What is SMAW?
Shielded metal arc welding (SMAW) also known as stick welding, is a manual process using a flux coated consumable electrode with a metal rod at the core.
Alternating current or direct current forms an arc between the electrode and the base metal creates the required heat. In the United States it is the most common method used.
The flux coating disintegrates and gives off vapors that serve as a shielding gas and provides a protective layer of slag.
Both protect the weld area from atmospheric contamination. As the metal rod inside the electrode melts it forms a molten pool which becomes the weld.
There are several variables the welder can control that will impact the width and height of the weld bead, the penetration of the weld and the quantity of spatter.
Stick welding is inexpensive when compared with other methods such as TIG. It is portable and works with any thickness and in any position.
The major downside is the slag created during the welding process along with slower speeds (unless you are highly skilled).
SMAW Arc Welding
Stick welding takes its’ name from the shape of the electrode, which looks like a stick. It can be used to weld many types of metals including steel, stainless steel and cast iron.
Stick welding machines provide constant current (CC) using direct current (DC) or alternating current (AC). Direct current operates on different directions based on the polarity. Alternating current switches between directions.
Power in the electrical circuit used to power the weld is measured in amperes. More current or amperage is needed for welding thicker metals or electrodes.
SMAW arc welding is primarily used to weld iron and steels.
It can be used in all positions:
SMAW Arc Welding (stick welding) uses the arc heat to melt the base metal and tip of a consumable electrode. The electrode and base metal are part of an electric circuit or welding circuit.
This circuit includes;
- Power source
- Welding cables
- Electrode holder
- Ground clamp
- The work or base metal
- Arc welding electrode
One cable is attached to the work and the other to the electrode holder.
Welding starts when an arc is struck between the tip of the electrode and base metal.
The heat melts the tip and the surface of the work.
Tiny globules of molten metal form on the electrode tip then transfer through the arc into the molten pool.
Filler is deposited as the electrode is consumed.
The Arc Welding, SMAW, Stick Welding arc is moved at an:
- appropriate arc length (approx. equal to the electrode diameter)
- appropriate travel speed
In turn, melting and fusing a part of the base metal and adding filler.
The SMAW arc is extremely hot (temperatures in excess of 9000ºF (5000ºC) at its center), melting occurs almost instantly as the arc touches the metal.
For welds made in the flat or the horizontal position, metal transfer is aided by:
- Gas expansion
- Electric forces
- Surface tension
Welds in other positions must overcome gravity.
In out of position welds, the base metal is unable to retain much molten metal in the crater. Smaller electrodes, lower amperages, and lower arc lengths should be used.
Gases are produced by the melting of the electrode coating and expand due to the heat of the boiling electrode tip.
The coating extends slightly beyond the metal tip of the electrode and controls the direction of gas expansion. This helps direct the molten metal into the weld metal pool.
Electromagnetic forces (arc travel or arc blow)
The tip is an electric conductor and so is the molten globule spray at the tip, so the globule spray is altered by magnetic forces acting at 90 degrees (sideways in most cases) to the direction of the current flow.
This is helpful in the horizontal, vertical, and overhead position welding.
Higher tensile strength rods have a higher tendency for arc blow.
The placement of the ground cable can have a major effect on these forces
The force keeping filler metal and slag in contact with molten base metal in the crater is surface tension.
It helps retain molten metal in horizontal, vertical, and overhead welding, and determines the shape of weld contours.
The characteristics of the weld (size of bead and penetration) can be controlled by adjusting the following variables when welding:
- Size and type of electrode
- Amperage (changed on the stick welding machine)
- Speed that you move the electrode along the joint being welded (called the speed of travel)
- Arc length (distance between the metal and the tip of the electrode). A rule of thumb is to use an arc length equal to the diameter of the core wire inside the electrode.
- Electrode angle
- Perpendicular (90 degrees) enables the most penetration
- 45 degrees equates to less penetration
- Weld width controlled by side to side motion of the electrode
- Polarity control (the direction the electrical current flows) when using DC or direct current
Advantages & Disadvantages of Arc Welding
SMAW or Stick Welding requires basic equipment and lends itself to field work because it is extremely portable.
- Cost is 30% to 50% of other welding methods
- Lightweight equipment
- Many types of available electrodes
- Good in tight spaces
- Cleaning metal surface before welding not as rigorous as other methods such as TIG
- Need to remove slag after welding. Entrapment of slag also is an issue in SMAW forming inclusions, which need to be removed.
- Unused electrode stubs – need to stop welding when you reach the last 2 inches of the electrode
- Slow relative speed of SMAW.
- Spatter cleanup and slag removal labor-intensive
- Creates more sparks and heat than other welding methods
- Chipping and grinding completed welds gives us harmful dust
- Need to stop during the welding process to replace used electrode and to chip away slag
Spatter and unused electrode stubs account for approx. 44 percent of consumed electrodes.