Arc welding – shielded metal arc welding or SMAW
Also sometimes referred to as stick welding.
Shielded Metal Arc Welding SMAW, also referred to as Stick welding or MMA welding is a process which melts and joins metals by heating them with an arc between a coated metal electrode and the metal that has to be welded. The electrode’s outer coating, called flux, creates an arc and provides the shielding gas and slag that covers and protects the finished weld from contamination. The electrode core provides most of the weld filler metal.
Electric arc welding has been used for more than 100 years, and the fact that it is still around today illustrates its continued usefulness. It is referred to as SMAW, which stands for Shielded Metal Arc Welding. The basic components include the machine, an earth cable and clamp, an electrode lead attached to an electrode holder that holds consumable electrodes.
The electrodes are metal rods covered with a flux coating. The flux shields the weld from atmospheric gasses. Therefore the name Shielded metal. The electrodes used here looks like a stick and that is why many people call it stick welding.
Arc welding uses high amperage of electricity to generate the intense arc, which melts the base metal of the item being welded. The central metal core of the electrode melts as the weld happens. As the work progresses, the welding rod, as it is commonly referred to, then becomes the filler metal, while the fluxed coating produces a shielding gas around the welding area that protects the metal being welded and filler metal from impurities in the air. Stick welding produces slag. This slag must be chipped off with a chipping hammer. Obviously this takes time, but if a good quality arc weld is made the slag tends to come loose as the weld cools down.
There are a wide variety of stick welding electrodes available to suit almost any purpose. Almost any metal can be welded with this method. The material being welded determines the type of electrode that will be used.
The rods vary in thickness, according to the thickness of the metal you are welding, and also in alloy and flux-coating content.
Rods are marked with a number at the tip and different colours indicate the fluxes for quick identification. The coatings on arcwelding rods are very susceptible to moisture in the air, and must be stored in a dry, secure container to remain effective. We use specially manufactured welding rod drying ovens to heat the welding rods and disperse any moisture before welding.
Shielded Metal Arc welding is suitable for most types of metal. It is thus a very versatile kind of welding. We also prefer to use this type of welding machine when welding on site in windy conditions. Co2 weldingis not possible in windy conditions. The wind blows away the shielding gas and this causes impure welds. We also use Shielded Metal Arc welding where it is difficult to haul heavy equipment around.
Shielded metal arc welding electrodes are available to weld carbon and low alloy steels; stainless steels; cast iron; cast iron welding applications, aluminium, copper, and nickel, and most other metals.
Techniweld can offer stick welding as an on site welding service throughout South Africa and in many parts of Africa. Please feel free to contact us to discuss your requirements. When offering our on site welding service the client will supply the correct current of electricity. Most of our welding machines are capable of using 380V as well as 550V power.
The client will be charged a living out levy if our welders have to sleep away from home.
Co2 welding or Gas metal arc welding GMAW
In South Africa this type of welding is most often referred to as co2 welding or MIG welding.
The elements of Gas Metal Arc Welding include a power supply a torch with a large-diameter cable, an earth wire with clamp, and compressed shielding gas.
The co2 welding electrode consists of a roll of relatively-thin wire and a motorized transport system for this wire. The common size is between 0.8mm and 1.2mm. The thickness of wire depends on the weld. Thicker base material needs thicker wire. You weld like arc welding, but the electrode is constantly fed through the cable to the gun and consumed at the weld. When you pull the trigger of the MIG welding gun, you start the supply of amperage of the feeding of the wire electrode and the flow of shielding gas, which is routed through the gun’s cable and comes out around the electrode, preserving the integrity of the weld like the flux coating does on ARC welding rods.
The advantage of co2 welding is that it is a much cleaner weld than either gas welding or arc welding. Good versatility in materials with the ability to do very well on thin metals, and there is no electrode or filler rod to keep replacing.
The weld from a MIG gun is much cleaner than arc welding in terms of spatter, and there is no slag coating to chip off. Because the welding wire in co2 welding is machine fed into the weld puddle, the heat and wire-feed rate can be tuned so that production welds can be made faster than with other systems.
Co2 welding is an ideal method for indoor welding where clean-looking weld beads are desired. The shielding gas around the weld process is subject to being disturbed by wind and draft, so when welding outdoors we prefer to use flux core welding.
All common metals like carbon steel, stainless steel, aluminium, and copper can be welded with this process in all positions by choosing the appropriate shielding gas, electrode, and welding conditions.
Because the electrode is constantly fed it saves time because the welding electrode does not need to be changed so often as in stick welding.
It is important to keep the feeder lining clean and dust free. This can be achieved by blowing compressed air through the liner once a week, depending on how much the machine is used.
Gasses generally used are CO2, Terrell or a Terrell mixture.
Techniweld can offer CO2 welding as awelding on site service throughout South Africa and in many parts of Africa. Please feel free to contact us to discuss your requirements.
When welding on site the client will have to supply the correct current of electricity. If needed we can supply a power generator at an additional cost. Our CO2 welding machines are capable of using 380V as well as 550V power.
The client will be charged a living out levy if our welding staff has to sleep away from home.
Flux cored arc welding
Flux Cored Arc Welding is achieved by continuously fed wire. The electrode looks very much the same as the electrode for GMAW but the electrode is hollow and the flux is contained within that void. Self-shielded flux cored arc welding contains a flux which produces a large amount of gas for the arc and this ensures deoxidisation of the weld pool. This type of welding is used when the machine needs to be applied for welding outdoors when welding on site. With gas-shielded wires, which are only used in the welding shop, an additional shield (co2 welding gas or an argon-CO 2mixture) is needed to protect the weld pool. As fluxed cored arc weldingis normally employed at high welding current levels and higher duty cycle, more fume will be produced compared with MMA welding.
When welding on site and working outside and when welding thicker material fluxed core wire welding is better. The weld isn’t quite as clean as with co2 welding, and fluxed welding wire doesn’t do as good a job on thin sheet metal, but these machines are more practical for the welding on site, which is usually on heavier materials anyway.
The fluxed-wire machine never need to have a bottle refilled, so as long as you have plenty of wire inside the machine, you can’t have your work delayed by running out of shielding gas.
The flux cored arc welding machine is in essence the same as aCO2 welding machine.
We do often do flux cored arc welding when welding on site in windy conditions. If you need us to provide this service please contact us to discuss your individual needs.
TIG welding, Tungsten Inert Gas Welding or Gas Tungsten Arc WeldingGTAW
With gas tungsten-arc welding, often referred to as TIG welding an arc is drawn between a non consumable tungsten electrode and the metal that is being welded. The welder must be careful not to touch the electrode to the metal being welded as this contaminates the electrode and the electrode must then be cleaned before continuing to weld.
The TIG process includes a welding machine, a torch with a tungsten electrode, an earth cable, a foot-operated amperage control pedal (although these days you get hand controlled units) and compressed shielding gas such as argon or even helium. The welding electrode is not consumed, and the filler rod is hand-fed into the weld puddle when needed. This takes some practice to master, but once the welder gets the feel of it, it becomes a natural process.No metal passes through the arc, so there arevery little welding fumes. When welding in a well ventilated workshop or when welding on site exposure will not normally exceed WELs.
In TIG welding, high frequency (HF) is used to start the arc and to stabilise the AC arc. High frequency consists of the sparks of a few thousand volts and lasts for only microseconds. These sparks occur at low current so the chance of electric shock is very low. High frequency can startle the operator and this could cause injury. A concentration of high frequency on the skin can result in deep burns.
Argon is the most commonly used gas for TIG welding but, in certain exceptional cases helium also gets used. Shielding gas has the capacity to exclude foreign materials during the welding process, as well as being unable to combine with other elements to form chemical compounds detrimental to the weld.
TIG welding produces the cleanest, flux-free and spatter-free beads with virtually no contamination. It is ideal for pipeline welding and for welding on site.
Used in applications such as race cars, aircraft, pipe frames, pipelines, cycles, and tank fabrication. This is the most commonly used method of welding on thin aluminium.
TIG welds are strong, ductile and corrosion-resistant with virtually no cleanup required, making it popular for welding stainless-steel and aluminium.
The types of metals that can be welded with TIG welding include: aluminium alloys, aluminium castings, all steel alloys, stainless steel, magnesium, titanium, copper and nickel alloys, and metals like zirconium.
It is ideal for welding dissimilar metals and joining metals of different thicknesses.
TIG welding is ideal for thinner materials
We do TIG welding as awelding on siteservice throughout South Africa and in many parts of Africa. When doing this type of welding outside adequate shelter has to be provided to prevent the shielding gas from blowing away. When offering our on site welding service the client will supply the correct current of electricity.
The client will be charged a living out levy if our welders have to sleep away from home.
Please feel free to contact us to discuss your requirements.
Oxyacetylene gas welding
Gas welding is the oldest and most versatile method of welding. Oxyacetylene gas welding is commonly referred to as gas welding. This is a process which uses the combustion of oxygen and acetylene. When these two gasses are mixed together in correct proportions within a hand-held torch an extremely hot flame is produced with a temperature of about 3,000 degrees Celsius. The chemical action of the flame is then adjusted by changing the ratio of the volume of oxygen to acetylene.
A regular gas-welding package consists of two high-pressure cylindrical tanks, one for oxygen, and one for acetylene. The pressure of the gas is regulated by a set of gauges and regulators which controls the gas flow. The welding torch is connected to the bottles with special hoses. There is obviously also a torch. The torch is different from the ones used for cutting. The torch comes with a variety of tips, tip cleaners and a spark lighter. For safety reasons one must always use the spark lighter and not matches or a cigarette lighter.
The oxy-acetylene system is extremely versatile. It is a system that can do cutting as well as welding. This is invaluable in both repair work and fabrication welding. Cutting away damaged or unwanted material is easily done with a properly-used cutting-torch attachment, and you may at times have projects where you need to cut a shape out of steel plate on site. Of course when we are working at the workshop we have the CNC plasma cutter and profile gas cutting machine to do the profile cutting. This method is extremely accurate and very quick. The bulk of extruded steel profiles are usually cut with a cropper, a saw or a cut-off machine. Unfortunately these machines can only make a straight cut and cannot cut around corners. Cutting with a torch takes skill to closely follow a line, and even then the edges of the metal will require some finishing getting a smooth edge. There are tools available to guide the welder’s hand. We have a straight line cutter that consists of a set of wheels that guides the gas cutting flame to cut in a straight line. These are cheap tools and easy to use. Naturally using these tools make the cut cleaner and more accurate than cutting free-hand. When doing this kind of profile gas cutting one must not cut on the line, but next to the line, on the side of the waste material. After cutting it is usually necessary to do some grinding to smooth out the edges and get the dimensions just right. Most experienced welders know just how much to cut outside their pattern with the oxyacetylene torch.
Techniweld offers Oxyacetylene gas welding as an on site welding service in all provinces of South Africa and in many parts of Africa. Please feel free to contact us to discuss your requirements.
The client will be charged a living out levy if our welding staff that has to sleep away from home.