| 摘要 |
<p>Foundry cores are prepared by mixing a foundry aggregate with a binder-forming composition comprising a combination of an air-drying constituent which is a synthetic drying oil, oil-modified alkyd resin, a polyhydric alcohol ester of an ethylenically unsaturated fatty acid, an ethylenically unsaturated petroleum polymer, or a mixture of two or more such materials, together with a polyisocyanate, introducing the mix into a pattern or mould to form a green core which is maintained therein until the core acquired sufficient stripping strength to be removed therefrom with damage and finally completing the cure after removal of the core. The foundry aggregate is preferably foundry sand. Suitable air-drying constituents are synthetic drying oils containing ethylenic unsaturation such as the hydrocarbon polymers and copolymers derived from butadiene, styrene and cyclopentadiene, oil-modified alkyds such as the long-oil alkyds and polyhydric alcohol esters of ethylenically unsaturated fatty acids such as the tall oil esters of glycerine or pentaerythritol. Petroleum polymers suitably containing cyclopentadiene or dicyclopentadiene may also be used. More preferably alkyd resins derived from pentaerythritol, phthalic acids and linseed oil are used. The polyisocyanate may be aliphatic, cycloaliphatic or aromatic. A catalyst for accelerating the drying of the air drying constituent and/or for the reaction thereof with the polyisocyanate may also be added to the composition, a preferred catalyst being a mixture of cobalt naphthenate and dibutyl tin dilaurate. The ingredients of the foundry mix may be stored in two separate packages for mixing with foundry aggregate, the first package containing the air-drying constituent, usually in a solvent solution and the second package the polyisocyanate. The catalyst and a monomeric alcohol may also be included in the first package and the polyisocyanate of the second package may be dissolved in a solvent.</p> |
