The production process of general seamless steel pipes can be divided into cold drawing and hot rolling. As the name implies, hot rolling has a high temperature of the rolled piece, so the deformation resistance is small and a large deformation amount can be achieved. Taking the rolling of steel plates as an example, the thickness of the continuous casting billet is generally around 230 mm, and after rough rolling and finishing rolling, the final thickness is 1~20 mm. At the same time, due to the small width-to-thickness ratio of the steel plate, the dimensional accuracy requirements are relatively low, and it is not easy to have plate shape problems, and the main focus is on controlling the convexity.
The basic process of hot-rolled pipes is:
(1) The ingot or billet is punched into a hollow thick-walled rough tube on a punching machine. The methods of punching the billet are divided into two-roller oblique rolling punching, pressure punching, push rolling punching, and three-roller oblique rolling punching.
(2) The rough tube is rolled thin on an elongating machine and stretched into a rough tube with a wall thickness close to that of the finished tube. The rough tube extension, i.e. the rough tube rolling methods, include: automatic tube rolling, continuous tube rolling, three-roll and two-roll tube rolling (see tube material rolling extension), periodic tube rolling, and tube jacking.
(3) The rough tube is finished on the finishing mill into a finished tube. The rough tube finishing includes tube leveling and tube sizing for the purpose of improving quality, and tube diameter reduction and tube hot expansion for the purpose of expanding product specifications.
The production process of cold-rolled seamless steel pipe is generally more complicated than hot rolling. The tube blank must first be subjected to three-roll continuous rolling, and then a sizing test must be performed after extrusion. If there is no response crack on the surface, the round tube must be cut by a cutting machine and cut into a blank of about one meter in length.
Cold-rolled seamless steel pipe process flow
The production process of cold-drawn seamless steel pipe is: round tube billet → heating → perforation → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → billet tube → heat treatment → straightening → water pressure test (defect detection) → marking → storage.
The difference between hot-rolled tube and cold-drawn tube
- From the dimensional accuracy: the dimensional accuracy of cold-rolled steel pipe is high.
- From the appearance: the surface of cold-rolled steel pipe is bright, and the surface of hot-rolled steel pipe has obvious oxide scale or red rust.
- From the caliber size: the caliber of cold-rolled steel pipe is smaller than that of hot-rolled steel pipe (mainly due to different machines, each has its own specialty).
- From the price: cold-rolled steel pipe is 1000-2000 per ton more expensive than hot-rolled steel pipe (don’t be greedy for cheapness).
- From the use: hot-rolled steel pipe is used in fluid transportation, mechanical structure and other occasions with low dimensional requirements, cold-rolled steel pipe is used in precision instruments, hydraulic systems, pneumatics and other places with high requirements.
