Tube drawing is very similar to bar drawing, （拔管非常类似于酒吧图,）.pdf

Tube drawing is very similar to bar drawing, except the beginning stock is a tube. It is used to decrease the diameter, improve surface finish and improve dimensional accuracy. A mandrel may or may not be used depending on the specific process used. The diameter and wall thickness of tubes that have been produced by extrusion or other processes can be reduced by tube drawing process. The process of tube drawing shown in Fig. 5 is similar to wire or rod drawing except that it usually requires a mandrel of the requisite diameter to form the internal hole. Tubes as large as 0.3 m in diameter can be drawn. Fig. 5 Tube Drawing Drawing Equipment Drawing equipment can be of several designs. These designs can be classified into two basic types; Draw bench, and Bull block. A draw bench (Fig. 5) uses a single die and the pulling force is supplied by a chain drive or by hydraulic means. Draw bench is used for single length drawing of rod or tube with diameter greater than 20mm. Length can be as much as 30 m. The drawing speed attainable on a draw bench ranges from 5 m/min to 50 m/min. Draw benches are available having capacities to provide pull force of upto 1 MN. Bull block or rotating drum (Fig. 3) is used for drawing rods or wires of very long length. Production of this kind of products is far beyond the reach of the hot rolling, and so a substantial proportion of tubing is still cold drawn for the following reasons. • To produce tubes with thinner walls than can be hot rolled. • To produce tubes with smaller diameters. • To produce tubes longer than can be hot rolled in certain sizes. • To secure better surface finishes. • To obtain closer dimensional tolerances. • To increase certain mechanical