In 1888, Russia invented the manual arc welding technique, using a bare metal rod without a coating to create a protective gas. It was not until the early 20th century that the Swedish electrode was developed after the Swedish invention of the Kjellberg process and the Quasi-arc method. It is worth noting that due to the high cost, people are not using the electrode electrode at first. But as people's demand for good weld quality has grown, manual arcs have also begun to use coated electrodes. An arc formed between the metal rod (electrode) and the workpiece melts the surface of the metal rod and the workpiece to form a weld pool. At the same time, the melted coating on the metal rod forms gas and slag, protecting the weld pool from the surrounding air. Because the slag cools and solidifies, the slag must be removed from the weld bead once the weld is welded (or before the next weld is welded). The manual arc welding process can only complete the welding of short welds before the welding tongs are replaced with new ones. The weld is shallow and the quality of the weld depends on the skill of the welder.
Flux / electrode type
The chemical composition of the electrode coating has a great influence on the stability, penetration, metal deposition rate and positioning ability of the arc. Welding rods can be divided into three main categories:
Cellulose type electrode; titanium oxide coating electrode; basic electrode.
1. The cellulose-type electrode contains a large amount of cellulose, which is characterized by deep arc melting and fast friction deformation, which also improves the overall welding speed. However, since the weld deposit is coarse and mixed with the flowing slag, it is difficult to remove the slag. This electrode can be used in any position and is familiar with its use in the 'stovepipe' welding technique.
Features: Deep penetration can be formed in all positions; suitable for downright welding; good mechanical properties; large amounts of hydrogen generated - risk of cracking in the heat affected zone (Haz).
2. The coating of titanium oxide electrode contains a large amount of rutile. Titanium oxide facilitates arcing, smooth arc operation, and reduced arc splashing. This universal electrode has good welding characteristics. They can be used for welding in all positions under AC or DC, especially for joint welding in the horizontal/angular position.
Features: Suitable weld metal mechanical properties; viscous slag can form a good weld bead shape; positioning welding may produce flowing slag (fluoride); easy to remove slag.
3. The alkaline electrode coating contains a large amount of calcium carbonate (limestone) and calcium fluoride (fluorite). This makes it easier to flow the slag than the slag of the titanium oxide type electrode, which is also a method to assist in the rapid cooling of vertical welding and overhead welding. These electrodes are used for welding medium and large structures and require high weld quality, good mechanical properties and resistance to cracking (excessive restraint can cause cracks).
Features: low hydrogen weld metal; high welding current/speed required; poor weld bead formation (bending and rough surface profile); difficulty in removing slag; metal powder electrode containing metal powder coating to maximize welding current Allowable current. Therefore, compared with the electrode containing no iron powder in the coating, the metal deposition speed and efficiency (metal deposition ratio) of the metal powder electrode are improved, and the slag is easily removed. Due to the fast deposition rate, iron powder electrodes are mainly used for flat welding, horizontal welding and vertical welding. Titanium oxide electrodes and alkaline electrodes have no significant arc characteristics, and the arc force is small, which reduces the penetration of the weld bead.
power supply
The electrode can be used under AC or DC power. Not all DC electrodes can be used with AC power, but AC electrodes are typically used with DC power.
Welding current
The choice of welding current depends on the size of the electrode, and the manufacturer recommends the normal operating range and welding current to the user. The standard operating range for selecting the electrode size is shown on the left. According to experience, the standard of the electrode on which the current is selected is about 40 A/mm (diameter). Therefore, a preferred current for a 4mm diameter electrode should be 160A, but the actual operating range can be 140~180A.
At present, transistor inverter technology can produce small power supplies with light weight. These power supplies are increasingly being used in construction welding, and they can be easily moved between various working points. These power supplies are controlled by power and can be used for MIG and TIG welding to improve power supply adaptability. Welding rods can now also be used in sealed containers. These vacuum-packed electrodes do not need to be baked before use. However, if the package is opened or damaged, the electrode must be re-baked according to the manufacturer's instructions.
Manual arc welding
The welding method of manually operating the electrode and using the arc as a heat source is also called hand arc welding (see figure). The electrode and the workpiece are each an electrode, and an arc is ignited therebetween. The weld core forms a weld metal with the molten metal of the workpiece, and the gas and slag generated by the electrode coating protect the molten pool, stabilize the arc and penetrate the alloy. Different types of carbon steel, low alloy steel, stainless steel, cast iron, nickel and nickel alloys, copper and copper alloys, aluminum and aluminum alloys can be welded using different welding rods. The electrode has a range of sizes from 2 to 6 mm. Small diameter welding rods are suitable for thin plates (1 to 3 mm) and welding in various positions; large diameter welding rods are suitable for flat welding and horizontal welding of thick plates. The manual arc welding machine is relatively simple, and the main components are the power supply and the welding tongs, which are convenient and flexible to use. Although the application of manual arc welding has been reduced due to the development of gas-shielded arc welding and other high-efficiency welding methods, it is still a common welding method used in various industrial sectors. It is most economical for many types and small batches of welded parts. Welding and repair welding cannot be replaced by other welding methods. However, the technical level of the welder has a great influence on the quality of the manual arc welding, so the welder must undergo rigorous training in order to perform such welding work. 
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