Submerged Arc Welding

Write both down: a granular blanket blocks radiation, and a granular blanket keeps heat in the joint. They are separate claims.

Cut two matched coupons from the steel flat bar and sand both bright. They must start identical for the comparison to mean anything.

Heat coupon A to about 400 °C with the torch, then remove the flame and start the clock. Record temperature every 30 seconds.

Heat coupon B the same way, then immediately cover it with 30 mm of clean dry sand. Start the clock again.

The infrared thermometer cannot see through sand. Use the thermocouple probe placed against the coupon before burying, and read every 30 seconds.

Plot temperature against time for A and B together. The buried coupon holds heat markedly longer — that is the thermal-efficiency claim, confirmed.

Point the infrared thermometer at each coupon's surface from 300 mm. The sand surface reads far cooler than the bare coupon. That is why no helmet is needed.

Uncover coupon B once cold and compare its surface with coupon A's. The buried one carries much less scale — the sand kept oxygen out too.

Brush both coupons and weigh. Quantify what you saw in step 8 rather than trusting the eye.

Record the difference: welding flux melts to a slag, deoxidises the pool and can carry alloying elements. Sand is inert — it models the blanket, not the chemistry.

The operator cannot see the arc. Write down what that implies: the travel speed, wire feed and current must be set by machine, not judged by eye.

Loose powder falls off anything that is not roughly flat. Note the consequence: submerged arc welds flat and horizontal joints only — no overhead, no vertical.

An invisible arc is still an arc. Submerged arc welding is famous for needing no helmet, and that breeds carelessness: if the flux blanket thins or breaks — at the start of a run, at a joint edge, or when the hopper empties — the arc flashes through and the ultraviolet is as damaging as any other. Operators keep eye protection to hand precisely because the exposure is unexpected.

Hot flux looks exactly like cold flux. Fused slag and unfused powder are the same colour and sit side by side at wildly different temperatures. Recovered flux is handled with tools, and slag is chipped only behind eye protection — it detaches under tension and flies.

In this blueprint the sand is the hazard. Sand heated against a 400 °C coupon holds that heat for a long time and gives no visual warning at all. Leave it to cool fully and check with the thermometer before putting a hand near it.

US 2,043,960, “Electric Welding”, filed 9 October 1935, granted 9 June 1936, assigned to Union Carbide and Carbon Corporation. The named inventors are Lloyd Theodore Jones, Harry Edward Kennedy and Maynard Arthur Rotermund — three men. The process is habitually credited to one, and the third name is regularly misspelled Rothermund. The document settles both points.

Slavyanov got there first, sort of. In the 1890s at Perm he covered the weld pool with a molten slag blanket, for the same reason. The 1936 patent is the industrialised, granular, machine-fed form of an idea that had been floating around since arc welding began — which is a fair description of a good many welding patents.

Why the numbers are so different. Because none of the energy escapes as light or radiated heat, submerged arc welding runs at currents that would be unusable in the open — commonly 300 to 1000 A and, on multi-wire installations, far more. Thermal efficiency approaches 90 per cent against roughly 60 to 70 for open-arc processes, and deposition rates are several times higher than manual stick welding. On thick plate it is not a little faster; it is a different order of magnitude.

Where you have seen it without knowing. Pressure vessels, shipbuilding, wind-turbine towers, structural I-beams and large-diameter pipe are almost all submerged arc welded, usually with the work rotating under a fixed head. It arrived just in time for the Second World War, where it welded ship hulls and armour plate at rates riveting could not approach.

The strange consequence. This is the only common welding process where the operator's protection is not equipment but the process itself. The arc is not shielded from the welder; the welder is shielded from the arc — by the same blanket that shields the weld.