Forge Welding by the Numbers

About this book

Forge welding is the oldest way of joining iron, and for thousands of years it was the only one. Two pieces of iron are heated in a fire until they are nearly white, cleaned of scale with a flux, laid together and hammered, and they become one piece without either being melted. Chain, anchors, tools, wheel tyres, gates, ship fittings and the wrought iron that built the nineteenth century were joined that way. Today the craft survives in blacksmiths’ shops, heritage repair, toolmaking and art, and its principle, joining metal in the solid state by heat and pressure, lives on in resistance butt welding, the welding of pipe and the cladding of one metal onto another.

This book is for blacksmiths, heritage metalworkers, instructors and engineers who make or judge forge welds. It explains, with numbers, how a solid-state weld forms and what prevents it, how much heat and fuel bring a bar to welding heat, how scale forms and how fluxes deal with it, how joints are shaped and how much stock they need, how few seconds there are between the fire and the anvil, which metals forge weld and why, how strong forge welds are, and how chain, laminates and heritage repairs are made.

Early manuals as a starting point

When fusion welding arrived in the early twentieth century, its manuals began with the forge, because every reader knew it. The Davis-Bournonville course of 1919 opened with a lecture on the blacksmith’s fire and why its blast made it so hot. George W. Cravens’s treatise of 1921 gave a full chapter to smith welding: the fire, the fuels, the fluxes and the scarf, butt, lap and cleft welds, with a rule for the stock needed to weld a ring. Richard N. Hart’s book of 1910 described the wide welding range of wrought iron, reported tests in which experienced smiths’ worst welds had less than three-quarters of the strength of the bar, and recorded an experiment in which polished iron surfaces partly welded under pressure far below red heat. Calvin F. Swingle, in 1915, listed the drawbacks of fire welding that pushed industry towards the new processes.

Their accounts are the best record of how forge welding was done when it was still an industrial process. Each chapter takes one of their themes and works it through with modern understanding.

The running case

This is an illustration. A small blacksmith’s shop in a country town makes tools, hardware and gates, runs weekend classes, and repairs heritage wrought iron railings, gates and verandah work for owners and local councils. Its owner wants to teach forge welding with reasons rather than rules, cut the shop’s fuel and scrap, make welds that can be tested and trusted, and price heritage repairs honestly.

The shop, its students, customers, jobs and figures are invented for teaching. They are not KEVOS® work. Forge welded parts that carry loads where failure could injure people, such as lifting chain, hooks and structural members, must be made and certified to the standards that apply, or not forge welded at all.

How to use the book

Chapter 1 explains how a forge weld forms. Chapter 2 covers the fire and its fuel, and Chapter 3 scale and fluxes. Chapter 4 deals with joint shapes and stock, and Chapter 5 with timing the heat and the hammer. Chapter 6 compares the metals, and Chapter 7 the strength and testing of forge welds. Chapter 8 covers rings and chain, Chapter 9 laminated and clad metal, and Chapter 10 heritage repair, hazards and the shop record. Every chapter ends with an exercise and its worked answer.

Limits and professional responsibility

This book is educational. Forge fires, hot metal and hammering bring hazards of burns, fire, carbon monoxide, fumes from fuels, fluxes and coatings, eye injury from flying scale, and noise, which must be managed under the work health and safety laws of each jurisdiction. Lifting chain and other safety-critical items are made only to their standards by qualified makers. Heritage fabric is repaired only with the consent the heritage authority requires.

An original treatment

READOS covers resistance and flash butt welding in Resistance Welding by the Numbers, large repair welds in Thermit Welding by the Numbers, and solid-state joining in general in Weldability by the Numbers; this book links to them rather than repeating them. The explanations, the shop case, the calculations, figures and exercises are original KEVOS® writing. The historical sources are public-domain works in the United States; their methods are summarised in new words, and none of their text, tables or illustrations is reproduced.