工艺因素对首饰石膏铸型强度的影响

Effect of Process Factors on Strength of Gypsum Mould for Jewelry

金、银首饰主要采用石膏型精密铸造工艺成形,铸型的强度对铸件表面质量有很大影响。本文以业内某品牌饰用石膏铸粉为试验材料,采用智能砂型强度仪检测了铸型在不同工艺条件下的抗压强度。研究结果表明,石膏浆料凝结成形时,随着静置时间的延长,铸型湿态强度不断提高;铸型经高温焙烧后,其强度随着铸型温度降低不断下降,且焙烧过程中如受热不均会降低其强度;随着水粉比增大,铸型强度不断降低,而采用一定浓度的硼酸水制作铸型时,可以明显提升其热压强度。为使铸型强度满足生产需要,应根据气温条件相应调整水粉比,铸型灌注后应静置足够时间,铸型焙烧时应采用“缓慢升温+多台阶保温+控制最高焙烧温度”的焙烧工艺。

Gold or silver jewelry is mainly formed by gypsum investment casting process, and the strength of the mould has a great influence on the surface quality of the casting. In this paper, a certain brand gypsum powder was used as the experimental material, and the compressive strength of the mould under different technical conditions was tested by using the intelligent sand mould strength meter. The results show that the green strength of the mould increases with the standing time. After burning-out, the dry strength of mould will continuously decrease during the cooling, and uneven heating or cooling will diminish the strength. Both the green strength and dry strength will successively decrease with the increase of the water-to-powder ratio, while the dry strength can be obviously improved if boric acid solution with a certain concentration is used to mix the slurry. To ensure the mold strength meet the needs of production, the water-to-powder ratio should be adjusted according to the temperature conditions, and the mould should be left standing for enough time after perfusion, and the mould should be fired by the process as "slow heating + multi-steps insulation + controlling the maximum firing temperature".