THE SHIELDED METAL ARC WELDING PROCESS
STICK
INTRODUCTION
The shielded Metal Arc Welding Process (SMAW) is also widely known by the shop term Stick Welding. The term stick is a reference to the electrode used to provide the filler metal for welding with this process.
The Shielded metal Arc Welding process is one of the oldest and most widely used methods of joining metals by welding. The process is popular because of the simplicity of equipment involved, its portability, reliability and adaptability to outdoor use.
The process may be used to weld a variety of metal types and shapes in any position.
DESCRIPTION
In the SMAW process, welding is done by setting up an electrical circuit using a welding machine to produce the electricity, a welding cable with an electrode holder to hold the electrode and a ground cable with a clamp to fasten to the work-piece to complete the circuit. The weld is made by touching the electrode to the work-piece closing the electrical circuit and causing the electrode to melt and form the weld.
The electrical circuit for welding
The electrode has a metal core with a covering referred to as the flux by welders
The metal core of the electrode is either the same as, or is compatible with, the metal being welded.
The main difference between the electrodes used to weld mild steel is the composition of the flux. Manufactures add Ingredients to the flux to influence the characteristics (the way the electrode operates) of the electrode. These characteristics include; the current and polarity, penetration, spatter, slag type and weld appearance.
The covering on the electrode decomposes during welding to provide a gaseous shielding that protects the molten weld puddle from the nitrogen and oxygen in the air that can cause welds to become brittle or have holes (porosity) in them.
The covering also aids in arc stability, cleaning (deoxidizing) the metal to be welded and forms the protective black slag that covers the weld metal.
KEY POINTS: The slag should be removed before more welds are added to the joint when multiple pass welding.
Electrodes are classified by the American Welding Society based on their specific requirements and intended use.
Electrode guidebooks (available at welding supply stores) are a good source of information regarding appropriate choices of electrodes.
To start the weld the electrode is tapped (or scratched like striking a match) on the work-piece then immediately a small gap is held between the electrode tip and work-piece.
Since the gap creates an electrical arcing effect between the electrode tip and the work-piece, the gap is referred to as the welding arc.
The distance from the tip of the electrode to the work-piece can be varied from lightly touching the work-piece at an angle sufficient to maintain an arc to a distance approximately equal to the electrode core.
When viewed through the welding helmet’s filter plate the molten metal from the melting electrode and work-piece is known as the weld puddle.
THE WELDING MACHINE
The welding machine (or power source) may vary in style and type but they all produce a steady flow of electrical current with relatively low voltage to maintain a welding arc.
The type of welding machine used for stick welding is known as a constant current machine which means the current stays relatively constant as set by the operator while the voltage varies with the arc length.
The machine may produce either Alternating Current; Direct Current; or offer a selection of either Alternating Current or Direct Current.
Welding machines that utilize Direct Current usually have a method of changing the direction of current flow (polarity) in the welding circuit. Some machines have a switch to change the polarity, while on others the welding cables must be switched from one terminal to the other. To switch the cables it may be necessary to loosen the terminal bolts or plugs may be provided.
When the electrode cable is attached to the positive + terminal and the ground clamp is attached to the negative – terminal the polarity is Direct Current Electrode Positive (DCEP) or sometimes called Reverse polarity.
When the electrode cable is attached to the negative terminal and the ground cable is attached to the positive terminal the polarity is Direct Current Electrode Negative (DCEN) or sometimes called Straight Polarity.
KEY POINT; some electrodes are designed to work best on one polarity or the other.
Alternating Current does not have a polarity (direction of flow) since the current constantly alternates from one direction to the other.
The welding machines may be further classified by input line voltage which may be single phase or three phase for example: 230 volts 460 volts or in some cases 110.
One of the most important considerations may be the amount of amperage the machine is capable of producing and the duty cycle. The duty cycle may be given in a percentage for example: 60% duty cycle means the welder can run at capacity for 6 minutes out of ten. Since with stick welding the welder must stop to change electrodes the duty cycle may not be as critical as with Mig welding.
The size of the electrodes to be used determines the amount of amperage the machine will need to produce.
Types of welding machines
There are four basic types of welding machines that produce the required low voltage high amperage constant current for stick welding.
1. Transformers.
2. Transformer – Rectifiers.
3. Motor Driven Generators.
4. Inverters
1. Transformers.
A transformer welding machine takes the high voltage low amperage line current and transforms it to the low voltage high amperage current suitable for stick welding. These machines are relatively simple in construction with low power consumption and are economical to operate.
These machines produce only Alternating Current (AC).
The electrodes selection is limited to those designed to operate on AC current.
These machines are often used by home hobbyists.
AC Transformers or alternating current may be used to virtually eliminate the problems of arc blow when using Direct Current.
(Arc blow is the deflection of the arc from its intended path caused by the magnetic effects of the direct current.)
An ac transformer machine
LINCOLN AC 225 AMPS
2. TRANSFORMER – RECTIFIERS
The Transformer rectifier welding machines changes line current to suitable welding current similar to the transformer machine except that the addition of the rectifier changes the output current to Direct Current (DC). On some machines a switch is used to pass the current through only the transformer to produce AC current, allowing the operator the choice of AC or DC current.
The addition of a polarity switch allows a full range of currents from AC to DC electrode negative or DC electrode positive.
KEY POINT: Some machines require the terminals or plugs to be switched to change polarity. Some machines produce only DC current.
transformer rectifiers machine
LINCOLN IDEALARC AC DC 250 AMPS
A multi-process welding machine is one that may be used to weld with STICK, MIG or TIG, when the necessary components are added.
MILLER MULTI – PROCESS MACHINE
3. MOTOR DRIVEN GENERATORS
In the motor driven generator, the motor turns a generator to produce the electric current for welding.
The motor that turns the generator may be powered by electricity or by a fuel powered internal combustion engine driven by gasoline or diesel.
The fuel gas types are the type of welding machine commonly seen on trucks and job sites. These machines may also have components added for multi-process welding.
MILLER TRAILBLAZER
4. INVERTERS
Relatively recent technology has allowed welding machine manufactures to take advantage of electronics to rectify and transform line current for the welding circuit in a much smaller size called inverters.
Inverter models are available that produce either DC current or offer a choice of AC or DC current.
Models available provide either constant current used for STICK and TIG or Constant voltage used for MIG or may combine both.
The great benefits of this technology include the production of a line of machines that offer smaller more portable multiple process machines that are capable of providing a range of amperages and are less costly than traditional machines.
The illustration below shows an invertec V 250 S which is a DC 250 amp stick welding machine used at the Delta School Of Trades.
LICOLN INVERTEC 250 AMPS
WELDING MACHINE CONTROLS
There are a variety of welding machines produced by manufactures for stick welding, each with their particular arrangement of controls for selecting the variables for welding. Although controls may differ with machine type and style, they serve the same basic functions.
Two of the welding machines used at the school are the Lincoln Invertec V250-S and the Miller Dimension 400. These machines will be used to describe the welding machine controls.
Lincoln Invertec V250-S Controls
(1) ON OFF SWITCH
The on off switch is pushed upwards to turn the machine on and down to turn the machine off.
(2) THE NEGATIVE AND POSITIVE TERMINALS
The negative and positive terminals are used to change polarity between Electrode positive work negative or Electrode Negative and work positive.
The work (ground) cable plug and the Electrode cable plug are twisted, pulled out and switched to change from one polarity to the other.
(3) RUNNING LIGHT OR PILOT LIGHT
The pilot light is red when the machine is on and running.
(4) HOT START
The hot start Control regulates the amount of starting energy when initiating the arc in Stick welding. The higher setting may be used for esier arc starting with some electrodes.
(5) AMPERAGE CONTROL
The amperage control sets the amperage for Stick welding and becomes the upper limit when using a remote control.
(6) ARC FORCE
This control is used to adjust the force of the arc. The arc is more forceful or digging at the higher settings. Adjustments are made based on the type of electrode and the application.
(7) GTAW SMAW SETTING
This control offers a choice of GTAW SMAW SOFT OR SMAW CRISP.
The GTAW setting is used when the TIG (GTAW) equipment is attached and aids in touch starting the arc.
The SMAW SOFT setting is used to soften the arc for Electrodes like the E-7018 and E-7028.
The SMAW CRISP setting allows a crisper arc when using Electrodes like the E-6010.
(8) THE REMOTE CONTROL
The remote control switches control of the amperage between
(9) REMOTE RECEPTACLE
The remote receptacle has a cover that can be removed to attach a remote device to control the amperage from zero to the upper limit set on the machine. This control is often utilized for adding a foot pedal when TIG (GTAW) welding, or when a hand operated remote control is used.
MILLER DIMENSION 400 MULTI-PROCESS WELDING MACHINE CONTROLS
(1) Start switch
The black push button switch starts the welding machine.
(2) RUNNING LIGHT
The running light is red when the welding machine is running.
(3) STOP SWITCH
The red push button switch is depressed to stop the welding machine.
(4) PROCESS SELECTOR
The process selector is used to switch from CC CONSTANT CURRENT used for Stick (SMAW) and Tig (GTAW) welding to CV CONSTANT VOLTAGE used for Mig (GMAW) welding.
(5) ARC CONTROL
The arc control dial provides better arc starting for certain electrodes when Stick welding. Examples: When using E-6010 Electrodes the higher range aids in striking the arc. When using E-7018 Electrodes the lower range is used to lessen the effects of arc blow.
(6) AMPERAGE CONTROL
This control is a dial that is turned clockwise to increase the amperage when Stick welding or to increase the voltage when Mig welding. There are two sets of numbers around the dial. The lower numbers in white squares are read as voltage for Mig welding. The higher numbers indicate the amperage level for stick welding.
(7) REMOTE CONTROL SWITCH
The remote control switch is a toggle switch with two settings ON or OFF. The switch position is off for stick welding and on when using a remote control device such as a foot pedal.
(8) AMPERAGE METER
The amperage meter or AMMETER is a gauge that indicates the amount of amperage the welder is using during welding. The Ammeter setting will fall to zero when the welder stops welding.
(9) VOLTAGE METER
The Volt meter acts in the same manner as the ammeter except it shows the voltage during welding.
(10) THE REMOTE CONTACT SWITCH
The remote contact switch is a toggle switch with two settings ON or OFF. The switch position is off for stick welding and on for MIG welding or Tig welding with a foot pedal attachment.
ARC BLOW
DESCRIPTION
A condition called arc blow may occur when using Direct Current (DC) to weld some joint designs with the stick welding process. The direct current passing through the electrode and the base metal sets up a magnetic field around the electrode. The force of this magnetic field can be strong enough to pull the arc from its intended path causing an unstable weld puddle resulting in a poor weld with excessive spatter. Arc blow may become very severe at the ends of a joint for example; the top part of Vee groove or when welding the inside corners of a T joint.
Severe Arc Blow may appear to the welder as if someone is blowing the arc with an air hose.
REDUCING THE EFFECTS OF ARC BLOW
USE ALTERNATING CURRENT (AC)
Alternating current flow changes direction constantly and as a result the magnetic field does not build up enough to cause severe arc blow.
When welding certain joint configurations, and arc blow prevents producing quality welds, if possible switch from Direct Current to Alternating Current.
Although using AC current virtually eliminates the problems associated with Arc Blow it may not be possible to switch current on the machine or use another machine. Try one or more of the following tips to reduce the effects of Arc Blow.
WORKING WITH THE GROUND CLAMP
Arc Blow usually occurs either forward or backward along the joint being welded. If forward Blow occurs, place the ground connection at the edge of the joint to be welded. If backward Blow occurs, place the ground connection at the start of the joint and weld towards a heavy tack, prior weld bead or run off tab. If you are unsure whether forward or backward Blow is occurring, try moving the ground connection to another location.
If the ground connection is very close to the workpiece, try moving it as far from the joint as possible.
Try adding a connection to the ground clamp so that you have one ground lead, but two ground clamps. Place one clamp on opposite ends of the section to be welded.
Some welders wrap a short section of the ground cable around the workpiece to set up a magnetic field to counteract the effects of the magnetic field causing the Arc Blow effect. Caution must be used to prevent burning the ground cable.
Try uncoiling the ground cable and electrode cable and stretching them out.
SEQUENCE OF WELDING
The effect of Arc Blow may be reduced by changing the sequence of welding. Try some of the following:
Weld the outsides of angles, channels or beams first where arc blow may not be as severe.
Place a weld at the opposite ends of long sections first.
Instead of welding from one end to the other, use a series of shorter welds in staggered locations to completely weld the joint.
Weld towards a heavy tack weld or prior weld. Stop and change the direction of travel when Arc Blow occurs.
Use a smaller diameter electrode if possible.
TECHNIQUE
A change in technique will reduce the effects of Arc Blow. Try the following:
Change the electrode angle. Slight angle changes during welding, when arc blow occurs, helps to lessen the effects enough to finish the weld bead. Try changing the angle to follow the direction of blowing, even if the electrode seems to burn down one side unevenly.
Use the lowest amperage setting practical, especially on root passes when welding grooves. Some electrodes, such as the E-7018, have iron powder in the flux and are more prone to Arc Blow. If possible use an alternative electrode, such as the E-6010, for the root or first pass before using the E-7018 for the balance of the passes.
Maintain a short arc length and decrease the length of arc if Arc Blow occurs.
Turn the arc control settings on the machine to a lower value when welding joints that seem prone to Arc Blow.
WELDING THE ONE INCH VEE GROOVE
One of the projects at the School is to weld a vee groove in the vertical up position. When welding the first and second passes Arc Blow may occur at the top inch and a half. Try the following to reduce the effects of Arc Blow:
Make sure you put a heavy weld on both sides of the backing strip in the flat position before welding the groove.
Check the amperage is set correctly and not too high.
Use the backing strip as a run off tab. Start well below the joint on the backing strip and run the bead out past the joint at the top.
If Arc Blow occurs on the first pass keep the arc length low and the electrode pushed against the backing strip. Keep the electrode angle low and steep. If the electrode burns down on one side, do not change the angle.
