ESAB Lesson 1

BASIC WELDING FILLER METAL TECHNOLOGYA Correspondence Course LESSON I THE BASICS OF ARC WELDING An Introduction to Metals Electricity for Welding ESAB ESAB Welding & Cutting Products ©COPYRIGHT 2000 THE ESAB GROUP, IN TABLE OF CONTENTS LESSON I THE BASICS OF ARC WELDING PART A. Section Nr. 1.1 1.1.1 1.1.2 1.1.3 1.1.4 1.1.5 1.2 1.2.1 1.2.2 1.2.3 1.3 1.4 1.4.1 1.5 1.5.1 1.5.2 1.5.3 1.5.4 1.5.5 1.5.6 1.5.7 1.6 1.6.1 1.6.2 1.6.3 1.6.4 AN INTRODUCTION TO METALS Section Title Source and Manufacturing............................................................. Rimmed Steel ................................................................................... Capped Steel .................................................................................... Killed Steel ........................................................................................ Semi-Killed Steel............................................................................... Vacuum Deoxidized Steel ................................................................. Classification of Steels................................................................... Carbon Steel ..................................................................................... Low Alloy Steel.................................................................................. High Alloy Steel ................................................................................. Specifications ................................................................................. Crystalline Structure of Metals ...................................................... Grains and Grain Boundaries ........................................................... Heat Treatment ................................................................................ Preheat ............................................................................................. Stress Relieving ................................................................................ Hardening ......................................................................................... Tempering ......................................................................................... Annealing .......................................................................................... Normalizing ....................................................................................... Heat Treatment Trade-Off ................................................................. Properties of Metals........................................................................ Tensile Strength ................................................................................ Yield Strength.................................................................................... Ultimate Tensile Strength .................................................................. Percentage of Elongation ................................................................. Page 1 2 2 3 3 3 3 3 3 4 5 6 7 8 8 9 9 9 9 10 10 10 10 11 11 11 © COPYRIGHT 1998 THE ESAB GROU TABLE OF CONTENTS LESSON I - Con't. Section Nr. Section Title Page 1.6.5 1.6.6 1.6.7 1.6.8 1.6.9 1.6.10 1.6.11 1.6.12 1.7 1.7.1 1.7.2 1.7.3 1.7.4 1.7.5 1.7.6 1.7.7 1.7.8 1.7.9 1.7.10 1.7.11 1.7.12 1.7.13 1.7.14 1.7.15 PART B. Section Nr. 1.8 1.8.1 1.8.2 1.8.3 1.8.4 Reduction of Area ............................................................................. Charpy Impacts ................................................................................. Fatigue Strength ............................................................................... Creep Strength.................................................................................. Oxidation Resistance ........................................................................ Hardness Test ................................................................................... Coefficient of Expansion ................................................................... Thermal Conductivity ........................................................................ Effects of Alloying Elements .......................................................... Carbon .............................................................................................. Sulphur ............................................................................................. Manganese ....................................................................................... Chromium ......................................................................................... Nickel ................................................................................................ Molybdenum ..................................................................................... Silicon ............................................................................................... Phosphorus....................................................................................... Aluminum .......................................................................................... Copper .............................................................................................. Columbium........................................................................................ Tungsten ........................................................................................... Vanadium .......................................................................................... Nitrogen ............................................................................................ Alloying Elements summary ............................................................. ELECTRICITY FOR WELDING Section Title Electricity for Welding ....................................................................... Principles of Electricity ...................................................................... Ohm’s Law ........................................................................................ Electrical Power ................................................................................ Power Generation ............................................................................. 11 11 12 13 13 13 14 14 14 14 14 15 15 15 15 15 15 15 15 16 16 16 16 16 Page 17 17 18 19 20 © COPYRIGHT 1998 THE ESAB GROU .................Con't....... Section Nr........ Constant Current or Constant Voltage ......2 1................... Power Requirements ..........................................................3 1..................... Section Title Page 1....................8...............................................8............. Power Source Controls ..........TABLE OF CONTENTS LESSON I ....................................9 1.........7 1...............9... 22 24 25 26 26 26 27 28 29 © COPYRIGHT 1998 THE ESAB GROU ....... Glossary of Terms ........................... Rectifying AC to DC ................................................................................................................................... Constant Voltage Characteristics ....................5 1...9...6 1....... Types of Welding Power Sources ..........9.9................................8... Constant Current Characteristics ................4 Appendix A Transformers ........................................1 1............. light weight and strength. which is primarily carbon. A typical blast furnace is a circular shaft approximately 90 to 100 feet in height with an internal diameter of approximately 28 feet. 1.1. 1.1 SOURCE AND MANUFACTURING Metals come from natural deposits of ore in the earth’s crust. ferrous and nonferrous. There is approximately 20 times the tonnage of iron in the earth’s crust compared to all other nonferrous products combined.0. © COPYRIGHT 1999 THE ESAB GROU . it is the most important and widely used metal. PART A AN INTRODUCTION TO METALS 1. The ore consists of iron oxide about four inches in diameter. such as copper and aluminum. 1.1.1. and a ferrous metal is one that has a high iron content. therefore. The flux is limestone that decomposes into calcium oxide and carbon dioxide. flux and coke.1. The two methods of mining employed are known as “selective” in which small veins or beds of high grade ore are worked.0. Most ores are contaminated with impurities that must be removed by mechanical and chemical means. Commercial aluminum ore. and “bulk” in which large quantities of low grade ore are mined to extract a high grade portion. Coke. Metal extracted from the purified ore is known as primary or virgin metal. 1.1. The steel shell of the furnace is lined with a refractory material.0.0. is a residual deposit formed at or near the earth’s surface. the main agent for reducing iron ore into iron metal. and metal that comes from scrap is called secondary metal.4 The largest percentage of commercially produced iron comes from the blast furnace process. 1. Most mining of metal bearing ores is done by either open pit or underground methods. is the next most widely used metal.2 Aluminum.0.3 Some of the chemical processes that occur during steel making are repeated during the welding operation and an understanding of welding metallurgy can be gained by imagining the welding arc as a miniature steel mill. known as bauxite. is the ideal fuel for blast furnaces because it produces carbon monoxide gas. Nonferrous metals. dense clay firebrick. because of its attractive appearance.1 There are two types of ores.LESSON I. usually a hard. are those that contain little or no iron. The lime reacts with impurities in the ore and floats them to the surface in the form of a slag. The three different materials used for the charge are ore.5 The iron blast furnace utilizes the chemical reaction between a solid fuel charge and the resulting rising column of gas in the furnace. The term ferrous comes from the Latin word “ferrum” meaning iron. 1.0. are used to continue this refining process. Large amounts of lime are contained in basic slags and high quantities of silica are present in acid slags. 1.LESSON I. The ingot produced is a rather large square column of steel.9 After passing through the refining furnace. refining furnaces are classed as either acid or basic. therefore.1% carbon. 1.0. and the common ingots resulting from each are as follows: 1. and it is accomplished through additives that tie up the oxygen either through gases or in slag.1. There are various degrees of oxidation. the metal is poured into cast iron ingot molds. phosphorus.1. the metal is saturated with oxygen. The metal that comes from the blast furnace is called pig iron and is used as a starting material for further purification processes. 1. most notably the open hearth. and sulfur segregate to the central core. Each furnace performs the task of removing or reducing elements such as carbon.6 The basic operation of the blast furnace is to reduce iron oxide to iron metal and to remove impurities from the metal. used in applications © COPYRIGHT 1999 THE ESAB GROUP.1. PART A 1. This process is known as deoxidation. The chief advantage of rimmed steel is the excellent defect-free surface that can be produced with the aide of the pure iron skin.0. As the ingots solidify. The oxygen forms carbon monoxide gas and it is trapped in the solidifying metal as blow holes that disappear in the hot rolling process.7 Pig iron contains excessive amounts of elements that must be reduced before steel can be produced. 1. silicon. a substantial portion of the oxygen must be removed.8 Depending upon the type of slag that is used. electric and basic oxygen.Capped steel regulates the amount of oxygen in the molten metal through the use of a heavy cap that is locked on top of the mold after the metal is allowed to reach a slight level of rimming. Capped steels contain a more uniform core composition than the rimmed steels.1.1 Rimmed Steel . INC . and practically all the carbon. Different types of furnaces.1. To avoid the formation of large gas pockets in the cast metal. a layer of nearly pure iron is formed on the walls and bottom of the mold. This differential between acid and basic slags is also present in welding electrodes for much of the same refining process occurs in the welding operation.The making of rimmed steels involves the least deoxidation. Capped steels are. The oxygen reduces elements by forming gases that are blown away and the slag attracts impurities as it separates from the molten metal. At this point. phosphorus. sulfur and nitrogen by saturating the molten metal with oxygen and slag forming ingredients.2 Capped Steel .0. Most rimmed steels are low carbon steels containing less than . Reduced elements pass into the iron and oxidized elements dissolve into the slag. as the name implies.1.Steel is basically an alloy of iron and carbon. The carbon reacts with the oxygen to form carbon monoxide. These are referred to as the “type” of steel.2. and it attains its strength and hardness levels primarily through the addition of carbon. This is done by increasing the carbon content of the steel and then subjecting the molten metal to vacuum pouring or steam degassing.2 Low Alloy Steel .2. Low Carbon Mild Carbon Steels Up to 0. 1. INC .2. is added.59% carbon High Carbon Steels 1.70% carbon The largest tonnage of steel produced falls into the low and mild carbon steel groups. They are popular because of their relative strength and ease with which they can of alloying elements that produce remarkable improvements in their properties. generally ferro-silicon or aluminum. 1.3 Killed Steel .1. the steel produced by this process is quite clean.Semi-killed steel is a compromise between rimmed and killed steel. leaving a dense and homogenous metal. PART A that require excellent surfaces.29% carbon Medium Carbon Steels . The amount is just sufficient to kill any rimming action. leaving some dissolved oxygen.1. 1.1 be welded. Alloying © COPYRIGHT 1999 THE ESAB GROUP.30% to 0. a more homogenous composition.LESSON I. Because no deoxidizing elements that form solid oxides are used.4 Semi-killed Steel . and as a result.1 Carbon Steel . A small amount of deoxidizing agent. 1. and high alloy. low alloy. Carbon steels are classed into four groups. and better mechanical properties than rimmed steel.Unlike rimmed or capped steel. depending on their carbon levels.2 CLASSIFICATIONS OF STEEL The three commonly used classifications for steel are: carbon. This removal is accomplished by adding a ferro-silicon alloy that combines with oxygen to form a slag.15% carbon . 1. 1. killed steel is made by completely removing or tying up the oxygen before the ingot solidifies to prevent the rimming action.1.60% to 1.15% to 0.The object of vacuum deoxidation is to remove oxygen from the molten steel without adding an element that forms nonmetallic inclusions.5 Vacuum Deoxidized Steel .Low alloy steel. the carbon and oxygen levels fall within specified limits. contains small amounts . molybdenum. 1. The term austenitic refers to the crystalline structure of these steels.2. giving them outstanding properties.3 High Alloy Steel . This characteristic is mainly due to the high chromium content.e. 1.LESSON I. To provide for this loss of strength at elevated temperatures.3. heavy equipment. extruding dies. silicon. Depending upon their properties and usage. Therefore.2. the ability to harden while undergoing cold work and great toughness. that give it two exceptional qualities. and vanadium.2. Nickel is also used in substantial quantities in some stainless steels. small amounts of chromium or molybdenum are levels in excess of 10%.4 Because of the high levels of alloying elements. that exhibit brittleness at low temperatures.2. 1. INC . Since they have high strength-to-weight ratios. Common alloying elements are manganese.This group of expensive and specialized steels contain alloy Steels lose much of their strength at high temperatures.3.2.3 added.2. chromium. low alloy steels with nickel additions are often used for low temperature situations. they are sometimes referred to as water hardening. oil hardening..2.1 Low alloy steels have higher tensile and yield strengths than mild steel or carbon structural steel. 1. and hot work tool steel.3 Tool steels are used for cutting and forming operations.3. Low alloy steel is generally defined as having a 1.2 Stainless steels are high alloy steels that have the ability to resist corrosion. 1. nickel.1 Austenitic manganese steel contains high carbon and manganese levels.2 Ordinary carbon steels. © COPYRIGHT 1999 THE ESAB GROUP. special care and practices are required when welding high alloy steels. punches. forming dies. they reduce dead weight in railroad cars. 10% or greater. truck frames. shock resisting. i. are unreliable in critical applications. air hardening. They are high quality steels used in making tools.5% to 5% total alloy content.3. 1.2. etc. 1. forgings and so forth.2. to decrease or increase the response to heat treatment. 1. and to retard rusting and corrosion. Low alloy steels may contain as many as four or five of these alloys in varying amounts.2. PART A elements are added to improve strength and toughness.2. A variety of technical. Society of Automotive Engineers (SAE). The prefix letter indicates the class of a material.10% or .0. but usually a type of steel is referred to by its specification.1 The American Iron and Steel Institute (AISI) and the Society of Automobile Engineers (SAE) have collaborated in providing identical numerical designations for their specifications. testing methods and recommended practices for a variety of materials ranging from textiles and plastics to concrete and metals. and the American Society of Mechanical Engineers (ASME). but a 308 stainless has a different overall composition than a 347 type. and so forth within the series. respectively.3 SPECIFICATIONS Many steel producers have developed steels that they market under a trade name such as Cor-Ten. which can change within the same series. The numbers 36 and 242 © COPYRIGHT 1999 THE ESAB GROUP. the class of widest interest in welding. The specification agencies most closely related to the steel industry are the American Iron and Steel Institute (AISI). It has compiled some 48 volumes of standards for materials. Likewise. INC . The last two digits indicate an approximate average content of . but there are different types such as 410. properties or usage. 430. American Society for Testing and Materials (ASTM). PART A 1. or SS-100.0. The last two digits will change within a series.3 The American Society for Testing and Materials (ASTM) is the largest organization of its kind in the world.3. are somewhat different.4 Two ASTM designated steels commonly specified for construction are A36-77 and A242-79. For example. give an approximate average of the carbon range.2 The AISI classifications for certain alloys.LESSON I. While the last two digits.3. specifications. In this case. The first two digits of a four digit index number refer to a series of steels classified by their composition or alloy combination. 1. The “4” of a 400 series indicates the main alloy as chromium. the “41” of a 4130 type steel refers to a group that has chromium and molybdenum as their main alloy combination with approximately . such as stainless steel. 420.0. governmental and industrial associations issue specifications for the purpose of classifying materials by their chemical composition. 1. the first two digits of a type 1010 or 1020 steel indicate a “10” series that has carbon as its main alloy.30% carbon content. For example.3. 1. NA-XTRA. 1.20% carbon.3. but are of an arbitrary nature being agreed upon by industry as a designation for certain compositions within the series. HY-80. the “3” in a 300 series of stainless steel indicates chromium and nickel as the main alloys. the letter “A” indicates a ferrous metal.0. T-1. They follow a three digit classification with the first digit designating the main alloy composition or series. . As the temperature of a crystal is raised. 3000 2795°F 2000 1000 SOLID TIME SOLID-LIQUID TRANSFORMATION.LESSON I. more thermal energy is absorbed by the atoms or molecules and their movement increases.) or particular products fabricated from steel (i.0. the lattice breaks down and the crystal melts. This fixed position is called a crystal lattice. a common example of an ASME classification is SA 387 Grade 11. An example of a full designation is A285-78 Grade A or A485-79 Class 70. the user may select from a number of different types of steel under the same classification. its atoms will assemble into a regular crystal pattern and we say the liquid has solidified or crystallized. PART A are index numbers. bar.6 The American Society of Mechanical Engineers (ASME) maintains a widely used ASME Boiler and Pressure Vessel Code. while the remainder is identical with ASTM with the exception that the date of adoption or revision by ASTM is not shown. etc.3.0. Since many standards for ferrous metals are written to cover forms of steel (i.. 1. etc. All metals solidify as a crystalline material.). heat treatment.5 The ASTM designation may be further subdivided into Grades or Classes. Therefore. pipe.e. 1. In a crystal the atoms or molecules are held in a fixed position and are not free to move about as are the molecules of a liquid or gas. sheet. the conditions are the same at all points throughout the lattice. chain. steel rail. 1. The 77 and 79 refer to the year that the standards for these steels were originally adopted or the date of their latest revision.3. PURE IRON FIGURE 1 © COPYRIGHT 1999 THE ESAB G . The different types are than placed under grades or classes as a way of indicating the differences in such things as chemistries. If a lattice contains only one type of atom. LIQUID as in pure iron. The material specification as adopted by the ASME is identified with a prefix letter “S”. As the distance 4000 between the atoms increases. and the crystal melts at a single temperature (see Figure 1). etc. Class 1. plate.e.4 CRYSTALLINE STRUCTURE OF METALS When a liquid metal is cooled. properties. Where these crystals meet is called a grain boundary. The capability of the atoms of a material to transform into two or more crystalline structures at different temperatures is defined as allotropic.. Gamma iron is commonly known as austenite and is a nonmagnetic structure.4. the metal is known as alpha iron.0. This is known as phase transformation. As crystallization continues. but at this temperature. However.As the metal is cooled to its freezing point.2 Each metal has a characteristic crystal structure that forms during solidification and often remains the permanent form of the material as long as it remains at room temperature. their free growth hampered. Often. At a temperature of 1670°F. a small group of atoms begin to assemble into crystalline form (refer to Figure 3). TIME Solid-Liquid Transformation. more crystals are formed from the surrounding liquid. they take the form of dendrites. the pure iron structure transforms back to the delta iron form. it may start to melt at one temperature but not be completely molten until it has been heated to a higher temperature (See Figure 2).1 However.2 A number of conditions influence the initial grain size.4.0. as in any alloy-steel. the delta structure transforms into a structure referred to as gamma iron.4.1. These two phases are given different names to differentiate between the high temperature phase (delta) and the low temperature phase (alpha). pure iron solidifies at 2795°F. Liquid Liquid and Solid Solid 1. This creates a situation where there is a combination of liquids and solids within a range of temperatures. and the remaining liquid freezes to the adjacent crystals until solidification is complete.LESSON I. Steels and iron are allotropic metals. © COPYRIGHT 1999 THE ESAB GROU . PART A 1. For example. It is important to know that cooling rate and temperature has an important influence on the newly solidified grain structure and grain size. 1. To illustrate differences in grain formation. the crystals begin to touch one another. The solid is now composed of individual crystals that usually meet at different orientations. These small crystals scattered throughout the body of the liquid are oriented in all directions and as solidification continues. let's look at the cooling phases in a weld.4. or a treelike structure. Alloy Metal FIGURE 2 1.1 Grains and Grain Boundaries . if the lattice contains two or more types of atoms. some metals may undergo an alteration in the crystalline form as the temperature is changed. the heat from the center of the weld deposit will dissipate into the base metal through the outer grains that solidified first.3 Initial crystal formation begins at the coolest spot in the weld.1. the tendency is for it to start in the area where the grains are largest. and that this atomic pattern or microstructure determines the properties of the metals. Some of the more common ways are as follows: 1. Grain size can have an effect on the soundness of the weld. The atomic pattern of a single element can change its arrangement at different temperatures. Consequently.4.5 HEAT TREATMENT The temperature that metal is heated. As a result. In some metals.5." determines the specific properties of metals. The shape and characteristics of crystals are determined by the arrangement of their atoms. all have an effect on a metal's crystalline structure. This crystalline structure. There are various ways of manipulating the microstructure. The smaller grains are stronger and more ductile than the larger grains. the grains that solidified first were at high temperatures for a longer time while in the solid state and this is a situation that encourages grain growth.1. this rapid cooling may contribute to the formation of microstructures in the weld zone that are detrimental. That spot is at the point where the molten metal and the unmelted base metal meet. the length of time it is held at that temperature.LESSON I. commonly referred to as "microstructure. either at the steel mill or in the welding procedure.Most metals are rather good conductors of heat. it should be understood that all metals are composed of crystals of grains. This is explained by the fact that as the weld metal cools. and the rate that it is cooled. you will note that the grains in the center are smaller and finer in texture than the grains at the outer boundaries of the weld deposit. As the metal continues to solidify.4. PART A GRAIN BOUNDARIES BASE METAL DENDRITE FORMATION INITIAL CRYSTAL FORMATION FIGURE 3 COMPLETE SOLIDIFICATION 1. 1. 1.4 To summarize this section. Preheating the weldment before it is welded is a method of slowing the cooling © COPYRIGHT 1999 THE ESAB GROU . If a crack occurs.1 Preheat . the heat in the weld area is rapidly dispersed through the whole weldment to all surfaces where it is radiated to the atmosphere causing comparatively rapid cooling. . held at that temperature for a sufficient time for a uniform change to take place. One way to minimize these stresses or to relieve them is by uniformly heating the structure after it has been welded.5.5. In a weldment. i. Steels that respond to this type of treatment are known as "quenched and tempered steels. usually in a furnace.After a metal is quenches. and then cooled at a very slow rate. 1. and as the distance from the weld zone increases.4 Tempering .5. © COPYRIGHT 1999 THE ESAB GROU .The hardness of steel may be increased by heating it to 50°F to 100°F above the temperature that a microstructure change occurs. the metal may not be able to resist these stresses and cracking or early failure of the part may occur. The preheat temperature may vary from 150°F to 1000°F. This rapid cooling. Welded parts are seldom annealed for the high temperatures would cause distortion." locks in place microstructures known as "martensite" that contribute to a metal's hardness characteristic. This nonuniform heating causes nonuniform expansion and contraction and can cause distortion and internal stresses within the weldment. the maximum temperature reached decreases. it is then usually tempered. Tempering reduces the brittleness that is characteristic in hardened steels.Metals expand when heated and contract when cooled.e.3 Hardening . The amount of expansion is directly proportional to the amount of heat applied. the more likely will it be necessary to preheat. held at that temperature for a length of time. because the heat will be conducted away from the weld zone more rapidly as the mass increases. Tempering is a process where the metal is reheated to somewhere below 1335°F. 1. The thicker the weld metal.5.5 Annealing .2 Stress Relieving . but more commonly it is held in the 300°F to 400°F range." 1. and then cooled to room temperature. Salt Brine (fastest). known as "quenching. More information on these properties will be covered later in this lesson and in subsequent lessons. The term toughness. the metal closest to the weld is subjected to the highest temperature. The principal reason for annealing is to soften steel and create a uniform fine grain structure. as it applies to metals. thereby producing a good balance between high strength and toughness. The metal is heated to temperatures just below the point where a microstructure change would occur and then it is cooled at a slow rate. Oil (fast). Depending on its composition and usage. PART A rate of the metal. 1. and then placing the metal in a liquid solution that rapidly cools it.LESSON I. Water (faster). usually refers to resistance to brittle fracture or notch toughness under certain environmental conditions.A metal that is annealed is heated to a temperature 50° to 100° above where a microstructure change occurs. The quenching solutions used in this process are rated according to the speed that they cool the metal. 1.5. but sometimes at the expense of another desirable property.1.1.6. Normalized steel is heated to a temperature approximately 100° above where the microstructure transforms and then cooled in still air rather than in a furnace.2 The tensile strength TEST SPECIMEN RECORDING DIAL test gives us 4 primary pieces of information: (1) Yield Strength.7 Heat Treatment Trade-Off . part of a machine. especially if it is to be a structural member.LESSON I.It must be noted that these various ways of control- ling the heating and cooling of metals can produce a desired property.5.1 Tensile Strength .6.The main difference between normalizing and annealing is the method of cooling.6 Normalizing . 1. susceptible to welding problems. 1.6. It becomes obvious that before a material is recommended for a specific use. PART A 1. 1. (2) Ultimate Tensile Strength. A metal that is stamped into an automobile fender must be softer and more pliable than armor plate that must withstand an explosive force. The specimen is then pulled to the point of fracture and the data recorded. but the same treatments will also make the metal less ductile or more brittle.Tensile strength is one of the most important determining factors in selecting a metal. and therefore. (3) Elongation. and (4) Reduction in Area. or the material used for an oil rig on the Alaska North Slope must perform in a quite different climate than a steam boiler. the physical and mechanical properties of that metal and the weld metal designed to join it must be evaluated. TENSILE TESTING APPARATUS FORCE FIGURE 4 © COPYRIGHT 1999 THE ESAB GROU .6 PROPERTIES OF METALS The usefulness of a particular metal is determined by the climate and conditions in which it will be used. The test specimen is machined to exact standard dimensions and clamped into the testing apparatus at both ends. Some of the more important properties of metals and the means of evaluation are as follows: 1. An example of this trade-off is evident in the fact that certain heat treatments can increase the strength or hardness of metal. or part of a pressure vessel.1 The tensile test is performed as shown in Figure 4. is susceptible to fracture if © COPYRIGHT 1999 THE ESAB GROU .3 Ultimate Tensile Strength . PART A 1.6. See Figure 5. and thus. it acts somewhat like a rubberband. This is called the plastic region of the metal and is represented by the letter B in Figure 5. the metal will reach a point where it will no longer return to its original shape but will continue to stretch.STRAIN CURVE FIGURE 5 withstood or resisted the maximum applied load is its ultimate tensile strength. and Ultimate Strength Elongation Reduction of Area Yield Strength Fracture an increased load must be applied to stretch the metal. but will remain in its elongated form. This information reflects the relative ductility or brittleness of the metal. This is the percentage of elongation and it gives an indication of the ductility of the metal at room temperature. the area where it breaks is reduced in size.Metal that is normally strong and ductile at room temperature may become very brittle at much lower temperatures.Once a metal has exceeded its yield point. the distance between the marks is measured and recorded as a percentage of the original distance. it will continue to stretch or deform. As the load is increased. 1. This information is usually recorded in pounds per square inch (psi). This is the elastic characteristic of metal and is represented by letter A in Figure 5. and if the load is suddenly released.When a metal is placed in tension.A tensile specimen is machined to exact dimensions. the metal will finally reach a point where it A B C STRAIN .6. As a greater load is applied.2 Yield Strength . the metal strains against further elongation. See Figure 5. As this plastic deformation increases. 1. 1.5 Reduction of Area . the metal returns to its original shape. two marks at a measured distance are placed on the opposing ends of the circular shaft.INCHES no longer resists and any further load applied will rapidly cause the metal to break.6 Charpy Impacts .LESSON I. and when the load is released. The area of its midpoint cross-section is a known figure. When a load of limited magnitude is applied. As the specimen is loaded to the point of fracture.6.Before a tensile specimen is placed in the tensile tester.6. Yield strength is the point where the metal reaches the limit of its elastic characteristic and will no longer return to its original shape.4 Percentage of Elongation . This reduced area is calculated and recorded as a percentage of the original cross-sectional area. That point at which the metal has NOMINAL STRESS . the metal will not return to its original shape. the metal stretches. 1. After the specimen is fractured.6. Quite often. and therefore. The specimen is in the direct path of a weighted hammer attached to a pendulum (Figure 6).6. it will eventually fracture and it is said to have exceeded its fatigue strength. For example.6. ENERGY IN FT/LBS FRACTURES CRACKS DEFORMS CHARPY V-NOTCH SPECIMEN CHARPY IMPACT TEST MACHINE CHARPY V-NOTCH IMPACT TEST FIGURE 6 1. the notch is in the form of a "V" and the test in this case is referred to as a Charpy V-Notch Impact Test. An impact tester measures the degree of susceptibility to what is called brittle fracture. The specimen is cooled to a predetermined temperature and then placed in a stationary clamp at the base of the testing machine.6.6. PART A a sharp abrupt load is applied to it. 1. but if it is bent back and forth repeatedly. The specimen that withstood 40 ft-lbs energy is said to have better toughness or notch toughness. if a thin wire is bent once.A metal will withstand a load less than its ultimate tensile strength but may break if that load is removed and then reapplied several times. A specimen that is cooled to -60°F and absorbs 40 ft-lbs of energy is more ductile. more suitable for low temperature service than a specimen that withstands only 10 ft-lbs at the same temperature. 1.LESSON I. © COPYRIGHT 1999 THE ESAB GROU .6. The fatigue strength is calculated from the number of cycles the metal withstands before the point of failure is reached.2 The hammer is released from a fixed height and the energy required to fracture the specimen is recorded in ft-lbs.1 The impact specimen is machined to exact dimensions (Figure 6) and then notched on one side. A common test for this strength is to place a specimen in a machine that repeatedly applies the same load first in tension and then in compression.7 Fatigue Strength . the material may rupture depending on the temperature of the metal. The Rockwell is further divided into different scales. PART A 1.9 Oxidation Resistance .8 Creep Strength . its creep strength. 1. Knoop and Rockwell. Diameter Steel Sphere 10 mm Sphere of Steel or Tungsten Carbide BRINNELL VICKERS Diamond Pyramid KNOOP Diamond Pyramid Types of Indenters .Hardness Tests FIGURE 7 © COPYRIGHT 1999 THE ESAB GROU . 1. the most visible being rust and scale. In other metals.LESSON I. These materials have high oxidation resistance. If that same load were applied to a metal heated to a high temperature. This characteristic is called creep. Eventually.If a load below a metal's tensile strength is applied at room temperature (72°F).6. The most common tables are the Brinell. but there will be no further measurable elongation if the load is kept at a constant level. All three of these factors determine a metal's ability to resist creep. the bond is very loose. creating a situation where the oxides will flake off. Although the load is held at a constant level. The measurement is converted into a hardness number through the use of a variety of established tables.10 Hardness Test . The depth of the penetration or the size of the impression is measured. it will cause some initial elongation. To test for hardness. In some metals.6. a fixed load forces an indenter into the test material (Figure 7). these oxides will adhere very tightly to the skin of the metal and effectively seal it from further oxidation as is evident in stainless steel.The atoms of metal have a tendency to unite with oxy- gen in the air to form oxide compounds. and HARDNESS TEST ROCKWELL A C D B F G E INDENTER DESCRIPTION SHAPE OF INDENTER } } Diamond Cone 1/16 in. and therefore.The resistance of a metal to indentation is a measure of its hardness and an indication of the materials's strength. Diameter Steel Sphere 1/8 in. and the metal gradually deteriorates as the time of exposure is extended. the degree of load applied and the length of time that it is applied. Vickers.6. the situation would change. the metal will gradually continue to elongate. This characteristic contributes to the fact that some metals will melt or undergo transformations at much lower temperatures than others.7. From the time it was discovered that the properties of pure metals could be improved by adding other elements. the one with the higher numerical coefficient will expand and contract more than the one with the lesser coefficient.7 EFFECTS OF THE ALLOYING ELEMENTS Alloying is the process of adding a metal or a nonmetal to pure metals such as copper. 1.Carbon is the most effective.11 Coefficient of Expansion . Normally. most widely used and lowest in cost alloying element available for increasing the hardness and strength of metal.All metals expand when heated and contract when cooled. Although carbon is a desirable alloying element. every effort is made to reduce the sulphur content to the lowest possible level because it can © COPYRIGHT 1999 THE ESAB GROU . The sulphur causes the machine chips to break rather than form long curls and clog the machine.7. This dimensional change is related to the crystalline structure and will vary with different materials.7% carbon is known as cast iron. alloy steel has increased by popularity. aluminum or iron.Some metals will absorb and transmit heat more readily than others.12 Thermal Conductivity . ductility and corrosion resistance. high levels of it can cause problems. the conversion tables may differ. When two different metals are heated to the same temperature and cooled at the same rate. 1.6. 1.Sulphur is normally an undesirable element in steel because it causes brittleness.2 Sulphur .LESSON I. metals that are welded are rarely in their pure state. In fact. tensile strength. An alloy containing up to 1. special care is required when welding high carbon steels and cast iron. The different expansion and contraction rates are expressed numerically by a coefficient of thermal expansion. They are categorized as having high thermal conductivity. For example. the shape of the indenter and the load applied. 1. It may be deliberately added to improve the machinability of the steel. PART A depending on the material being tested.1 Carbon . Common alloying elements and their effect on the properties of metals are as follows: 1.6. therefore. whereas the combination above 1.7% carbon in combination with iron is known as steel. a material listed as having a hardness of Rb or Rc means its hardness has been determined from the Rockwell "B" scale or the Rockwell "C" scale. The major properties that can be improved by adding small amounts of alloying elements are hardness. Manganese in contents up to 1% is usually present in all low alloy steels as a deoxidizer and desulphurizer. is a powerful hardening alloying element.10 Copper .7. This group of steels is usually referred to as chrome-moly steels. 1. 1. That is to say.8 Phosphorus . In addition to its hardening properties. phosphorus is added in very small amounts to some steels to increase strength.5 Nickel .Chromium. Efforts are made to reduce it to its very lowest levels.7. it is the most effective of all alloying elements in improving a steel's resistance to impact at low temperatures.Molybdenum strongly increases the depth of the hardening characteristic of steel. Manganese also increases the tensile strength and hardenability of steel. but high levels of copper can cause welding difficulties. It may also be used in very small amounts to control the size of the grains.7. © COPYRIGHT 1999 THE ESAB GROU .LESSON I. Silicon will add strength to steel but excessive amounts can reduce the ductility. PART A create welding difficulties.Copper contributes greatly to the corrosion resistance of carbon steel by retarding the rate of rusting at room temperature.7.7. In this respect.7.Phosphorus is considered a harmful residual element in steel because it greatly reduces ductility and toughness.6 Molybdenum .4 Chromium . Chromium is the primary alloying element in stainless steel.The greatest single property of steel that is improved by the presence of nickel is its ductility or notch toughness.7. in combination with carbon. 1. 1. 1. 1. chromium increases corrosion resistance and the strength of steel at high temperatures. It is quite often used in combination with chromium to improve the strength of the steel at high temperatures.Aluminum is primarily used as a deoxidizer in steel.3 Manganese . Nickel is also used in combination with chromium to form a group known as austenitic stainless steel.7.9 Aluminum . 1. Additional amounts of silicon are sometimes added to welding electrodes to increase the fluid flow of weld metal. it readily combines with oxygen and sulphur to help negate the undesirable effect these elements have when in their natural state. Electrodes with high nickel content are used to weld cast iron materials.7 Silicon . 1.Silicon is usually contained in steel as a deoxidizer. however. 1. Tungsten also joins with carbon to form carbides that are exceptionally hard.7. leaving the chromium free for corrosion protection.LESSON I. The range in which the change takes place may be wide or narrow.7. therefore. then that characteristic will occur over a range of temperatures with the alloyed metal.12 Tungsten .Tungsten is used in steel to given strength at high temperatures. the production costs of that steel.11 Columbium .7. oxygen and nitrogen from steel because their presence can cause brittleness.It should be understood that the addition of elements to a pure metal may influence the crystalline form of the resultant alloy.13 Vanadium . depending on the alloys and the quantities in which they are added. special care is often needed in the welding of low and high alloy steel. Nitrogen has the ability to form austenitic structures. and therefore have exceptional resistance to wear. and therefore. 1. These factors are closely controlled at the steel mill. but since the welding operation involves a nonuniform heating and cooling of metal.7. 1. PART A 1. © COPYRIGHT 1999 THE ESAB GROU . it is sometimes added to austenitic stainless steel to reduce the amount of nickel needed. a means of making carbon ineffective must be found. Since the carbon in the stainless steel decreases the corrosion resistance. The alloying element may also effect the crystalline changes by either suppressing the appearance of certain crystalline forms or even by creating entirely new forms.Columbium is used in austenitic stainless steel to act as a stabi- lizer.14 Nitrogen . efforts are made to eliminate hydrogen. It also helps increase the depth of hardening and resists softening of the steel during tempering treatments. 1. All these transformations induced by alloying elements are dependent on heat input and cooling rates. If a pure metal has allotropic characteristics (the ability of a metal to change its crystal structure) at a specific temperature.7. Columbium has a greater affinity for carbon than chromium.15 Alloying Elements Summary .Usually.Vanadium helps keep steel in the desirable fine grain condition after heat treatment. PART B 1.8.8. Unlike charges attract and like charges repel. One of these particles is the electron. In this process.8. The electrode (conductor) is either melted and added to the base metal or remains in its solid state. there would be no current flow. is the proton and under normal conditions the proton will remain stationary.000. sometimes referred to as electromotive force. whereby they are joined. about 1800 times as heavy as the electron. is commonly known as voltage. The rate that current flows through a conductor is measured in amperes and the word ampere is often used synonymously with the term current. All arc welding utilizes the transfer of electrical energy to heat energy.1. 1. the tendency is for the electrons to move from a position of over-supply (negative charge) to an atom that lacks electrons (positive charge). There are two kinds of electrical charges in existence .2 Science has established that all matter is made up of atoms and each atom contains fundamental particles. it has been theoretically established that one ampere equals 6.000. It should be noted that voltage that does not move through a conductor. 2.8.000.000) electrons flowing past a fixed point in a conductor every second.3 quintillion (6.4 Since we know that like charges repel and unlike charges attract.1. 3. 1. which has the ability to move from one place to another. bringing the metals to a molten state.LESSON I.3 Material is said to be in an electrically uncharged state when its atoms contain an equal number of positive charges (protons) and negative charges (electrons). 1. The electron is classified as a negative electrical charge.negative and positive. 1.300. Charges can be transferred from one place to another. To give an idea of the quantities of electrons that flow through a circuit. and to understand this principle. © COPYRIGHT 1999 THE ESAB GROU .1 The three basis principles of static electricity are as follows: 1. but without voltage. This tendency becomes reality when a suitable path is provided for the movement of the electrons. Another particle.Arc welding is a method of joining metals accom- plished by applying sufficient electrical pressure to an electrode to maintain a current path (arc) between the electrode and the work piece.1. For our purposes. electrical energy is changed into heat energy. The transfer of electrons from a negative to a positive charge throughout the length of a conductor constitutes an electrical current. it is easiest to think of voltage as the electrical pressure that forces the electrons to move.8.1 ELECTRICITY FOR WELDING Principles of Electricity .8 1.000. a basic knowledge of electricity and welding power sources is necessary. This balance is upset when pressure forces the electrons to move from atom to atom. This pressure.1. 1. Substances. we stop the flow.1. the water will move in the direction of the arrows. their ratio did not. Directly proportional means that even though the voltage and amperage may change. It may also be thought of as the resistance to current flow. have large amounts of electrons that transfer freely. PART B 1. Their comparatively low electrical resistance classifies them as good electrical conductors.8. the ratio of their relationship will not.8. such as wood and rubber.7 To better understand the electrical terms discussed above.6 Electrical resistance is primarily due to the reluctance of atoms to give up their electron particles. have what is called a tight electron bond and their atoms greatly resist the free movement of electrons. 1. and this can be compared to opening a switch in an electrical circuit. As can be seen. For example. even though the voltage and amperage changed in numerical value.8.Resistance is basic to electrical theory and to understand this principle. the current flow in amperes is directly proportional to the circuit voltage applied and inversely proportional to the circuit resistance. This flow rate in an electrical circuit is a unit of measure known as the ampere. The pump can be compared to a battery or a DC generator. on the other hand. 1. we might compare the closed water system with the electrical diagram shown in Figure 8. If we close the valve in the fluid circuit. This unit resistance is known as the ohm. The small pipe in the fluid circuit restricts the flow rate and can be likened to a resistor. It moves because pressure has been produced and that pressure can be likened to voltage in an electrical circuit.LESSON I. if we have a circuit of one volt and three amps. Such materials are considered poor electrical conductors. Now if we increase the volts to three. The term "inversely proportional" simply means that if the resistance is © COPYRIGHT 1999 THE ESAB GROU .1. You can see that as the pump is running. Metals. 1. we say the ratio is one to three.8. which is stated as follows: In any electrical circuit.2 Ohm's Law . our amperage will increase proportionately to nine amps. we must know the Ohm's Law. The water flows VALVE SWITCH LARGE PIPE RESISTOR 10 OHM PUMP SMALL PIPE BATTERY 12 VOLT CLOSED WATER SYSTEM ELECTRICAL DIAGRAM FIGURE 8 through the system at a certain rate.5 Different materials vary in their ability to transfer electrons. and the watt is a unit of power. E = Volts. It is defined as the amount of power required to maintain a current of one ampere at a pressure of one volt. © COPYRIGHT 1999 THE ESAB GROU . but the amperage drawn from the utility company depends on the number of watts required to run the electrical appliance.2. R = Resistance (Ohms)) 1. I = Amperes.1 1) The equation is easy to use as seen in the following problems: A 12 volt battery has a built-in resistance of 10 ohms.3.1 The amperage used by an electrical device can be calculated by dividing the watts rating of the device by the primary voltage for which it is designed. When we pay our electrical bills. What is the amperage? 12 ÷ 10 = 1. 1.8. the energy they generate is partially used to overcome the resistance created by the arc gap.8. The circuit voltage that comes into your home is a constant factor.8. I = Amperes) 1.2.3 Electrical Power . Ohm's Law can be stated mathematically with this equation: I=E÷R or E=I×R or R=E÷I (E = Volts. The watt is figured as a product of volts times amperes and is stated mathematically with the following equation: W =E × I E =W÷I I =W÷E (W = Watts.The word "watt" is another term frequently encountered in electrical terminology. PART B doubled.32 ohms 1.2 amps 2) What voltage is required to pass 15 amps through a resistor of 5 ohms? 15 × 5 = 75 volts 3) When the voltage is 80 and the circuit is limited to 250 amps. This energy becomes evident as heat. we are actually paying for the power to run our electrical appliances.2 The theory of electrical resistance is of great importance in the arc welding process for it is this resistance in the air space between the electrode and the base metal that contributes to the transfer of electrical energy to heat energy. In the welding process. the current will be reduced to one-half. what is the value of the resistor? 80 ÷ 250 = .LESSON I.8. the temperature increases to the point where it brings metals to a molten state. As voltage forces the electrons to move faster. the galvanometer needle will deflect plus (+). 1. one kilowatt is 1. With alternating current.8. 1. Starting at 0° rotation. the coil wire is moving parallel to the magnetic lines of force and cutting none of them. With direct current.4. most direct current is developed from alternating current.8. or DC generators). With this principle of converting mechanical energy into electrical energy understood. 1.4 Power Generation . the electron movement within the conductor is in one direction only. an electrical current is induced into the wire.3 Kilowatt is another term common in electrical usage. The current increases to the maximum because the wire is now at right angles to the lines of force. PART B 1. the coil wire cuts an increasing number of magnetic lines of force and reaches the maximum number at 90° rotation. then the amperage drawn by the appliance when in operation is determined as shown: 5 ÷ 115 = .Electrical energy is supplied either as direct current (DC) or alternating current (AC).2 For example.8. if the conductor is moved downwards the needle will deflect minus (-).8.1 Through experimentation. The sketch in Figure 9 will help to illustrate this principle. no current is being induced into the winding. therefore.8. 1.3 Figure 10 is a simplified sketch of an AC FIGURE 9 ELECTRO-MAGNETIC INDUCTION generator. the electron flow reverses periodically.4.8.4.000 watts of power. Likewise.3. Therefore. dry cells. 1.04 amperes 1. Although some types of electrical generators will produce current directly (such as batteries.4. we can apply it to the workings of an AC generator. if an appliance is designed for the common household primary voltage of 115 and the wattage stamped on the appliance faceplate is 5. © COPYRIGHT 1999 THE ESAB GROU .000 units of something.2 If the conductor is moved upwards in GALVANOMETER the magnetic field between the N and S poles. it was discovered that when a wire is moved through a magnetic field.LESSON I. The preface "kilo" is a metric designation that means 1. and the current is at its maximum when the motion of the conductor is at right angles to the magnetic lines of force.8.3.4 From 0° to 90° rotation. ALTERNATING CURRENT FIGURE 11 © COPYRIGHT 1999 THE ESAB GROU .4. we can visualize the rate at which the lines of force are cut throughout the cycle.4. The frequency of alternating current is the number of such complete cycles per second. we get the familiar sine wave as seen in Figure 11. PART B ROTATING COIL OR ARMATURE N 0° 90° S N S N 180° 270° S N S N S CONTACTS PERMANENT MAGNETS OR FIELD COILS BASIC AC POWER GENERATION FIGURE 10 1. 60 cycles per second (60 Hertz) is the standard frequency in North America. 0 0 0 MAXIMUM (–) (–) 0° START 90° 1/4 TURN 180° 1/2 TURN 270° 3/4 TURN 360° FULL TURN ONE CYCLE . 1.6 From 180° to 270°. 1. the coil wire cuts a diminishing number of lines of force and at 180° again reaches zero. For most power applications.LESSON I.4.4.8. If we plot the current versus degree of rotation.8.9 With this sine wave.8.5 From 90° to 180° rotation. 1. 1.8 With the aid of a graph.8.4.7 One cycle is completed as the coil wire moves from 270° to 0° and the current again drops to zero. we can (+) MAXIMUM (+) see that one complete cycle of alternating current comprises one positive and one negative wave (negative and positive meaning electron flow in opposing directions).8. the current begins to rise again but in the opposite direction because now the wire is in closer proximity to the opposite pole. 380.10 Some welders use a three-phase AC supply.4.8. 1. PART B 1. the voltage is generated at the power plant at 13. and conversely. 1. transmitted over long distances. and then reduced in steps for the end user.4. Therefore. welding machines for both single-phase and three-phase power are available.000 V 13. or 460 volts.LESSON I. then secondary current (amperes) decreases as the primary voltage increases. Three-phase is simply three sources of AC power as identical voltages brought in by three wires.12 FIGURE 12 Since all shops do not have three-phase power.600 V 208V 230V 460V FINAL USE FIGURE 13 © COPYRIGHT 1999 THE ESAB GROU . whereas industrial power requirements may be 208. If the sine wave for the three phases are plotted on one line.1 As can be seen in Figure 13.The function of a transformer is to increase or decrease voltage to a safe value as the conditions demand. they will appear as shown in Figure 12.8. It is increased. Transmitting such relatively low voltages over long distances would require a conductor of enormous and impractical size.800 V POWER PLANT 287.5 Transformers . Common household voltage is usually 115 or 230 volts. 230.000 V STEP UP 300 MILES POWER TRANSMISSION 132. secondary current increases as primary voltage decreases. the three voltages or phases being separated by 120 electrical degrees.11 This illustrates that three-phase power is 1 CYCLE THREE PHASE AC 0° 120° 240° smoother than single-phase because the overlapping three phases prevent the current and voltage from falling to zero 120 times a second.4. 1. If power supplied to a transformer circuit is held steady. Since the current flow (amperes) determines the wire or conductor size.800 volts. the high voltage line may be of a relatively small diameter.8. power transmitted from a power plant must be stepped up for long distance transmission and then stepped down for final use 1.8. HIGH VOLTAGE 34. thereby producing a smoother welding arc.000 V STEP DOWN 4.8.5. Remember that all transformers operate only on alternating current.5. the energy that is stored in this fluctuating magnetic field in the core is induced into this secondary coil. the voltage between the electrode and the work piece is 80 volts. This is best illustrated with an explanation of how a single transformer works.5.8. From that point.6 A simplified version of a welding transformer is schematically shown in Figure 15. where the cycle begins again.5.3 In the preceding paragraphs. we have found than an electrical current can be induced into a conductor when that conductor is moved through a magnetic field to produce alternating current. it is stepped down to a useable voltage. 1.5. Before the arc is struck.8. We need 80 volts for initiating the arc in the secondary or welding circuit.8. Therefore. When a second coil is wound around that same steel core. If this alternating current is passed through a conductor. the magnetic field will decay during the next quarter cycle until the voltage or current reaches zero at 180 electrical degrees. and if voltage is applied to one of its terminals and the circuit is completed. © COPYRIGHT 1999 THE ESAB GROU . that is the magnetic field will build in intensity through the first 90 electrical degrees. PART B 1. This welder would operate on 230 volts input power and the primary winding has 230 turns of wire on the core. current will flow.8.2 The transformer in a welding machine performs much the same as a large power plant transformer.4 If that conductor is wound around a material with high magnetic permeability (magnetic permeability is the ability to accept large amounts of magnetic lines of force) such as steel. thus we have 80 turns of wire in the secondary winding of the core. or the first cycle. From that point the current and the magnetic field again begin to decay until they reach zero at 360 electrical degrees. Immediately.8. the magnetic field permeates that core. See Figure 14. This conductor is called the primary coil. a pulsating magnetic field will surround the exterior of that conductor. BASIC TRANSFORMER 460 TURNS PRIMARY COIL 460 V STEEL CORE SECONDARY COIL 80 V 80 TURNS 1. This causes an electrical current of the same frequency as the primary coil to flow when the secondary circuit is completed by striking the welding arc. Remember that no current (amperage) flows until the welding circuit is completed by striking the arc.LESSON I.5. 1. the current direction reverses and the magnetic field will begin to build again until it reaches a maximum at 270 electrical degrees in the cycle. 1. The primary voltage coming into the machine is too high for safe welding.5 It is the build-up and collapse of this magnetic FIGURE 14 field that excite the electrons in the secondary coil of the transformer. 6 Power Requirements .5. and that is power consumption. etc. some means must be used to lower this voltage to a suitable level.6.LESSON I. 1.5. This being so. we explained that the watt was the unit of electrical power and can be calculated by the formula: Watts = Volts × Amperes 1.2 The primary side of our transformer must be capable of supplying 9600 watts From Figure 15. Theoretically.8.8.6. © COPYRIGHT 1999 THE ESAB GROU . we can see that the instantaneous power in the secondary also (disregarding losses due to heating. the voltage in that circuit will be 32 volts because it is then being controlled by the output control. we can calculate the required supply line current or amperage: Amperage = Watts ÷ Volts A = 9600 ÷ 230 = 41.74 AMPS 9600 WATTS 230 TURNS 230 VOLTS 9600 WATTS 80 TURNS SECONDARY OCV 80 necessary for initiating the arc is too high for practical welding.7 Since the 80 volts 41. PART B 1.6.8.74 Amps 1.8. a variable resistor of the proper value could be used as an output control since voltage is inversely proportional to 32 VOLTS 300 AMPS PRIMARY OUTPUT CONTROL SIMPLIFIED WELDING TRANSFORMER FIGURE 15 resistance as we saw when studying Ohm's Law. power factor.8.1 circuit is: Watts = 32 × 300 Watts = 9600 Watts 1. so by rearranging the formula. Earlier. and helps to determine the input cable and fuse size necessary.We can make another calculation by looking back at Figure 15. 1. you can see that adjusting the output control will also adjust the amperage or welding current.3 This information establishes the approximate power requirements for the welder. Ohm's Law also stated that the amperage is directly proportional to the voltage.8.).8 After the arc is initiated and current begins to flow through the secondary or welding circuit. 1. the old selenium rectifiers and the more modern silicon rectifiers. half-wave rectification takes place as shown in Figure 17.8. See Figure 18. See Figure 16. The commercially produced AC power that operates the welding machine must then be changed (rectified) to direct current for the DC arc.8. 1. the majority of industrial welding is done with machines that produce a direct current arc. current is allowed to flow through the rectifier. This is accomplished with a device called a rectifier. 3 PHASE FULL WAVE RECTIFICATION FIGURE 19 © COPYRIGHT 1999 THE ESAB GROU . 1. producing a considerably smoother direct current than half-wave rectification. a bridge rectifier is created.1 The function of a rectifier in the SILICON RECTIFIER SELENIUM RECTIFIER FIGURE 16 circuit can best be shown by the use of the AC sine wave.7. Two types of rectifiers have been used extensively in welding machines. During the positive half-cycle.8.3 By using four rectifiers connected in a certain manner.7. a relatively smooth DC voltage results as shown in Figure 19.Although much welding is accomplished with AC welding power sources. often referred to as diodes. During the negative half-cycle.LESSON I.2 SINGLE PHASE HALF WAVE RECTIFICATION FIGURE 17 The negative half-wave is simply cut off and a pulsating DC is produced.7.8. the current is blocked. PART B 1.7 Rectifying AC to DC . With one diode in the circuit.7. The bridge rectifier results in 120 positive half-cycles per second. This produces a DC composed of 60 positive pulses per second. 1.4 Three-phase AC can be rectified to 1 CYCLE SINGLE PHASE FULL WAVE RECTIFICATION FIGURE 18 produce an even smoother DC than single-phase AC. Since three-phase AC power produces three times as many half-cycles per second as singlephase power. producing full wave rectification.8. The operator can vary the arc voltage somewhat by increasing or decreasing the arc length. Increasing the wire feed speed increases the amperage.Constant current power sources are used primarily with coated electrodes. or both.300 A 100 200 300 AMPERES CONSTANT CURRENT VOLT / AMPERE CURVE FIGURE 20 Constant Voltage Characteristics . A slight decrease in arc length will cause a decrease in arc voltage and a slight increase in amperage.2 O L T S 34V . 1. also known as constant potential. the voltage output remains relatively constant. the output current or amperage is set by the operator while the voltage is designed into the unit.1." V 70 60 50 40 30 30V . the curve of a constant current machine drops downward rather sharply and for this reason.9.290 A 32V . the voltage is set at the machine and amperage is determined by the speed that the wire is fed to the welding gun. 1. This type of power source has a relatively small change in amperage and arc power for a corresponding relatively large change in arc voltage or arc length.1 In welding with coated electrodes.9. The characteristics of this power source are best illustrated by observing a graph that plots the voltampere curve. thus the name constant current. this type of machine is often called a "drooper.1 Constant Current Characteristics .1 Arc length plays an important part in welding with solid and flux cored electrodes.9.LESSON I. They may supply either AC or DC. 1.Constant voltage power sources.9. arc length caused by operator error.308 A 20 10 80 VOLT / AMPERE CURVE CONSTANT CURRENT 1. when using a constant voltage power source and a wire feeder that delivers the wire at a constant speed. and as the name implies.2. and they may have various means of controlling their voltage and amperage output. and puddle movement are automatically © COPYRIGHT 1999 THE ESAB GROU . are used in welding with solid and flux cored electrodes. A slight increase in arc length will cause an increase in arc voltage and a slight decrease in amperage. A power source that produces a satisfactory arc when welding with coated electrodes will be less than satisfactory for welding with solid and flux cored wires. PART B 1. The reasons for this is that the power source must be capable of producing the proper arc characteristics for the welding process being used. However. plate irregularities. Decreasing the wire feed speed decreases the amperage. As can be seen in Figure 20. just as it does in welding with a coated electrode.9 CONSTANT CURRENT OR CONSTANT VOLTAGE Welding power sources are designed in many sizes and shapes. On this type of power source. and the melt-off rate of the wire increases. the rate that the wire melts is dependent upon the amperage.9. This condition will advance the end of the wire towards the work piece until the proper arc length is reached where again. PART B compensated for by the characteristics of this process. The two major categories of static power sources are the transformer type and the rectifier type. this melt-off rate decreases and if the amperage increases.A great variety of welding power sources are being built today for electric arc welding and we shall mention some of the major types briefly. it melts back to the proper arc length where the melt-off rate equals the feeding rate. the voltage increases slightly. voltage. The wire is now feeding faster than it is melting off. and therefore. but to emphasize that their main difference is in the way they control the voltage and amperage output. we see that condition #2 produces the desired arc length.3 There are a variety of different welding machines. Since the wire is now melting off faster than it is being fed.3 Types of Welding Power Sources . If the arc length is decreased as in #3. Welding power sources can be divided into two main categories: static types and rotating types. amperage setting.3.9. so does the melt-off rate. 1.9.1 Static Types .LESSON I. To understand this. This is often referred to as a self-adjusting arc. 1.CONSTANT VOLTAGE FIGURE 21 internal design. © COPYRIGHT 1999 THE ESAB GROU . the amperage decreases considerably. If the arc length is increased as in #1. steps the line voltage down to useable welding voltages. the voltage drops off slightly. Our purpose is not to detail the function of each part of the machine. 1. the amperage is increased considerably. in turn. These automatic corrections take place in fractions of a second.2 In Figure 21. If the amperage decreases.Static type power sources are all of those that use commercially generated electrical power to energize a transformer that. keep in mind that with the proper voltage setting. and arc length.2. each with its own unique 100 200 300 AMPERES 400 30 V O L T S 40 1 2 3 20 10 VOLT / AMPERE CURVE .2. 1. and amperage.9. the melt-off rate equals the feeding rate. the melt-off rate of the wire decreases. and usually without the operator being aware of them. Available in either the constant current or the constant voltage type. They contain a transformer. however.3.2 Rotating Types .3. 1.1 A detailed discussion of the many types of welding power sources on the market today is much too lengthy a subject for this course.3.4 Power Source Controls . some manufacturers offer units that are a combination of both and can be used for coated electrode welding.9.4. Few.Rotating type power sources may be divided into two classifi- cations: 1. such as magnetic amplifiers or saturable reactors. or a combination of both. although additional information on the type of power sources for the various welding processes will be covered in Lesson II.3.1 The transformer type produce only alternating current. but due to the moving parts. are also utilized and the most modern types.9. © COPYRIGHT 1999 THE ESAB GROU . 1. required considerable maintenance. PART B 1. Both rotating types can deliver either AC or DC welding power. Electrical types of controls. but rectify the AC or DC by the use of selenium rectifiers.9.1.2 The rectifier types are commonly called "Welding Rectifiers" and produce DC or. silicon diodes or silicon controlled rectifiers.2 Excellent literature is available from power source manufacturers." All AC types utilize single-phase primary power and are of the constant current type.4.Welding power sources differ also in the method of controlling the output current or voltage. They may utilize either single phase or three phase input power.LESSON I.2. 1.3. containing silicon controlled rectifiers. 1. non-consumable electrode welding and for welding with solid or flux cored wires. 1. Both types are available as constant current or constant voltage models.9.9.2 Engine driven types consist of a gasoline or diesel engine coupled to a generator or alternator that produces the desired welding power.9. and should be consulted for further reference.1 Motor-generator types consist of an electric motor coupled to a generator or alternator that produces the desired welding power. a moveable shunt or diverter. if any. AC and DC welding current. These machines produced excellent welds. They are commonly called "Welding Transformers. or a moveable coil. Output may be controlled mechanically as in machines having a tapped reactor.9. 1. give precise electronic control. They are used extensively on jobs beyond commercial power lines and also as mobile repair units. Motor-Generators Engine Driven 1. 2.2. are being built today.1.9. Metals are good conductors. In 60 cycles per second (60 Hz) AC.A. ASME ASTM Atom — — — American Society of Mechanical Engineers American Society for Testing and Materials The smallest particle of an element that posses all of the characteristics of that element. Carbon content is usually below 0.3%. the frequency used in the U.) An alloy of iron and carbon. the current direction reverses 120 times every second. Carbon Steel — (Sometimes referred to as mild steel.GLOSSARY OF TERMS AISI — — American Iron and Steel Institute A material in which the atoms are capable of transforming into two or more crystalline structures at different temperatures.) A welding power source which will produce a relatively small change in amperage despite changes in voltage caused by a varying arc length.. neutrons.S.LESSON I. and electrons. © COPYRIGHT 1999 THE ESAB GROU . It consists of protons. Amperage is commonly referred to as the “current” in an electrical circuit. Ampere — Unit of electrical rate of flow. Used mostly for welding with coated electrodes. Constant Current — (As applied to welding machines. Allotropic Alternating Current — An electrical current which alternately travels in either direction in a conductor. GLOSSARY APPENDIX A LESSON I . Conductor — A material which has a relatively large number of loosely bonded electrons which may move freely when voltage (electrical pressure) is applied. ” Today. scrap limestone. relatively few electrons which will move when voltage (electrical pressure) is applied. we say 60 Hertz or 60 Hz. stainless steel. low alloy steels. Direction of current is dependent upon the electrical connections to the battery or other DC power source. glass. Used mostly for welding with solid or flux cored electrodes. Insulator — A material which has a tight electron bond. GLOSSARY Constant Voltage — (As applied to welding machines. High Alloy Steels — Steels containing in excess of 10% alloy content. Reversing the leads will reverse the direction of current flow. Ferrous — Containing iron. Wood. Induced Current or Induction — The phenomena of causing an electrical current to flow through a conductor when that conductor is subjected to a varying magnetic field. Hertz — Hertz (Hz) is the symbol which has replaced the term “cycles per second. coke.) A welding power source which will produce a relatively small change in voltage when the amperage is changed substantially. that is. Electron — Negatively charged particles that revolve around the positively charged nucleus in an atom. etc. Direct Current — An electrical current which flows in only one direction in a conductor.LESSON I. © COPYRIGHT 1999 THE ESAB GROU . Terminals on all DC devices are usually marked (+) or (-). ceramics and most plastics are good insulators. Stainless steel is considered a high alloy because it contains in excess of 10% chromium. Example: carbon steel. Ingot — Casting of steel (weighing up to 200 tons) formed at mill from melt of ore. rather than saying 60 cycles per second or simply 60 cycles. GLOSSARY Kilowatt Low Alloy Steels — — 1. An electrical device used to change alternating current to direct current. — The changes in the crystalline structure of metals caused by temperature and time. copper alloys. Volt — Unit of electromotive force. Proton Rectifier — — Positively charged particles which are part of the nucleus of atoms. Non-Ferrous — Containing no iron. Ohm Phase Transformation — Unit of electrical resistance to current flow.LESSON I.000 watts Steels containing small amounts of alloying elements (usually 1½% to 5% total alloy content) which drastically improves their properties. SAE Transformer — — Society of Automotive Engineers An electrical device used to raise or lower the voltage and inversely change the amperage. copper. or electrical pressure which causes current to flow in an electrical circuit. Example: Aluminum. Watts = Volts x Amperes © COPYRIGHT 1999 THE ESAB GROU . Watt — A unit of electrical power.