The production process of hot-rolled seamless steel pipe includes basic processes such as billet preparation before rolling, billet heating, piercing, rolling, sizing and reducing, cold-out of steel pipe, cutting end and tail of steel pipe, segmenting, straightening, flaw detection, manual inspection, spray mark printing, bundling and packaging, etc. There are three main deformation processes in hot-rolled seamless steel pipe production nowadays: piercing, pipe rolling and sizing and reducing. Their respective technological purposes and requirements are as follows.
Piercing is to make hollow capillary from solid billet. Its equipment is called piercing mill. The requirements of piercing technology are as follows:
(1) To ensure that the wall thickness of the perforated capillary is uniform, the ellipticity is small and the geometric dimension accuracy is high;
(2) The inner and outer surface of the capillary is smooth, and there shall be no defects such as scarring, folding or cracking.
(3) Corresponding piercing speed and rolling cycle should be required to adapt to the production rhythm of the whole unit so that the final rolling temperature of capillary can meet the requirements of the mill.
2、 rolling pipe
Pipe rolling is to roll thick-walled capillary tubes into thin-walled barren tubes after piercing to achieve the required thermal size and uniformity of finished pipes. That is to say, the wall thickness of the barren pipe in this process is determined according to the following process diameter reduction and empirical formula, and the equipment is called pipe rolling mill.
The requirements for pipe rolling process are:
(1) When the thick-walled capillary is turned into thin-walled barren pipe (wall reduction and extension), the barren pipe must first have a high uniformity of wall thickness;
(2) The barren pipe has good internal and external surface quality. The selection of tube rolling mill and its reasonable matching with the deformation between the piercing process are the key to determine the quality, output and technical and economic indexes of the product.
3、 sizing and reducing (including stretching and reducing)
The main function of sizing and reducing is to eliminate the discrepancy of the outer diameter of barren pipe caused by the rolling process in the previous process, so as to improve the outer diameter accuracy and true roundness of hot-rolled finished pipe. Diameter reduction is to reduce the large diameter to the required size and accuracy. Tension reducing is to reduce diameter and wall under the action of tension of front and rear frame. The equipment used for sizing and reducing is sizing machine.
The requirements for sizing and reducing process are as follows:
(1) To achieve the goal of sizing under the condition of a certain total reduction rate and a smaller single rack reduction rate;
(2) It can realize the task of producing finished pipes of various specifications by using one kind of pipe blank.
(3) To further improve the external surface quality of steel pipe.