The CNC controlled machine is suitable for polish the external surface of the LNG tanks. The work cycle is that a piece needs about 25 minutes to15 minutes. The head can be adjusted according to the different tank size . High efficiency and low cost. After the first grinding wheel passes through, the fourth grinding wheel in sequence, the desired finish can be achieved. Continuous and automatic polishing process can meet various needs such as mass production and single-piece multi-variety processing.