GB773338A - Improvements in or relating to sand moulds and cores for casting metals - Google Patents

Abstract

A binder composition, for use in making sand moulds or cores for casting metals, contains particles of a water-soluble cellulose ether and particles of a natural and/or a thermosetting synthetic resin, together with Portland cement or plaster of Paris and water. The preferred proportions by weight are 100 parts of sand (dry bases), 2 to 25 parts (particularly 6 to 12 parts) of cement, 0.2 to 2.0 parts (particularly 0.4 to 0.8 parts) of cellulose ether and resin and 3-7 parts of water, including any water present as moisture in the sand. The relative proportions of cellulose ether and resin may be 20 to 90 (preferably 70) per cent by weight of cellulose ether and 80 to 10 (preferably 30) of resin. The cellulose ether may be methyl, ethyl, methyl ethyl, hydroxyethyl, or methyl ethyl hydroxyethyl cellulose, a water-soluble salt of a cellulose ether carboxylic acid, cyanoethyl cellulose or sulphoethyl cellulose. Natural resins used may include rosin, tall oil rosin, esterified rosin, or a saponified rosin such as potassium, calcium, ammonium or hydroxyalkylamine resinate. Synthetic resins used may include urea-formaldehyde or phenol-formaldehyde resins, melamine resins, polyvinyl resins, sulphamide resins and acrylate resins. Cement hardening accelerators such as calcium chloride, sodium silicate or sodium carbonate may be added to the composition, e.g. in a proportion of 0.2-4 per cent based on the weight of the sand. In an example, 100 litres of fresh sand containing 2 per cent by weight of moisture are mixed with 8 kgs. of cement followed by 1 kg. of a mixture of 70 per cent by weight of ethyl hydroxyethyl cellulose and 30 per cent by weight of a melamine resin, and finally with 2.5 litres of water. In the second example half the fresh sand is replaced by mould sand. Specifications 696,965 and 754,823 are referred to.