Filler Materials and Flux
The metals added during the welding process are known as filler materials or filler metals. Filler materials used in welding processes include welding rods and electrodes.
In welding processes in which space is left between the parts to be joined, filler metals provide the intimacy of contact necessary for coalescence.
Welding Rods
A "welding rod" refers to a filler metal, in wire or rod form, used in gas welding and brazing processes and in certain electric welding processes (tungsten inert gas) in which the filler metal is not a part of the electric circuit. A welding rod serves only one purpose - it supplies filler metal to the joint.
As a rule, rods are uncoated except for a thin film resulting from the manufacturing process. Welding rods for steel are often copper-coated to protect them from corrosion during storage. Most rods are furnished in 36-inch lengths and a wide variety of diameters, ranging from 1/32 to 3/8 inch. Rods for welding cast iron vary from 12 to 24 inches in length and are frequently square rather than round in cross section. The rod diameter selected for a given job is governed by the thickness of the metals being joined.
Electrodes
In electric welding, electrodes are important parts of the electrical circuit. They help create the arc needed to melt the metal. There are two main types of electrodes: consumable and non-consumable. Below is a breakdown of their uses and differences:
- Consumable Electrodes: These electrodes melt during welding and serve as the filler metal. They are used in processes like Shielded Metal Arc Welding (SMAW) and Gas Metal Arc Welding (GMAW). Materials can include steel, aluminum, copper, and alloys.
- Non-Consumable Electrodes: These are mostly made of tungsten. They do not melt during welding and are used in Gas Tungsten Arc Welding (GTAW). They help create the arc, but the filler metal comes from a separate rod.
- Solid Electrodes: Solid electrodes can be either consumable or non-consumable. They generally produce fewer fumes than flux-cored wire or coated electrodes.
- Covered and Coated Electrodes: These two terms are often used interchangeably in welding literature and practice. Both refer to an electrode consisting of a metal core wire with an external flux material that performs several functions during welding, such as stabilizing the arc, shielding the weld pool from atmospheric gases, forming slag, and enhancing weld properties. The choice between "covered" and "coated" generally depends on regional usage or industry preference, but there is no technical distinction between them.
Fluxes
Welding or brazing certain materials requires the use of flux to produce a sound joint. Fluxes are available as liquids, pastes, and powders. They have a melting point below that of the base and filler metals, and they are not incorporated into the weld. Their primary purpose is to prevent the formation of oxides on the weld joint before and during welding operations. Fluxes should never be used as a substitute for proper cleaning.
Observe the following precautions when you are working with fluxes.
- Unless the base metal is properly cleaned and the correct flux applied to the joint, fluxing will hinder rather than aid in making the joint.
- Flux should not be overheated, or it will fail to serve its purpose.
- Fluxes will also deteriorate if they are kept at brazing temperatures for too long.
- Fluxes should always be used in a well-ventilated space.
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4-14. What is the purpose of a welding rod?
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