Electro-slag welding

The electric arc process of consumable electrode melting has successfully been used in welding practice for about 100 years. For a long time the welders were making use of an open arc only.

Thirty years ago when carrying out a mechanized welding of vertical joints on a blast furnace jacket, being mounted at the “Zaporozhstal” plant, the arc burning under a layer of a solid flux suddenly extinguished. Yet the process of welding was not interrupted but went on already as arcless one. Later on this process of arcless melting of consumable electrodes was named electro-slag welding (ESW).

A radically new method of welding in a vertical position, the ESW, came into being. Electro-slag welding is a very efficient, single pass process carried out in the vertical or near vertical position and used for joining steel plates or sections in thickness of 25 mm and above. Its characteristic feature lies in the fact that the edges to be welded are fused not by the heat of an electric arc, as in all versions of arc welding, but by means of molten flux whose temperature is much higher than the melting temperature of the metal to be welded. In its original form, plates are held vertically approximately 30 mm apart with the edges of the plate cut normal to the surface.

The ESW marked a revolutionary leap in the field of thick metal welding. In the ESW process the source of heat is pool of a liquid current-conductive slag. It turned out to be feasible, by means of one or several welding wires, when moving them along the welding gap, to maintain the slag pool of the required size in molten state in order to perform welding of large section billets in one pass.

Great changes were achieved by the process of electro slag re-melting (ESR) in which the ingots of extra class metal can be produced with the process of re-melting the consumable electrode and solidification of the molten metal in a water-cool mould.

The theoretical and practical achievements of the ESR have brought about a new qualitative leap in the development of electro slag welding process. In 1969-70, the Paton Electric Welding Institute developed two more applications new in essence: the electro slag casting (ESC), and the electro slag welding by bifilar scheme (ESWB) specially developed to solve the problem of enlargement of steel billets into blocks weighing up to 200-400 and more tons and having a weld section up to 10 m².

The principle benefits of the process are:

-speed of joint completion

-lack of angular distortion

-high quality welds produced

-simple joint preparation

-major repairs can be made simply by cutting out total weld and re-welding.

The principal risks.

Electro slag welding is not one of the major welding processes because the high heat input generates large, coarse grained weld metal and heat affected zones, which lead to poor fracture toughness properties in these areas. Toughness improvement can only be achieved by post-weld normalizing treatment. Additionally, the near parallel-sided geometry of the weld, combined with the coarse grains, can make it difficult to identify defects at the fusion boundary by standard ultrasonic techniques.

The process has considerable potential for increasing productivity. However, its use has been limited because of relatively poor understanding of the process and, for specific applications, the significance of the fracture toughness values. As a result, use of the process has been restricted to a few applications.

Exercises

1. Learn the new words and word combinations:

consumable -той, що плавиться

blast furnace jacket -кожух доменної печі

layer of a solid flux -шар твердого флюсу

to interrupt -переривати

leap -стрибок

source of heat -джерело тепла

pool of a liquid current -ванна рідкого

conductive slag електропровідного шлаку

feasible -можливий

welding wires -зварювальні дроти

welding gap -зварювальний зазор

billet -заготівка

in one pass -за один прохід

ingot -зливок

mould -ливарна форма

achievement -досягнення

application -застосування

new in essence -принципіально новий

casting -лиття

bifilar scheme -біфілярна схема

cross-section -поперечний переріз

Дата добавления: 2015-11-16