Welding Consumables

Welding sees utility in many different industries which include automobile and transportation, building and construction, power generation, marine and ship building, and oil and gas. The world wide welding consumables market continues to be predicted to experience substantial growth as a consequence of positive outlook of end-use industries for example the automotive and transportation, marine and ship building, and construction industries.

The primary developments which are positively influencing the growth in the market are definitely the future technologies which are currently being developed, and furthermore specifically those technologies that happen to be designed to weld thick metal parts. Additionally, the welding consumables market is actually shifting in the direction of automation involving the various stages within the welding process, as well as being forecasted that the development of robots in addition to automation software definitely will positively have an impact on growth. Welding consumables are generally segmented based on welding technique, welding consumable type, end-use industry, along with region.

Choosing Welding Consumables

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Stick electrode, flux-cored wires, solid wires, SAW wires and fluxes usually are many of the welding consumables utilised during the welding process. Nonetheless, flux doesn't form part of the final weld and for that reason is 'wasted' during the duration of welding.

Welding consumables varieties comprise of:

• Stick electrodes
• Solid wires
• Flux-cored wires
• SAW wires
• Fluxes
• Others

A number of different types of electrodes are intended for some of the widespread welding processes.

• Shielded metal arc welding utilizes a powder-coated electrode (flux). When it burns off, the coating shields the weld from oxygen. Filler metal is usually added onto the coating to help hasten the process.
• Gas-tungsten arc welding uses a non-consumable tungsten rod to heat the metal along with filler metal. The rod merely heats the metal and does not add to the filler material.
• Gas metal arc welding is a process which uses a wire consumable using a wire spool feeding the wire into the weld joint.

In conjunction with making certain the consumable has got the same melting point as the base metal, it is additionally essential to match the strength of the filler with the strength of the metals being welded to achieve the most effective results. Nonetheless, “matching” the strength of the base metal along with the filler material is not really as simple as matching the strength classifications of metals by using a chart considering that base and filler metals possess different minimum yield and tensile strengths. The yield strength is the amount of stress a material can handle prior to when it commences to deform plastically, whilst the tensile strength is the amount of stress a material will take prior to when it breaks.

In addition, “matching” yield and tensile strength is not probable considering that matching necessitates working together with minimum specified material properties rather than actual properties. Instead, matching will require taking into account all the possibilities on the chart that possess a filler metal tensile strength which is as strong or even stronger as compared to that of the base metal and selecting the best one. Occasionally “undermatching” could yield a more suitable weld in certain applications. For instance, undermatching filler metals to high-strength steel may well greatly reduce cracking tendencies.

There are various factors which enter into selecting the most appropriate consumable for the task. Selecting the right material increases weld strength in addition to bead quality and additionally helps make cleanup simplier and easier. Much more practical experience with these critical welding components along with the different welding processes becomes necessary for the best suited selection.

Fluxes, Electrodes & Wires

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Irrespective of whether a flux is in an electrode coating or is in granular form, like for example a submerged arc flux, the requirements are definitely the same.

• The flux is required to be capable of furnishing a protective shield to circumvent atmospheric contamination of the electrode tip, the filler metal considering that it is transferred across the arc along with the molten weld pool. Typically, it does this as a result of decomposing within the heat of the arc to create a protective gaseous shield.
• It is required to be effective at removing any oxide film. Failing to accomplish this will result in lack of fusion defects and additionally oxide entrapment. It does this by means of chemically reacting together with the oxide.
• It will enhance mechanical properties by providing clean, high quality weld metal as well as perhaps by way of transferring alloying elements across the arc.
• It is required to be effective at furnishing the required weld metal composition, once again as a result of transferring alloying elements across the arc.
• It should facilitate arc striking in addition to arc stability.
• It should produce a slag which will shape the molten pool as well as contain the weld pool in position in the course of positional welding, if necessary.
• Any kind of slag must be easily removable in addition to preferably being self-detaching.
• It ought not to generate considerable amounts of fume and additionally any which it does generate, must not be harmful to the welder.

These kind of requirements have contributed to a multitude of varied consumables, several being apparently identical, and this also tend to make filler metal selection a challenging as well as complicated task.

The majority of MMA electrodes can be suitably divided into three groups as a result of their coating composition. These are cellulosic, rutile and basic coatings, each of which supplies the electrode with a distinctive range of characteristics.

Cellulosic Electrodes

Cellulosic electrodes contain a significant percentage of cellulose, above 30%, and typically comprising wood flour. This is combined with rutile (titanium dioxide, TiO₂), manganese oxide and ferro-manganese as well as being bonded onto the core wire by using sodium or potassium silicate. Moisture content of these electrodes is fairly high, characteristically 4 to 5%. The cellulose burns in the arc to form a gas shield of carbon monoxide, carbon dioxide and, in conjunction with the moisture in the coating, it generates a substantial amount of hydrogen, usually 30 to 45ml hydrogen/100gm weld metal.

The hydrogen elevates arc voltage and provides the electrodes their characteristics of deep penetration and high deposition rates. The high voltage requires a high open circuit voltage of approximately 70 volts permitting convenient arc striking and also to maintain arc stability. The forceful arc moreover brings about considerable levels of weld spatter and this also restricts the maximum current which can be used on the larger diameter electrodes. A thin, friable and effortlessly removed slag is generated, providing a rather coarsely rippled weld profile. The slag is additionally fast freezing to make certain that, as opposed to the majority of electrodes, they can be employed in the vertical down position - 'stove piping'.

Electrodes which includes a sodium silicate binder can be utilised only on DC electrode positive (reverse polarity). People that have a potassium silicate binder can be utilised either as DC electrode positive or on AC. The electrodes necessitate some moisture within the coating to assist the running characteristics and they also must never be baked, as can be done on basic coated electrodes. This has the advantage that the electrodes are generally tolerant to site conditions. Should they become damp, drying out at a temperature of approximately 120°C is going to be acceptable.

Electrode compositions are only available for welding low carbon non-alloyed steels however nickel inclusions can be made to enhance notch toughness. The high hydrogen level signifies that any steel welded using these electrodes should be chosen to possess a extremely high level of resistance to hydrogen induced, cold cracking. They should not be used without having given due consideration to the steel composition, restraint as well as the requirement for preheat. The characteristics of deep penetration, high deposition rates along with the capability to be used vertically down signifies that the primary usage with regard to these kind of electrodes is for cross country pipelining however they are employed to a more limited extent for the purpose of welding storage tanks.

Rutile Electrodes

Rutile coatings, as the name signifies, include a large amount of rutile, titanium dioxide, apart from cellulose, limestone (calcium carbonate), silica (SiO₂) mica (potassium aluminium silicate), ferro-manganese as well as some moisture. Binders are generally either sodium or potassium silicate. The cellulose along with the limestone decompose in the arc to generate a gas shield that contains hydrogen, carbon monoxide and carbon dioxide. The electrodes possess medium penetration characteristics, a gentle, quiet yet stable arc and very little spatter, making these a 'welder friendly' electrode. Striking as well as re-striking is straightforward and the electrodes will operate on minimal open circuit voltages. The electrodes develop a dense covering of slag which can be effortlessly removed and provides a smooth evenly rippled weld profile.

The existence of cellulose together with moisture implies that the electrodes generate comparatively higher levels of hydrogen. This particularly limits their usage to mild steels less than 25mm thickness and thin section, low alloy steels of the C/Mo and 1Cr1/2Mo type. These are essentially the most extensively used general purpose electrode. Rutile coated austenitic stainless steel electrodes can be easily procured and can be used in any thicknesses for the reason that cold cracking isn't a problem with these alloys.

Rutile electrodes, similar to cellulosic electrodes, necessitate certain moisture inside the coating and in addition they must not be baked. Should they become damp, re-drying at approximately 120°C ought to be sufficient. Those electrodes which includes a sodium silicate binder can be utilised on DC electrode negative or AC. Electrodes with the potassium silicate binder can be utilised on both polarities and additionally on AC. The potassium silicate binder electrodes typically possess improved arc striking along with stability characteristics ın comparison to the sodium silicate binder types in addition to a more conveniently detachable slag.

Basic Electrodes

Iron Powder Electrodes

Besides the 'standard' cellulosic, rutile and basic electrodes previously mentioned, electrodes can be classified as 'high recovery' electrodes. With the addition of significant amounts of iron powder, upto 50% of the weight of the flux coating, to either basic or rutile electrode coatings, it's possible to deposit an increased weight of weld metal than is contained in the core wire. These electrodes are identified as possessing an efficiency higher than 100%, for example 120%, 140%, and so on, and this 3 digit number is usually included in the electrode classification.

The electrodes have thicker coatings compared to 'standard' electrodes that can cause them to be challenging to make use of in restricted access conditions. They are, nevertheless, welder friendly by means of superior running characteristics in addition to a smooth stable arc. The iron powder not only melts in the heat of the arc to enhance deposition rate but additionally enables the electrode to handle a higher welding current compared to a 'standard' electrode.

The iron powder is electrically conducting, consequently allowing a portion of the welding current to pass through the coating. High welding currents can consequently be used without the associated risk of the core wire overheating, subsequently increasing both the burn-off as well as the deposition rates. The high recovery electrodes are essentially suited for fillet welding, providing a smooth, finely rippled surface accompanied by a smooth blend at the weld toes. They are typically alot more tolerant to variations in fit-up and their stability on low open circuit voltages ensures that they're excellent at bridging wide gaps. On the other hand, the large weld pool means that they're not suitable for positional welding and tend to be restricted to welding in the flat (PA) as well as horizontal-vertical (PC) positions.

Acid Electrodes

The final type of electrode covering is referred to as 'acid' or acid electrodes. These kind of electrodes contain copious amounts of iron oxides in the flux coating that would create a high oxygen content in the weld metal in addition to poor mechanical properties. Hence, it is essential to incorporate considerable amounts of de-oxidants like ferro-manganese and ferro-silicon in the flux. Despite the fact that that they generate smooth flat weld beads of good appearance and can also be used upon rusty and scaled steel items, the mechanical properties are typically substandard to the rutile and basic coated electrodes. Also, they are far more susceptible to solidification cracking consequently they are little made use of.

Cored Wires

Wire consumables are being used with the gas shielded MIG/MAG, metal cored (MC) and flux cored (FC) arc welding processes. Cored wires now are made use of not only in the MIG/MAG process but additionally in TIG, plasma-TIG and submerged arc welding.

Cored wires meant for welding carbon and alloy steels, are often produced from mild steel along with the alloying elements included in the flux filling. This permits a small amount of wire being economically produced matching the composition of steels in which the application is limited, for instance high chromium creep resistant steels or hard facing. Non-ferrous and austenitic steel wires, aluminium, nickel based, stainless steel and many others, nevertheless, commonly match closely the parent metal composition and obtaining ingots meant for drawing into wire is usually not as much of a challenge.

MIG/MAG welding solid wires are supplied in diameters ranging from 0.6 to 2.4mm, probably the most frequently used diameters being 1.2 and 1.6mm. The solid wires are typically engineered to match the composition of the alloy being welded. Silicon, 0.5 to 0.9%, and possibly aluminium, upto 0.15%, usually are included in ferritic steel wires to provide de-oxidation; carbon content will likely be less than 0.1%.

Alloying elements which include manganese, chromium, nickel and molybdenum are included in the ingot to deliver enhanced mechanical properties along with corrosion resistance. Additionally, the carbon and low alloy steel wires are frequently copper coated, both to minimize corrosion in the course of storage and also to enhance welding current pick-up in the contact tip.

The stainless steel and non-ferrous wires will not be copper coated. Poor control during the drawing operation could create laps on the wire surface which trap contaminants and gives rise to porosity, as can an unsatisfactory quality copper coating on ferritic steel wires.

Porosity because of drawing defects can be quite a particular problem relating to aluminium alloy wires and wherever high quality weld metal is required, in that case shaving the wire to eliminate defects over the wire surface is advisable.

The cored wires are actually small diameter tubes wherein fluxes as well as alloying elements are packed. There are two primary types of cored wires, one containing for the most part fluxes, the other containing metal powders. There exists a sub-class of the flux cored wires, the self-shielded wires, which incorporate gas-generating compounds which decompose in the arc to produce sufficient shielding gas ın order that additional gas shielding is not necessary.

In cross-section, the wires can be seamless tubes packed with the flux thereafter extruded prior to being drawn into a wire. Conversely, they can be or manufactured by rolling a flat strip into a 'U' shape, filling this with the flux or metal power thereafter folding this into a tube. The edges of the tube could be butted together or overlapped.

The seamless and closed butt wires generally have thicker walls and for that reason reduced fill ın comparison to the overlapped wires, possibly as little as 20% of cross sectional area in comparison to 50% for the overlapped wires. This permits the overlapped wires to incorporate additional alloying elements and they are consequently typically utilized for stainless steel and hard facing welding.

Cored wires possess a range of advantages over the solid wires. The reduced current carrying cross-sectional area of the wire translates into greater current density as well as an increase in burn-off rate with additional deposition.

The flux moreover generates a slag which will control the weld bead shape making it possible for increased welding currents being made use of in positional welding than can be used with MAG. The slag will in addition react with the weldpool and provides improved properties when compared to what can be achieved by means of MAG.

Whereas solid wires typically generate islands of a glassy slag which have a tendency to be located in the finish craters, this doesn't necessarily prevent a multi-pass weld being produced without the need of deslagging. This isn't achievable by using flux cored wires, restricting their use in applications, among them robotic welding to single pass welds. Metal cored wires tend to be less of a problem within this context consequently they are typically employed in fully automated, multi-pass applications.

Similar to MMA electrodes, the flux inside the core can be either rutile or basic, the rutile flux delivering a smooth arc, convenient slag removal as well as 'welder appeal', the basic fluxes delivering improved mechanical properties along with tidier radiographic quality welds.

Hydrogen control is less of a challenge when compared to MMA electrodes. Rutile, basic and metal cored wires, all possess minimal hydrogen potential levels, enabling reduced preheat when compared to what could otherwise be the case not to mention making it possible for rutile wires being employed in applications including the welding of high strength or thick section steels. Hydrogen pick-up on the shop floor is furthermore less of a concern for the reason that flux/metal powder is contained inside of a sealed tube, preventing moisture ingress. Seamless wires are typically superior in this regard as compared to seamed wires.

Gas Metal Arc Welding Consumables

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Several aspects have an impact on gas metal arc welding (GMAW) consumable selection, primary among that is productivity. Considering that 85% of the cost of producing a weld is actually labour, consumables need to be selected based on enchancment in welder productivity in addition to downtime minimisation. All factors have to be comprehended prior to making decisions to achieve the longest life from GMAW consumables. Three fundamental GMAW welding consumables usually are contact tips, nozzles, and liners.

Contact Tips

GMAW employs continuously fed welding wire, and to transmit current to this particular wire, the welding gun needs to make electrical connection with the wire. This particular electrical contact takes place using a contact tip which the welding wire feeds through.

The contact tip's size corresponds to the wire diameter. Nevertheless, the contact tip sizing selected additionally is dependent upon the welding application. Industrial welding applications necessitate large contact tips which have additional mass and additionally assist in keeping the tip temperatures reduced.

Generally, tapered as well as non-tapered contact tips are obtainable. Tapered tips tend to be long and used in combination with tapered nozzles in welding applications having restricted access in addition to limited space, for instance, pipeline welding. Non-tapered tips have extra mass in the front and likewise typically endure heat better as well as last longer.

Contact tips are also available in threaded as well as non-threaded varieties. A few varieties of contact tips tend to seize the diffuser making them problematic to remove and replace. Seizing is unlikely to happen by using non-threaded contact tips. Non-threaded tip designs have more area and additionally conduct heat along with electricity better than threaded contact tips and frequently require reduced time to change following a burnback.

Whenever contact tips begin to wear, an oval hole begins to develop. This particular phenomenon is referred to as keyholing and can result in irregularities in the arc because of inadequate electrical pickup. Irregularities in the arc can increase spatter resulting in additional postweld grinding.

Nozzles

The nozzle guides the shielding gas to the weld. Nozzles are either threaded or non-threaded and are available in a variety of sizes and shapes intended for diverse applications. Non-threaded nozzles tend to be easier to switch as compared to threaded nozzles nonetheless they do not fit as tightly as threaded nozzles. Threaded nozzles are more secure nonetheless many necessitate additional effort to swap. Threaded nozzles typically stay on the welding gun better and provide better tip-nozzle concentricity. Slip-on nozzles typically tend to be speedier to switch as well as clean.

For the purpose of spray arc transfer mode or pulse spray of solid welding wire, the nozzle will need to extend past the contact tip which in turn helps to supply the shielding gas closer to the arc whenever longer electrode stick-out becomes necessary. In addition, it assists the contact tip operate cooler.

In short-circuit transfer mode, the contact tip needs to be flush or extend only slightly past the nozzle, making it possible for the short electrode stick-out which is necessary. Considering the fact that a certain amount of spatter with this particular type of transfer happens, extending the contact tip can assist to decrease the spatter buildup on the nozzle. This permits the gas to flow unrestricted.

The dimensions of the nozzle opening is dependent upon the dimensions of the weld puddle, the volume of shielding gas necessary, along with the challenges in reaching the area that requires welding. For the purpose of welding deep V-groove butt joints, a small, tapered nozzle might be necessary to get the contact tip close sufficiently to the weld puddle. In comparison, high-voltage, high-amperage applications typically necessitate high gas flow rates, consequently a nozzle having a large inside diameter provides improved shielding gas coverage of the bigger weld pool.

An excellent general guideline is to make use of the largest nozzle which fits the application. For any application which has restricted clearance or limited visibility, a small nozzle is perhaps the best option. However, typically, larger is usually superior for the reason that larger the nozzle, the more gas coverage it provides. Certain nozzles possess built-in orifices which help direct gas, smoothing the gas flow and covering the weld better.

Nozzles characteristically are manufactured from brass or copper. Copper nozzles tend to be well-suited with regard to use in heavy industrial applications considering their capability to withstand intense heat. Brass nozzles resist spatter superior to copper, however typically melt or burn whenever exposed to extreme heat.

Liners

The welding electrode wire is fed to the welding gun via a cable liner and a spring steel coiled liner is necessary for steel applications. For the reason that these kind of liners are constructed of steel, they are rigid, resist buckling, and provide a long life.

Aluminium applications characteristically necessitate liners constructed from nylon, Teflon or plastic considering that these kind of materials possess lower friction when compared to steel, additionally, they assist in keeping contamination out of the weld. Whenever aluminium wire is pushed via a steel liner, the wire might pick-up little bits of steel which can contaminate the weld.

Liners must be replaced for the reason that they wear out as a result of continuous usage or become kinked because of improper usage. Reducing the friction between the liner and the wire in addition to preventing improper usage, both aid to minimise liner replacement and additionally maximise welder uptime. Kinks inside the liner cause the wire to catch and can lead to erratic arc performance, which could result in additional operator downtime as a result of extra spatter cleanup.

The liner can be blown out by using compressed air to increase liner life as well as decrease postweld cleanup. The liner can be blown out from the contact tip end or from the feeder end to remove dirt or copper flaking.

Liners typically should be switched whenever switching electrode size. However some liners can be employed for several wire size, however, if they are too big or too small, they could result in poor feeding. The most significant factors behind poor feeding is an inappropriately trimmed liner, consequently a burr on the liner impedes the welding electrode feeding. Jump liner technology enables a tool-less switch of the common liner wear point, that is at the radius of a GMAW gun's body tube, as opposed to the entire liner.

Gas Tungsten Arc Welding Consumables

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Consumables consist of only a modest component of the total cost of gas tungsten arc welding (GTAW), nonetheless they are a key factor in generating superior welds. The characteristics of GTAW torch consumables, among them back caps, collets and collet bodies, gas lenses, and nozzles, have an impact on welding performance, expenses, productivity, as well as downtime.

Back Caps

Back caps apply pressure to the back end of the collet in order to force it against the collet body. This particular pressure secures the tungsten electrode in position and additionally seals the torch head from the atmosphere. Back caps thread into the back of the torch to assist in creating a viselike hold which prevents the tungsten rod from slipping.

Back caps are constructed of a variety of phenolic compounds, each of which features a different resistance to temperature. Using these differing characteristics, back caps are usually matched to specified applications.

A back cap constructed from a low-temperature phenolic compound is suitable with regard to general applications, nevertheless it might shrink, crack, or split in a demanding or high-duty-cycle application. For those applications, a back cap having a high thermal resistance is necessary to prevent weld discontinuities which can originate from shielding gas leaks.

Back caps are available in three varieties - short or button, medium, and long, all of these compare in performance however are different in line with application. All types of back caps are obtainable designed for both air- as well as water-cooled torches.

A short, or button, back cap is the smallest type of back cap. It's physical size enables welding in restricted areas, however it necessitates nonstandard tungsten which is 2 inches or less in length. Welders might have to fabricate this particular tungsten electrode size from a longer piece, considering that shorter tungsten is usually expensive as well as difficult to acquire.

In the event that joint access isn't a consideration, a medium or long back cap is suitable. A medium back cap typically accommodates tungsten upto 3 inches long. Long back caps make use of the industry-standard tungsten of upto 7 inches in length. Additionally, they are the most frequently employed.

Collets and Collet Bodies

Collets secure the tungsten electrode into position as the back cap is tightened and additionally establish the electrical contact essential for good current transfer. They are typically constructed from standard-grade copper or tellurium copper.

Collet bodies screw into the GTAW torch and accommodate a variety of tungsten electrode sizes in addition to their respective collets, every one of which range in size according to torch model. They are constructed from standard-grade copper or tellurium copper.

Two primary considerations whenever selecting collets and collet bodies are:

1. Price: Standard-grade copper collets and collet bodies are generally more economical as compared to those constructed from tellurium-copper alloy, however they also are typically less durable, specifically in high-temperature applications. Subsequent to extended usage, they cannot secure the tungsten electrode reliably.
   Tellurium-copper alloy collets and collet bodies tend to be more expensive however possess superior heat resistance with higher-amperage applications. They often resist twisting or elongating as well as secure the tungsten electrode more securely subsequent to extended periods of usage.
2. System type:Single- and two-piece collet systems are obtainable according to application requirements. Collets and collet bodies are offered independently to complement a specific tungsten electrode size. This system is effective and additionally accommodates all sorts of tungsten electrode sizes, specifically small ones.
   Single-piece systems combine the collet and collet body. This particular combination offers a strong securing force and additionally enables simplified removal during demanding applications considering that the collet mechanism is situated away from the heat and therefore is significantly less susceptible to distortion.

Gas Lenses

Gas lenses are obtainable for both air- and water-cooled torches. Typically constructed from brass along with stainless steel mesh screens, they substitute the collet body to enhance shielding gas coverage as well as reduce turbulence. In addition, they minimize weld discontinuities linked to atmospheric contaminants.

The most affordable gas lenses characteristically contain a lesser number of screens, coarser mesh configurations, or both. The higher-quality gas lenses typically necessitate several layers of screens, nevertheless most expensive gas lenses incorporate an engineered porous filter media rather than multiple screen layers.

Application along with performance objectives determine gas lens selection. For the purpose of welding of materials which react to atmospheric contaminants, large gas lenses provide enhanced gas coverage. On complex joints, large gas lenses additionally permit increased tungsten stick-out to gain visibility of the weld puddle or to get considerably more access to the joint.

A smaller torch profile will reduce weight and additionally facilitates access to tight joints. In case the torch profile and weight aren't factors, a large or extra-large gas lens is appropriate.

Nozzles

Nozzles otherwise known as cups supply a specified amount of shielding gas coverage to the weld pool in accordance with their size. Nozzles likewise vary in length from short to extra-extra long, in price, as well as in performance.

The most affordable nozzles, that happen to be 90% or 95% alumina oxide, effectively work for the purpose of low-amperage applications. The thermal shock of high-amperage applications, however, can result in these kind of nozzles to crack or fall off.

Lava nozzles cost in excess of alumina oxide nozzles and tend to be more resistant to cracking. They are appropriate choice for medium-amperage applications. Lava nozzles are machined, so they generally have varying wall thicknesses around the inside diameter, that could result in nonuniform gas coverage.

Silicon nitrate nozzles would be the costliest. They resist heat and cracking in high-amperage, high-duty-cycle applications and additionally last longer when compared to alternative nozzle types.