Method for forming a tank bottom

A method for forming the bottom of a tank for liquids, said tank having generally upwardly extending sides and a sloped bottom for complete drainage of liquid from the tank, said method comprising the steps of:

• (a) providing a generally flat, rectangular shaped plate member having a plurality of corner portions, wherein at least one corner portion is trimmed along a line which is approximately equal to the diameter of a finished curved corner of the bottom;
• (b) positioning said plate member in a head forming device having punch and die members, and
• forming said plate member in said head forming device by deforming said flat plate member against said punch and die members to provide a bottom wall portion and upwardly extending side wall portions which extend continuously around the periphery of said bottom wall portion, and with an upward crease in the bottom wall portion of the plate member and a drain opening in said bottom wall portion, said bottom wall portion including a pair of downwardly sloping surfaces which slope downwardly from the side wall portions and which intersect in a region adjacent said drain opening to establish said crease so as to extend radially in a direction from said opening in an upward fashion towards said side wall portions, and with said bottom wall portion being generally contoured smoothly and continuously upwardly to the side wall portions from the entire circumference of the drain opening, thus providing a one-piece tan bottom which is formed without welding in the region adjacent said drain opening or in said corner portion.