Hot rolling is rolling performed above the recrystallization temperature. It can destroy the casting structure of the steel ingot, refine the grains of the steel, and eliminate the defects of the microstructure so that the steel structure is dense and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction so that the steel is no longer isotropic to a certain extent; the bubbles, cracks, and looseness formed during pouring can also be welded under high temperatures and pressure.
Hot-rolled steel pipe production process: The production process of hot-rolled seamless steel pipe includes several basic processes such as billet pre-rolling preparation, tube blank heating, piercing, rolling, sizing and reducing, and steel pipe cooling and finishing. There are generally three main deformation processes in the production of hot-rolled seamless steel pipes today: piercing, rolling, and diameter reduction; their respective process purposes and requirements are:
Hot-rolled steel pipe production piercing
Turning a solid tube blank into a hollow capillary; we can understand it as shaping, that is, setting the section of the rolled piece as a ring; its equipment is called a piercer. The requirements for the perforation process are: firstly, to ensure uniform wall thickness of the pierced capillary, small ellipticity, and high geometric precision; secondly, the inner and outer surfaces of the capillary should be relatively smooth, without scarring, folding, cracks, and other defects; The third is to have a corresponding piercing speed and rolling cycle to adapt to the production rhythm of the entire unit so that the final rolling temperature of the capillary can meet the requirements of the rolling mill.
2.1.2 Production of hot-rolled steel pipes
Change the thick-walled capillary into a thin-walled (close to the wall thickness of the finished product) steel pipe; we can regard it as a fixed wall, that is, determine the wall thickness of the steel pipe in this process according to the subsequent process diameter reduction and empirical formula; this equipment is called For the rolling mill. The requirements for the rolling process are: first when changing the thick-walled capillary tube into a thin-walled steel tube (wall reduction and extension), it must first ensure that the steel tube has a high average wall thickness; secondly, the steel tube has good internal and external surface quality.
2.1.3 Diameter reduction (including tension reduction) for hot-rolled steel pipe production
The large circle becomes a small circle, referred to as sizing; the corresponding equipment is a sizing (reducing) sizing machine. The requirements for the sizing and reducing process are: firstly, the purpose of sizing can be achieved under the conditions of a certain total reducing rate and a small single frame reducing rate; The third task is to further improve the outer surface quality of steel pipes. At the end of the 1980s, there was an attempt to cancel the pipe rolling process, and only use the method of piercing plus fixed reduction to produce seamless steel pipes, referred to as CPS, which is the English abbreviation of cross-rolling perforation and tension reduction).
2.2 The characteristics of the production process of each hot rolling mill
We usually call the wall thickness processing of capillary pipe rolling. Pipe rolling is the most important process link in the steel pipe forming process. The main task of this link is to thin the thick-walled capillary tube to a degree suitable for the finished steel tube according to the requirements of the finished steel pipe, that is, it must take into account the change in wall thickness during the subsequent sizing and reducing processes, and this link also needs to improve the thickness of the capillary tube. The quality of internal and external surfaces and the uniformity of wall thickness. The tubes after the tube rolling, wall reduction, and extension process are generally called plain tubes. The basic feature of the rolling tube wall reduction method is to press a rigid mandrel inside the capillary tube and use an external tool (roller or die hole) to compress and reduce the capillary wall thickness. According to different deformation principles and equipment characteristics, it has many production methods. It is generally customary to name the hot rolling unit according to the form of the rolling mill. The pipe rolling mill is divided into single-stand and multi-stand, and the single stand includes an automatic pipe rolling mill, Assel rolling mill, and so on.
Post time: Jun-20-2023