Guide written by:
Michael, Professional and passionate welder, Sheffield
Rutile, basic, cellulosic - one type or other, these are essential for successful welding! Adjust your MMA setup, secure your welding rod in the clamp, don your protective gear... And you're ready to weld. Stainless steel, cast iron, auto-hardening, discover the different types of electrodes and get welding!
- Welding position
What's a welding rod for?
In case you didn't know, a welding rod is the essential consumable element in MMA welding for the assembly of two separate parts. Also referred to as an electrode, the welding rod is held in a clamp that forms part of your welding setup. An electric current passes through it and the rod melts when the current is earthed, generating an electric arc.
Since you might want to weld a range of metals of different chemical compositions and thicknesses, different rods are available to suit the substrate metal.
What are welding rods made of?
In terms of appearance, a welding rod looks rather like a sparkler. It is to supply the filler metal for arc welding joints. It consists of two distinct parts:
- A metal core - the central part of the rod;
- A brittle coating around the core.
Although the core has to match the metal you're welding (same or compatible), the coating is a key element and plays several roles:
- Acts as primary electrical conductor for priming and protects the arc during welding;
- It orientates the arc according to the welding position - flat, rising, falling or raised;
- It protects the pool of molten metal by forming a slag which rises to the surface.
What are the different families of electrodes?
For welding common metals such as carbon steel, stainlesssteel, cast iron, and alloy steels, there are three types of rod coating: rutile, basic and cellulosic.
- Rutile or acid / rutile coating is the most common. It produces an attractive weld when welding flat or angled. This type of electrode is used for general framework and locksmithing applications. With a little training, the welding can be carried out in position - flat or on an upwards or downwards incline. Your choice of electrode diameter will depend on the thickness of the parts to be welded. Choose a product marked "all positions" for occasional or regular use. In terms of purchase format, packs contain a large number of electrodes and are not negligible in cost. It's worth having plenty of rods of diameter 1.6, 2.5 and 3.2mm - these will cover most common assembly situations. Special electrodes are available on the market for welding in a descending or rising fashion, giving a good finished weld with a little practice. Decent suppliers provide data sheets with an indication of how to adapt to different rod diameters and metal thicknesses.
- A basic coating is also used by professionals boilermakers and welders. It is suitable for all welding positions and has excellent mechanical performance. This type of coating is fragile; it must always be kept dry and even preheated before welding (steaming). Inexperienced users should be aware of the risk of sticking. The slag separates easily.
- Cellulosic coating is a thin, fine coating used primarily on pipes. Best left in the hands of experienced welders - if you're reading this, hands off!
Are there any other types of electrodes?
For welding stainlesssteel, cast iron and hard steels, you can get specializedelectrodes to be handled with care:
- Stainless steel electrodes suffer from frequent sticking. The slag cracks on cooling, and protective goggles are needed in addition to a welding hood. Note that this type of electrode can be used on a mixed weld - e.g. stainless steel-iron or stainless steel-hard steel;
- Cast iron electrodes must be handled with care. Like the part to be welded, they need to be preheated. One last hurdle to jump: parts must be cooled slowly and gradually to protect them from cracking on contact with cool air (by placing sand or hot gravel under and around them).
- Self-hardening electrodes are designed for hard steels and are used on blunt cutting tools to resharpen them. This is a costly investment to be weighed up according to your needs!
Nature of metals, thickness, diameter of the electrodes ... can you explain me further?
Rutile electrodes are the most commonly used type - makes sense, since carbon steel is of course the most commonly welded metal.
When welding sheet metal end to end without chamfering, diameters of 1.6-2.5mm can be used for sheet thicknesses of 1-3mm. Thicker than this (up to 10 or 12mm end to end welding), mating edges must be chamfered: that is to say, a bevel is cut into each edge and this V-shaped chamfer is filled with electrodes of, say, 2.5mm (as a first pass) and then refilled with larger-diameter electrodes (3.2 or 4mm, for example). This process lets you weld to the core to obtain a solid assembly. At even greater sheet thicknesses, semi-automatic welding takes over as the preferable method.
In the case of overlapping or angled welds, even with differing thicknesses, a first pass can also be made with a smaller diameter rod, letting you fill the corner thoroughly before continuing with larger-diameter rods. With experience you'll come to "feel" the right diameter of rod to use each time.
So, the two key criteria for choosing what to buy are metal type and thickness - you can't go far wrong!
What is polarity?
Since the connectors are identical, you can place the electrode at the positive (DC+) or negative (DC-) pole depending on its type. As a general rule, rutile rods need to be connected to the negativeand basic rods to the positive pole. If in doubt, follow the manufacturer's advice on your electrode pack.
Handy tip: with stainless steel electrodes, choose DC+ as the piece will then heat up less.
What are martyr pieces?
Often, at the beginning and end of the welding process, the electric arc forms a crater that "eats" at the edges of the sheet.
To avoid this phenomenon and be left with a beautiful full weld, just take two pieces of scrap metal and place them at the top and bottom of the weld. Start and finish welding on these "martyr pieces", then take them straight to the grinder. Believe me, this is one handy little trick!
What welding positions are there?
There are four main welding positions:
- Flat - the simplest;
- Cornice - the piece is vertical but the weld is made horizontally;
- Vertical, upward or downward;
- Overhead - the hardest since you're under the piece you're welding - e.g. car chassis or floorpan.
In all these cases, the choice of electrode is paramount and worthy of attention.
So now you know what they're used for, what they're made of and how to use them. The only thing left to do is to get your kit on, get yourself in position - and go for it!
Any safety advice?
Also, the end of the rod that remains in the clamp when your electrode is burned up should be collected carefully in a metal box - a tin can, for instance! Since they're very hot or even incandescent, they can easily cause fires if left on the ground.
Don't forget to ensure your workspace is well ventilated before welding.
Learn more about welding equipment...
To find out more about welding equipment, follow our editors' advice and check out their other guides:
- How to choose your protective eyewear?
- How to choose your protective gloves?
Guide written by:
Michael, Professional and passionate welder, Sheffield, 68 guides
I was trained as a pipe worker and a pipe-welder and after having traveled for 35 years working around the UK, I became the head a metal shop and then a designer and in the end the head engineer. I have designed and built a workshop where I make metal sculptures: I managed to find a piece of paradise where I can to let my imagination run wild. Auctions and garage sales are no secret to me. I find unusual objects and old tools there that I collect or transform into works of art. I also like decoration, painting on canvas, and gardening. I am developing new technologies concerning tools. To share my passion and humbly advise you in your choice of materials is a real pleasure.