RU2232655C1 - Method for making electrically welded straight -seam tubes - Google Patents

Abstract

FIELD: manufacture of electrically welded straight-seam tubes, namely small-diameter steel water- and gas-supply tubes welded with use of high-frequency electric current.

SUBSTANCE: method comprises steps of shaping from band tubular blank in the form of oval cylinder with slit having small axis equal to diameter of next cylindrical welding gage; heating edges and welding them at squeezing in welding gage. Blank is shaped until making symmetrical portions with radiuses equal to radius of welding gage. Centers of said portions are laid on large axis of oval cylinder. Ratio of large axis of oval cylinder to its small axis is in range 1.03 - 1.30.

EFFECT: stability of edges during welding process, enhanced contour of welded tube.

1 tbl, 1 dwg

Description

The invention relates to the production of longitudinally welded pipes, in particular the production of high-frequency welded steel pipes of small diameter.

A known method for the production of longitudinal welded pipes, including forming a tube billet from a strip in single-radius gauges with a successively decreasing radius, edge heating and pipe welding [1].

The disadvantage of this method is the low strength of the weld, since a significant part of the compressive force of the rolls of the welding stand is dispersed along the entire perimeter of the crimp pipe billet, and the edge compression force is small.

A known method of manufacturing longitudinal welded pipes, comprising forming a tape into a tube stock in a series of successively arranged calibers with bending of the extreme sections of the tape in the first molding gauge with a radius of (1.05-1.1) R _t , where R _t is the radius of the finished pipe, in the last molding caliber, the central section of the workpiece is formed with a radius of (0.85-0.9) R _t , and the extension of this section is carried out in a welding caliber [2].

The disadvantage of this method is the low quality of the weld due to the small compressive force at the edges in the welding gauge. In addition, part of the force exerted by the rolls goes to the bending of the central section of the pipe billet, which also reduces the force of pressing the edges during welding and the strength of the seam.

The closest to the proposed invention in its technical essence and the achieved results is a method of manufacturing an electric-welded straight-seam pipe, comprising forming from a tape a tube stock in the form of an asymmetric oval cylinder with a slit, the small axis of the cross section of which is equal to the diameter of the subsequent round welding gauge, and the upper parts of the semi-perimeter are formed equal radii, edge heating and welding during compression in the welding stand [3] - prototype.

The disadvantages of this method are the low strength of the weld due to insufficient compression of the edges in the welding gauge. Part of the effort from the welding rolls with a given shape and aspect ratio of the workpiece is dispersed around the entire perimeter of the pipe workpiece and is spent not only on the compression of the edges, but also on the molding of the workpiece.

The technical problem solved by the invention is to increase the strength of the weld seam of longitudinally welded pipes.

To solve the technical problem in the known method, comprising molding from a tape a tube stock in the form of an oval cylinder with a slit, the minor axis of which is equal to the diameter of the subsequent cylindrical welding gauge, heating the edges and welding them by crimping in a welding gauge, according to the proposal, the blank is formed to obtain symmetrical parts with radii equal to the radius of the welding gauge, the centers of which are located on the major axis of the oval cylinder, and the ratio of the major axis to the minor axis is 1.03-1.30.

The drawing shows a diagram of the formation of the pipe profile in the last molding (profile 1) and welding (profile 2) calibers according to the proposed method,

where R is the radius of the finished pipe and welding gauge, B and H are the major and minor axes of the pipe billet in the form of an oval cylinder, respectively.

The invention consists in the following. For water and gas pipes that work under pressure, not only the absence of weld defects, such as lack of penetration, but also the strength of the weld itself is of great importance. The strength of the seam is directly related to the force of pressing the edges against each other at the time of welding in the welding gauge. In order to exclude the forming of the radius of the tube billet in the welding gauge and to maximize the compression force of the edges while maintaining their stability, the tube billet in front of the welding stand is formed in the form of an oval cylinder (profile 1) with a slit, the small axis of the cross section of which H is equal to the diameter of the welding gauge (H = 2 · R), and the lateral parts of the pipe billet mating with each other are formed by a radius R equal to the radius of the welding gauge. In this case, the ratio of the large B and small H axes of the oval cylindrical workpiece is set, which ensures the stability of the edges during the welding process and the correct shape of the welded pipe (profile 2).

The lateral parts of the tube billet are formed until a radius equal to the radius R of the welding gauge is obtained, in order to prevent the forming of the lateral parts of the billet in the welding gauge. In this case, the force from the side of the welding gauge rolls is concentrated mainly on edge compression. In this case, the centers of radii R are located on the major axis B of the cross section of the oval cylinder, which additionally provides an increase in the compression force of the welded edges. The conjugation of the two side parts of the profile is made along an arc of a circle in order to prevent the formation of marks on the surface of the workpiece.

It was experimentally established that when the ratio of the major axis of the oval cylinder B to the small H less than 1.03, the edges of the workpiece are not compressed enough, formation of imperfections is possible, and the weld strength is low.

When the ratio of the major axis B of the oval cylinder to the small H is more than 1.30, the edge compression is too large, which leads to an increased burr, it is also possible to lose the stability of the edges in the welding gauge and, as a result, the formation of the edge offset defect (table).

Method implementation examples

On a tube-welding unit (TESA) “19-50” in eight horizontal and seven vertical stands from a strip of 1.5 × 140 mm, continuous multi-junction forming of a pipe billet for a pipe with a diameter of 46 mm in the form of an oval cylinder with a slit (profile 1) is carried out, small axis which H is equal to the diameter of the subsequent round welding gauge with a diameter of 46 mm (pipe diameter), and the major axis B has a length of 53.59 mm. Moreover, the preform is molded to obtain mating side parts with radii R = 23 mm equal to the radius of the welding gauge, the centers of which are on the major axis B of the oval cylinder, and the ratio of the major axis to the minor axis is B: H = 53.59 mm: 46 mm = 1.165 . The edges of the molded tube billet are heated by high-frequency currents using an annular two-turn inductor and compression is welded in a round welding gauge (profile 2). Samples of 100 mm in length are cut from the finished pipe and the strength of the weld is evaluated by a distribution test.

After finishing, the finished pipe is cut with circular saws to measured lengths, sorted out and packaged in bundles.

Implementation options of the proposed method and the prototype method, as well as indicators of the strength of the seam and the effectiveness of various options for forming pipes are shown in the table.

It follows from the table that when using the proposed molding method (options 2-4), the maximum strength of the welded joint is achieved and the yield is maximized. With transcendental values of the declared parameters (options 1 and 5) and with the implementation of the prototype method (option 6), a decrease in the level of strength of the weld is observed.

The technical and economic advantages of the proposed method consist in the fact that during its implementation the strength of the weld is increased, there are no defects and the yield is increased. As a basic object in determining the technical and economic efficiency of the proposed method, the prototype method was selected. Using the proposed method will increase the profitability of the production of longitudinal steel welded pipes by 5-10%.

Literature

1. A.P. Grudev and other rolling technology. M .: Metallurgy, 1994, p. 604.

2. RF patent No. 2056961, B 21 C 37/08, 1996.

3. Auto USSR No. 1613213, B 21 C 37/08, 1990 - prototype.

Claims (1)

A method of manufacturing an electric-welded straight-seam pipe, comprising forming from a tape a tube stock in the form of an oval cylinder with a slit, the minor axis of which is equal to the diameter of the subsequent round welding gauge, heating the edges and welding them by compression in a welding gauge, characterized in that the workpiece is formed to obtain symmetrical parts with radii equal to the radius of the welding gauge, the centers of which are located on the major axis of the oval cylinder, and the ratio of the major axis to the minor axis is 1.03-1.30.