A self-propelled carriage carrying the wire feeder, flux hopper, welding head and controls, which drives itself along the joint at a set travel speed. It is used where the seam is long and the work cannot practically be moved - tank shells and floors, deck plating, beam webs and flanges - running on the plate itself, on the beam flange, or on a rail.

On circumferential seams and on work that can be rotated. Vessel and pipe joints are welded with the head held on a boom or bench while turning rolls or a positioner move the work under it, which keeps the arc at the top of the rotation with the flux sitting naturally on the joint. Short or intricate joints rarely justify the setup time either.

A constant-speed feeder runs the wire at a set rate and relies on a constant-voltage power source to self-regulate burn-off. A voltage-sensing feeder measures arc voltage and varies feed speed to hold arc length, which is what a constant-current source requires. Pairing the wrong feeder to a source gives an unstable arc and erratic penetration.

From a hopper on the head, gravity-fed through a tube that lays a covering just ahead of the arc, deep enough to submerge it but no deeper. Consumption is roughly comparable by weight to the wire deposited, which is why recovery is normal practice: most of the flux laid down is never melted and can be reclaimed and reused.

By guidance rather than by the operator's aim. Options run from a hand wheel with the operator correcting against a scribed line, through guide rollers or wheels riding a flange or rail, to a laser or mechanical seam tracker driving a cross-slide automatically. Guidance choice usually matters more to bead placement than travel speed does.

Yes, and horizontal fillets are among the most common submerged arc applications, particularly on beam and girder fabrication where twin-head tractors weld both sides of a web simultaneously. The flux must still be supported on the joint, so the fillet is welded in the horizontal position with the plate arranged accordingly.

Commonly from about 2.0 mm up to 5.0 mm and larger on heavy equipment, which is well beyond what a gas metal arc feeder handles. Drive rolls, guides and the contact assembly are specific to the diameter range, and changing size means changing those components as well as resetting the parameters.