mill scale

例句：

1. 1.The millstone grinds the grain into flour.
   磨坊的石磨将谷物磨成面粉。
2. 2.The sieve separates the sand from the gravel.
   筛子将沙和砾石分开。
3. 3. The millstone is a crucial part of the milling process.
   磨坊的石磨是磨制过程的关键部分。