Electric Arc Welding Shielded Metal Arc Welding

In this presentation, the shielded metal arc welding is discussed in detail regarding the process, parameters, response, precautions, welding types, electrode types.

1. My name is mohsin iqbal qazi , working as lab engineer at IED UET Peshawar, Jalozai Campus. The topic which I have selected for my demo is electric arc welding Welding is permanent joining process that joins two or more than two surfaces at their

2. Joining process in which two (or more) parts are coalesced at their contacting surfaces by application of heat and/or pressure  Many welding processes are accomplished by heat alone, with no pressure applied

3. Provides a permanent joint Welded components become a single entity. Usually the most economical way to join parts in terms of material usage and fabrication costs. Not restricted to a factory environment, Welding can be accomplished "in the field“. Welding can be performed on both similar and dissimilar metals.

4. Welding processes can be divided into two major categories:  Fusion welding  Solid state welding

5. Fusion Joining processes that melt the base metals  In many fusion welding operations, a filler metal is added to the molten pool to facilitate the process and provide bulk and added strength to the welded joint.

6.  Arc welding (AW) – melting of the metals is accomplished by electric arc  Resistance welding (RW) melting is ‑ accomplished by heat from resistance to an electrical current between faying surfaces held together under pressure  Oxyfuel gas welding (OFW) melting is ‑ accomplished by an oxyfuel gas such as acetylene

7. Joining processes in which coalescence results from application of pressure alone or a combination of heat and pressure.  If heat is used, temperature is below melting point of metals being welded.  No filler metal is added in solid state welding. Plasma arc welding, laser beam welding, electron beam welding, resistance welding, spot welding

8.  Diffusion welding (DFW) –coalescence is by solid state fusion between two surfaces held together under pressure at elevated temperature  Friction welding (FRW) coalescence by heat ‑ of friction between two surfaces  Ultrasonic welding (USW) coalescence by ‑ ultrasonic oscillating motion in a direction parallel to contacting surfaces of two parts held together under pressure

9. Now I will explain shielded metal arc welding process that lies under the category of fusion welding.

10. Arc Welding Also known as “stick welding”, manual metal arc welding It is a fusion welding processes which uses an electric arc to produce the heat required for melting the metal. The welder creates an electric arc that melts the base metals and filler metal (consumable) together so that they all fuse into one solid piece of metal

11. ELECTRIC ARC WELDING In this process heat required to melt the base metal and electrode is obtained from the electric arc produces between work piece and electrode. This electric arc is generated as current passes through the highly resistant air gap and act as flame of intense heat. Pressure is not applied.

12. ELECTRIC ARC WELDING

13. Arc Welding It is a manual arc welding process that uses a consumable electrode coated in flux agents and slag formers to lay the weld. An electric current , in the form of either alternating current or direct current from a welding power supply , is used to form an electric arc between the electrode and the metals to be joined . As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as a shielding gas and providing a layer of slag, both of which protect the weld area from atmospheric contamination.

14. Tiny drops of metal enter the arc stream and are deposited on the parent metal

15. Ultraviolet radiation emitted in arc welding is injurious to human vision Welder must wear a special helmet with a dark viewing window Filters out dangerous radiation but welder is blind except when arc is struck Sparks, spatters of molten metal, smoke , and fumes add to the risks

16. SMAW, MMAW,Stick Heat, Electric Arc, 5500 C. Electrode (covering, holder, compatible) Flux (composition, function) Slag (Function, removal) Power AC DC Removal of electrode Application Advantages Defects Plasma arc welding, laser beam welding, electron beam welding, resistance welding, spot welding

17. Arc Welding Arc welding is a process that melts and joins metals by heating them with an arc established between a stick like covered electrode and the metals. The core wire conducts the electric current to the arc and provides filler metal for the joint. The electrode holder is essentially a metal clamp with an electrically insulated outside shell for the welder to hold safely. The heat of the arc melts the core wire and the flux covering at the electrode tip into metal droplets. Molten metal in the weld pool solidifies into the weld metal while the lighter molten flux floats on the top surface and solidifies as a slag layer.

18. Coated Electrodes The electrode is coated in a metal mixture called flux, which gives off gases as it decomposes to prevent Weld contamination Introduces deoxidizers to purify the weld Causes weld-protecting slag to form Improves the arc stability, and Provides alloying elements to improve the weld quality.

19. Arc Welding

20. Principle of Arc A suitable gap is kept between the work and electrode A high current is passed through the circuit. The electric energy is converted into heat energy, producing a temperature of 3000°C to 4000°C. This heat melts the edges to be welded and molten pool is formed. On solidification the welding joint is obtained

21. Arc Welding Process: Intense heat at the arc melts the tip of the electrode Tiny drops of metal enter the arc stream and are deposited on the parent metal As molten metal is deposited, a slag forms over the bead which serves as an insulation against air contaminants during cooling After a weld ‘pass’ is allowed the cool, the oxide layer is removed by a chipping hammer and then cleaned with a wirebrush before the next pass.

22. Arc Welding Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the world's most popular welding processes.

23. Basics of Arc Welding The arc is struck between the electrode and the metal. It then heats the metal to the melting point. The electrode is then removed, breaking the arc between the electrode and the metal. This allows the molten metal to “freeze” or solidify.

24. Basic Steps of Arc Welding Prepare the base materials: remove paint and rust Choose the right welding process Choose the right filler material Assess and comply with safety requirements Use proper welding techniques and be sure to protect the molten puddle from contaminants in the air Inspect the weld

25. Electric Power for Welding Current used may be 1. AC 2. DC For most purposes, DC is preferred.

26. Arc Welding Equipments

27. Arc Welding The choice of electrode for SMAW depends on a number of factors, including The weld material Welding position and The desired weld properties.

28. Welding Electrodes The composition of the electrode core is generally similar and sometimes identical to that of the base material. But even though a number of feasible options exist, a slight difference in alloy composition can strongly impact the properties of the resulting weld.

29. Functions of electrode (flux) covering Provides the gaseous shield to protect the molten metal from air. Cellulose-type electrode (C6H10O5)x , providing gas mixture of H2, CO, H2O and CO2. Limestone-type electrode (CaCO3) – low in hydrogen and it is used for welding metals that are susceptible to hydrogen cracking such as high- strength steels.

30. Functions of electrode (flux) covering Deoxidation - Provide deoxidizers and fluxing agent to deoxidize and cleanse the weld metal. The solid slag also protects the weld metal from oxidation. Arc stabilization - Provide arc stabilizers which are compounds such as potassium oxalate and lithium carbonate. They readily decompose into ions in an arc, which increase electrical conductivity. Metal addition - Provide alloying elements (for composition control) and metal powder (increase deposition rate) to the weld pool.

31. Arc Welding Power Supplies The current for arc welder can be supplied by line current or by an alternator/generator. The amount of heat is determined by the current flow (amps) The ease of starting and harshness of the arc is determined by the electrical potential (volts).

32. Amperage Output Current setting formula is 4 * Dia of Rod 185 to 225 amps is a common size. For an individual weld, the optimum output amperage is determined by thickness of the metal type of joint and type of electrode

33. DC Arc Welding D.C. machines are made up to the capacity range of 600 amperes. 45 to 95 volts D.C. can be given in two ways: Straight polarity Reverse polarity The polarity will affect the weld size and application

34. Direct Current Direct current : The type of current where the flow of electrons (polarity) is in one direction. Controlling the polarity allows the welder to influence the location of the heat. When the electrode is positive (+) D C E P it will be slightly hotter than the base metal. (reverse) When the base metal is positive (+), D C E N the base metal will be slightly hotter than the electrode. (straight) DC is required for GMAW It is frequently used for SMAW

35. Ampe r e Electricity passing through a resistance causes heat. An air gap is a high re sistance The greater the amperage flowing through the resistance (air gap)  the greater the heat. The electrode also has resistance. Excessive amperage for the diameter of the electrode (current density) over heats the electrode. Insufficient amperage for the diameter of electrode makes the electrode hard to start.

36. Arc Welding Defects The most common quality problems associated with SMAW include 1. Weld spatter Weld spatter, while not affecting the integrity of the weld, damages its appearance and increases cleaning costs. It can be caused by excessively high current . 2. Porosity Porosity, often not visible without the use of advanced nondestructive testing methods, is a serious concern because it can potentially weaken the weld.

37. Arc Welding Defects 3. Poor fusion Another defect affecting the strength of the weld is poor fusion, though it is often easily visible. It is caused by low current, contaminated joint surfaces, or the use of an improper electrode. 4. Shallow penetration Shallow penetration, another detriment to weld strength, can be addressed by decreasing welding speed, increasing the current or using a smaller electrode . 5. Cracking. Any of these weld-strength-related defects can make the weld prone to cracking, but other factors are involved as well. High carbon, alloy or sulfur content in the base material can lead to cracking, especially if low-hydrogen electrodes and preheating are not employed . Furthermore, the workpieces should not be excessively restrained, as this introduces residual stresses into the weld and can cause cracking as the weld cools and contracts.

38. Advantages of arc welding 1. Simple welding equipment 2. Portable 3. Inexpensive power source 4. Relatively inexpensive equipment 5. Welders use standard domestic current. 6. Process is fast and reliable 7. Short learning curve 8. Equipment can be used for multiple functions 9. Electric arc is about 5,000 o C 10. Used for maintenance, repair, and field construction

39. Disadvantages Not clean enough for reactive metals such as aluminium and titanium. The deposition rate is limited because the electrode covering tends to overheat and fall off. The electrode length is ~ 35 mm and requires electrode changing lower the overall production rate.

40. Arc Welding

41. Arc Welding

42. ASME SEC IX WELDING CODES FOR PLATES S.No WELDING POSITION CODE 1 FLAT WELDING 1 G 2 HORIZONTAL WELDING 2 G 3 VERTICAL WELDING 3 G 4 OVERHEAD WELDING 4 G

43. ASME SEC IX WELDING CODES FOR PIPES S.No WELDING POSITION CODE 1 When pipe can rotated 1 G 2 If pipe is at front and cannot be rotated 2 G 3 If pipe is horizontal, we have To move while it cannot be rotated 5 G 4 If pipes are at angle of 45 degree or less or more between 0 and 90 means they are at an angle and cannot be rotated 6 G

44. Joint Types Butt joint 2) Corner Joint 3) T-Joint 4) Lap Joint 5) Edge Joint

45. Factors Plate/Pipe Current Root Gap Arc Voltage Weld Joints Design (V , U , Double V , Double U) Materials (Steel Types) Post Weld Heat Treatment (PWHT) (Yes/No) Angle Electrode Diameter (3.2mm,4mm,5mm) Electrode Pre-Heat (Yes/No) Welding Position (Flat , Horizontal , Vertical , Overhead)

46. Response Variables Hardness Impact Strength Tensile Strength Micro-Structure Fatigue Bend Minimizing defects ( Cracks, Pin Holes, Under Cut, Slag Intrusions) Weld Bead (Width/Height)