It's overcasting for rain.

天阴暗起来要下雨了。

The overlock machine combines straight and overcasting stitches and outs and sews the fabric while stitching the seams.

包缝机的线迹由直线线迹和锁边线迹组成并且缝纫时边剪边缝。

Loose covering layer that consisted of water containing fine powder sand layer was encountered in the overcasting at Zhaodianzi Iron Mine.

赵店子铁矿在露天开采中遇到了含有含水粉细沙层的松散覆盖层。