| 摘要 |
<p>Foundry moulds are made from sand bound with melamine-formaldehyde or other aldehyde condensation product of an aminotriazine, one to several per cent being used. There may also be added to the sand a similar amount of another binder, such as an aldehyde condensation product of urea or other carbamide, dextrin, sulphite cellulose waste liquor, cherry stone resin, or grape seed oil and a little water. Hardening may be expedited by adding an acid or acid-forming substance, such as formic or phosphoric acid or an ammonium salt of a strong acid. To remove the water from the mould, before casting a substance capable of combining with water, e.g. phosphorous pentoxide or silica gel, may also be added to the sand, the former reacting with the water to supply acid desirable for hardening. The mould or core may be polished with graphite directly after stoving, e.g. at 200 DEG -220 DEG C., and when dry may be used for casting at once. 100 parts by volume of quartz sand, containing 2 per cent of water, may be mixed with 2.8 to 3.3 parts of dry, ground, water-soluble and hardenable melamine-formaldehyde, and about 0.72 part of formic acid, 85 per cent strength. The acid is added after the mixing has been in operation about 7 minutes and after 10 minutes the mixture is ready for use. The moulds harden at ordinary temperature but may be stoved. Another example has less of the condensation products and formic acid but includes 0.25 parts of silica gel or of phosphorous pentoxide and 1.2 of water. In another example 4 parts of the melamine product, 0.4 of acetic acid and 1.4 of water are added and in another 1 part of the melamine product, 1 of dextrine, 0.24 of formic acid, and 1.2 of water. The aldehyde condensation products described in Specifications 455,008, 468,677, 486,519 and 486,577 may also be used.</p> |
