, then removal from the material after a pre-determined transmission of heat has taken place. A layer of granular material is fluidized in an iron tank by streams of compressed gas escaping upwards from the tank bottom which is porous, being of porcelain or brick or of wire cloth which has been subjected to a rolling operation as in Specification 709,265, [Group XXX]. Heat is supplied by electric resistance heaters at least partly immersed in the fluidized bed and the gas may be pre-heated. If the gas is selected to provide a controlled atmosphere it may be circulated in a closed path. The granular material is alumina or ground crystalline material such as calcium fluoride (fluorspar), silica or sand and is of 30-100 microns particle size. A metal such as an aluminium-manganese alloy, to be annealed is plunged and suspended in the fluidized material maintained at 450 DEG C. The vertical walls of the tank may be heated or cooled. By use of this method a body may be heated for hot-working, for relieving stresses or for modifying its structure and constitution or it may be cooled or quenched. For example, cold-worked brass or copper is annealed, aluminium alloys are solution treated, aluminium is degassed, steels are carburized and carbon steels are quenched p from above 760 DEG C. Aluminium-magnesium-silicon alloy, H.S.10, is heat treated and, after water-quenching, aged in fluidized material. The gas may react with the substance of the treated body and the granular material may be such that it acts chemically on the body in the presence of a selected gas or vapour introduced with, or as, the fluidizing medium. Hydrogen may be used and nitralloy steel may be nitrided in alumina fluidized by ammonia.