wheel 71 secured to a slide shaft 65 supported by bearings 64 on the lifting frame 52 resulting in rotation of a screw 66 formed on the slide shaft 65 and engaging a nut 67 secured to the base 61 to cause the axial motion of base 61 to permit the positional adjustment of the base 61 a cylinder support 73 secured to the base 48 is provided with a brush lifting cylinder 72 a rod 74 secured to the lifting frame 52 through a joint 75 so that the wire brushes 53 are vertically displaced by the vertical movement of lifting frame 52 is actuated by a cylinder 72 as is seen from the drawings four wire brushes 53 are driven by two motors 76 and 77 rotation of one motor 76 being transmitted through chains 78 and 79 to two bearing shafts 54 and the rotation of the other motor 77 being transmitted in the same manner to the other two shafts the polishing section 46 balances itself by locating the two motors 76 and 77 at positions symmetrically spaced from the central axes of the section both sides of the mother plates 12a are sumultaneously polished by disposing two identical polishing sections at opposed sides of the conveyor 15 the mother plats 12a stripped of the deposited zinc 11 at the stripping device 17 are transferred to the polishing device 10 by the conveyor 15 and stopped by the stopper plate 29 which has been brought to the.