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SMA-welding-tips are useful reminders of basic information items.
Eevery good welder has them embedded into his/her own skill whenever brandishing the torch.
Nevertheless by reviewing this page anybody might find hints on practical tips useful in specific situations.
Shielded Metal Arc Welding (SMAW) is one of the oldest practical processes.
It uses electrical energy as the power source, and it is still one of the most widely applied.
It evolved in time, with progress in understanding the functions of the ingredients in the shielding cover.
It stands now as the baseline process to which all other processes are compared.
For basic information on the physics of electric arc for welding, see our new page on Arc Welding.
Among SMA-welding-tips one should remember that this is the process that uses an electric arc between a covered electrode (stick) and the work, to melt base and filler metal, to produce the weld.
The electrode cover, heated by the arc, decomposes and evolves shielding gases that protect the weld pool and the hot metal.
It leaves a solid slag cover that prevents the weld from becoming oxidized while still hot and contaminated by contact with the surrounding air.
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The process is versatile, useful for an extensive range of applications, materials, shapes and dimensions. It produces welds of suitable mechanical properties even in hard to reach spots.
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SMA-welding-tips on Advantages
- Suitable for a large variety of metals
- Equipment relatively simple, economic, portable
- Electrode provides both filler metal and shielding means
- Favorable for reaching limited access spots
- Flexible, applicable to different joint configurations and welding positions
- Reliable and consistent good results
- Applicable to underwater welding
- Semi automatic with gravity feed and firecracker welding
- Suitable for outdoor welding
An Article on Gravity Welding was published in the July 2006 Issue of Practical Welding Letter No. 36. To read the article click on PWL#036.
An Article on Backing Bars was published in the January 2007 Issue of Practical Welding Letter No. 41. To read the article click on PWL#041.
A short note on firecracker welding was published (9.5) in Issue 42 of Practical Welding Letter for February 2007. Click on PWL#042 to see it.
A special issue of Practical Welding Letter, Mid Month Bulletin for May 2008, is full of Online Resources on SMAW and SMA-welding-tips.
Click on PWL#057B to see it.
A new website Page on Tack Welds was introduced (8) in Issue 85 of Practical Welding Letter for September 2010.
Click on PWL#085 to see it.
A new website Page on Vapor Degreasing, an essential process to be used before cleaning for welding, was introduced (8) in Issue 92 of Practical Welding Letter for April 2011.
Click on PWL#092 to see it.
An Article on Welding Articles from the Forging Magazine, dedicated to welding tool steels, was published (4) in Issue 159 of Practical Welding Letter for November 2016.
Click on PWL#159.
SMA-welding-tips on Limitations
- Not suitable for certain metals like low temperature melting or reactive metals
- Lower weld deposition rates than other specialized continuous processes
- Stub loss and low operator factor
- Not suitable to robotic applications
- Requires a certain degree of manual dexterity and skill
- Requires slag removal especially between passes
SMA-welding-tips on Power sources
See the recent Power Sources page.
Power supplies are available that output either ac or dc or both.
Those of the constant current (CC) with a drooping volt ampere characteristic curve type are preferred because they provide better current control as a function of arc length (determining arc voltage).
Constant voltage (CV) power supplies are not well suited to SMAW because the current cannot be readily controlled.
SMA-welding-tips: from the available types, whether transformer, rectifier, generator or inverter, the selection is based mostly on personal experience and work requirements as listed hereafter.
We think that, before purchasing, welders should look for leasing for a short time the equipment they need in order to test it and find out if it meets their expectations.
SMA-welding-tips: An article on inverters, that owe their popularity to their light weight, a big advantage for portability, when needed, was written in Issue 5 of Practical Welding Letter for January 2004.
To see the article click on PWL#005.
SMA-welding-tips on Selection
The selection of a power source suitable for a given job depends on:
- Welding current type, either ac (alternating current) or dc (direct current)
- Volt-ampere characteristic drooping curve of power supply
- Amperage range, depending on the maximum size of electrodes to be used
- Duty cycle that should be at least 60% for maximum current required for the application.
- Availability of electricity supply. (Combustion Engine generators required where electricity is not available)
Depending on welder's skill, useful SMA-welding-tips suggest suitable electrode types that can be selected for specific applications. Electrode type may prescribe the preferred current.
How to Compare AC and DC Shielded Metal Arc Welding
SMA-welding-tips on AC: it is generally preferred:
- For limiting the cost of the power source
- For larger electrode sizes and higher currents
- Whenever the magnetic blow of dc might be disturbing
- When using relatively long cables, to reduce voltage drop
Note that cables carrying ac should not be coiled because of inductive losses.
SMA-welding-tips on DC: it is preferred:
- For lower currents and small size electrodes because of stabler arc
- For easier arc starting
- For welding with short arc (low voltage) to obtain better mechanical properties.
- For easier out of position welding (vertical or overhead)
- For welding sheet metal
SMA-welding-tips on Polarity
This term refers to the connection of the electrode to the direct current (dc) power supply terminal.
Most covered electrodes work better when connected to the positive terminal (electrode positive).
In general the electrode manufacturers recommendations should be followed.
It is known that heat generated by an electric arc is not equally divided between its two ends.
One should distinguish the electrode end from the work side.
When the electrode is connected to the negative terminal, the major part (~70%) of the heating is concentrated on the work side.
When the electrode is connected to the positive terminal, the major part of the heating is concentrated on the electrode end.
Therefore by changing polarity one changes quite substantially the heat balance between electrode and work.
Some confusion on the interpretation of the results may follow because the electrode size and current are rarely maintained when changing polarity and it is therefore difficult to compare results.
It is generally agreed that with straight polarity (electrode negative) melting and deposition rate is higher than with opposite polarity.
SMA-welding-tips on Penetration
However when dealing with penetration, one can find different conclusions from different authors.
Some argue that with electrode negative penetration is shallow, making it suitable to weld thin sheet metal.
Other authors write that electrode negative produces deep, narrow weld beads.
We think that the difference of opinions stems form the different conditions used in the tests.
If the electrode size is kept constant, the current should be reduced when connecting it to the positive terminal.
Otherwise the same current as before (when the electrode was connected to the negative terminal) might overheat the electrode.
If to compare penetration at the same current level, the electrode size is changed, then the current density in the electrode changes.
This again changes conditions so that the results are not comparable.
Our practical SMA-welding-tip or suggestion, if penetration and weld shape is important, is to conduct two independent sets of tests to decide which polarity to select.
Provided that the electrode cover supports both polarities, the electrode size and the current level should be selected for each polarity to produce an acceptable weld.
Then shape and penetration should be examined in macro sections, see Weld Macro, to determine which of them is more suitable to the intended application.
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SMA-welding-tips on Electrode Classification
The AWS Classification of Electrodes used for SMAW was explained in the first issue of Practical Welding Letter for September 2003. To see the article click on PWL#001.
We report hereafter a few SMA-welding-tips on characteristics of covered electrodes of specific types:
E6010: suitable for direct current electrode positive (DCEP). Recommended for all welding positions with substantial penetration. The slag is thin, easily removable.
E6011: designed for use with alternating current (AC), to reproduce the characteristics and mechanical properties obtained with E6010.
E6012: may be used with direct current electrode negative (DCEN), suitable for vertical welding with low penetration and dense slag. May produce higher yield strength and lower ductility than the first two above.
E6013: can work with AC at low amperages and low open circuit voltage. Suitable for light sheet metal welding with low penetration. Easy slag removal. Otherwise similar to E6012.
E6019: electrodes of this type provide deep arc penetration with good ductility. Meet requirements for radiographic standards and specific impact properties at low temperature. Suitable for use with all currents (AC, DCEP or DCEN).
E6020: suitable only for flat or horizontal fillet position welding on thick material because of low viscosity slag. Medium to deep penetration depending on current level. With iron oxide in the covering.
E6022: suitable for flat and horizontal single pass welding at high speed with high current.
E6027: suitable for thick base metal in flat and horizontal position with all types of current with medium penetration. Thick cover containing iron. Easily removable slag.
E7014: similar to above E6012 and E6013 but usable at higher amperage. With iron powder in the covering to increase deposition efficiency. Suitable for all positions and wide root gap due to poor fit. Easily removable slag.
E7024: With iron powder in the covering, suitable for all types of current, low arc penetration. High travel speed possible.
E7024-1: Similar to the above (without suffix) but for greater ductility and lower Ductile to Brittle Transition Temperature.
E7027: Similar to E6027 but with higher mechanical properties. Must meet specified requirements on chemical composition.
SMA-welding-tips on Low Moisture Electrodes (Low Hydrogen).
The following electrodes, designated with the suffixes -15, -16, -18, -28 and -48 are needed for preventing Hydrogen cracking.
These are used for welding susceptible steels whenever the conditions require that no or minimum Hydrogen be introduced in the weld.
Ingredients in the covering reduce oxide inclusions and promote higher impact properties.
Hardenable carbon steels and thick materials should be welded with this class of electrodes because these steels are prone to Hydrogen Induced Cracking.
An Article on Benefits of Low Hydrogen Filler Metal Electrodes was published (4) in Issue 141 of Practical Welding Letter for May 2015.
Click on PWL#141 to see it.
SMA-welding-tips require that all these electrodes be stored in dry conditions and, if exposed to dampness must be dried in an oven for sufficient time before use.
Arc length should always be kept short to reduce the risk of porosity.
E7015: like all the -15 electrodes, are used with DCEP for welding thick materials, also for high sulfur and enameling steels, in all welding positions (excluding the larger sizes). The heavy slag is easy to remove.
E7016: (and other -16 electrodes) have a potassium rich covering to stabilize the arc in AC. Otherwise the characteristics are similar to the above.
E7016-1: have higher manganese content, intended to develop lower Ductile to Brittle transition temperature.
See a note in 9.3 in PWL#026. Click on PWL#026 to read it.
E6018: electrodes similar to E7018 (hereafter) but at lower strength level. Suitable as buffer layers in cladding applications.
E7018: similar to E7015 but with iron powder in the thicker cover. For AC and DCEP in all welding positions. Useful also for high strength high carbon and low alloy steels.
E7018-1: higher manganese content than the above, for lower transition temperature.
E7018M: intended for optimum mechanical properties, but sometimes classified as E7018
E7028: similar to E7018 but limited to flat or horizontal position. With iron content in the cover to produce higher deposition rate.
E7048: again similar to E7018, optimized for vertical down+ applications, but difficult to achieve consistently good X-Ray quality results in multiple pass applications.
All electrodes have optimum current ranges for each size, as specified by manufacturers and usually published on the cardboard box.
We report hereafter, as practical SMA-welding-tips, a few AWS Specifications for Covered Electrodes.
Specification for Carbon Steel Electrodes for Shielded Metal Arc Welding
American Welding Society / 10-Apr-2012 / 62 pages
Specification for Low-Alloy Steel Electrodes for Shielded Metal Arc Welding
American Welding Society / 22-Mar-2006 / 68 pages
Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding
American Welding Society / 05-Oct-2012 / 54 pages
Specification for Welding Electrodes and Rods for Cast Iron
American Welding Society, 01-Jan-1990, 10 pages
ANSI/AWS A5.3/A5.3M:1999 (R2007)
Specification for Aluminum and Aluminum Alloy Electrodes for Shielded Metal Arc Welding
American Welding Society, 11-Feb-1999, 26 pages
Specification for Copper and Copper-Alloy Electrodes for Shielded Metal Arc Welding
American Welding Society / 06-Nov-2007 / 38 pages
Specification for Nickel and Nickel Alloy Welding Electrodes for Shielded Metal Arc Welding
American Welding Society / 15-Dec-2009 / 52 pages
Specification for Surfacing Electrodes for Shielded Metal Arc Welding
American Welding Society / 24-Mar-2010 / 44 pages
Specification for Bare Electrodes and Rods for Surfacing
American Welding Society / 23-Dec-2010 / 42 pages
A short Video on SMAW, called also MMA (Manual Metal Arc in the UK) can be watched at :|
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