• E.M.F.

    Abbreviation for electromotive force.

  • EARTH GROUND

    The side of an electric circuit grounded to the earth by means of a copper rod driven into the ground.

  • EDDY CURRENT

    A current running contrary to the main current. The eddy current in armatures, pole pieces, and magnetic cores is induced by changing electromotive force. It is wasted energy and creates heat. 

  • EDDY-CURRENT LOSS

    The loss of energy in an electrical machine which is caused by eddy currents.

  • EDGE EFFECT, Thermal Spraying

    Loosening of the bond between the thermal spray deposit and the substrate at the edge of the thermal spray deposit. 

  • EDGE JOINT

    A joint between the edges of two or more parallel or nearly parallel members.

    An edge joint is formed by placing a surface of one base metal part on a surface of another base metal part so that the weld joining the parts is within the outer surface planes of both the parts joined. 

  • EDGE LOSS, Thermal Spraying

    Thermal spray deposit lost as overspray beyond the edge of the workpiece. 

  • EDGE PREPARATION

    The preparation of the edges of the joint members, by cutting, cleaning, plating, or other means.

    Cleanliness is important in welding. The surfaces of the workpieces and the previously deposited weld metal must be cleaned of dirt, slag, and any other foreign matter that would interfere with welding. To accomplish this, the welder should have a steel wire brush, a hammer, a chisel, and a chipping hammer. These tools are used to remove dirt and rust from the base metal, remove tack welds, and chip slag from the weld bead.

    Edge preparation may be done by any of the thermal cutting methods or by machining. The accuracy of edge preparation is important, especially for machine or automatic welding. For example, if a joint designed with a 6.4 mm (1/4 in.) root face were actually produced with a root face that tapered from 7.9 to 3.2 mm (5/16 to 1/8 in.) along the length of the joint, the weld might be unacceptable because of lack of penetration at the start and excessive melt-through at the end. In such a case, the capability of the cutting equipment, as well as the skill of the operator, should be checked and corrected.

    Weld Cleaning

    Preweld and postweld cletaning are part of the welding operation. Preweld cleaning occurs by default in some types of acetylene wellding, where the pre-heating operation of the torch automatically cleans the weld site. In other instances welding and brazing fluxes aid in the cleaning. Gas welding operations rarely require postweld cleaning unless they include a corrosive type of flux, in which case the operation includes flux removal to prevent weld or base metal corrosion.

    Cleaning processes are: usually chemical or mechanical. The condition of the workpieces, the nature of any contamination, the degree of cleanliness required, and the type, shape, size, and thickness of the workpieces to be cleaned determine the choice between mechanical or chemical cleaning.

    Chemical Cleaners

    A chemical bath provides uniform cleaning. This uniformity is necessary, for example, to produce consistent welds in resistance welding operations. Certain chemical cleaners require accurate timing, and the operator’s ability to control the exposure time of the material in the bath is critical to achieving a high degree of uniformity. The cleaning solution will be ineffective if the exposure time of the workpiece is insufficient. If left in the bath too long, the chemical may react with the base metal and cause a high-resistance film or other undesirable chemical reaction.

    Chemical cleaning processes also present a safety hazard and require precautionary measures to prevent injury to workers.

    Chemical cleaning solutions are usually one of four types: alkaline, solvent, petroleum spirits, and emulsifiable.

    Alkaline Cleaners. The alkaline cleaner is probably the most popular because it will emulsify greases and oils, and because of its low cost. Since alkaline cleaners are sprayable at high pressure, the mechanical action of the spray assists in removing solid particles and dirt. Most alkaline cleaners are not caustics and therefore are less hazardous to the worker. Alkaline cleaners are effective in almost all metal cleaning applications, although they may cause corrosion in various nonferrous alloys, especially aluminum, brass, and zinc.

    Solvent Cleaners. These cleaners are commonly used in resistance welding operations. In this application, the workpieces are soaked in a tank of solvent so that the cleaning penetrates rolled edges, pockets, and seams. Water-based solvents are not easily rinsed

    from edges, pockets and seams. Solvent cleaners are ideal for cleaning nonferrous metal particles in applications where water and steam might allow corrosion or contamination.

    Petroleum Spirit Cleaners. These cleaning agents primarily remove processing contaminants, and do not provide the chemically cleaned surface required by some finishing operations, such as plating. Petroleum spirit cleaners are highly flammable and present a fire hazard.

    Emulsified Cleaners. Emulsified cleaners do not damage or attack the metal surface. This type of cleaner is effective as a spray or in a bath. Exposure time is usually short, sometimes as little as 30 seconds. After a brief drainage period, a water spray rinse removes contaminants and cleaning solution. An alternative to solvent and alkaline cleaners, emulsified cleaners are not temperature dependent, although a hot water rinse assures more satisfactory results and rapid self-drying.

    Mechanical Cleaning

    Mechanical cleaning requires skilled operators who must remove undesirable surface coatings and particles without roughening the surface of the material or causing other undesirable surface conditions. Mechanical cleaning is effective for both resistance and arc welding applications. A wire brush or abrasive wheel is the most common mechanical cleaner.

    The major advantage of mechanical cleaning is that it requires cleaning at the weld site only; chemical cleaning involves the entire surface of the workpiece. 

  • EDGE SHAPE

    The shape of the edge of the joint member.

    The shape of the edge will vary with plate thickness. See Figure E-2 for typical edge shapes based on plate thickness. 

  • EDGE WELD

    A weld in an edge joint, a flanged butt joint or a flanged corner joint in which the full thickness of the members is fused. See Figure E-1.

  • EDGE WELD SIZE

    The weld metal thickness measured from the weld root.

     

  • EDGE-FLANGEWELD

    A nonstandard term for an edge weld in a flanged butt joint. 

  • EFFECTIVE LENGTH OF WELD

    The length of the correctly proportioned cross section of a weld. In a curved weld, it is measured along the weld axis. 

  • EFFECTIVE THROAT

    The minimum distance minus any convexity between the weld root and the face of a fillet weld.

  • EFFICIENCY

    The ratio of the amount of useful energy, power or work delivered by a machine to the amount of energy, power or work required to operate it, or effective operation measured by a comparison of production with cost.

  • ELASTIC LIMIT

    The maximum load (or stress) a metal will sustain before it deforms permanently or plastically. See ELONGATION. 

  • ELASTICITY

    The resilience of a material; the property of resisting deformation by stretching,. Elasticity is the characteristic of a material to return to its original shape quickly after the deforming force is removed. 

  • ELECTRIC ANNEALING

    See ANNEALING, Electric.

  • ELECTRIC ARC SPRAYING

    A nonstandard term for ARC SPRAYING.

  • ELECTRIC BONDING

    A nonstandard term for surfacing by thermal spraying.

  • ELECTRIC BRAZING

    A nonstandard term for ARC BRAZING and RESISTANCE BRAZING. A group of brazing processes in which heat is obtained from electric current. See also INDUCTION BRAZING. 

  • ELECTRIC CIRCUIT

    The complete path of the flow of electric current, usually including the source of electric energy. The intensity or pressure of the electric current is expressed as volts. The rate of flow or current in the circuit is expressed as amperes.

    In a direct-current (d-c) circuit (sometimes called a continuous current circuit), the product of the volts and the amperes in the circuit represents the amount of electrical power (watts) produced. The product of the volts and the amperes in the circuit, together with the time of flow, is expressed as watt hours of energy expended in the circuit. One thousand watts are expressed as a kilowatt. Electrical energy is measured in kilowatt hours.

    As an example of this calculation, if the voltage across a portion of an electrical circuit is 50 volts and the current flowing in the circuit is 600 amperes, the amount of power being consumed in the circuit is 30 kilowatts, or 30 000 watts. If the circuit is maintained for one hour, 30 kW-hr of energy will be expended. 

  • ELECTRIC CONDUCTIVITY

    The electrical conducting characteristics of a material; the reciprocal of electrical restivity. Table E-1 shows a comparison of the electrical conductivity of various metals, considering copper as 100. 

  • ELECTRIC CURRENT

    The path of movement or rate of movement of electricity; flow of electricity.

  • ELECTRIC INDUCTION HEATING

    Heating a material by means of an electric current that is caused to flow through the material by electro-magnetic induction.