SU540712A1 - The method of welding pipes made of aluminum and its alloys with a tube sheet - Google Patents

Description

one

The invention relates to methods of connecting aluminum pipes of small diameter with a massive pipe grid and can be used in the manufacture of heat exchanging equipment in the crystal engineering, as well as in other industries.

There is a known method of joining aluminum pipes with a tube sheet, in which an annular ledge with a thickness equal to the thickness of the pipe wall is made on the grid around each hole.

The disadvantages of this method are the time-consuming processing of the lattice and the increased spacing between the pipes due to the protrusions, which increases the cost of the heat exchanger, in addition, the difficulty of welding pipes of minimum diameter and thickness and the possibility of through pores in the jurater.

The aim of the invention is to develop a method for joining aluminum thin-walled pipes of small diameter with a massive tube sheet, which forms a reliable connection.

This goal is achieved through the use of an aluminum alloy layer, on the coated tube surface of the tube sheet and having a lower melting temperature as compared to ic material of M tubes, and

also the use of a corrosion-resistant flux for cryogenic apparatuses.

The proposed method is illustrated in the drawing.

Due to the large difference in thickness to be welded and the possibility of cracking, it is difficult to weld the aluminum tubes directly into the aluminum tube sheet without these protrusions or using filler wire. During welding, pipes overheat and melt before the high-mass tube sheet material reaches its melting point. Additive use

wire to eliminate cracks when welding thin-walled pipes of small diameter is almost impossible. In the implementation of the proposed / method, the role of filler material is performed by a cladding layer of an aluminium alloy. Its lower melting point allows to achieve the simultaneous melting of the pipe and cladding layer during welding and to obtain a reliable connection. To eliminate the oxide film and obtain

After the usual preparation of the edges for welding, the required penetration depth is additionally applied with an alcoholic flux solution, which contributes to a better destruction of the oxide film in the gap between the pipe and grille, and

The thickness of the deposited layer of aluminum alloy must be at least five times the thickness of the welded pipes.

The proposed method is carried out as follows.

For the fabrication of tube sheets 1 or using sheets clad with aluminum alloy 2 of the desired composition, or a layer of alloy 2, characterized by a lower melting temperature and good fluidity, is specially applied onto sheets of the required grade. In grill 1, holes 3 are drilled out in accordance with the diameter of pipes 4. First, preparation for welding of the grid 1 and pipe 4 is carried out according to the usual technology for aluminum alloys: degreasing, etching in caustic soda solution followed by clarification in nitric acid solution. Then, the surfaces to be welded are additionally treated with an alcoholic solution of a flux safe from the point of view of corrosion for the specified operating conditions. The pipes 4 are inserted into the holes 3 flush with the tube sheet 1. Welding in shielding gas with a non-consumable electrode is used. The welded joint is formed by fusing the pipes 4 with the alloy 2 covering the entire surface of the grid 1.

The best results are obtained with the use of micron-plasma welding on alternating current, which, compared to argon-arc welding, provides greater arc stability at low currents and an increased penetration depth.

In order to increase the reliability of the joints, as well as to eliminate the gap between the pipes 4 and the holes 3 in the grill 1 in order to increase the explosion safety, the proposed method may provide for the expansion of the pipes 4 before or after welding. In addition, it is possible to use preheating or concomitant welding for heating the pipe grid 1 assembled with pipes 4.

Claims (1)

Invention Formula The method of welding pipes made of aluminum and its alloys with a tube grid with a non-consumable electrode in a protective gas environment, characterized in that, in order to improve the quality when welding thin-walled pipes, a low-melting layer is applied to the entire surface of the grid without welding alloy, with the welded joint is obtained by fusing pipes with a clad layer.