银币模压加工过程中表面发蓝的发生机理及克服方法

Micro-adhesion in Coining Process Bluing on Proof Silver Coins:What it is,and How to Remove it

在银币的生产过程中,硬币表面发蓝是非常普遍的现象。许多硬币收藏者用放大镜,甚至是显微镜去观察硬币发蓝。如果不满意硬币的外观,收藏者将退还硬币给造币厂。为了清除银币表面的发蓝,造币生产线必须被中断,以抛光或清洗压印的模具。如果毛胚没有处于良好的准备状态,抛光一副冲模的时间就超过了压印硬币的时间。文中分析了硬币表面发蓝的原因,揭示了在模压过程中值得注意的摩擦学现象,并且提出了无需人工抛光冲模去除发蓝的方法,实现了银币的高效生产,清洗模具周期由冲压80次,提高到800次以上。

Bluing on coins is a common phenomenon in proof coin manufacturing. Thousands of coin collectors use magnifying glasses, even microscopes, to observe coin bluing. If dissatisfied by the coins＇ appearance, collectors will return the coins to the Mint. To remove bluing on proof coins, the continuous production must be stopped to polish or clean the die on a press. If the blanks are not prepared in good condition, the time to polish a pair of dies exceeds the time for stamping coins. This paper analyzes the cause of bluing on coins, reveals notable tribological principles in the coining process, and suggests methods to remove the bluing without manually polishing the die. Therefore, more efficient production of proof coins can be achieved. The periods of die polishing is increased to more than 800 coins from 80 coins