CS270371B1 - Welding method for precision square tubes - Google Patents

Abstract

The solution falls into the field of welding relatively long square tubes, e.g. from austenitic materials with the addition of boron B, by electron beam. It is mainly used in nuclear or chemical engineering. The essence of the solution is welding with a concentrated energy stream, e.g. by electron beam, in which the ends of individual tubes are machined exactly perpendicular to the axis of the edge and then the ends are brought together, clamped and the end joints are then welded while the tubes are rotated together. During this welding, the walls rotate 40 to 70% faster than the edges. The changes in the rotation speed are smooth.

Description

The invention relates to a method of butt welding square tubes with a concentrated energy stream, for example an electron beam, which results in a square tube of very precise dimensions, especially made of austenitic steels with the addition of boron B.

When producing square tubes and similar profiled shapes, which are not part of the standard range of rolling mills or drawing mills, the method of production by welding from suitably pre-bent shell parts is usually chosen. This is especially the case when using special materials, for example with a large shape memory. In the field of nuclear engineering, there is a current need to produce hexagonal tubes from austenitic stainless steel with boron B and with various basic tube dimensions, including different thicknesses of the base material or with its various modifications. At the same time, the total quantity required is usually very small, so that a metallurgical order would be unprofitable. '

Therefore, this industry mostly uses its own method of producing precise square pipes, which consists of welding, for example, two pre-bent troughs of the required length, which are welded in the usual way with a longitudinal weld. In nuclear engineering, it is necessary to maintain precise dimensions, especially external ones, and therefore it is necessary that the pre-bent is precise and that the machining at the weld seams is also precise. However, sheets as a starting material, and especially sheets made of austenitic steel, return somewhat to their original shape after being pre-bent to the required shape, even over time. Therefore, it is possible to obtain the precise shape of the pre-bent only in a die, in which the shape memory of the sheet was taken into account during production, and therefore precise machining of edges and bevels is only possible in a similarly dimensioned fixture. However, the subsequent welding of pre-bent troughs often results in deformations in the transverse and longitudinal directions due to irregular temperature effects on the material, sometimes changing the original shape of the pre-bent edges and making it impossible to effectively join the pipe ends by butt welding. The current technology is therefore very complicated and does not ensure sufficient accuracy of the final product. Therefore, welding must be followed by straightening or calibration, usually with problematic results. If it is then necessary to alternatively change the pipe dimensions or the thickness of the starting sheet metal, the pressing dies and fixtures for machining the weld seams must be manufactured again.*

The above-mentioned shortcomings are significantly reduced by the method of end welding of precision square tubes according to the invention, using a stream of concentrated energy, in particular an electron beam, whereby the ends of the individual tubes are machined exactly perpendicular to the axis of the edge and then brought together with the end edges, clamped and the end joints are then welded while the tubes are rotated together. The essence of the invention lies in the fact that the tube walls rotate 40 to 70% faster than the edges, with the changes in the rotation speed being smooth.

The advantage of the method of butt welding of precision square tubes according to the invention is its simplicity and adaptability when changing the width of the tube walls. This change is solved by a simple adjustment of the tube rotation cycle. The tubes can be manufactured from any alloyed materials and also from laminated sheets. Sheets of any thickness can be used as semi-finished products and the method itself requires only a minimum of preparations in comparison with previous methods.

Example: To create a square, hexagonal tube for a nuclear reactor control rod, austenitic stainless steel sheet saturated with boron B was used, which, when bent by 20 to 30°, shows cracks at the bend point. Two 1,000 mm long tube blanks were made from this 3 mm thick sheet. Both blanks were machined in a jig on their end contact surfaces exactly perpendicular to their axis. They were then brought together with these end surfaces so that all edges were always in line and were welded with an electron beam at a continuously variable rotation. The rotation speed was continuously varied so that the tube walls rotated together 66% faster than the edges, and so that the edges were slightly longer under the influence of the electron beam than the walls. This was to ensure that the thicker layer of material on the tube edges was well welded. After removal from the jig, it was found that a 2 m long pipe had been created within the permitted dimensional tolerances.

Claims (1)

2 CS 270 371 Bl OBJECT OF THE INVENTION A method of butt welding precision square tubes by welding with a concentrated energy stream, in particular with an electron beam, whereby the ends of the individual tubes are machined exactly perpendicular to the axis of the edge and then brought together with the end edges, clamped and the end joints are then welded while the tubes are rotated together, characterised in that the walls rotate 40 to 70% faster than the edges, with the changes in the speed of rotation being smooth.