| 摘要 |
1508020 Coating composition for shell moulds STAUFFER CHEMICAL CO 17 July 1975 [18 July 1974] 30059/75 Headings C3T and C3N A coating composition for the preparation of shell moulds comprises a refractory material and a binder composition which is substantially free of water, the binder composition comprising a prehydrolysed silicate ester, an amino alcohol of the formula HORN(R<1>)2 in which R is a C1-C6 divalent hydrocarbon radical, and R<1> is hydrogen, an alkyl radical or a radical of the formula -ROH, and an organic solvent, the mol ratio of amino alcohol to silicate ester being from 1 : 1 to 10 : 1. The shell mould is prepared by coating a cleaned and etched expendable pattern with the coating composition having a SiO2 content of 10 to 35% wt. of the binder composition, stuccoing the coated pattern, air drying and repeating the above steps until a coating of the desired thickness is built up, then optionally applying a seal coat thereto, comprising a hydrolysed silicate ester, a refractory material and an organic solvent. The expendable pattern is then removed and the shell mould subsequently fired generally at 500-3000‹ C. Suitable silicate esters are "condensed" ethyl silicate, ethyl silicate "40" and those obtained by the hydrolysis and condensation of ethyl silicate "40". Suitable amino alcohols are mono-, di-, and tri-ethanolamine, monoisopropanolamine, 2-amino-butan-l-ol, 3- aminopropanol and 2 - dimethylamino - 2- methylpropan-1-ol. The preferred solvents have a B.Pt. below 250‹ C., e.g. aliphatic alcohols, ketones, aromatic hydrocarbons and glycol ethers and esters. Suitable refractories are the oxides and silicates of Si, Al, Zr, Zn, Mg, Cr and Ti; zeolites, molecular sieves and ion-exchange resins; zircon, grog, calcined clay, silica flour, sand and fused silica. The weight ratio of refractory material to binder may range from 4-100 : 1. A gelling accelerator, e.g.NH3, or an organic amine, may be added to the seal coating composition. The stability of the binder compositions may be improved by adding boron compounds, e.g. boric acid and alkyl borates or organic acids, e.g. C1-C10 monocarboxylic acids. In the examples a binder composition comprising (1) "condensed" ethyl silicate or ethyl silicate "40", (2) ethanol or ethylene glycol monoethylether, and (3) ethanolamine is mixed with zircon and fused silica and the resultant slurry coated on to an etched wax tree pattern for a shell mould, then stuccoed with a fused silica sand and air dried; the coating and stuccoing being repeated several times. The resulting coated pattern is optionally coated with a seal coat consisting of a slurry of a partially hydrolysed silicate binder, isopropyl alcohol, a fine fused silica flour and water, then stuccoed with a coarse fused silica flour; the coating and stuccoing being repeated several times. The shell mould is then dewaxed and fired at 1000‹ C. |
