GB1002512A - Process for improving the physical and/or surface properties of metal objects - Google Patents

Abstract

<PICT:1002512/C6-C7/1> <PICT:1002512/C6-C7/2> The physical and/or surface properties of a metal object are improved by submerging it in a fluidized bed 2 (see Fig. 1) of finely divided solids, e.g. powdered carbon, coke, sand, zirconia, ferro-silicon, silica gel, alumina, bauxite, brick dust, iron oxide, clay, ground porcelain, used powdered silica alumina cracking catalyst or powdered metals through which passes a gaseous medium such as flue gas containing CO or unburnt propane supplied via conduits 5, 4, 3, wherein the temperature is controlled to give the desired differential between the bed 2 and the metal object 25 by removing part of the solids of the bed, heating or cooling them and returning them to the bed, e.g. using a separate heating or cooling vessel 10 containing a supplementary body 11 of solids fluidized by a gaseous medium supplied via conduit 17 and connected to the main vessel 1 by transfer conduits 13, 15 to effect gravity circulation of the solids, and/or by circulating a liquid heat exchange medium through coils 8 submerged in the bed 2. The control may be effected additionally by heating or cooling the fluidizing gases and/or controlling their flow rate. As shown in Fig. 1, the gaseous medium passes from the top 12 of the body 11 through a cyclone separator 20 to outlet 22, solids entrained therein being returned via dipleg 21. The object 25 to be treated is suspended from a conveyer 24 to pass continuously through the bed. Fig. 2 shows a modificatoin of the apparatus adapted for passing the object through a series of successive stages, wherein the vessel is subdivided by a baffle 34 and partition 37 into a well 36, a treating chamber 40 and a heating or cooling chamber 39, the latter communicating by passageways 42, 43 adjustable with closure plates 44, 45. Chambers 39 and 40 are similarly fitted with cyclone separators 70 and 61 for returning entrained solids in the gaseous medium supplied from conduits 68 and 54-56 (with pump 57) via nozzles 67 and 53 respectively; alternatively, chamber 39 may be fitted with a fuel burner 67. The invention may be applied for heat treatment involving heating and/or cooling of ferrous or non-ferrous metal or alloys objects, including annealing, hardening and quenching followed by tempering. For carburizing ferrous metal objects, e.g. at 1600-1750 DEG F., the fluidized solids may be carburizing, e.g. powdered charcoal, petroleum coke, metal carbides such as of iron, charcoal bone, bituminous coal, preferably with such activators as Ba, Ca or Na carbonates, the gaseous medium being N2, or non-carburizing, the gaseous medium being petroleum gas. For nitriding ferrous metals, e.g. at 650-2550 DEG F., iron powder may be used fluidized with HCN or NH4CN, or the solids may be Na/KCN or powdered Al, Mg, Zn, Ni, Cr, Cd, W, V, Co, Ti, Zr, Mo, Ta, Mn, Be, B or Si fluidized with N2, H2 or He. For coating iron sheets with zinc by sherardizing, equal parts by weight of Zn and ZnO powder fluidized at 700 DEG F. with N2 may be used.