Straight answers to the questions people ask most when choosing and using MMA (stick) welding electrodes.
How do I choose the right MMA electrode?
Start with the metal you are welding, because the electrode must be suited to it: mild steel, low alloy steel, stainless steel, cast iron and other metals each need their own types. Then consider the strength and toughness required, the joint and welding position, the thickness, and the current your machine can supply.
For general work on mild steel, a rutile electrode is the easy choice. For structural and pressure work, or where toughness matters, a low hydrogen (basic) electrode is common. The job specification may fix the electrode type.
What is the difference between rutile, basic and cellulosic electrodes?
The coating decides how an electrode behaves. Rutile electrodes give a smooth, stable arc, little spatter and a neat bead, and are easy to use for general fabrication. Basic (low hydrogen) electrodes give tougher, cleaner weld metal, with low hydrogen content that reduces the risk of cracking, but they are harder to use and need careful storage.
Cellulosic electrodes give a deep, forceful arc and are used mainly for pipe welding, particularly for root runs and vertical-down welding.
Do I need to dry low hydrogen electrodes?
Yes, usually. Low hydrogen coatings absorb moisture from the air, and moisture puts hydrogen into the weld, which can cause cracking, especially in thicker or higher-strength steels. Electrodes are normally supplied in sealed packs, and once opened they should be kept in a heated holding oven, or re-dried following the maker's instructions.
The temperatures and times depend on the electrode, so follow the pack and the welding procedure. Do not use electrodes that have been left out in damp air.
What electrode size and current should I use?
Choose a diameter to suit the thickness of the metal and the joint. Thin material needs a thin electrode and low current, thicker material allows larger diameters and higher current. Smaller diameters are easier to use out of position, such as vertical and overhead.
The pack gives a recommended current range for each diameter, so set the machine within it. Too low a current gives a lumpy weld that sticks, and too high a current overheats the electrode, causing spatter, undercut and a coating that breaks down.
Can I use AC or DC, and does polarity matter?
Many electrodes run on both AC and DC, while some are designed for DC only. The pack states which current types and polarity suit that electrode, and some electrodes need a higher open-circuit voltage than a small machine can supply on AC.
Polarity affects penetration and bead shape. Different electrode types are generally run with the electrode connected to the positive or negative terminal, so check the maker's instructions before setting up. Using the wrong polarity can give a poor arc and weak welds.
What do the codes on an electrode mean?
Electrodes carry a classification code, printed on the pack, and often on the electrode itself. It tells you things such as the strength of the weld metal, the type of coating, the welding positions it suits and the type of current to use. For stainless and other alloys, the code shows the type of alloy deposited.
There are different classification systems, and a single electrode may carry more than one, so read the maker's data sheet. Always check that the code meets what your job specification requires.