The main advantage of manual metal arc (MMA) gouging is that the same power source can be used for welding, gouging, or cutting, simply by changing the type of electrode.
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As in conventional MMA welding, the arc is formed between the tip of the electrode and the workpiece. MMA gouging differs because it requires special purpose electrodes with thick flux coatings to generate a strong arc force and gas stream. Unlike MMA welding where a stable weld pool must be maintained, this process forces the molten metal away from the arc zone to leave a clean cut surface.
The gouging process is characterised by the large amount of gas which is generated to eject the molten metal. However, because the arc/gas stream is not as powerful as a gas or a separate air jet, the surface of the gouge is not as smooth as an oxyfuel gouge or air carbon arc gouge.
According to the size of gouge specified, there is a wide range of electrode diameters available to choose from. These grooving electrodes are also not just restricted to steels, and the same electrode composition may be used for gouging stainless steel and non-ferrous alloys.
MMA gouging can be carried out using conventional DC and AC power sources. In DC gouging, electrode polarity is normally negative but electrode manufacturers may well recommend electrode polarity for their brand of electrodes and for gouging specific materials. When using an AC power source, a minimum of 70V open circuit (OCV) is required to stabilise the arc.
Although most MMA welding power sources can be used for gouging, the current rating and OCV must be capable of accommodating current surges and longer arc lengths.
Guidance on gouging parameters can be found below:
Typical operating data for MMA gouging Electrode diameter (mm)Current (A)Gouging dimensionsGouging speed (mm/min) Depth (mm)Width (mm) 3.2 210 2 6 4.0 300 3 8 4.8 350 4 10 800The arc is struck with an electrode which is held at a normal angle to the workpiece (15 degrees backwards from the vertical plane in line with proposed direction of gouging). Once the arc is established, the electrode is immediately inclined in one smooth and continuous movement to an angle of around 15-20 degrees to the plate surface. With the arc pointing in the direction of travel, the electrode is pushed forward slightly to melt the metal. It should then be pulled back to allow the gas jet to displace the molten metal and slag. This forward and backward motion is repeated as the electrode is guided along the line to complete the gouge.
To produce a consistent depth and width of gouge, a uniform rate of travel must be maintained, together with the angle of electrode: 10-20 degrees. If the electrode angle becomes too steep, in excess of about 20 degrees, the amount of slag and molten metal will increase. This is a result of the arc penetrating too deeply. Digging the electrode into the metal causes problems in controlling the gouging operation and will produce a rough surface profile. For gouging in positions other than vertical, the electrode is always pushed forward. With vertical surfaces, the electrode is directed and pushed vertically downwards.
MMA gouging is used for localised gouging operations, removal of defects for example, and where it is more convenient to switch from a welding electrode to a gouging electrode rather than use specialised equipment. Compared with alternative gouging processes, metal removal rates are low and the quality of the gouged surface is inferior.
When correctly applied, MMA gouging can produce relatively clean gouged surfaces. For general applications, welding can be carried out without the need to dress by grinding. However when gouging stainless steel, a thin layer of higher carbon content material will be produced - this should be removed by grinding.
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This Job Knowledge article was originally published in Connect, July/August . It has been updated so the web page no longer reflects exactly the printed version.
Gouging and welding are two distinct processes commonly used in metalworking and fabrication. While both involve the manipulation and shaping of metal, they serve different purposes and utilize different techniques. In this article, we will explore the key differences between gouging and welding processes, their applications, and the tools used for each.
Gouging is a metal removal process that involves cutting or removing material from a workpiece to achieve a specific shape or prepare the surface for subsequent operations. The primary purpose of gouging is to remove unwanted material, such as excess weld metal, defects, or old welds. Gouging is typically performed using specialized tools and techniques, such as carbon arc gouging, air carbon arc gouging, or plasma gouging.
Gouging requires specific tools and equipment designed for metal removal. These may include carbon electrodes, gouging torches, air carbon arc gouging systems, or plasma gouging equipment. The tools generate intense heat and produce a focused arc or plasma stream to melt and remove the metal.
Gouging Torch K
Gouging involves the controlled melting of the metal using heat generated by an electric arc or plasma. The operator manipulates the gouging tool over the workpiece, directing the arc or plasma stream to remove material. The depth and width of the gouge can be adjusted based on the desired result.
Gouging is commonly used in various applications, such as:
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Weld preparation: Gouging is often employed to remove excess weld metal or defective welds, creating a clean and sound base for subsequent welding operations.
Repair and maintenance: Gouging is used to remove damaged or worn-out components, such as machinery parts, to prepare them for repair or replacement.
Demolition and construction: Gouging is employed to cut or remove metal in construction projects, such as removing old structures or preparing surfaces for new installations.
Gouging Torch
Welding, on the other hand, is a joining process that fuses two or more pieces of metal together to form a strong and continuous joint. The primary purpose of welding is to create a permanent bond between the workpieces, allowing them to function as a single component. Welding involves the application of heat, pressure, or a combination of both, along with a filler material, if necessary.
Welding requires specific tools and equipment depending on the welding process used. Common welding techniques include shielded metal arc welding (SMAW), gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), and flux-cored arc welding (FCAW). Each process may require different types of welding machines, welding electrodes, shielding gases, or consumables.
Welding involves the creation of a molten pool at the joint interface by applying heat generated from an electric arc or other heat sources. The operator then introduces a filler material, if needed, to join the workpieces. The molten metal solidifies, creating a strong bond between the materials.
Welding is widely used in various industries and applications, including:
Construction: Welding is crucial in the construction of structures, bridges, pipelines, and other infrastructure projects.
Automotive and aerospace: Welding is employed in the manufacturing and assembly of vehicles, aircraft, and their components.
Manufacturing and fabrication: Welding is used to join metal components in the production of machinery, equipment, and consumer goods.
Repair and maintenance: Welding is utilized to repair damaged or worn-out metal parts, extending their service life.
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