Welding is the process of creating joints between metals where other modes of establishing stable junctions within structures are insufficient. This requires heating the metal components to be joined so that a fusion between them can occur once the materials have sufficiently cooled.

Welding can occur between materials made of the same kind of metal or between materials of different composition. A wide variety of welding types and tools exist for the purpose of creating stronger joints in buildings, bridges and other wide-scale everyday applications.

Arc welding involves the use of an electric arc generated by current in the welding tool, known as an electrode. One common such electrode is the 7018 or E7018 electrode, which gets its label from a standard nomenclature system.

• Arc welding: This has become the most common technique in the construction industry for most large-scale needs. The 7018 and the 6010 are typical examples. Temperatures in this process can reach 7,000 degrees Fahrenheit.

  
  
  Oxyfuel gas welding: Also known simply as gas welding, this type of welding makes use of heated gas to generate a flame suitable for making welds. Oxyacetylene and oxyhydrogen are common varieties.
  
  Resistance welding: If you have ever done "spot welding" in shop class in school, this is an example of resistance welding. Here, a current is used to heat sheet metal, which warms because it resists the flow of current, liberating significant amounts of heat.
  
  Solid-state welding: In this unusual type of welding, the metals are not melted. Instead, advantageous combinations of temperature and pressure are used to create the joint. 
  
  Other types of welding: Electron-beam welding, slag welding, laser-beam and thermite welding represent especially modern forms of the technique.

The formal name of stick welding is "shielded metal arc welding," and the two are often used interchangeably, though this is imprecise.

As the name implies, the arc welding tool is an electrode in the shape of a stick. The electrode itself contains a consumable element, meaning that it is burned as the weld is generated. The heat is created using electric current delivered to the area from an external source to maintain a voltage difference.

As the weld is made, a film of gas is released from the electrode materials to protect the hot electric arc (a tiny gap) between the electrode tip and the metal surface of the objects being welded. The part of the electrode that is consumed in effect serves as filler or glue to tighten the weld further as the materials cool.

Welding rods are given three or four digits. In the case of a four-digit number, the first two represent the lowest tensile strength of the weld the electrode creates in thousand of pounds per square inch (psi); thus, "61" means 61,000 psi, or 61 ksi (ksi = kilopound per square inch).

The next two numbers give independent information. The first, which is 1, 2 or 4, indicates the physical position in which the tool can be used. The last two numbers in combination indicate the type of electrode coating and the correct polarity (positive or negative) or current (AC or DC) to use.

You can now determine the characteristics of the 7018 electrode meaning from the four-digit classification scheme detailed above, in combination with a standard chart like the one in the Resources.

The "E" in E7018 electrode indicates a tool used for an arc-welding process. The 70 means it makes welds that are very strong (70,000 psi). The 18 means two things: The "1" means the electrode can be used in any position, and the "18" means low hydrogen and usually DC current.