THE FIVE ESSENTIAL VARIABLES OF SMAW (STICK) WELDING
Welding is a practical skill that requires continual practice and careful attention to the variables that the welder controls to improve. The old golden rule “practice makes perfect” applies to welding in that the more you do, as long as you or someone evaluates your welds, the better you become.
The term variable as used in this text means something the welder has control of either before welding or during welding.
Review the following five essential variables and the weld discontinuities that may result if control is not maintained.
KEY POINT: An easy way to remember the variables is by remembering the first letter in each one spells the word CLASS.
1. Current Setting.
2. Length of Arc.
3. Angle of Electrode.
4. Speed of Travel.
5. Selection of Electrode.
1. Current Setting.
The welding current or amperage is essential to producing welds with good appearance and the required strength characteristics. The welder controls the amperage variable by setting the amperage on the welding machine prior to welding.
The amperage is set from recommended ranges according to the size of the electrode, the type of electrode, and the type of current AC, DCEN or DCEP you are using.
KEY POINT: AC means Alternating Current, DC means direct current and can be set for Direct Current Electrode Negative (Straight Polarity) or Direct Current Electrode Positive (Reverse Polarity).
Some electrodes are designed to work best on a given Current and Polarity, for example an E-6010 should be used with DCEP (direct current electrode positive).
Some electrodes are designed to work best on DCEN while others allow a selection of Current to be used.
The chart below shows typical amperage ranges
Amperage may be referred to as the heat by some welders.
An excellent place to find amperage ranges, recommended current and polarity and information on electrode applications are the Electrode Selection Guidebooks available at any welding supply store.
The amperage range is fine tuned by the welder to the correct amperage before welding on an actual workpiece or testpiece by running practice welds on a piece of scrap metal in the position of welding as follows;
The chart below gives an idea of the evaluation process;
In example A the E-6010 weld made with the correct amperage appears properly formed with the appropriate width and consistency.
In example B the weld made with amperage setting too low appears thin and stringy.
In example C the weld made with amperage setting too high appears wide and flat with excessive spatter and evidence of undercut.
A B C
A) Amperage correct
B) Amperage too low
C) Amperage too high
KEY POINT: Remember conditions may change for example; if you are welding multiple passes in the vertical position and using a weave technique you may need to increase the amperage when weaving over a prior weld bead.
You may want to use higher setting for welding flat and horizontal than for welding in other positions.
A setting used on one machine may need to be adjusted when using another machine, if the machines are not calibrated the same.
One welder (operator) may prefer to use a slightly higher setting and travel faster than you, so set the amperage for your technique.
The correct amperage is one that provides a good weld and is not based on a specific number on the machine.
2. Length of Arc
When electricity is made to jump across a gap it is said to arc across the gap. In Shielded Metal Arc Welding (Stick) it is this arcing effect that creates the intense heat required for melting the electrode and the base metal together.
The Arc is the term used to describe the distance from the tip of the electrode to the base metal and can be varied from lightly touching the metal at an angle sufficient to maintain an arc to a distance far enough from the base metal to extinguish the arc.
If the electrode is held in contact with the work using the slight angle to maintain the arc it is referred to as the drag technique. This technique is often used to weld in the flat and horizontal positions, especially with larger or iron powder electrodes. If contact with the base metal is made too quickly however; the electrode will stick or freeze to the metal.
Another method to employ is to allow a slight gap between the electrode tip and the base metal. The length of the arc gap affects the appearance of the weld.
The welding machines used in Shielded Metal Arc Welding are known as Constant Current machines which mean that the current stays relatively constant through changes in the voltage. The machine increases the voltage as the arc length is increased to maintain current flow at the amperage level set on the machine. If the voltage is increased too much the arc may become unstable and result in a poor quality weld.
The correct arc length may vary according to the type of electrode and the position of welding.
When production welding flat or horizontal the drag method is often used for ease in welding and faster travel speeds.
When a slight gap is maintained the force of the arc provides a weld bead with a slightly flatter appearance with less chance of slag inclusions and better joint penetration.
KEY POINT: make sure you are maintaining a proper arc length before adjusting the amperage on the welding machine. If the arc length is too long and the voltage increases it may seem as though the amperage is too high or the sticking caused by too low an arc length with some electrodes may seem as though the amperage is too low.
3. ANGLE OF ELECTRODE
In the Shielded Metal Arc Welding (STICK) process there are two electrode angles that the welder must control. The first angle is the one formed between the electrode and the base metal, called the work angle. The second angle is the angle the electrode is held at relative to the direction of travel, called the travel angle.
The travel angle for the flat, horizontal and overhead can be either pulled or pushed and
the travel angle for the vertical can be either upward or downward.
Note: The direction of travel across the plate for both drag and push methods:
The work angle should be one that places the weld metal between the members to be welded in the manner desired. The weld metal will be deposited in a relatively straight line from the tip of the electrode to the work. The decision to push or pull is largely one of experience and practicality. I believe a flatter somewhat less rounded weld can be achieved with a slight push angle when welding flat and horizontal. When welding in the vertical upward position a more extreme angle using the side of the electrode seems to produce a flatter weld with tighter ripples.
KEY POINT: because of the high deposition rat of an E-7018 electrode it is more difficult to weld vertical downward.
4. SPEED OF TRAVEL
The rate of travel across the joint is controlled by the welder during welding and greatly affects the appearance and strength characteristics of the weld.
The amount of weld metal deposited (weld deposition rate) and the travel speed may vary with the type and size of electrode being used. The correct weld speed will result in a well formed weld bead that shows good fusion, penetration and a gradual transition of weld metal into the corners of the joint.
Since the travel speed is not timed in stick welding, the welder must be able to read the molten weld pool as the electrode is manipulated across the joint. A weld speed that is too fast results in a thin stringy weld with poor strength. A weld bead that is too slow a speed will result in a heavy weld that has too much convexity.
5. SELECTION OF ELECTRODE
There are a variety of electrodes available for welding a wide range of metals. The electrode for a given application must be selected carefully to provide the strength characteristics required for the weld joint. One of the most useful tools for electrode selection is the Electrode Handbooks available from welding supply outlets. These handbooks provide information from electrode classification to application and usability.
In general the electrode weld metal must be matched to the type and composition of the base metal being welded. Further some electrodes within the available scope are designed for specific purposes.
Some of the most widely used Electrodes are those used for welding carbon Steel.
The following is a brief description of the most commonly used electrodes for welding Carbon Steel.
The electrodes are classified by a letter and numbering system as follows:
The tensile strength is defined as the ability of the weld metal to withstand forces acting to pull it apart.
The last digit indicates the type of flux or electrode covering and in turn determines the type of current, penetration and appearance of the weld.
The following are some commonly used electrodes and their characteristics.
The E-6010 and E-6011 Electrodes are similar with only a slight change in the electrode covering to enable the E-6011 to be used with AC current.
These electrodes have a deep penetrating and forceful arc with quickly solidifying weld metal. They may be used in all positions including Vertical Downward. Because of the arc characteristics they may be used on dirty or rusty metals and for root passes in open root grooves and pipe.
These electrodes have a certain amount of moisture content to enable the forceful arc and should not be stored in ovens.
The E-6012 and E-6013 electrodes are also similar with some variations in the electrode covering. These electrodes have shallow to medium penetration making them useful for welding thinner sections, sheet metal and for welding gaps due to poor joint fit up. Trapping slag may be a problem when using E-6013 at lower amperages or on dirty metal surfaces.
Both the E-7018 and E-7028 electrodes are Iron powder Low hydrogen electrodes. The E-7028 is used for flat and horizontal position only and may be used with a drag technique to produce a smooth weld with good appearance.
The addition of Iron powder to these electrodes covering adds to the available weld metal resulting in heavier convex welds.
These electrodes are classified as low hydrogen meaning they are low in moisture content and should be stored in ovens or moisture free environment once the container is opened.
Because these electrodes are low hydrogen they are the choice for welding higher carbon steels.
A short arc length should be maintained especially when striking the arc to avoid surface porosity (tiny holes).
If control of these variables are not properly maintained the result may be a weld with one or more discontinuities or defects.
KEY POINT: A discontinuity is defined as; an irregularity or imperfection in the appearance of the weld or surrounding base metal. A defect is defined as; a single or group of discontinuities severe enough to cause rejection or rework of the weld or assembly.
When the five essential variables are properly controlled the weld profile should be properly formed and free of discontinuities.
Note: In the above diagrams the size of the fillet weld is shown in dotted lines and the throat is from the root of the joint to the face of the weld.
CHART SHOWING DISCONTINUITIES IN SMAW AND THEIR CAUSES
Slow travel speed that allows weld metal to build up
Welding currents too low
A combination of Travel speed to fast and current too high
Improper placement of weld beads when multiple pass welding
Amperage too high
Arc length too long increasing the force of the arc so that it cuts into corners
Improper weld technique causing the corners to be left unfilled or cut into
Groove joint not completely filled and overlapped
Insufficient Leg Size
Using the wrong electrode angle causing the weld to be deposited to heavily on one side
Using the wrong angle on multiple pas welds Causing the welds to overlap incorrectly
Amperage too low
Travel speeds too fast
Using too large an electrode for the root of the joint
Improper electrode angle at the root of the joint
Improper weave technique
Using the wrong electrode for the desired joint penetration: (using E-6013 instead of E-6010)
Amperage too low
Travel speeds too fast
Improper electrode angle at the sides of the joint
Improper weave technique that does not allow enough time at the sides of the joint
Using the wrong electrode for the application
Amperage too low and /or travel speed too slow
Electrode too large with low currents
Dirty base metal painted or galvanized surfaces
Arc length too long especially with E-7018 Electrodes
Moisture in low hydrogen electrodes
Wind or fans strong enough to break down the shielding gas
Improper manipulation of the electrode especially with E-6013
Improper cleaning and slag removal between multiple pass welds
Using the wrong Electrode for the application
Using Excessively high amperage on some metals
Amperage too high
Electrode angle too extreme
Arc length too long