A welding electrode is a piece of wire or rod, which can be of metal or alloy and has a flux with or without flux and carries an electric current to obtain sufficient heat for welding.
At one end it is fastened to a holder and an arc is installed at the other.
Types of welding electrode
Depending on the function, electrodes can be classified as follows:
- Non-Consumable Electrode
- Consumable electrode
- These electrodes do not fuse at the time of welding and only act as electrical conductors that generate arcs to obtain sufficient heat, called none-consumable electrodes, and they are made up of high melting point metals Such as tungsten ( melting point 6150 °F), carbon (melting point 6700).
These electrodes do not melt while welding, and a separate filler wire is required with these electrodes to fill the joint. However, due to the evaporation and oxidation of the electrode during welding, the length of the electrode decreases with the passage of time.
No consumable electrode may be classified as follows:
a- Carbon or Graphite electrodes
b- Tungsten Electrodes
Non-consumable electrodes often have copper-coated carbon or graphite electrodes. The copper coating increases the electrode’s electrical conductivity or current conduction capacity.
Carbon electrode and graphite electrode
Carbon Electrode is less expensive than graphite electrodes. The resistive capacitance inside the carbon electrode is higher as compared to the graphite electrode, as a result, this current stream takes comparatively less, short life due to soft material while the graphite electrode is more expensive, carrying current more because of less electrical resistance. Its material is hard and brittle, thus the carbon electrode has longer life compared to the carbon electrode.
The next electrode in the series of non-consumable electrodes is tungsten which can be basically classified as follows:
Zirconiated tungsten, (0.3 to0.5%)
Thoriated tungsten (1 -2%).
In pure tungsten the alloy increases, resistance to contamination, arc stability, and electrode life. In addition, arc initiation is easy, the electrode tip remains cold (compared to pure tungsten electrodes), electrode consumption is low, and current carrying capacity gains. Compared to carbon electrodes, tungsten electrodes are much more expensive and alloy tungsten electrodes are still more COStlier. Tungsten/alloy tungsten electrodes from 0.5 mm to 6 mm directors are commonly available for welding purposes
Consumable (Metallic) Electrode
These type of welding electrodes have a low melting point, and act as electrical conductors that generate arcs to obtain sufficient heat, melts the metal, and fills the joint, are called consumable welding electrodes,
Consumable electrodes can be classified as follows:
a- Bare electrode
b- Flux-covered electrode
a- Bare Electrodes:
This type of electrode requires additional shielding to protect the metal from atmospheric contamination of the molten weld pool which may be in the form of gas or flux.
b- Flux-covered electrode
This type of electrode does not require any additional shielding to protect the metal from atmospheric contamination. These are themselves coated with fluxes that would completely cover the weld pool as slag at the time of welding. And are subsequently removed after cooling.
Flux Covered Electrodes
Electrode coating ingredients
The covering/coating on the core wire consists of several materials that provide a variety of properties to the electrode.
These ingredients and their functions are as follows:
Slag forming ingredients
Slag-forming ingredients produce a lightweight slag that forms a layer on the molten metal and protects the weld pool from atmospheric contamination.
silicates of sodium, potassium, magnesium, aluminum, iron oxide, china clay, mica, etc., are responsible for the slag-forming process.
Gas Shielding ingredients,
The gas shielding ingredients produce a protective gas shield around the electrode tip arc and the weld pool.
Cellulose, wood flour, starch, calcium carbonate, etc., are used as gas shielding ingredients.
Deoxidizing elements refine the molten metal, for this ability, ferromanganese, and ferrosilicon, are used.
Purpose of using ingredients in electrodes
Proper coated ingredients produce weld metals resistant to cold and hot cracking and improve metal deposition rate.
- The coating protects the welding operator from electric shock and radiation.
- Alloying elements such as iron alloys of manganese, molybdenum, etc. may be added to provide suitable properties and strengths to the weld metal and to make up for the loss of certain elements, which vaporize during welding.
- Coating/covering Improves, weld penetration and surface finish, it limits spatter, produces a quiet welding arc, and easily removable slag.
Sizing of welding electrodes
Wires of different chemical compositions and sizes are obtained from electrode manufacturing companies. Manufacturing companies, chemically cleaned, cut into different lengths, and straightened in the electrode-making plant. Generally, electrodes come in sizes 300, 350, 450, etc.
Flux application on the Welding Electrodes
The flux coating is applied on the core wire by two methods, which are as follows:
Several core wires cut to the desired length are clamped vertically into a fixture and immersed in a bath of molten flux. When a suitable thickness of flux is glued to the core wire, the fixture is raised up and the flux is allowed to dry.
The extrusion method is much faster than the dipping method and is widely used these days.
In this method, the coating material is mixed in the desired quantity, and the resultant mass is brought to a thick, viscous, hard paste. The paste is shaped like a cylinder that is poured into the extrusion press.
The thick paste of core wire and flux are simultaneously passed through a die under pressure, thus enclosing the flux coating on the core wire. The thickness of the coating depends on the opening of the die and can be varied.
As a next step the flux from the gripping end of the electrode is removed by an electrically rotating wire brush; After which the electrodes are fed into an oven where they are dried and baked to remove excess moisture.