GB1094590A - Improvements in or relating to nitrogen-free resin-coated granular refractory materials - Google Patents

Abstract

A moulding composition comprises refractory granules coated with (a) an ortho-linked novolak resin and (b) a partly condensed resole resin and is substantially free of nitrogen-containing substances. The composition may also include, as conditioner, a minor amount of a water-absorbing non-deliquescent substance. The novolak resin may be prepared from phenol, m-cresol, 3:5-xylenol or resorcinol or mixtures and mixed isomers of these with formalin or paraformaldehyde, i.p.o. an ortho-directing catalyst, preferably using 0.5-0.88 moles CH2O per mole of phenol. The resole is prepared from phenol, optionally containing some cresol or xylenol, and 1.2-3.0 molar proportions of formaldehyde i.p.o. an alkaline catalyst. Suitable conditioners are synthetic CaSiO3, CaSO4. 1/2 H2O, CuSO4 and silica gel. Suitable refractory materials include silica sand, zircon, olivine, chromite sands and granulated quartz. Preferably the novolak is added to the heated sand, then an acid curing catalyst if required e.g. H2SO4, (COOH)2, salicylic or p-toluenesulphonic acid, then the resole, then the conditioner. In Examples the novolak is prepared from 10 moles phenol and 7 moles 44% formalin i.p.o. zinc borate or zinc acetate, and the resole from 10 moles phenol and 20 or 30 moles 44% formalin i.p.o. NaOH, Ca(OH)2, MgO or Ba(OH)2. 17.5 p.b.w. each of a novolak and a resole are mixed with 1000 p.b.w. silica sand to which is then added 1 p.b.w. synthetic calcium silicate; 1 or 1.5 p.b.w. salicylic acid may also be added.ALSO:A foundry moulding composition comprises refractory particles, e.g. of silica sand, zircon, olivine or chromite sands or granulated quartz, coated with (a) an ortho-linked novolak phenolic resin, and (b) a partly crosslinked resole phenolic resin. There may also be added a water-absorbent conditioner, e.g. synthetic calcium silicate, calcium sulphate hemihydrate, anhydrous copper sulphate or silica gel, and an acid catalyst, e.g. sulphuric, oxalic, salicylic or p-toluenesulphonic acid. The novolak resin may be prepared from phenol, m-cresol, 3 : 5-xylenol or resorcinol or mixtures and mixed isomers of these with formalin or paraformaldehyde, i.p.o an ortho-directing catalyst, preferably using 0.5-0.88 moles CH2O per mole of phenol. The resole is prepared from phenol, optionally containing some cresol or xylenol, and 1.2-3.0 molar proportions of formaldehyde i.p.o. an alkaline catalyst.