RU2240882C2 - Electrically welded straight-seam tube making method - Google Patents

Abstract

FIELD: rolled stock production, namely process of continuous manufacture of electrically welded straight-seam tubes.

SUBSTANCE: method comprises steps of forming tube blank from band; elongating tube blank at elongation factor 1.005 - 1.012; welding it in welding stand by means of annular inductor; determining position of annular inductor relative to point of edge meeting at stepwise removing it relative to point of edge meeting along axis of tube blank until elimination of occurring of metal splash out in edge meeting point at heating edges until their fusion.

EFFECT: enhanced quality of welded seam, elimination of incomplete fusion, saw-tooth like fins, less loss of yield.

1 tbl, 1 ex

Description

The invention relates to rolling production, and more particularly to the continuous production of longitudinally welded pipes.

A known method for the production of longitudinal welded pipes, including feeding the strip, forming the strip into the pipe billet, welding longitudinal edges and calibrating the pipe [1].

The disadvantage of this method is the low quality of the weld due to the formation of imperfections and line defects of the seam.

A known method of manufacturing longitudinal welded pipes, comprising forming a tape into a pipe billet in a number of successively arranged calibers, flattening the edges and welding them in a welding gauge [2].

The disadvantages of this method are the low quality of the weld, the possibility of the formation of imperfections and line defects of the seam, which reduces the yield.

Closest to the proposed invention in its technical essence and the achieved results is a method of manufacturing an electric-welded straight-line pipe, including forming a tube billet from a tape, heating the edges with high-frequency currents with a ring inductor, flattening the edges to converge and welding during compression in a welding stand [3] - prototype.

The disadvantages of this method are the low quality of the seam due to the formation of imperfections, sawtooth fillets and, as a result, low yield.

The technical problem solved by the invention is to improve the quality of the weld, the elimination of imperfections, sawtooth burr and increase yield.

To solve the technical problem in the known method, including forming a tube billet from tape, heating the edges with high-frequency currents with a ring inductor, reducing the edges to converge and welding in a welding stand, according to the proposal, a tube billet is drawn in a welding stand equal to 1.005-1.012, and the position of the ring inductor relative to the point of convergence of the edges is determined by its step-by-step removal from the point of convergence of the edges along the axis of the pipe billet to exclude the formation of a splash of metal at ke convergence of the edges when heating the edges to reflow.

The invention consists in the following. To ensure good quality of the weld, the heated edges after converging must be compressed with sufficient compressive stresses, which are achieved by drawing in the welding stand, equal to 1.005-1.012. This range of hoods provides optimal compressive stresses and does not lead to loss of stability and edge displacement during welding. When the edges are heated by a ring inductor, an electromotive force is induced in the tube billet. The current, passing along the perimeter of the pipe billet and meeting an open slot in its path, deviates to the point of convergence of the edges, reaching a maximum concentration in it. Moreover, due to electromagnetic repulsive forces during metal melting, a splash of liquid metal from the edge compression zone is possible. When a part of the metal splashes up and down from the edge compression zone, the edge compression stresses sharply decrease due to a lack of metal, which leads to a weakening of the seam, the formation of a sawtooth burr and partial periodic lack of penetration. With significant splashes, fistulas and other line defects are possible. Increasing step by step the distance from the ring inductor to the point of convergence of the edges, find the position of the ring inductor at which splashes are not guaranteed to form, since the metal at the point of convergence does not have time to melt. In this case, the weld is formed uniform in length, without lack of fusion, line defects and sawtooth, which allows to improve the quality of the weld and increase the yield.

The optimal position of the inductor relative to the point of convergence of the edges depends on the geometric dimensions of the pipe, the design features of the inductor supplied to the inductor of electric power, the speed of the pipe billet, the angle of convergence of the edges, the chemical composition of the steel and other parameters, so it is impossible to determine it in advance. The step-by-step removal of the inductor from the convergence point to the disappearance of visually observed metal bursts ensures the exact location of the inductor at the front end of the endless tube billet, and all subsequent welded pipes have a high-quality weld.

An exhaust in the welding stand is necessary in order to provide sufficient compressive stresses at the edges when welding the pipe.

It was experimentally established that when drawing less than 1.005, the edges of the workpiece are not sufficiently crimped, the formation of imperfections is possible, and the weld strength is insufficient.

When drawing in the welding stand for more than 1.012, there is an increased gratuity, a loss of stability of the pipe edges and their displacement relative to each other is possible, which leads to the defect “displacement of the edges”, weakening of the weld strength and an increase in the curvature of the finished pipe.

The position of the ring inductor is regulated in order to eliminate splashes of liquid metal during welding at the point of convergence of the edges and, as a result, to eliminate lack of penetration and other construction defects. An annular inductor is installed as close as possible to the point of convergence of the edges, and on the stationary tube billet, a short-time welding current is switched on until the edges are melted. In this case, the presence of a splash at the point of convergence of the edges is visually determined. If there is a splash, the inductor is removed one step from the point of convergence of the edges along the axis of the workpiece and the described operation is repeated in a new section of the pipe workpiece. Removal of the inductor is carried out until the splashes disappear. A further increase in this distance leads to a decrease in temperature and depth of heating of the edges and to a deterioration in the strength of the seam.

An example implementation of the method

On a tube-electric welding unit (TESA) “19-50” from a strip of 1.5 × 132 mm, continuous multi-junction molding of a steel billet pipe is carried out in eight horizontal and seven vertical stands, the edges of the molded tube billet are heated by high-frequency currents using an annular double-coil inductor, reduce the edges to their convergence and carry out welding in the welding stand. In the welding stand carry out the extraction of the workpiece, equal to 1.01 in rolls with calibers. Moreover, the position of the ring inductor relative to the point of convergence of the edges is determined at the front end of the fixed tube billet by its step-by-step removal from the point of convergence of the edges along its axis to eliminate the formation of a splash of metal at the point of convergence of the edges when the edges are heated to reflow.

Samples of 100 mm in length are cut from the finished pipe and tested for distribution.

The finished pipe with a diameter of 42 mm is cut with circular saws to measured lengths, sorted out and packaged in bundles.

Variants of the method and indicators of the quality of the seam and the effectiveness of various options for forming pipes are given in the table.

The table shows that when using the proposed molding method (options 2-4), the best quality of the seam is achieved, there are no defects and the yield is maximized.

With exorbitant values of the declared parameters (options 1 and 5) and the implementation of the prototype method (option 6), there is a decrease in yield due to the occurrence of lack of fusion, which also leads to a decrease in the level of strength of the weld.

The technical and economic advantages of the proposed method consist in the fact that when it is implemented, the quality of the weld is improved, the number of imperfections is reduced 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 steel longitudinal welded pipes by 15-20%.

Sources of information

1. Auto USSR No. 1489868, cl. B 21 C 37/08, 37/06, 1989.

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

3. A.P. Kolikov et al. Machines and assemblies of pipe production. M .: MISIS, 1998, p. 35-36 - prototype.

Claims (1)

A method of manufacturing an electric-welded straight-seam pipe, including forming a tube billet from a tape, heating the edges with high-frequency currents with a ring inductor, flattening the edges before converging and welding in a welding stand, characterized in that the workpiece is drawn in a welding stand equal to 1.005-1.012, and the position ring inductor relative to the point of convergence of the edges is determined by its stepwise removal from the point of convergence of the edges along the axis of the pipe billet to prevent the formation of a splash of metal at the point of convergence of the edges when heating the edges to reflow.