Submerged Arc Welding Machines for Booms, Chassis and Long Seams

A submerged arc welding machine is an automated system in which the arc burns beneath granular flux (SAW, ISO 4063-121). On long, straight seams it delivers high deposition, deep penetration and a smooth bead, which is why it is a first choice for long parts such as machinery booms, trailer and machine chassis, welded girders and tank shells.

This article explains how a submerged arc welding machine works, what it brings to linear seams, boom welding and chassis welding, and what drives quality. For process parameters see our SAW technical guide.

How Does a Submerged Arc Welding Machine Work?

The machine consists of a power source, a wire feeder, a flux delivery and recovery system and a carrier that moves the welding head along the part. The carrier can be a rail-mounted gantry or a column-and-boom manipulator. During welding:

• The wire electrode is fed continuously and an arc forms between it and the workpiece.
• Granular flux is laid ahead of the arc and covers it completely; the arc is not visible.
• Part of the flux melts and forms the slag that protects the weld; unfused flux is recovered and reused.
• The head travels along the seam at the constant speed and parameters set in the WPS.

The machine's working length sets the seam length that can be welded in one set-up. A 35 m line, for example, lets long boom and chassis members be welded without repositioning the part.

Submerged Arc Welding for Long Linear Seams

Web-to-flange joints of welded I-girders, box sections, plate butt joints and longitudinal tank seams are typical linear welds. On these seams SAW:

• Fills thicker sections in fewer passes,
• Gives uniform penetration and appearance thanks to constant travel speed,
• Reduces start and stop points, and with them the craters, porosity and lack of fusion that often occur there.

Boom Welding: Continuous Seams Against Fatigue

Excavator, crane and aerial platform booms are usually box sections exposed to variable loads, i.e. fatigue. Fatigue cracks often start at weld toes and where a seam was interrupted. Boom welding therefore depends on:

• Continuous long corner seams with smooth toes,
• A welding sequence planned to balance distortion,
• Keeping heat input and interpass temperature within WPS limits on high-strength steels (S690QL, Strenx and similar).

Because SAW lays long corner seams in one go at constant parameters, it suits these requirements well. See our heat input guide.

Chassis Welding: Straightness and Repeatability Over Length

The backbone of trailer, agricultural and construction machinery chassis is usually long side members. Customers expect two things from them: dimensional consistency and straightness. With SAW the seam runs at the same parameters along the whole part, so in series production each chassis comes out close to the last. Proper tacking, fixturing and a balanced sequence keep weld distortion under control.

Submerged Arc or MAG?

Criterion	Submerged arc (SAW, 121)	MAG (135)
Long straight seams	Ideal	Suitable, more stops
Deposition rate	Very high	Medium–high
Thick sections	Fewer passes	More passes
Welding position	PA and PB	All positions
Short, complex seams	Not suitable	Ideal
Arc light and spatter	Practically none	Present

In practice the two are combined: long main seams by SAW, brackets, bosses and short seams by MAG. See our MIG/MAG guide.

What Drives Quality in Submerged Arc Welding

1. Qualified WPS: current, voltage, travel speed, wire diameter and flux type come from a procedure qualified to EN ISO 15614-1. See What is a WPS?
2. Joint preparation and gap: a constant root gap along long parts is a precondition for uniform penetration.
3. Flux handling: flux must be kept dry and re-baked per the manufacturer's instructions when needed; damp flux raises the risk of hydrogen cracking and porosity.
4. Inspection: besides visual inspection, MT or UT is applied as the project requires. See NDT methods.

Frequently Asked Questions