| 摘要 |
Method for obtaining moulding and core sands from moulding sands cemented with urea-formaldehyde resin hardened with maleic anhydride, characterised in that to the moulding sand a fixing agent is introduced in the quantity from 0.4 to 16% by weight in the form of moulding sand coated with maleic anhydride in the quantity from 2 to 50% by weight, possibly with addition of butyl phthalate in the quantity from 0.2 to 1.5% by weight, the sand with the hardener is thoroughly mixed, and than resin is introduced to the prepared mixture of sand with hardener, in the quantity from 0.8 to 2.5% by weight, which comprises of 50-95 parts by weight of urea-formaldehyde resin and 5-50 parts by weight of etherified melamine resin, or resin comprising of 50-80 parts by weight of urea-formaldehyde resin and 20-50 parts by weight of etherified urea-melamine-formaldehyde resin, the whole is thoroughly mixed and formed.
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