Copper plumbing tube is sold in either the hard, i.e., as drawn, condition or in a soft, annealed state. Further, both hard-drawn and annealed tube is sold both in coils and straight lengths. The next steps in the tube-making process therefore depend on the type of product to be produced. Tube that is to be sold in straight lengths is passed through a series of straightening rolls that are arranged in a slight zigzag pattern. The rolls' positions are set such that the tube is bent slightly less at each step in the series.
Tube emerges straight and ready to be cut to length.
Tube that is to be sold in coils is treated very similarly, the only difference being the position of the rolls. For coils, they are set so as to impart a bend of appropriate radius to the tube as it emerges. The furnace is essentially a long heated box filled with a protective atmosphere to prevent the copper from oxidizing. In plants that are not equipped with continuous annealing furnaces, annealing is done in batches in what are aptly called bell furnaces. These furnaces look very much like large cylindrical church bells, the open bottoms of which can be sealed to keep air out.