Abstract: An acid pickling tank 11 is filled with an acid liquid L, and a lid 12 is attached to the acid pickling tank 11. A central part of the lid 12 is depressed downwards to form a covering portion 12b. The covering portion 12b is located at a lower position than the liquid level of the acid liquid L in the acid pickling tank 11 to cover a free surface of the acid liquid L. Immersion guide rolls 20a to 20e are provided on the covering portion 12b, support blocks 21a to 21e are provided at the bottom of the acid pickling tank 11, and skids 23a to 23e are provided on the support blocks 21a to 21e via a bottom plate 22. Thus, the free surface of the acid liquid L in the acid pickling tank 11 is decreased to suppress a loss of the acid, and prevent an overflow of the acid liquid L to the outside of the tank, thereby making acid pickling of the strip steel plate S efficient.

Abstract: An acid pickling tank body 11 is partitioned with a partition wall 12 into a first tank 13 and a second tank 14. The first tank 13 and the second tank 14 are filled with acid liquids L1 and L2, respectively, of different concentrations. A lid 15 is attached to the top of the acid pickling tank body 11. On the lid 15, immersion guide rolls 25a to 25d, 26a to 26d are mounted. On the bottom surface of the first tank 13 and the second tank 14, skids 31a to 31e, 32a to 32d are mounted via support blocks 27a to 27e, 28a to 28d. A liquid seal 22 is provided which has a cushion nozzle 38 for jetting the acid liquids L1 and L2 toward the surface of a strip steel plate S. traveling above the partition wall 12 for the first tank 13 and the second tank 14.