GB923771A - Improvements in and relating to thermosetting products prepared from syrups and tannins - Google Patents

Abstract

For the preparation of foundry cores and moulds, sand is coated with the reaction product of a tannin and a carbohydrate-containing syrup, which may have other compounds added during preparation to modify its properties (for example hardening agents-aniline and a minor proportion of an acid being preferred) (for details, see Group IV(a) Abridgment). Any of the known methods may be used, but the following is preferred, as it provides a means of dehydrating the resin (and therefore completing its preparation) while coating the sand. The sand is first heated to above 100 DEG C. (e.g. 110 DEG -150 DEG C.) and the resin is then added. When the evolution of steam ceases, the process is completed and the product is ground to give discreet particles. The temperature of operation may be lowered by application of reduced pressure. Various additives are listed. Examples 3 and 6 may be of interest. In Example 5, a solution of stearic acid pitch in carbon tetrachloride is added to a coated sand prepared as in Example 3 and the solvent evaporated, to give a more free-flowing product. In Example 7, an uncured novolac and Wyoming bentonite were added to a coated sand prepared in the manner described above. Examples 1 and 2 are for comparison; in 1, cane sugar molasses to which a surfactant (alkyl phenol-ethylene oxide adduct) has been added, is heated and added to hot sand; in 2, molasses is reacted with aniline and sulphuric acid and added to hot sand to give a resin-coated sand.ALSO:A thermosetting product is made by heating a syrup with 10% or less of its weight of at least one tannin. This may be done by heating the compounds together until steam is no longer seen to be emitted and the product is a hard, clean-breaking solid with a tacky surface and is ground, or by heating the syrup to its boiling point and adding the tannin, to give a liquid product. The syrup is molasses, blackstrap or other heavy viscous liquid containing mainly mono- and di-saccharides with or without other substances, e.g. organic acids, fats, waxes, nitrogenous bodies and gums, as impurities. Cane, beet or other sugars, usually with added water, and distillery slops, are also included. Hydrolysable and condensed tannins, e.g. quebracho, mimosa, myrabolam and oak extracts, may be used. Various compounds may be added to alter the properties of the product, as follows: (a) talc, stearates, clays and zinc oxide or mixtures thereof, being up to 20% by weight of the thermosetting product, to reduce tackiness and facilitate grinding; (b) up to 10% by weight of the syrup of thermosetting substances, e.g. phenol- or urea-formaldehyde condensates, silicones, unsaturated polyesters or melamine resins, to improve the strength of articles made from the products; (c) up to 10% by weight of the syrup of thermoplastic materials to increase the resileence and thermal shock resistance of articles made from the products; (d) up to 20% by weight of the syrup of additives to facilitate stripping of moulded articles made in moulds made from the products and to improve the coverage of sand by the thermosetting products, e.g. plumbago, talc, silicones, diatomaceous earth and surface active agents; (e) up to 15% by weight of the syrup of hardening agents, e.g. acids (many listed) and their anhydrides if any, aromatic amines, anhydroformaldehyde aniline, thiocarbanilamide, paraamino phenol, paraphenylenediamine, pyridine, urea, thiourea, isoamylamine, hydroxylamine, ammonia, hexamethylene tetramine, paraformaldehyde and other compounds yielding formaldehyde on heating, or combinations thereof, aniline and a small proportion of an acid being a particularly advantageous combination. Fillers such as wood meal, cotton linters, mica, asbestos and mineral powders may also be added. Shell moulds are made using the products of the invention by mixing them with sand, normally in the proportion of 2-10% by weight of binder, based on the sand. Alternatively sand may be coated with the binder in the normal way to give a resin-coated sand, or the following procedure may be used: sand is heated to above 100 DEG C., e.g. 110-150 DEG C., and the binder, preferably with up to 2% of a surface active agent added to it, is added, and dehydration of the binder and coating of the sand effected together; when steam evolution ceases, the product is ground; if reduced pressure is used during mixing, the temperature need not be so high. Up to 20% by weight of the binder of one or more of the following may be added: ZnO; CaO; Al(OH)3; Ca(OH)2; NaCl; MgCl2; NH4Cl; ZnCl2; steari acid pitch; Ca, Zn or Al stearates; Mg, Zn, alkali or alkaline earth carbonates; MnO2; ammonium persulphate; KNO3; NaNO3; benzoyl peroxide; compounds containing isocyanate groups; CH3COONa; montmorillonites. Up to 10% of finely divided substances such as iron oxide, manganese dioxide or silica, may be added to give castings a smoother finish and ammonium borofluoride, boric acid, sulphur or other inhibiting agents to prevent oxidation of magnesium or magnesium based alloys may also be added to the mix. For comparison, in Example 1, sand is coated with a product made from cane sugar molasses alone, with a alkylated phenol ethylene oxide condensate as surface active compound, and in Example 2 sand is coated with the reaction product of molasses, aniline and sulphuric acid. In Example 7, sulphited quebracho extract, aniline, molasses and concentrated hydrochloric acid are heated and added to heated sand. Then an uncured novolac is added to the coated product along with Wyoming bentonite.