Arc Welding by the Numbers

About this book

Arc welding is the workhorse of fabrication. An electric arc between an electrode and the work melts both, and the molten metal joins the parts as it freezes. Almost every steel structure, frame, tank, trailer and machine base made in an Australian workshop depends on it. Much of what decides whether arc welding is done well, safely and profitably can be calculated before anyone strikes an arc: how much power the arc uses, whether the machine can sustain it, how much weld metal a joint needs, how long that metal takes to deposit, and what each metre of weld costs.

This book is for the people who make those decisions: fabricators, welding supervisors, estimators and manufacturing engineers. It assumes basic familiarity with welding and with simple algebra in SI units. It does not teach welding technique, which comes from qualified instruction and supervised practice, and it does not replace welding procedures, standards or the equipment maker’s instructions. It explains, with numbers, why the work takes the time and costs the money it does, and where the risks lie.

A 1921 railway book as a starting point

Metallic arc welding spread rapidly during and after the First World War, especially in American railway shops, where it repaired locomotive fireboxes, frames and boiler tubes. Electric Arc Welding by E. Wanamaker and H. R. Pennington, two electrical engineers with the Chicago, Rock Island and Pacific Railroad, was published in 1921 and is the main historical source here, alongside the arc welding chapters of Hamilton and Oberg’s Electric Welding of 1918, H. A. Hornor’s Spot and Arc Welding of 1920 and George W. Cravens’ Welding of 1921.

These books recorded careful measurements. Wanamaker and Pennington calculated how much power the resistor-ballast welding sets of the time wasted, weighed electrodes and plates to measure deposition, and costed welds in kilowatt-hours per pound of metal. Their numbers make a clear baseline against which modern inverters, electrodes and processes can be compared. Each chapter takes one of their themes, restates it in modern terms and works it through a modern case.

The running case

This is an illustration. A fabrication shop builds belt-conveyor frames for quarries and recycling plants. Each frame has two 150 mm parallel-flange channel side rails 6 m long, joined by angle cross-members and fitted with legs and brackets, with about 20 m of 6 mm fillet weld in total. The shop welds them by manual metal arc with low-hydrogen electrodes, mostly 4.0 mm at 170 A, and is considering a change to gas metal arc welding. Some frames need repairs and modifications on site.

Through the book the shop works out its arc power, checks its machines and cables, estimates weld metal and arc time, deals with arc blow and stray current, controls fume and other hazards, and costs a metre of weld by both processes. The shop, the frames, settings, measurements and costs are invented for teaching. They are not KEVOS® work, and the settings are not recommended values for any electrode, machine or joint. Real settings come from qualified welding procedures and the consumable and equipment makers’ data.

How to use the book

Chapters 1 to 3 cover the electrical side: the arc as a heat source, power sources and their characteristics, and duty cycle, supply and cables. Chapters 4 to 6 cover the metal and the time: electrodes and deposition, weld metal in fillet welds, and arc time and operator factor. Chapter 7 deals with polarity, arc blow and the return path, Chapter 8 with positions, access and fit-up, Chapter 9 with fume, radiation and electrical safety, and Chapter 10 with cost per metre and the job record. Every chapter ends with an exercise and its worked answer.

Limits and professional responsibility

This book is educational. Structural, pressure-containing and other safety-critical welds must be made to qualified welding procedures by qualified welders, designed and inspected as the applicable standards, codes and regulators require, such as the AS/NZS 1554 series for structural steel welding. Arc welding exposes people to electric shock, fume, ultraviolet and infra-red radiation, fire, noise and burns; welding fumes and ultraviolet radiation from welding are classified as carcinogenic to humans. Work must follow Safe Work Australia’s model code of practice on welding processes as adopted in each jurisdiction, and the equipment and consumable makers’ instructions and safety data sheets. The 1918 to 1921 practices are described as history, not practice.

An original treatment

READOS covers weld repair of steel plate, including heat input, groove volume, preheat and procedure qualification, in Weld Repairs That Hold, and the way metals behave in welding in Weldability by the Numbers. This book links to those topics rather than repeating them and concentrates on the arc process itself. The explanations, the conveyor-frame case, the calculations, figures and exercises are original KEVOS® writing. The historical books are public-domain works in the United States; their facts are summarised, discussed and corrected in new words, and none of their text, tables or illustrations is reproduced.