Perfectionnements aux metières thermodurcissables

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 t