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Shielded Metal Arc Welding of Plate

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1 Shielded Metal Arc Welding of Plate
Chapter 4 Shielded Metal Arc Welding of Plate

2 Objectives Demonstrate safe work practices
Demonstrate the ability to strike an arc at a specific point List the problems that can result if the welding current is set too low or too high Discuss how to select the correct diameter of welding electrode for a weld Describe the effects of overheating a weld by comparing the bead’s shape for width, reinforcement, and appearance

3 Objectives (cont'd.) Define arc length, and describe the effects of using too short or too long an arc length Compare a leading electrode angle to a trailing electrode angle Tell what characteristics of the weld bead can be controlled by the movement or weaving of the welding electrode Demonstrate ten weave patterns for weld beads Discuss the importance of positioning the welder and the plate properly before starting to weld

4 Objectives (cont'd.) Give the characteristics of the three filler metal groups E6010 and E6011, E6012 and E6013, and E7016 and E7018 Define stringer beads and tell how they are used Demonstrate a vertical up stringer bead and a horizontal stringer bead Demonstrate how to make a welded square butt joint in the flat, vertical up, and horizontal positions

5 Objectives (cont'd.) On an edge joint, demonstrate how to make a flat weld, a vertical down weld, a vertical up weld, a horizontal weld, and an overhead weld On an outside corner joint, demonstrate how to make a flat weld, a vertical down weld, a vertical up weld, a horizontal weld, and an overhead weld

6 Objectives (cont'd.) Demonstrate how to make a welded lap joint in the flat position, a welded horizontal lap joint, a vertical up-welded lap joint, and an overhead-welded lap joint Demonstrate how to make a welded tee joint in the flat, horizontal, vertical, and overhead positions

7 Introduction Shielded metal arc welding (SMAW)
Common method used to join plate Also called stick welding Provides high temperature and heat concentration Allows a weld pool to be built up quickly Filler metal from the electrode increases strength Minimum equipment required High-quality welds can be consistently produced

8 Figure 4-1 Striking an arc and running short beads
Figure 4-1 Striking an arc and running short beads. © Cengage Learning 2012

9 Effect of Too High or Too Low Current Settings
Each welding electrode must be operated in a specific current range Current set too low results in poor fusion and poor arc stability Arc length is very short Results in frequent shorting and sticking of the electrode Weld bead at a high amperage is wide and flat with deep penetration Spatter is excessive Causes electrode to discolor, crack, low red, or burn

10 Electrode Size and Heat
Welding electrode size depends upon: Welder skill and welding codes or standards Metal thickness and size Small diameter electrodes Require less skill, but more time Large diameter electrodes May overheat: can cause a burn-through Chill plate Large piece of metal that absorbs excessive heat

11 Figure 4-9 The effect on the shape of the molten weld pool caused by the heat input.
© Cengage Learning 2012

12 Arc Length Distance the arc jumps from the end of electrode to the plate or weld pool surface To maintain a constant arc length: electrode must be lowered continuously Narrow range for the arc length to remain stable Higher settings must be within the amperage range for the specific electrode

13 Figure 4-11 Welding with too long an arc length. Larry Jeffus.

14 Electrode Angle Measured from electrode to surface of the metal
Leading electrode angle: pushes molten metal and slag ahead of the weld Flat position: caution must be taken to prevent cold lap and slag inclusion Rapid cooling: prevents the metals from fusing together

15 Electrode Angle (cont'd.)
Preventing cold lap and slag inclusions: Use as little leading angle as possible Ensure arc melts the base metal completely Use a penetrating-type electrode Move arc back and forth across molten weld pool to fuse both edges

16 Electrode Angle (cont'd.)
Trailing electrode angle Pushes molten metal away from leading edge of pool Solidifies toward the back Molten metal is forced away from bottom of weld Arc melts more of the base metal Reinforces weld

17 Figure 4-21 Welding with a trailing angle. Larry Jeffus.

18 Electrode Manipulation
Weaving the welding electrode Controls several bead characteristics Penetration Buildup Width Porosity Undercut Overlap Slag inclusion

19 Electrode Manipulation (cont'd.)
Weave pattern for each weld Personal choice of the welder Some patterns are especially helpful for specific welding situations Many weave patterns are available

20 Figure 4-23 Weave patterns.
© Cengage Learning 2012

21 Position of the Welder and the Plate
Should be in a relaxed, comfortable position before starting to weld Welding helmet is down Welder is blind to surroundings Several factors led to swaying Lean against or hold a stable object Find most comfortable angle

22 Practice Welds Grouped according to: Instructor or welder Students
Type of joint Type of welding electrode Instructor or welder Selects order in which welds are made Students Find it easier to start with butt joints Flat position allows welder to build skills slowly

23 Electrodes Arc welding electrodes used for practice welds are grouped into three filler metal classes F3 E6010 and E6011 electrodes Cellulose-based flux F2 E6012 and E6013 electrodes Rutile-based flux F4 E7016 and E7018 electrodes Mineral-based flux Should be the last choice

24 Stringer Beads Characteristics
Straight weld bead with little or no side-to-side electrode movement Used to practice maintaining arc length and electrode angle Should be straight Easily made once the welder develops the ability to view the entire welding zone

25 Square Butt Joint Made by tack welding two flat pieces of plate together Root opening: space between the plates Changing the root opening affects penetration Excessively large openings can cause burn-through

26 Figure 4-43 Square butt joint in the flat position.
© Cengage Learning 2012

27 A B FIGURE 4-44 (A) After the arc is established, hold it in one area long enough to establish the size of molten weld pool desired. (B) Weld back over the arc strike to melt it into the weld. A & B Larry Jeffus.

28 Edge Weld Made by placing the edge of the plate evenly
Plates should be clamped tightly together Make tack welds to hold the plates together Size of weld should equal the thickness of the plate being joined Weld bead should have a slight buildup

29 FIGURE 4-49 Make tack welds at the ends of the joint.
© Cengage Learning 2012

30 Outside Corner Joint Made by placing the plates at a 90 degree angle to each other Make small tack welds Weld bead should completely fill the V-groove formed by the plates Slightly convex surface buildup Back side can be used to practice fillet welds

31 Lap Joint Made by overlapping edges of the two plates
Can be welded on one side or both sides with a fillet weld Buildup should equal the thickness of the plate Good weld has smooth transition from the plate to the surface of the weld

32 FIGURE 4-69 Lap joint. © Cengage Learning 2012

33 Tee Joint Made by tack welding one piece of metal on another piece of metal at a right angle Heat is not distributed uniformly between both plates Most heat should be directed toward the base plate Can be strong if welded on both sides Flat or slightly concave appearance

34 Figure 4-83 Tee joint in the flat position.
© Cengage Learning 2012

35 Summary Shielded metal arc welding
Referred to as stick welding Stick shape of electrode Tendency of electrode to stick to the workpiece Difficult to view entire welding zone Developing visual skill is essential Takes time and practice Objectively inspecting work Enhances skills

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