• C.G.S.

    Abbreviation for centimeter-gram-second units; the centimeter is the unit of length, the gram is the unit of weight, and the second is the unit of time.

  • C.P.

    Abbreviation for constant potential. See CONSTANT VOLTAGE POWER SOURCE. 

  • C02 WELDING

    A nonstandard term for gas metal arc welding with carbon dioxide shielding gas.

  • CABLE AND CABLE CONNECTORS

    Two cables, an electrode cable and a workpiece cable, are required to complete the electrical circuit between the welding machine and the workpiece. The correct size and the quality of cable are basic to welding operations. If the cable is too small for the current, it will overheat and could cause rapid deterioration of the cable insulation. It will also cause a voltage drop which could affect the welding conditions.

    Copper Cable Construction

    The cable most frequently chosen for welding applications is a neoprene-covered, multiple-strand copper cable specifically developed for welding service. Neoprene, a synthetic rubber, is used as the outer jacket because of its superior toughness, flexibility, and resistance to heat, abrasion, and oil or grease.

    Size of Workpiece Cable

    In arc welding, the work forms part of the electrical circuit, so it is essential that the workpiece cable be the same size as the electrode cable. The workpiece cable does not need to be as flexible as the electrode cable, since it stays in one spot most of the time.

    The shortest cable possible should be used. If the distance from the machine is too great, the voltage drop becomes so large that it affects the amount of electrical energy transmitted to the welding arc. If the work has to be located at a considerable distance from the welding machine, it is important that the connecting cable be larger in diameter than if the distance is short. The cable size must be selected for length as well as amperage. Table C-1 shows recommended copper cable sizes for distances from 7.5 to 38 m (25 to 125 ft) from the welding machine (distance = total length of electrode and workpiece cables divided by two) and currents from 100 to 600 amp.

    Aluminum Cable

    One of the advantages of aluminum cable is that it weighs less than half that of copper, although the diameter must be about 30% larger to compensate for its greater resistivity.

    If the duty cycle is medium to high, a good rule of thumb is to increase the size of aluminum cable by one size or number of the American Wire Gauge (AWG) rating over the size of copper cable normally used. As an example, if 1/0 copper cable is used for an application, it can be replaced by 2/0 aluminum cable.

    To obtain the lowest resistivity, electrolytic aluminum is used for welding cable. This grade of aluminum cable is only half as strong as copper, so to achieve the same flexibility and resistance to breaking, the aluminum wire is semi-annealed, while the copper wire can be dead soft.

    To assure a good connection, it is important to thoroughly clean the aluminum conductor prior to making either a soldered or mechanical joint.

    Connections

    Every welding circuit has at least four cable connections and possibly more. All are extremely important. If a cable connection is inadequate, the resulting voltage drop in the electrical circuit will affect the quality of welding as seriously as an inadequate cable.

    The four necessary connections are those connecting the two cables to the welding machine; cable to a device for the electrode to receive the welding current; and cable to workpiece clamp.

    Many of the difficulties encountered in welding can be traced to the workpiece cable. If a welder attempts to “get by” with an inefficient contact between the workpiece cable and the workpiece, the result will be unsatisfactory welding and lost time.

    Although there are several ways in which the workpiece cable can be connected to the work, the prime requisite is to ensure a positive means of contact. Regardless of which connection is used, it must provide sufficient contact surface held firmly in place to complete the electrical circuit. Cleanliness of the contact area is of utmost importance. A dirty contact can allow arcing between the workpiece connector and the work, which not only heats the workpiece connection, but results in poor arcing characteristics between the electrode and the work.

    The welding machine frame should be connected to an earth ground, or a person accidentally touching it may receive a noticeable shock. The cable connecting the power supply frame to ground should not be confused with the workpiece cable and its connection.

    Checking Power Loss

    Voltage drops due to poor connections in a welding circuit may also show up in the welding machine, misleading the welding operator by disguising the exact source of trouble. Before assuming that a welding machine is at fault, the operator should check the cable and cable connections to assure that they are tight.

    Loose connections in the machine, or overloaded usage, can cause a transformer winding or insulation to burn. A visual inspection of the entire welding circuit should be made to check for cable breaks or shorts, followed by checking the lugs and terminals bolted to the machine studs for tightness and possible corrosion at the contact points.

  • CADMIUM FUMES

    See WELDING FUMES.

  • CADMlUM

    (Chemical symbol: Cd). A malleable, ductile, toxic, bivalent metallic element added to plating to protect against corrosion, and used in bearing metals. It is also used in low-friction alloys, solders, brazing alloys, and nickel-cadmium storage batteries. Cadmium is found in nature as a carbonate or sulphide of certain zinc ores. Cadmium has an atomic weight of 112.41; atomic number, 48; specific gravity, 8.65; melting point, 321°C (610°F).

  • CALCIUM

    (Chemical symbol Ca). A silvery, metallic element that occurs in nature in shells,  limestone and gypsum. In the field of welding, calcium is commonly associated with carbon to form calcium carbide. Calcium has a strong affinity for oxygen and becomes coated with an oxide film when exposed to air. When heated in nitrogen, it forms calcium nitride. It decomposes readily in water with the evolution of hydrogen and formation of calcium hydroxide. Atomic number, 20; atomic weight, 40.07; melting point, 810°C (1490°F); specific gravity, 1.54.

  • CALCIUM CARBIDE (CaC,)

    Historical Background

    In 1836, English chemist Edmund Davy observed that a by-product incidental to the production of potassium decomposed water and produced a gas which contained acetylene. In 1862, a German chemist, Wohler, discovered that acetylene could be produced from calcium carbide which he had made by heating a mixture of charcoal and an alloy of zinc and calcium to a very high temperature. Like Davy’s material, it decomposed water and yielded acetylene. He also reported that the ignited gas produced a brilliant, smoky flame. But it was a French chemist, Berthellot, who in 1862 thoroughly described the reactions. Unfortunately, for the next thirty years only a few chemists observed the acetylene flame, and none of them saw any commercial potential.

    However, with the development of the electric arc furnace, Thomas Willson, an electrical engineer in Spray, North Carolina, attempted to produce metallic calcium from lime and coal tar. Instead of calcium metal, he produced a dark molten mass which cooled to a brittle solid. When he discarded it in a stream, a large quantity of gas was suddenly liberated. On being ignited, the gas produced a bright but smoky flame. It was not the clean hydrogen flame which would have been produced by the reaction of calcium and water, but obviously because of the soot, was a rich hydrocarbon. Repeating the smelt and analyzing the solid, which showed it to contain calcium carbide, Willson sent a specimen with a letter to Lord Kelvin in Glasgow on September 16, 1892. This dated document secured Willson the honor of being the first to produce calcium carbide on a commercially promising scale.

    During the same time, others in French and German laboratories had been studying and describing carbides, but none were able to produce them on a commercial  scale. Thus, as the result of an accident, the industrial possibilities of calcium and acetylene were recognized for the first time. The practicality of using acetylene as a means of illumination was demonstrated in 1892, and with the establishment of the Willson Illuminating Company in Spray, in the spring of 1895, the first factory to manufacture calcium carbide came into being.

    Calcium Carbide Production

    Calcium carbide is produced in electric arc furnaces which attain temperatures of about 2760 to 3900°C (5000 to 7000°F). The arc established between two electrodes is used to heat a mixture of lime and coke, causing the following changes to occur:

    CaO + 3C + CaC2 + CO Quicklime + coke yield calcium carbide +carbon monoxide

    To obtain high quality acetylene, it is necessary to use quicklime that is essentially 99% pure, and low-ash coke. The phosphorus and sulfur levels of both must also be very low.

    The solidified calcium carbide resembles dark brown or black or bluish black stone; its density is 2.24 times greater than water. It will not burn except at very high temperatures in the presence of oxygen. It is not affected by organic solvents and it is unaffected by shock. It can be stored indefinitely if sealed from air. It is odorless, but gives off a smell due to the presence of small amounts of acetylene produced by the interaction of moisture in the air. In the presence of that moisture, it slowly slakes to a dry lime.

    Gas Production

    The value of calcium carbide comes from the reaction which occurs when placed directly in contact with water according to the following equation:

    CaC2 + 2 H20 + Ca(OH)2 + C2H2 Carbide + water yield slaked lime + acetylene

    One kg (2.2 lb) of calcium carbide will produce 0.33 m3 (1 1.5 ft3) of acetylene at room temperature.

  • CALESCENT

    See CURIE POINT.

  • CALORIE

    A unit of heat. The amount of heat required to raise the temperature of one gram of water one degree Celsius.

  • CALORlZlNG

    A process of coating a metal with a fine deposit of aluminum similar to galvanizing with zinc. It is used primarily as a means of protecting steel from oxidation at elevated temperatures, rather than from the more familiar types of corrosion.

  • CAP

    A nonstandard term for the final layer of a groove weld.

  • CAPACITANCE

    The property of an electric non-conductor that permits the storage of energy as a result of electric displacement when opposite surfaces of the non-conductor are maintained at a difference of potential.

  • CAPACITOR

    A condenser. An element of an electrical circuit used to store charge temporarily; the primary purpose is to introduce capacitance in an electric circuit. It usually consists of two metallic plates separated by a dielectric.

  • CAPACITOR DISCHARGE STUD WELDING

    See ARC STUD WELDING.

  • CAPACITY

    The capability of holding or carrying an electric charge. Capacity is measured in farads or microfarads.

  • CAPACITY REACTANCE

    The measure of the opposition to the passage of alternating current through a condenser as expressed in ohms.

  • CAPILLARY ACTION

    The force by which liquid, in contact with a solid, is distributed between closely fitted faying surfaces of the joint to be brazed or soldered. See STANDARD WELDING TERMS.

    Capillary action is the phenomenon by which adhesion between the molten filler metal and the base metals, together with surface tension of the molten filler metal, distribute the filler metal between parts of the brazed or soldered joint.

  • CARBIDE

    A binary compound of the element, carbon, with a more electropositive element.

    Among the commercially important carbides are silicon (i.e., the abrasive, Carborundum), iron (the strengthening constituent in steel), and calcium (used to produce acetylene). As a class, they are hard, opaque solids. See CALCIUM CARBIDE.

  • CARBIDE TOOLS

    See BRAZING, CARBIDE TOOLS.

  • CARBON

    (Chemical symbol: C). A nonmetallic element that occurs in many inorganic and all organic compounds. An element of prehistoric discovery, carbon is widely distributed in nature. It is found native in diamond and graphite, and as a constituent of coal, petroleum, asphalt, limestone and other carbonates. In combination, it occurs as carbon dioxide and as a constituent of all living things. Carbon is unique in forming an almost infinite number of compounds. It has an atomic weight of 12; atomic number, 6; melting point, above 3500°C (6300°F); specific gravity, amorphous 1.88, graphitic 2.25, diamond 3.51.

    The addition of carbon to iron produces steel; carbon is the principal hardening agent in steel. In most cases, alloy steels containing carbon up to about 0.20% are considered easily weldable. Alloy steels containing over 0.20% carbon are generally considered heat-treatable steels, and are heat treated by quenching and tempering to obtain the best combinations of strength and toughness or ductility. In some cases, these steels are used in the as-rolled condition.

    As the principal hardening element in most alloy steels, carbon controls the strength and hardness of the steel, while alloying additions are used to increase hardenability and improve toughness.

  • CARBON ARC BRAZE WELDING (CABW)

    A braze welding process variation that uses an arc between a carbon electrode and the base metal as the heat source. See STANDARD WELDING TERMS.

  • CARBON ARC BRAZING

    A nonstandard term for TWIN CARBON ARC BRAZING.

  • CARBON ARC CUTTING (CAC)

    An arc cutting process that uses a carbon electrode. See STANDARD WELDING TERMS.

    Carbon arc cutting is primarily used for foundry work and in scrap yards. In carbon arc cutting, the intense heat of the arc melts a crevice through the parts being cut. A jagged cut results. In addition to the irregular appearance of the cut, considerable metal is wasted due to the width of the cut. Carbon arc cutting has largely been replaced by air carbon arc cutting. See AIR CARBON ARC CUTTING.

  • CARBON ARC WELDING (CAW)

    An arc welding process that uses an arc between a carbon electrode and the weld pool. The process is used with or without shielding and without the application of pressure. See STANDARD WELDING TERMS. See also BENARDOS PROCESS, GAS CARBON ARC WELDING, SHIELDED CARBON ARC WELDING, and TWIN CARBON ARC WELDING.

    Carbon arc welding is, for all practical purposes, an obsolete process. Like the gas-tungsten arc process (GTAW), it uses non-consumable electrodes, either carbon or graphite. Unlike GTAW, however, the electrodes erode rapidly. And unlike GTAW, which has the great advantage of inert gas shielding, fluxes were often used to protect the weld metal and some of the filler wires used were coated with suitable fluxes. Carbon contamination is a potential problem and must be carefully avoided when igniting the arc with a scratch start, or by accidental contact while using very short arcs. Because of the poor shielding and potential for carbon contamination, the process was used most frequently for welding copper and its alloys, and cast irons.

    Historical Background

    Carbon arc welding is presently used only to a very limited extent, but much was learned about shielding during the early development of arc welding (circa 1925) when CAW was popular.

    Welders using the carbon arc to fusion-weld iron and steel learned to control the nature of the welding atmosphere by resorting to simple methods. As an example, the oxidizing effect of air aspirated into the arc was reduced by inserting a string of combustible material into the arc alongside the electrode to combine with at least some of the oxygen in the arc area. If the string consisted of tightly rolled-up paper, it burned to form water vapor and carbon dioxide, both of which are more protective of the molten steel than oxygen. The string was fed into the upper part of the arc, the narrowest part which contained the largest amount of air. By removing a large portion of the uncombined oxygen from the arc, the combustible material sometimes permitted welding to be performed without a flux. When more effective protection was needed in carbon arc welding, the string of combustible material was impregnated with slag-forming ingredients. As the string burned, these ingredients melted and performed their functions right at the point where they were most needed. The nature of the slag and flux varied with the metal being welded.

    For steels, minerals such as clay and asbestos were used for forming the slag, and fluorspar was favored as the flux. From this simple beginning, shielding the arc with gases and protecting the molten metal with slag and flux developed into a highly refined and complex technology. Reference: George E. Linnert, Welding Metallurgy, Vol. 1, 4th Edition, 722-23. Miami, Florida: American Welding Society, 1994.