welding- smaw dec 2008

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SMAW WELDING PROCESS

INTRODUCTION

Shielded Metal Arc Welding (SMAW) is frequently referred to stick or covered

electrode welding. Stick welding is among the most widely used welding processes.

The flux covering the electrode melts during welding. This forms the gas and slag to

shield the arc and molten weld pool. The slug must be chipped off the weld bead after

welding. The flux also provides a method of adding scavengers, deoxidizers and alloying

elements to the weld metal. When an arc is struck between the metal rod (electrode) and

the work piece, both the rod and work piece surface melt to form a meid pool.

Simultaneous melting of the flux coating on the rod will form gas and slag which protects

the weld pool from the surrounding atmosphere. The slag will solidify and cool and must

be chipped off the weld bead once the weld run is complete (or before the next weld pass

is deposited). The process allows only short lengths of weld to be produced before a new

electrode needs to be inserted in the holder. Weld penetration is low and the quality of the

weld deposit is highly dependent on the skill of the welder.

There are many different types of electrodes used in the shielded metal arc welding,

(SMAW) process.

Arc welding electrodes are identified using the A.W.S, (American Welding Society)

numbering system and are made in sizes from 1/16 to 5/16 . An example would be a

welding rod identified as an 1/8" E6011 electrode.

The electrode is 1/8" in diameter

The "E" stands for arc welding electrode.

Next will be either a 4 or 5 digit number stamped on the electrode. The first two numbers

of a 4 digit number and the first 3 digits of a 5 digit number indicate the minimum tensile

strength (in thousands of pounds per square inch) of the weld that the rod will produce,

stress relieved. Examples would be as follows:


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E60xx would have a tensile strength of 60,000 psi E110XX would be 110,000 psi

The next to last digit indicates the position the electrode can be used in.

1. EXX1X is for use in all positions2. EXX2X is for use in flat and horizontal positions

3. EXX3X is for flat welding

The last two digits together, indicate the type of coating on the electrode and the welding

current the electrode can be used with. Such as DC straight, (DC -) DC reverse (DC+) or

A.C.

Table 1: Electrode Table

ELECTRODE

DIAMETER

(THICKNESS)

AMP RANGE PLATE

1/16" 20 - 40 UP TO 3/16"

3/32" 40 - 125 UP TO 1/4"

1/8 75 - 185 OVER 1/8"

5/32" 105 - 250 OVER 1/4"

3/16" 140 - 305 OVER 3/8"

1/4" 210 - 430 OVER 3/8"

5/16" 275 - 450 OVER 1/2"

Figure 1: Arc welding electrodes identification using the A.W.S, (American

Welding Society) numbering system


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LEARNING OBJECTIVES

At the end of this module, students will be able to

1. Describe what is SMAW welding2. Describe type of welding electrode

2. Identify the welding machine and it components

3. Perform SMAW welding process

Important Note:

Prior to carrying out the SMAW welding procedure, you are required to perform

equipment risk analysis and fill up a laboratory safety assessment form.

3. SMAW welding Set-UP PROCEDURE and SMAW welding PROCEDURE

Figure 2: Typical SMAW welding Set-Up

1. Work piece Make sure work piece is clean before welding

2. Work Clamp Place as close to the weld as possible


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3. Electrode Before striking an arc, insert an electrode in the electrode holder. A

small diameter electrode required less current than a large one.

4. Insulated Electrode Holder

5. Electrode Holder Position

6. Arc Length Arc length is the distance from the electrode to the work piece. A

short arc with correct amperage will give a sharp, crackling sound. Correct arc

length is related to electrode diameter. Arc length for 1/16 and 3/32 inches

diameter electrode should be about 1/16 in ( 1.6 mm ). Arc length for 1/8 and 5/32

inches diameter electrode should be about 1/8 in ( 3 mm ).

7. Slag Use a chipping hammer and wire brush to remove slag. Remove slag and

check weld bead before making another weld.

Striking an Arc Technique

When starting the arc, strike the electrode like a match on the work surface by gently and

quickly moving it along the weld metal.

Next, withdraw the electrode to form an arc length from the work piece of approximately

1/8.Reduce the arc length to the approximate length required to produce the desired

weld. Arc length is arc voltage.

As the arc length is shortened, the arc voltage is lowered. If the arc length is too close to

the work piece, the arc will go out or create a dead short. In this situation, the voltage

drops to 0 and the amperage rises significantly. This may cause the coating on the

electrode to break down or even catch on fire if it has an organic coating.

Arc length is dependent upon the type of electrode used. Arc length can vary in height

from just a drag to 3/16 distance from the work piece.

Too long of an arc length will cause the arc to go out. This situation is called a pop

out.


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Figure 3 : Scratch Start Technique

The scratch-start technique is preferred for ac welding.

1. Electrode

2. Work piece

3. Arc Drag electrode across work piece like striking a match, immediately lift

electrode slightly after touching work piece. If arc goes out, electrode was lifted too high.

If electrode sticks to work piece, use quick twist to free it.

Figure 3 : Tapping Technique


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1. Electrode

2. Work piece

3. Arc Bring electrode straight down to work piece, then lift slightly to start arc. If

arc goes out, electrode was lifted too high. If the electrode sticks to work piece,

use a quick twist to free it. Tapping Technique

Figure 4A : Positioning Electrode Holder (groove welds)

1. After learning to start and hold an arc, practice running beads of weld metal on

flat plate using a full electrode.

2. Hold the electrode nearly perpendicular to work piece. To produce the best results

hold a short arc, travel at a uniform speed and feed the electrode downward at a

constant rate as it melts.

Figure 5B : Positioning Electrode Holder (fillet welds)


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1. Tack welds.

2. Square Groove Weld Material up to 3/16 1n (5 mm) thick can often be weld

without special preparation using the square groove weld.

Figure 7 : Type of Tee Joint Welds

1. Electrode

2. Fillet weld Keep arc short and move at definite rate of speed. Hold electrode as

shown to provide fusion into the corner. Square the edge of the weld surface.

3. Multi layer deposits weld the second layer when a heavy fillet is needed. Use

any of the weaving pattern shown on Figure 4.

PRACTICAL ASSIGMENT

1. Perform SMAW welding Set-Up

2. Get 2 flat plates (approximately 5 in x 12 in)

3. Practice Striking an Arc Technique:

A. Scratch Start Technique

B. Tapping Technique

4. Practice running beads of weld metal on flat plate using a full electrode:

A. Stringer Bead

B. Weave Bead

C. Weave patterns

5. Perform Tack weld, Square Groove weld and Tee type joint weld.

welding- smaw dec 2008

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