Brazing and Soldering by the Numbers

About this book

Brazing and soldering are the quiet joining processes. They join copper pipes in every building, wires on every circuit board, carbide tips on saw blades, tubes in heat exchangers and refrigeration coils, and broken castings in repair shops. They melt a filler metal into a joint without melting the parts, and the filler is drawn in by capillary action, so the joint depends on things that cannot be seen: the gap, the cleanliness of the surfaces, the flux, the temperature and the time.

This book is for fabricators, maintenance fitters, manufacturing engineers and designers who braze or solder, or design parts to be brazed or soldered. It assumes basic physics and algebra in SI units. It explains, with numbers, why the rules of good practice work: why the gap must be small but not too small, why clearances change at brazing temperature, how long a lap must be, what flux does, how filler metals and solders are chosen, how much heat a joint needs, and how to keep the fume and fire hazards under control.

Early manuals as a starting point

The welding manuals of the early twentieth century treated brazing and soldering as close relatives of welding, often in the same chapter. Richard N. Hart’s Welding of 1910 described brazing with spelter and borax on a brick hearth with gas-air burners, dip brazing in a bath of molten spelter, and soldering with a copper bit and zinc chloride flux. Douglas T. Hamilton and Erik Oberg’s Electric Welding of 1918 described resistance soldering of spectacle frames, joint by joint, in a few seconds each. George W. Cravens’s Welding of 1921 summarised solders, fluxes and brazing practice, and noted that aluminium could not yet be soldered commercially.

Much of what they taught still holds, and some of it has been overturned. Each chapter takes one of their themes, checks it against modern understanding and applies it to a modern workshop.

The running case

This is an illustration. A small manufacturer makes copper and brass manifolds for hydronic heating systems, brazes copper tube into brass fittings and steel headers, solders electrical connections on its control boxes, and re-tips carbide cutting tools for a local machine shop. It has had leaks in the field, a run of cracked carbide tips and a question from a customer about lead in its solder, and its production manager wants to understand the processes well enough to fix them.

The business, its products, prices and failures are invented for teaching. They are not KEVOS® work. Real brazed and soldered products for pressure, potable water, electrical or safety-critical service must meet the applicable standards and regulations.

How to use the book

Chapter 1 defines brazing and soldering and why they work. Chapters 2 to 4 cover wetting and capillary flow, joint clearance and thermal expansion, and joint design and strength. Chapter 5 deals with fluxes and atmospheres, Chapter 6 with brazing filler metals and Chapter 7 with solders. Chapter 8 compares heating methods, Chapter 9 the difficult metals, and Chapter 10 inspection, hazards and cost. Every chapter ends with an exercise and its worked answer.

Limits and professional responsibility

This book is educational. Brazing and soldering involve heat, flame, fume and chemicals that can cause burns, fires and serious illness. Some filler metals contain cadmium or lead, and some fluxes contain fluorides; their fume and residues are hazardous. Work must follow the safety data sheets for each filler and flux, the equipment makers’ instructions, and the work health and safety regulator’s requirements, including Safe Work Australia’s model code of practice for welding processes as adopted in each jurisdiction. Joints for pressure equipment, gas, potable water and electrical installations are subject to their own standards, codes and licensing, which govern.

An original treatment

READOS introduces brazing and soldering briefly in Choosing a joining method, and discusses brazing for copper, cast iron and dissimilar metals in Weldability by the Numbers. This book goes further into the processes themselves. The explanations, the manufacturer’s case, the calculations, figures and exercises are original KEVOS® writing. The historical manuals are public-domain works in the United States; their facts are summarised, checked and corrected in new words, and none of their text, tables or illustrations is reproduced.