Heavy Metal. Preparing Metal for Welding, Oxidation of Metal - Part 1
Preparing your metal for welding, Oxidation.
Oxidation is going to always be present and an issue when welding steel or aluminum. Certain types of Oxidation such as mill scale can protect the metal from degradation and ionic corrosion, but it can also interfere with making a sound, proper weld. Mill scale involves several forms of iron oxide and other compounds which help prevent rust from forming, a more corroding form of iron oxide. While it isn’t as protective as paint and other treatments, it helps prevent decay of steel for a brief time. With steel whether it is rust or mill scale it must be removed. Acid baths, grinding, and media blasting all can be used to remove both mill scale and rust, but it must be welded immediately after wiping down with a neutralizer or cleaner or rust will reform. Usually for a joint that will be welded, mill scale and rust are removed from the immediate area with a grinder plus at least 1” additional distance from the combined joint edges to make sure no rust or mill scale is encroaching and getting trapped in the weld. MIG and stick are tolerant of some mill scale and rust but TIG has nearly a zero tolerance level and can cause the weld to become porous or oxidized looking while simultaneously contaminating the tungsten. Additionally many forms of tubing, pipe and structural beams have rust preventative coatings on them, ranging from a light oil to a primer coat of paint. Ideally these too should be removed in the weld area before proceeding to weld them. Metal that has been galvanized for protection from the elements must have the galvanized layer vigorously stripped away with a grinder. Care should be taken while welding anything with galvanized coating in order to avoid metal fume fever and serious medical complications from the galvanization burning off.
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