Carbon Arc Welding

Go to step 12 and read it now. An arc will damage your eyes before you decide it is bright. Nothing in this blueprint is worth an injury.

Lay two firebricks on a clear bench. Put the steel plate on them. Nothing flammable within two metres, and no bystanders without a helmet.

Clamp the return lead directly to the steel plate. A poor return connection makes its own arc where you are not looking.

Fit the graphite electrode in the holder. Grind the tip to a blunt cone about 30 mm long. A sharp point burns back immediately.

Put on the auto-darkening helmet, gloves and covered clothing. Test the lens on a bright lamp before striking anything.

Draw the electrode across the plate like a match and lift 3 mm. Tapping straight down sticks the electrode and stalls the supply.

Hold roughly 2 mm and have a second person read the voltage across the leads. Record it. Expect a low reading, in the region of twenty volts.

Hold roughly 6 mm and read again. The voltage rises with length. This is the arc's volt-ampere characteristic, measured directly.

Plot the readings. The near-straight rise is why welders are told to hold a short arc: length is the one variable the hand controls, and it sets the voltage.

Let the plate cool. Examine the bead under magnification. A carbon electrode adds carbon to the weld, leaving it harder and more brittle than the parent steel.

Write down what you saw: carbon pick-up, and a pool open to the air. Both are why the carbon electrode was replaced within a decade.

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 is the second hazard. Any arc over steel produces a fine metal-oxide smoke that should not be breathed. Work outdoors or with forced ventilation drawing the plume away from your face, never in a closed room. Galvanised (zinc-coated) steel is specifically excluded from this blueprint: heated zinc causes metal fume fever. Use plain mild steel.

And the obvious ones. The plate stays hot enough to burn for many minutes after it stops glowing, spatter travels, and a dropped electrode holder can short the supply. Gloves on, sleeves down, bare skin covered.

US 363,320, granted 17 May 1887, four sheets, application filed 1886. The granted title is “Process of and Apparatus for Working Metals by the Direct Application of the Electric Current” — note that it never uses the word welding. The claims cover cutting and piercing as well as joining, because the same arc does all three.

Nikolai Nikolaevich Bernardos (1842-1905) was a Russian inventor of Greek descent who filed the process in Russia, France, Britain, Germany, Italy and the United States between 1885 and 1887. Stanisław Olszewski is named with him on the American sheet and is missing from most accounts. The two are also credited with the first practical electrode holder — a detail that sounds trivial and is not, because without it there is no way to hold the arc steady.

Why the carbon electrode lost. Carbon does not melt into the joint, so filler has to be fed by the free hand, which halves the operator's control. Worse, the electrode transfers carbon into the weld metal, raising its hardness and cracking risk. Nikolay Slavyanov demonstrated the alternative — a metal electrode that melts and becomes the filler — in Perm in 1888, and Charles Coffin patented it in America in 1890. The next blueprint is that step.

What survived. Carbon arc welding is essentially extinct as a joining process, but the carbon arc itself did not disappear: it lit cinema projectors into the 1970s, and carbon-arc gouging — blowing molten metal out of a joint with a carbon rod and compressed air — is still standard practice for removing bad welds. The tool outlived the technique.