Types Welding Electrodes explained – Non consumable-Consumable electrodes

The piece of wire or rod used to carry current for welding is known as an electrode or welding electrode. It may or may not have flux covering. The electrode produces arc at one end and other end is gripped by a electrode holder. In this article we will discuss the classification of welding electrode as well as explain different welding electrodes types.

Types of Welding Electrodes explained  


welding electrode classification

different types of welding electrodes

For having a clear knowledge about different electrodes I would advisable to have a look at the above mentioned images.
Welding electrode is mainly classified into two broad categories
1. Non-consumable electrodes and
2. Consumable electrodes

Non-consumable or Refractory Electrodes  

Non-consumable electrodes are those which do not melt away or consumed during the welding process. These electrodes involves the use of high melting point materials such as carbon - MP 6700 degree Fahrenheit, pure tungsten MP 6150 degree Fahrenheit, or alloy tungsten. 

Main features of non-consumable welding electrode 
  • While welding with these electrodes a filler metal is needed to fill up the gap between the two metal parts. 
  • These are used in carbon arc welding and Tungsten Inert Gas (TIG) welding .  
  • Tungsten electrodes are much costlier than carbon or graphite electrodes. Tungsten alloy electrodes are costlier. 

Consumable Electrodes 

This electrodes are low melting point electrodes. When electrode and job is struck the arc starts to melt the end of the electrode. The molten electrode is transferred to the job in the form of metal droplets.  

Main features of Consumable welding electrode
  • these are more thermally efficient than non consumable electrodes. 
  • They are made of different materials depending upon the need and the chemical composition of metals to be joined. 
  • These are used in MIG welding in the form of bare electrode. 
  • Most commonly used core material is mild steel, low alloy steel and nickel steel. 
  Consumable electrodes can be classified in the following groups

1. Bare electrodes: They don't have any flux coating only the alloy or the metal wire.
2. Light coated electrodes: These are electrodes having coating factor of 1.25 . coating factor = diameter of the electrode / diameter of the core wire .
example : Citobest electrode from AO or Advani Oerlikon.
3. Medium coated electrodes: These have coating factor of about 1.45 .
example : Overcord
4. Heavily coated electrode : Coating factor is between 1.6 and 2.2 . example : citofine .

Covered electrodes can be classified as follows :

  • electrodes having cellulose 
  • Rutile (titania)
  • Electrode having iron oxide 
  • Electrode with iron powder 
  • Low hydrogen electrode   
welding electrode

Welding Electrode Explained in details 

  • Need of filler metal 

Depending upon the material of the electrode, it may melt and supply filler metal; if it is non-consumable, a separate filler metal addition becomes necessary. 

  • Core Wire composition 

The core wire is prepared by keeping in mind the type of metal to be welded. The composition of core wire is different for each metal. When mild steel is needed to be welded the core wire must have have similar composition to get a homogeneous weld joint. 

  • The size and length of the welding electrode 

The size (diameter) of the electrode core wire totally depends on the amount of metal deposition needed and the type of gap between the two metal plates to be joined. The length of the core depends of the electrical resistance, rigidity and diameter of the electrode. Typical coated electrode dimensions are 150 to 460 mm (6 to 18 in.) in length and 1.5 to 8 mm (j to in.) in diameter. As the thickness of the sections to be welded decreases, the required current and electrode diameter also decrease.

  • Current Requirements 

If bigger diameter welding electrodes are used then the requirement of the current will also be higher.


  • Specification of the welding electrodes 


Specifications for electrodes and for filler metals, including dimensional tolerances, quality control procedures, and processes, are stated by the American Welding Society (AWS) and the American National Standards Institute (ANSI); some appear in the Aerospace Materials Specifications (AMS) by the Society of Automotive Engineers (SAE).

  • Welding electrode numbering system 


Electrodes are identified by numbers and letters (Table 27.2), or by color code, particularly if they are too small to imprint with identification.


 
welding electrode numbering system
 Among other requirements, the specifications state that

(a) the wire diameter must not vary more than 0.05 mm (0.002 in.) from nominal size, and
(b) the coatings must be concentric with the wire.


Welding Electrode is sold by weight and are available in a wide variety of sizes and specifications. Selection and recommendations for electrodes for a particular metal and its application can be found in supplier literature and in the various handbooks

  • Electrode coating 

Claylike materials are used to coat the electrodes. These materials include silicate binder as well as powdered materials such as various oxides, metal alloys, fluorides and carbonates and cellulose. Cellulose includes cotton cellulose and wood flour. 
Brittle electrode coatings has some functions and they take part in complex interactions at the time of welding. The basic functions are 

a) they help in stabilizing the arc. 
b) Act as shield against the surrounding environment by producing gases. The gases produced are mainly carbon dioxide CO2 and water vapor and small amounts of carbon monoxide CO and Hydrogen. 
c) They control the rate at which the electrode melts. 
d) Act as a flux and protect the weld joint against the formation of oxides and other inclusions. The resulting slag also protects the molten weld pool. 
e) These coatings add alloying elements in the weld zone and enhances the properties of the weld joint. Deoxidizers help the joint from becoming brittle. 

To ensure a good weld the deposited coating or slag must be removed after each pass. A wire brush can be used for cleaning the deposited coating. 
Bare electrodes are also available which are made of stainless steel of aluminum alloys. 


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