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Arc Welding

Electric arc consumable nozzle welding

The electric arc welding with consumable nozzle (EWCN) is the new technological process developed at the PWI for joining steel parts of 16-250 mm thickness. Being the variety of a vertical electric arc welding with a forced weld formation, it is characterized by using a special electrode with an insulating coating, arranged in a gap between the edges being welded and having a role of a consumable nozzle, through which a feeding of welding wire (from one to four) is realized during the welding process. Welding is performed into a narrow gap (8-20 mm) without edge preparation, thus providing the high efficiency of the process (deposition coefficient reaches 22-24 g/Ah) at moderate specific heat input (25-50 kJ/cm2).

Two variants of the process have been developed (Figure 1): with a fixed nozzle for welding parts of 16-80 mm thickness and with a movable nozzle for welding of a compact section of thickness up to 250 mm. In the first variant the width of electrode is equal to thickness of parts being welded, in the second variant a narrow electrode is used, making reciprocal movements (oscillations) in a gap between the edges being welded to provide their complete penetration.
Specialized equipment and welding consumables have been designed for this method, allowing producing quality welded joints, including those in welding in site and field conditions.
The method of welding was patented in Ukraine (Patent No.68361) and Russia (Patent No.2219021).

The advantages of electric arc consumable nozzle welding are as follows:

  • high efficiency up to 20 kg/h of deposited metal;
  • capability to weld thick metal for one pass;
  • minimum expenses for edge preparation, grooving is not required;
  • capability of narrow-gap welding;
  • high level of process mechanization;
  • simplicity and mobility of equipment that allows the process to be used in site and field conditions.
On the basis of the above-mentioned process, the technology of welding cathode pins (blooms) of electrolyzers of 90x180, 80x220 and 115x230 mm section was implemented at aluminium plants of Russia (more than 16 000 welds were welded). Figure 2 shows the ADPM type machine for welding blooms under the site conditions, which can be also used in manufacture and repair of metal structures of electrolyzers (housings), including conditions under the effect of magnetic fields in electrolysis shops.

Table 1. Technical characteristics of machine ADPM

Rated voltage of d.c. mains, V
(Machine is supplied from welding source connector)
27/36
Rated welding current, A at duty cycle = 100% 800
Diameter and amount of wires, mm x pc 2,4 x 2
Ranges of adjustment of electrode wire feed speed, m/h 50 300
Speed of electrode movement, m/h 4 12
Electrode travel, mm 200
Range of thicknesses being welded, mm
- with a fixed nozzle
- with a moving electrode
 
16-40
40-250
Dimensions LxWxH, mm 990x500x930
Mass of machine without wire, kg, not more than 65
 
As to rail welding, the machine of ARS type has been designed. Welding is performed by a moving nozzle, making reciprocal movements of a variable amplitude, owing to which a complete penetration of edges being welded is realized over the full section of the rail. Characteristics of the ARS machine are given in Table 2, and mechanical properties of welded joints are given in Table 3.
The process allows 24 times increase in productivity of works as compared with traditional methods of welding.

Table 2. Technical characteristics of machine ARS

Rated voltage of d.c. mains, V
(Machine is supplied from connector of welding source FORSAZh-500)
27/36
Power, consumed by source, kVA, not more than 20 (3x380 V)
Rated welding current, A, at duty cycle = 100% 400
Diameter of used flux-cored wire, mm 2,4
Ranges of adjustment of electrode wire feed speed, m/h 50 300
Speed of electrode movement, m/h 4 12
Electrode travel, mm 180
Frequency of electrode oscillations, Hz 0,5 2
Amplitude of electrode end oscillations, mm 0 20
Dimensions LxWxH, mm 1320x520x850
Mass of machine without wire, kg, not more than 60
 

Table 3. Mechanical properties of welded joint of rail R65

Hardness of weld metal 280 320
Tensile strength of weld metal 850 900 MPa
Results of tests for static bending:
- fracture load
- bending
 
1500 1650 kN
16 22 mm
 

Field of application:

  • manufacture of industrial-purpose metal structures of low-carbon and low-alloy steels of 16-80 mm thickness;
  • welding of parts of a compact section in machine building, including those of a variable section of up to 250 mm thickness;
  • welding of butts of different-purpose rails (railway, tram, crane) in construction and repair of tracks.


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