| 摘要 |
As modifier for regulating the binding capacity, a urea formaldehyde resin-based binder for cold-setting moulding sand mixtures contains a homogeneous "oil in water" emulsion of a heavy fraction with a specific gravity of at least 1.01 g/cm<3> composed of a schist resin, an organic solvent for the carbonaceous constituents of the said fraction, an emulsifier and water. A product obtained by processing schist in gas generator ovens at approximately 500 degrees C, for example, may be used as the heavy fraction of schist resin. The binder is manufactured by mixing constituents of the modifier at reduced pressure to form a homogeneous "oil in water" emulsion and subsequent addition of urea formaldehyde resin. Per 100 parts by weight of filler (e.g. moulding sand), the moulding sand mixture may contain 2-5 parts by weight of binder, 0.3-1.0 part by weight of acid hardening compound and 0.5-1.0 part by weight of water. The moulding sand mixture has high thermal resistance and mechanical strength.
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