The erw steel pipe is formed on the forming machine by rolling and forming a steel plate through a plurality of molds. Because the strength of the steel plate is high, and its structure is a face-centered cubic lattice, it is easy to form work hardening, so that when the welded pipe is formed: on the one hand, the mold has to bear a large friction force, so that the mold is easy to wear; on the other hand, the steel sheet material It is easy to form a bond (bite) with the surface of the mold, causing strain on the surface of the welded pipe and the mold.
Therefore, a good steel forming mold must have extremely high wear resistance and anti-bonding (biting) properties. Our analysis of imported welded pipe molds shows that the surface treatment of these types of molds is treated with super hard metal carbide or nitride coating.
Straight seam welded pipe forming die materials are generally made of high carbon and high chromium Cr12MoV (or SRD11, D2, DC53). At present, the following process is commonly used in China to make molds: blanking → rough processing → heat treatment (high temperature quenching plus high temperature tempering) → finishing → nitriding → finished products (Note: in order to save costs, the general manufacturers now have saved the forging and Spheroidizing annealing is two time-consuming and costly processes). Since the Cr12MoV type material is a high carbon high chromium alloy steel, its original structure has a large composition segregation (this segregation cannot be eliminated even by general forging).
In this way, the internal structure of the mold after heat treatment (high quenching and high recovery) is extremely uneven, and the macroscopic performance is extremely uneven in hardness (about 40 to 60 for HRC). After nitriding treatment, the unevenness of the mold surface cannot be eliminated. The hardness is even further reduced. In actual use, the surface of the mold and the welded pipe are easily pulled, and the life of the mold is low.
The straight seam welded pipe has a simple production process, high production efficiency, low cost, and rapid development. The strength of the erw steel pipe is generally higher than that of the straight seam welded pipe. It is possible to produce a welded pipe with a large diameter by using a narrow blank, and it is also possible to produce a welded pipe having a different pipe diameter by using a blank of the same width. However, compared with the straight seam pipe of the same length, the length of the weld seam increases by 30 to 100%, and the production speed is low.
Application range
The products are widely used in water supply engineering, petrochemical industry, chemical industry, electric power industry, agricultural irrigation, urban construction, and are one of the 20 key products developed in China. For liquid transport: water supply, drainage. For gas transportation: gas, steam, liquefied petroleum gas. For structural use: for piling pipes, for bridges; for piers, roads, building structures, etc。