Cold processing of steel pipes by rolling and drawing at room temperature on cold rolling and cold drawing pipe units belongs to the deep processing of hot rolled pipes (including hot extruded steel pipes) and welded pipes. It can obtain steel pipes with smaller diameters, thinner wall thickness, higher dimensional accuracy, lower surface roughness, better performance, and various cross-sectional shapes. Various steel pipes with diameters of 0.2 to 765 mm and wall thicknesses of 0.015 to 50 mm can be produced by cold drawing. Various steel pipes with diameters of 4 to 450 mm and wall thicknesses of 0.03 to 35 mm can be produced by cold rolling.

Compared with cold rolling, the advantages of cold drawing are large deformation per pass, fewer processing passes, short production cycles, and low metal consumption. The disadvantages are that tool manufacturing is difficult and it is inconvenient to change specifications. The production flexibility is poor, the equipment investment is high and the maintenance is complicated; because it is cyclic rolling, the rolling time is long, the productivity is low and the energy consumption is high. The advantages of cold drawing are high productivity, convenient specification change during production, great flexibility, and simple equipment and tool manufacturing; the disadvantages are small deformation per pass, many processing passes, long production cycles, and high metal consumption.

Steel pipe cold drawing
Various conventional methods for drawing steel pipes:
(1) Pipe drawing without mandrel, which is used to reduce only the outer diameter of the steel pipe.
(2) Pipe drawing with a fixed short mandrel, which is used to reduce both the outer diameter and wall thickness of the steel pipe; this method has a large friction resistance and a large drawing force due to the fixed mandrel and the use of a fixed outer die, and is widely used because of its simple drawing method.
(3) Pipe drawing with a floating mandrel, which is often used for pipe drawing with a reel and can produce very long steel pipes (more than 100m). The drawing force is small during floating mandrel drawing, which can increase the deformation per pass; since there is no restriction on the pull rod, steel pipes with very small diameters can be drawn with a mandrel.
(4) Long mandrel drawing. When drawing, the mandrel moves with the steel pipe, which eliminates the friction resistance on the core holder, thereby reducing the drawing force and increasing the deformation per pass. The movement of the mandrel can also reduce the roughness of the inner surface of the steel pipe. The disadvantage of long mandrel drawing is that it has strict requirements on the mandrel and the rod must be removed after drawing. There are two methods to remove the rod: one is to roll the steel pipe and the mandrel together on the inclined rolling mill to expand the diameter of the steel pipe a little, and then pull the mandrel out on the rod extraction machine; the other is to use double-die drawing to expand the diameter before pulling the mandrel. The latter die is an additional die. When passing through the additional die, the tube wall has only a small amount of deformation, and the diameter of the steel pipe is slightly expanded, which can reduce the rod removal force when removing the rod; two four-roller rolling dies can also be used for rolling and removing the rod.
(5) Diameter expansion drawing. The wall thickness of the steel pipe is reduced, the diameter is increased, and the tube length is shortened. When expanding, the steel pipe is fixed and the pull rod drives the mandrel through the tube.

To overcome the shortcomings of conventional cold drawing methods, the following tube drawing methods have been continuously developed:
(1) Tube drawing with a conical mandrel, which has a smaller pull rod force Pc than that of a general short mandrel.
(2) Semi-continuous and continuous tube drawing. Various linear tube drawing machines work intermittently. After pulling a tube, they need to wait for the trolley to return before pulling the next tube. Therefore, semi-continuous and continuous tube drawings have been developed. There are two forms of semi-continuous cold drawing. One is to use a double-moving tube drawing trolley, which is fixed on the motion chain and runs along a guide rail with a certain shape. After the upper tube drawing trolley pulls out the previous steel pipe, the lower tube drawing trolley arrives in front of the center frame and clamps the next tube for drawing. The other is a semi-continuous tube drawing machine that moves the double tube drawing mold during drawing. Continuous tube drawing machines are crawler-type and double-trolley reciprocating type. The crawler-type tube drawing machine consists of several frames with tube drawing molds installed at the front. There are chain links on both sides of the frame, and track links are installed on the chain shaft to compress the steel pipe and force it into the pipe drawing die. This continuous pipe drawing machine can be used for drawing without a core rod and with a long core rod, which can increase the output by 3 times compared with ordinary pipe drawing machines; the problem is that it is easy to produce uneven longitudinal wall thickness when drawing without a core rod, and the resistance of the fixed die is large, the energy consumption is high, the surface quality of the product is poor, and it is difficult to remove the rod. In addition, there is a continuous pipe drawing with double trolley reciprocating motion, which is used for drawing without a core rod, see continuous welding and continuous drawing of precision tubes.
(3) Long core rod rolling die drawing process. The process of multi-roller rolling die long core rod drawing round tube successfully studied by Beijing University of Science and Technology in China is: before drawing, the tube head is first narrowed to match the conical transition area of the core rod to clamp the steel pipe. Then the core rod is inserted and the thin end of the long core rod passes through the rolling die. During drawing, the cold drawing machine jaws hold the thin end of the mandrel make a linear motion, and pull the steel pipe and the mandrel out of the rolling die together, realizing the wall reduction and extension deformation of the steel pipe, and changing the simple cold drawing method into a combined drawing and rolling method. This method can obtain a large deformation per pass, reduce energy consumption, have a simple structure, and have good surface quality of the steel pipe; the disadvantage is that it is difficult to remove the rod.
(4) Ultrasonic vibration drawing.
(5) Drum drawing.
(6) Warm drawing of steel pipe.
(7) Cold drawing of steel pipe rotary die.
(8) Reverse tensile force drawing.
(9) Torsion drawing, that is, the drawing process of twisting the steel pipe while drawing. The straightness of the steel pipe after the drawing is good, and the straightening process can be omitted.
(10) Fluid dynamic lubrication drawing. During tube drawing, a pressure tube is installed in front of the tube drawing die. The pressure tube has a certain length of lH, and there is only a small gap between its inner wall and the outer surface of the tube material. During the drawing process, the lubricant is carried by the forward-moving steel pipe through the pressure tube to the front of the deformation zone. Since the gap between the inner wall of the pressure tube and the surface of the steel tube is small, and the lubricant that leaves the deformation zone with the steel tube after drawing is relatively small, the lubricant is strongly squeezed when passing through the pressure tube, and the pressure P of the lubricating film gradually increases. This is the effect of fluid dynamic pressure, which is the physical basis for establishing fluid dynamic lubrication drawing. If the pressure of the lubricating film before the deformation zone reaches enough to separate the steel tube surface and the mold wall, so that the lubricant is filled between the two, forming liquid friction, this can greatly improve the lubrication conditions, achieve the purpose of reducing the drawing force, increasing the deformation per pass, and reducing mold consumption.