From the hot-drawn steel tubes just described are made seamless-steel cylinders for

Fig. 80. - Reducing the Opening in a Hot-Drawn Tube storage of gases under pressure. The bottom is left on the tube and the open end, after having had the defective part trimmed off, is heated and pressed under the dies B and C to a shape shown in Fig. 80. The opening is suitable for attaching a controlling valve to the cylinder.

These containers are made as large as 18 inches in diameter and 12 feet long.

Another method of closing the tube end is to hold the tube strongly in a rapidly revolving machine of great rigidity and bring the pressure of a steel roller against the side of the tube end. This pressure is so great that its friction heats the tube and closes it to the amount desired. The process is called spinning and may even be used to close and weld a tube end of mild steel.