Process for producing large-diameter core rods of pipe tandem mills

Abstract

The invention discloses a process for producing large-diameter core rods of pipe tandem mills, having the characteristics of improving the straightening efficiency of the core rods. The process for producing core rods of large-diameter pipe tandem mills comprises the following steps of core rod blank forging, first-time straightening, surface rough turning, tempering treatment, second-time straightening and finish turning in sequence, wherein in the steps of first-time straightening and second-time straightening, firstly the core rods are placed on a lathe for marking the bent positions of the core rods and measuring the bending values, and then targeted straightening is carried out on the core rods according to the marks and the bending values. Therefore, the core rods are straightened on a free hydraulic forging press according to the marked positions and the bending values so that the straightening efficiency and accuracy are greatly improved; and in addition, the whole-length bending of the straightened core rods is only 3.5 mm and is even lower, and when the large-diameter core rods are turned, the process can ensure that qualified finished products can be processed by using less turning allowances. The process is especially suitable for popularization and application in the production of the large-diameter core rods.

Description

technical field [0001] The invention relates to a rod body production process, in particular to a large-diameter continuous rolling pipe mandrel rod production process. Background technique [0002] At present, seamless steel pipes play a very important role in my country's national economic construction. Seamless steel pipes are widely used in petroleum, military industry, shipbuilding, machinery, automobiles, gas fluid transportation and other industries. The stop mandrel is one of the important tools for seamless steel pipe rolling. During the rolling process of the steel pipe, the stop mandrel is penetrated into the extension billet and sent to the rolling mill for rolling. During the rolling process, the mandrel on the one hand The steel pipe is rolled under the action of extrusion force and thrust, and on the other hand, it is limited by the action of power, and the mandrel is kept limited during the rolling of the steel pipe. After rolling, the mandrel is drawn out f...

AI Technical Summary

Problems solved by technology

The existing mandrels are generally small-diameter mandrels. The manufacturing process includes: smelting steel ingots, forging mandrel blanks, stress relief annealing blanks, first straightening, spheroidizing annealing, surface roughing, quenching and tempering treatment (including quenching, two tempering treatments), the second straightening, finishing and other processes, in the first straightening and second straightening, the mandrel is placed on a large-tonnage special hydraulic straightening machine , the straightening requires high straightening equipment, and the straightening efficiency is low. At the same time, the mandrel obtained after straightening has a large curvature, which is not conducive to the subsequent turning process; at the same time, when rough turning the outer surface of the mandrel , due to the production of small-diameter mandrels, there are more machining allowances on the outer circle, but if more machining allowances are left to produce large-diameter mandrels (such as stop mandrels with a diameter of 358.1mm) , after the mandrel forging is completed, if the large-diameter mandrel leaves a large machining allowance like the small-diameter mandrel, the effect of quenching and tempering treatment will not be good (because the diameter is too large, it cannot be hardened during quenching) , leading to poor quality of finished products; if there is a small machining allowance, although it is easy to harden to the core of the mandrel during quenching and tempering treatment, the turning allowance is not easy to control in rough turning and finishing turning , especially in the rough turning process, it is easy to turn too much and the diameter of the final finished product is smaller than the required size, so it can only be changed to a small-sized mandrel or directly scrapped; if there is less turning in the rough turning process to ensure the finished product size , because the mandrel has a certain curvature, it will cause many concave parts on the surface of the mandrel that cannot be turned after the rough turning is completed, and there is oxidized black skin in the concave part, which will affect the quality of subsequent quenching and tempering treatment (black skin) The existence of cracks and other defects on the surface will firstly make it difficult to detect and discover, leaving hidden dangers for quenching; secondly, during quenching, because the oxide layer at this place is thicker than other places, it affects the cooling effect, thus affecting the quenching effect. ), will also affect the product quality and the service life of the mandrel

In addition, mandrels are prone to cracks during processing. If the cracks extend to within the diameter of the finished mandrel, it will also affect the service life of the finished mandrel. To eliminate the cracks, it is necessary to continue turning (causing the diameter to be smaller than the required diameter of the finished product), it will also cause the mandrel to be scrapped or changed to a small-sized mandrel after the subsequent finishing car is completed, resulting in a decline in the yield