纯银首饰铸造气孔的形成及防治措施

气孔是铸造纯银首饰的主要缺陷之一,其根本原因是氢、氧等气体在熔融银液与固态银中巨大的溶解度差别而析出造成的。减少或避免纯银首饰中的气孔,熔炼铸造过程中必须采用适当的保护和除气措施,尽量减少进入金属液中的气体,并促使金属液中的气体在浇注前释放出来。实践证明,采用纯净干燥炉料、控制回用料比例、真空回充惰性气体保护、还原性火焰保护、液面覆盖木炭或脱水硼砂、吹氩脱气、多次冷凝和重熔等措施可有效降低气孔的产生。

Research on gas porosity formation in pure silver jewelry casting and its prevention

Gas porosity is one of the main defects in pure silver jewelry casting,and the fundamental reason of its formation is the precipitation of oxygen and other gas due to their much higher solubility in the molten silver liquid than that in solid-state silver.To reduce or avoid gas porosity in pure silver jewelry,appropriate protection and degassing measures that reduce the gas amount entering metallic solutions and lead to release of gases from the metallic solution before pouring should be taken.Practices have proved that such measures are effective in reducing gas porosity formation as purifying the furnace charge,controlling the proportion of scrap returns,vacuum backfilling inert gas,applying reducing flame protection,covering charcoal or dehydrated borax on liquid surface,degassing by blowing argon,and multiple condensation and remelting.