sand mulling

例句：

1. 1. The engineer is sanding the wood to smooth it before painting.
   工程师正在给木头上漆前进行砂磨。
2. 2. Sand-blasting is a common method for cleaning and finishing metal surfaces.
   喷砂是一种常见的金属表面清理和精饰方法。
3. 3. During sand mulling, the sand is forced through the material being treated.
   在砂磨过程中，沙子被强制通过待处理的材料。