Metal Electrode Arc Welding

Read step 12 before striking anything. Arc ultraviolet injures eyes faster than you can decide to look away.

Weigh a single bare steel electrode. Record the mass. This number is the whole experiment.

Clean a steel flat bar coupon with 220 grit until bright, then weigh it. Rust and scale would falsify the mass balance.

Lay the coupon on firebrick. Clamp the return lead to the coupon itself, not to the bench.

Auto-darkening helmet, leather gloves, covered arms. Test the lens before striking.

Strike by scratching, hold a short arc, and run one 40 mm bead along the coupon at a steady pace. Stop. Do not chase a second pass.

Cool to room temperature. Weigh the remaining electrode stub and the coupon again. Record both.

Electrode lost, coupon gained. Compare the two numbers. The coupon gains less than the electrode loses — the difference left as spatter and oxide.

Divide the coupon's gain by the electrode's loss and multiply by 100. That percentage is deposition efficiency, a number every welding consumable is still sold on.

Measure bead width and length with the caliper. Look at the plate around the bead: the scattered beads of frozen metal are the missing mass.

Note the bead's appearance: porous, dark, irregular. Nothing protected the pool from the air. Kjellberg fixes this seventeen years later.

An electric arc emits ultraviolet light strong enough to burn the cornea in seconds. The injury is called photokeratitis, or “arc eye”. It is not felt at the time — the pain arrives six to twelve hours later, typically in the middle of the night, and feels like sand under the eyelids. It normally heals in a day or two, but repeated exposure is cumulative.

Nobody in the room may look at an arc unshielded, including bystanders. Ordinary safety glasses do not protect against it and neither does a quick glance. Use an auto-darkening helmet, screen the work so passers-by cannot see it, and warn anyone nearby before striking. The same ultraviolet burns exposed skin like strong sunburn, so cover arms and neck.

Fume. Arc welding steel makes a metal-oxide smoke that should never be breathed. Ventilate, keep your head out of the plume, and use plain mild steel only — galvanised coatings release zinc oxide and cause metal fume fever.

Hot metal has no colour. Steel stops glowing at around 500 °C and is still hot enough to cause an immediate deep burn. Assume anything you have welded is hot until measured otherwise.

US 428,459, “Process of Welding Metals Electrically”, Charles L. Coffin, granted 20 May 1890. Coffin, of Detroit, is the first person to hold a verifiable American patent for using a metal electrode that is itself consumed into the joint.

Slavyanov came first and this blueprint says so. Nikolay Gavrilovich Slavyanov (1854-1897), chief of the Perm cannon works, demonstrated arc welding with a consumable metal electrode in 1888 and used it to repair castings and to cast metal directly in a mould under the arc. He also introduced a molten-slag blanket over the pool — an idea that reappears in 1936 as submerged arc welding. What is missing is a patent number that any source could confirm. The honest position is that Slavyanov was first to the technique and Coffin was first to the document, and the blueprint prints both.

Why metal transfer changes everything. With a carbon electrode the filler arrives cold and unmixed. With a consumable electrode the metal crosses as droplets that have passed through the arc's own plasma, arriving superheated and alloyed. That is why consumable-electrode processes penetrate deeper at the same current, and why every dominant welding process today — stick, MIG, flux-cored, submerged arc — is a consumable electrode process. TIG, in 1942, is the deliberate exception.

What Coffin's bare rod could not solve. A bare electrode leaves the pool naked in the atmosphere. Nitrogen and oxygen dissolve into it, giving porosity, brittleness and a weld with perhaps half the parent metal's ductility. Almost every welding process developed after Coffin is, one way or another, an answer to that single problem.