Carbon Arc Welding Equipment<\/h2>\n\n\n\n
The following paragraphs discuss in brief about the electrodes used in CAW, machines, welding current and welding circuit.<\/p>\n\n\n\n
Electrodes In Carbon Arc Welding<\/h3>\n\n\n\n
The electrodes in CAW are made of carbon. Similar to the SMAW process, the electrodes are held in electrode holders. The carbon electrodes come in two types: baked carbon electrodes and graphite electrodes. Graphite electrodes produce a \u2018soft\u2019 arc that makes less noise and easy to control. The baked electrodes make for a slightly noisy operation, but these electrodes last longer.<\/p>\n\n\n\n
The sizes of these electrodes vary from 1\/8 inch to almost 5\/16 inch (3.2 mm to 8 mm). The larger size electrodes require use of water-cooled electrode holders. The figure below illustrates typical air-cooled electrode holders.<\/p>\n\n\n\n Direct current is generally used for carbon arc welding. The power source is a rectifier type.<\/p>\n\n\n\n The welding circuit of single-electrode carbon arc welding is similar to that of shielded metal arc welding. The electrode is generally connected to the negative terminal of the power source. In other words, DCEN polarity is used. This is especially so when single electrode CAW is employed. This is done so as to keep the concentration of heat on the work-piece<\/em> (instead of electrode).<\/p>\n\n\n\n If the electrode is connected to the positive terminal, more heat would be generated at the electrode tip. This can cause erosion of carbon electrode, and possibly introduce carbon in the weld metal as well, which is highly undesirable. This also causes black smoke near the arc.<\/p>\n\n\n\n The power source is generally a constant current type, characterized by drooping current-voltage characteristics. A power source of 60% duty cycle is employed. The machine has a voltage rating of 50 volts since this much voltage is required for carbon arc welding of copper.<\/p>\n\n\n\n Alternating current is normally not used for single electrode carbon arc welding. This is because the rapidly changing polarity in AC brings positive polarity to the electrode tip, which can cause erosion of carbon electrode. This not only means that the electrode has to be frequently adjusted at the holder (such that a minimum 3 to 5 inches of electrode protrudes from the holder towards the work-piece), but there are chances of introducing carbon in the weld metal as well.<\/p>\n\n\n\n The electrode holder for CAW is slightly different from the one used in SMAW. Typical electrode holders are shown in figure 1 above. The carbon electrode becomes extremely hot during use.<\/p>\n\n\n\n Other than the above few aspects, the welding circuit of single-electrode CAW is largely similar to that of SMAW process.<\/p>\n\n\n\n The single electrode method is not used widely, any longer. It is used only for a few applications. One of its\u2019 uses for welding copper. Another use is welding of galvanized iron. This article in later paragraphs lists some recommended welding parameters for galvanized steel.<\/p>\n\n\n\n At lower base metal thicknesses, the process is used without a filler rod, that is \u2013 autogenously. At higher thicknesses, a filler rod is used. The filler rod is used to add weld metal to the weld puddle, by introducing it between the arc and base metal.<\/p>\n\n\n\n Carbon arc welding process can be used for making out of position welds as well.<\/p>\n\n\n\n Carbon arc welding is appropriate for welding of materials that do not get affected by carbon pickup in the weld puddke. Due to the carbon electrodes, evolution of carbon monoxide and carbon dioxide during the welding process is significant. The process is suitable for materials that are not affected by these gases.<\/p>\n\n\n\n The process is used for both ferrous and non-ferrous metals, and for welding both groove welds and surfacing welds. The following paragraphs discuss very briefly welding of steel, cast iron and copper using this process.<\/p>\n\n\n\n CAW is used for making autogenous welds in edge joints between thin sheet metals. The edges of the work-pieces are fitted closely together, and fusion is achieved using CAW, without use of a filler metal.<\/p>\n\n\n\n Another use is braze welding of galvanized steel. A bronze welding rod is used for the purpose. The arc should be directed at the filler rod (instead of the work-piece). This is done to protect the galvanizing coating. The arc is struck at the electrode or a run-on plate. Low amperage, high travel speed, a low voltage (a low arc gap) is used so that the heat input remains low. The melted filler rod is deposited on the galvanized steel.<\/p>\n\n\n\n Cast iron can be welded with carbon arc welding. A preheat of 1200\u00b0F (650\u00b0C) should be used so that rate of cooling is kept low. This is necessary if the metal has to undergo any further fabrication activity such as welding or machining. If the rate of cooling is not kept low, the resulting weld metal would be very hard.<\/p>\n\n\n\n As mentioned above, single electrode carbon arc welding is used for welding copper. The polarity used for this welding is DCEN. DCEP is avoided, because \u2013 as explained in the above paragraphs \u2013 positive polarity at electrode causes concentration of heat at the electrode tip. This, in turn, may cause erosion of the carbon electrode, and increases the unwanted possibility of carbon introduction in the weld metal.<\/p>\n\n\n\n A preheat of 300\u00b0- 600\u00b0F (150\u00b0 C – 650\u00b0C) should be used, based on the thickness of the base metal. Preheating is necessary because the thermal conductivity of copper is very high <\/a>. This causes heat from the welding zone to be dissipated to the adjoining base metal very rapidly.<\/p>\n\n\n\n A long arc length is used so that carbon from the electrode gets a chance to combine with oxygen and form carbon dioxide. The carbon dioxide provides some shielding to the molten metal from the atmospheric gases. A root gap of 1\/8 inch (3.2 mm) is recommended, and a high travel speed should be used.<\/p>\n\n\n\n The following figure illustrates the principles of carbon arc welding, showing a single carbon electrode. As can be seen, an arc is initiated between a carbon electrode and the work-piece. The heat of the arc heats the base metal and creates a weld pool. The filler metal is fed into the arc, such that it melts and deposits weld metal. As this pool solidifies, weld metal is produced.<\/p>\n\n\n\n The shielding of the arc from atmospheric gases is provided by carbon dioxide that evolves as a result of arc. The high temperatures of the arc cause the carbon available in the electrode to react with oxygen and produce carbon dioxide as the product. The carbon electrode undergoes rapid erosion due to this.<\/p>\n\n\n\n The carbon dioxide thus produced displaces atmospheric gases from the region surrounding the arc, thus protecting the weld metal from oxidation.<\/p>\n\n\n\n Similar to GTAW, filler rod is separately manually fed into the weld pool such that it melts and gets deposited as weld metal. The filler rod is fed with one hand, while the other hand is used to manipulate the arc. As the arc moves along the direction of welding, the arc is kept directed at the base metal, while the filler rod is fed into the pool. The speed of travel and the frequency of feeding the filler into molten pool determine the shape and size of the resulting weld bead.<\/p>\n\n\n\n![\"Carbon](\"https:\/\/mewelding.com\/wp-content\/uploads\/2022\/04\/electrode-holder-in-carbon-arc-welding.png\")
<\/figure>\n\n\n\nMachines<\/h3>\n\n\n\n
Welding circuit and welding current<\/h3>\n\n\n\n
Major Uses Of Carbon Electrode Welding <\/h2>\n\n\n\n
Weldable Metals<\/h2>\n\n\n\n
Steels<\/h3>\n\n\n\n
Cast Iron<\/h3>\n\n\n\n
Copper<\/h3>\n\n\n\n
Principles of Operation<\/h2>\n\n\n\n
![\"Carbon](\"https:\/\/mewelding.com\/wp-content\/uploads\/2022\/04\/principles-of-carbon-arc-welding.png\")
<\/figure>\n\n\n\n