| 摘要 |
1,158,945. Casting processes. E. I. DU PONT DE NEMOURS & CO. 3 March, 1967 [3 March, 1966; 13 April, 1966; 23 Jan., 1967], No. 10256/67. Heading B3F. [Also in Divisions C3 and C7] The formation of oxide inclusions in metals during casting is prevented by contacting the metals with a halocarbon and a hydrogen halide scavenger comprising a metal oxide, or precursor of such oxide, in the form of particles of surface area at least 5 square metres per gram as determined by nitrogen adsorption. Halocarbon is defined to include only chlorine, fluorine, or chlorine- and fluorine-substituted aliphatic hydrocarbons and thus comprises monomeric and polymeric halogenated alkanes and alkenes. The (metal oxide) scavenger has a lower free energy of formation than the corresponding metal fluoride or chloride and thus reacts with the objectionable HF or HCl produced by the halocarbon upon decomposition to form a metal halide. The weight ratio of halocarbon to scavenger should be between 1 : 10 and 10 : 1. Specified halocarbons are: P.T.F.E., polychlorotrifluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, copolymers of vinylidene fluoride and tetrafluoroethylene with hexafluoropropylene, 1,1 - difluoroethane, 1,1,1 - chlorodifluoroethane, 1 - fluoroethylene, 1,1 - difluoroethylene, CF 4 , fluoroform, chlorodifluoromethane, fluorodichloromethane, chlorotrifluoromethane, fluorotrichloromethane, dichlorodifluoromethane, hexafluoroethane, 1- chloro - 1,1,2,2,2 - pentafluoroethane, 1,2- dichloro - 1,1,2,2 - tetrafluoroethane, CCl 4 , chloroform, 1 - fluoro - 1,2,2 - trichloroethylene, 1,1,2,2 - tetrachloro - 1,2 - difluoroethane, 1,1,1,2 - tetrachloro - 2,2 - difluoroethane, hexachloroethane and octachloropropane. Specified scavengers are the oxides of Ni, Zn, Cu, Co, Cr, Ti, Zr, Si, Cd, Th, alkali metals and alkaline earth metals. Suitable oxide precursors (i.e. compounds which decompose upon heating to form oxides) are hydroxides, nitrates, carbonates, basic carbonates, acid carbonates and borates. There may also be included a flux, i.e. inorganic compound(s) which will cause the end products of the scavenging reaction to remain in liquid phase at a temperature below the melting point of the metal treated. Suitable fluxes are the alkali metal and alkaline-earth metal halides. The halocarbon and scavenger may be used separately as powders, or together as pellets, pebbles or annular rings. The latter shapes may be sintered from powder to which a binding agent such as sodium or potassium silicate or methyl cellulose is added. Alternatively, suspensions may be used which are applied to the mould walls prior to or during casting, e.g. through orifices in the top of the mould wall during continous casting. The suspension medium may be water or an organic liquid such as a lower alkane, lower alkanol, lower di-alkyl ether, cyclic ether, low alkyl alkanoate, halogenated lower alkane or alkene, or lower alkanone. The suspension may also include (a) a suspending agent, e.g. water-soluble resin (of which examples are given), alumina or bentonitic clay, (b) a wetting agent (of which examples are given), (c) an anti-foaming agent, e.g. silicone, (d) a pigment, e.g. of the quinacridone type, (e) a binding agent such as shellac, cellulose, starch, molasses or sodium silicate, to improve adherence of the suspension to the mould surface or core walls, and (f) in the case of aqueous suspensions, ethylene glycol to lower the freezing-point. In another mode of application, liquid or gaseous halocarbons are directed at the metal to be treated, the scavenger &c. being added as powder, a moulded article or as a suspension. Specified uses are in the casting of ferrous metal, copper and its alloys, brass, aluminium and its alloys, magnesium, beryllium, titanium and chromium. |
