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Flux Cored Arc Welding Helpful Tips
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FCA-welding-tips is the subject of this page. We are speaking of course of Flux Cored Arc Welding, a quite important process that could be exploited even more in certain industries.
Be alert to the benefits of putting it to good use.
First among them the potential to be the most cost effective for the correct application.
It competes directly with GMAW (Gas Metal Arc Welding) from which it derived, so that sometimes it may be quite difficult to find out which of the two is the most cost effective.
Because first the GMAW process must be optimized for the job, if one wants to look seriously at the comparison.
See also Mig Welding Tips.
For basic information on the physics of electric arc for welding, see our new page on Arc Welding.
FCA-welding-tips seekers should know that the process, that provides a continuously fed tubular electrode containing flux, comes in two versions for additional flexibility: self shielded FCAW-S and gas shielded FCAW-G.
It is contended though that when weld quality is of paramount importance, only GMAW or Gas Shielded FCAW should be considered.
The torches or guns should be selected according to the process version selected. They may be made for manual or mechanized application, air cooled for low current rating or water cooled for higher amperage, over 600 A, and continuous duty.
One of the important FCA-welding-tips is that torches designed to be gas cooled should be operated with the gas and flow rate indicated by the manufacturer. Cutting off gas supply or changing its type could compromise the cooling capacity and limit the torch life.
Shielding gas may be supplied concentrically to the electrode through proper gas passages and nozzle, or externally, from the side. Except for the provision of means needed to control the supply and flow of the shielding gas if required, other equipment elements are not significantly different for the two versions.
Explore a vast selection of equipment suitable also for Flux Cored Arc Welding (FCAW), by clicking on the link for the Welding Advisers Store. |
FCA-welding-tips: Consider both Advantages and Limitations
Special guns or torches with vacuum fume extraction may be useful if other solutions are less effective in providing comfort and health to welders.
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Listed with the FCA-welding-tips are the process main Advantages:
- Higher productivity because of higher deposition rate and efficiency (no interruptions and no stub-loss)(when compared with SMAW - Shielded Metal Arc Welding).
- Better quality because of greater forgiveness of the process and less skill required.
- Tolerance for contaminants (less precleaning necessary) and resistance to cracking.
- Tolerance of FCAW-S for light breeze in outdoor welding.
- All position welding.
- Easy to mechanize.
- Simpler and more adaptable than SAW (Submerged Arc Welding).
FCA-welding-tips should also consider Limitations:
- Only for ferrous, stainless and nickel base alloys.
- Slag must be removed.
- Equipment more expensive than for SMAW, comparable to GMAW.
- Consumable electrode more expensive on a weight basis.
- Feeder and power supply must be located quite near to the point of welding.
- Fume extractor required because of more fume generated.
- FCAW-G sensitive to air drafts in outdoor welding (may need curtain shielding).
Constant voltage power supply is generally recommended in FCA-welding-tips, with preset voltage for each job, and current dependent on electrode extension and feed speed. Usual polarity is DCEP (electrode positive), however for certain electrode types
DCEN (electrode negative) is recommended,
especially for surfacing.
The electrode extension is the length of electrode between the sliding contact tip and the arc. It is a feature common to other processes like GMAW and SAW using a consumable electrode, but should be included in a presentation of FCA-welding-tips.
This length of (steel) wire is preheated by the current flowing, as a result of resistance heating (Power P=I2R), contributing to moisture reduction. The current available to the arc (the welding current providing heat to melt the base metal) and the voltage across the arc are reduced when the electrode extension is increased.
In general FCA-welding-tips recommend longer electrode extension than corresponding GMAW for most applications, 18 to 25 mm (3/4 to 1") are common, but also up to 95 mm (3 3/4") in certain cases with proper torches, with at least 12 mm of which inside the nozzle.
FCA-welding-tips as to the primary functions of flux are:
- Adjusting chemical composition to provide required mechanical, metallurgical and corrosion resistance properties.
- Shielding the weld pool from air (oxygen and nitrogen).
- Removing impurities from the melt and producing a slag cover.
- Stabilizing the arc.
- Controlling shape and appearance of weld bead.
The flexibility of the FCAW process to suite a large range of requirements derives primarily from the wide variation of flux composition, much larger than what would appear from official Classifications.
Although the task of individual components is generally known, the exact composition is considered proprietary by electrode manufacturers. Alloying elements may be added to control chemical composition of deposited weld metal.
It would be highly desirable if each welder knew all the FCA-welding-tips for selecting recommended electrode type and starting parameters for every new job. This type of knowledge and expertise can come only with continuing learning and training followed by critical help from auxiliary services like a metallurgical laboratory in charge of examining the results and providing feedback.
In our opinion the task of selection of applicable FCA-welding-tips cannot be left only in welders' hands or on supervisors' shoulders. Management should establish a professional workforce capable and willing to lead research and improvement of the best welding conditions, with setting of goals and measurement of achievements.
Reference tables or graphs should be made available, as helpful FCA-welding-tips, to start with suitable parameters for given materials, thickness, joint preparation and position, together with target weld deposition rate.
It must be realized that there is not a single acceptable solution to any given job. Therefore the suggested starting parameters should be interpreted as indicating ranges of values, sometimes marked as hatched areas in certain diagrams. To optimize the conditions, parameters have to be probed on test pieces with variations and changes as best suggested by experience, common sense and test results.
Once the parameters are optimized, according to the suggested FCA-welding-tips, the data should be organized in formal Welding Procedure Specifications (WPS), to be followed by anyone involved in such a job.
A few selection outlines, possibly covering the majority of general applications in carbon steel, were included in a reference article on Selection of Electrodes for GMAW and FCAW that was published in Practical Welding Letter issue No. 06 for February 2004.
To see it click on PWL#06.
A short article on FCAW electrodes was presented again in Practical Welding Letter issue No. 18 for February 2005.
Click on PWL#018 for seeing it.
In the Practical Welding Letter issue No. 32 for April 2006 a short list of FCAW electrode manufacturers is presented, to help interested readers in finding the required information they may need.
Click on PWL#032.
An Interview with Greg Metko from Miller Electric Mfg. Co. on
ADVICE FOR WELDING WITH SELF-SHIELDED FLUX CORED WIRES
providing important FCA-welding-tips
was published in the Issue 41 of Practical Wewlding Letter for January 2007.
Click on PWL#041 to read it.
An Article on Advancements in Flux Cored Filler Metals was published (4) in Issue 92 of Practical Welding Letter for April 2011.
Click on PWL#092 to see it.
An Article on A new Open Specification for FCAW Filler Metals was published (4) in Issue 105 of Practical Welding Letter for May 2012.
Click on PWL#105 to see it.
An Article on Filler Metal for for Gas Shielded FCAW was published (4) in Issue 118 of Practical Welding Letter for June 2013.
Click on PWL#118 to see it.
An Article on Cored wire for welding galvanized steel was published (4) in Issue 135 of Practical Welding Letter for November 2014.
Click on PWL#135 to see it.
An Article on Metal Cored Filler Wire was published (4) in Issue 153 of Practical Welding Letter for May 2016.
Click on PWL#153.
An Article on Spatter Reduction was published (3) in Issue 158 of Practical Welding Letter for October 2016.
Click on PWL#158.
To get at no cost every issue of PWL as it is published, please subscribe.
For meeting special requirements, interested readers are urged to study official classifications and to obtain manufacturers' recommendations.
AWS established and maintains a Classification system for FCAW electrodes with a complex format of designators. A short presentation of AWS A5.20 is given in the first of the manufacturer references in PWL#032 above.
The first letter E designates electrodes, and the letter T just before the dash indicates Tubular shape, containing flux. (That is opposed to the letter S, indicating Solid wires). Other designators were selected for minimum tensile strength, welding position, usability, composition and possibly the shielding gas.
There may be a dependence on electrode size, with small sizes suitable for all positions, and larger sizes only for flat or horizontal welding. The suggested polarity may be included in the classification or in information supplied by the manufacturer.
Not all consumables are made equal, this is an important FCA-welding-tip, even if put by manufacturers in the same AWS class. Therefore it is advised, before committing to a large job, to contact different manufacturers explaining the type of application, and to devote sufficient time and energy in practical testing of proposed electrodes.
It should be noted that "all position" electrodes are usually not the best for flat and horizontal applications. All position means really "all other positions", excluding flat or horizontal. This capability is achieved by promoting fast freezing and thin slag, sometimes at the expense of correct fusion and acceptable weld appearance.
For complete information and additional FCA-welding-tips the interested reader is referred to specialized publications like the AWS Welding Handbook ninth edition, Volume 2, pages 225-239.
AWS Welding Handbook
9th Ed. Vol. 2
Welding Processes - Part 1
Document Number: AWS WHB-2.9
American Welding Society
While the classification presents suggestions and FCA-welding-tips, it is understood that the user may deviate from them. For example, a given electrode may be recommended for flat or horizontal position: it may also be suitable for other positions, depending on the (small) size selected, the current level and welder's skill.
It may be important to add to the FCA-welding-tips the reason why certain electrodes are suggested for single pass welding, while others are for multiple passes. Those for single pass may include increased proportions of deoxidizers like silicon and manganese that make the filler metal suitable for welding over light scale or rust without resulting in porosity. If used for multiple passes though, those elements would increase the weld metal alloy content, therefore increasing hardness and reducing ductility.
The same unwanted effects could be caused by using, instead of straight carbon dioxide as recommended by classification for the case in question, less reactive mixtures of 75-80% Argon and 25-20% carbon dioxide. However it should be noted that in certain cases experimenting with a different gas may give improved result and even be recommended by electrode manufacturers.
Selecting the right electrode from Classification lists might be quite difficult except possibly in a few well defined situations. Even the Welding Handbook urges users to contact electrode manufacturers and ask for their recommendations to find the proper filler to be used in given applications and for their suggested optimum settings.
In his important book "A Management and Engineers Guide to Mig-Welding, Quality-Cost-Training" Ed Craig (www.weldreality.com) suggests the following FCA-welding-tips for the selection of Flux Cored Wires instead of the more common solid wires used with GMAW:
- If the steel condition (rust, oil, paint, laminations or even mill scale) risks to compromise GMAW quality
- For larger than 8mm (5/16") single pass fillet welds
- For vertical up or overhead welding on steel thicker than 4.8 mm (3/16")
- If high impact properties are specified
- If weld crack resistance must be improved, weld porosity reduced or weld penetration increased
Specification for Carbon Steel Electrodes for Flux Cored Arc Welding
American Welding Society / 12-Jan-2005 / 50 pages
Specification for Low-Alloy Steel Electrodes for Flux Cored Arc Welding
American Welding Society / 18-Sep-2009 / 62 pages
Specification For Stainless Steel Flux Cored and Metal Cored Welding Electrodes and Rods
American Welding Society / 17-Jan-2012
Specification for Bare Electrodes and Rods for Surfacing
American Welding Society / 23-Dec-2010 / 42 pages
Welders already alert to the common hazards present in all welding operations should note that the specific danger of FCAW results from the increased emission of fumes. Every effort should be put in place, especially adequate fume extractors, to avoid breathing those noxious fumes that may include dangerous metals.
Also exposure to radiant energy, to excessive noise and to electric shock should be taken care of by applying proper provisions.
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FCA-welding-tips and skill, knowledge and practice will help in getting out from the process the increased productivity it is able to provide.