短语词组短语back filled sand 回填砂peeling back of sand cores 砂芯脱壳back -up sand 填Drop -back sand unit 落砂单元and back filling sea sand 海砂回填oil no -back sand mold 油改性树脂自硬砂型sand back 沙丘Fred sand back 弗雷德 返回 back sand