Joining Metals E-Book

Henry Tindell

• Herausgeber: The Crowood Press
• Kategorie: Fachliteratur
• Serie: Crowood Metalworking Guides
• Sprache: Englisch

Seitenzahl: 253

Veröffentlichungsjahr: 2022

Beschreibung

Joining metals is a fundamental process used in all aspects of modern life. It is vital wherever metals are used, which is just about everywhere. Small or large, simple or complex – no mode of transport or method of construction would be possible without the sound understanding of its theory and practice. Written for the home metalworker or model engineer, this book discusses the various methods of joining metals, including strength, testing and applications, and includes useful lessons from historical failures including the sinking of the Titanic, the Flixborough explosion, the capsize of the Alexander L. Keilland offshore platform, the Hyatt Hotel elevated walkway collapse and the Markham Colliery lift bolt failure. With over 100 diagrams and over 200 photographs, this book examines: Mechanical joining: bolting, riveting, clamping - Metallurgical joining: welding, brazing, soldering - Chemical joining: bonding difficult metals - Strength of joints: choice and analysis - Failure of metals and joints: stress, fatigue, corrosion - Design: use of theory and codes to avoid failure, and finally - Testing of metals and joints: destructive and non-destructive (NDT).

Leseprobe

First published in 2022The Crowood Press LtdRamsbury, MarlboroughWiltshire SN8 2HR

[email protected]

www.crowood.com

This e-book first published in 2022

© Henry Tindell 2022

All rights reserved. This e-book is copyright material and must not be copied, reproduced, transferred, distributed, leased, licensed or publicly performed or used in any way except as specifically permitted in writing by the publishers, as allowed under the terms and conditions under which it was purchased or as strictly permitted by applicable copyright law. Any unauthorised distribution or use of this text may be a direct infringement of the author’s and publisher’s rights, and those responsible may be liable in law accordingly.

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

ISBN 978 0 7198 4056 2

Cover design: Maggie Mellett

DisclaimerSafety is of the utmost importance in every aspect of metalworking. The practical workshop procedures and the tools and equipment used in metalworking are potentially dangerous. Tools should be used in strict accordance with the manufacturer’s recommended procedures and current health and safety regulations. The author and publisher cannot accept responsibility for any accident or injury caused by following the advice given in this book.

DedicationTo Henry John, Hamish Oisin, Robin Alastair and (just in time!) Nina Maeve,Love from Grandad H.

Contents

Acknowledgements

Preface

List of abbreviations

Introduction – background to joining metals

1A history of joining metals

2Mechanical joining

3Metallurgical joining

4Chemical joining

5Selecting joining methods

6Design for joining

7Limits to joining

8Corrosion in joining

9Testing joints – Non-Destructive Testing (NDT)

Bibliography

Resources and suppliers

Index

Acknowledgements

Firstly, my thanks to Heather Carslake, LRPS, and my appreciation of her photographic work – all unacknowledged photos are by Heather and myself. Once again, I am indebted to Joanne Hulse for turning my handwritten scribble into an accurately typewritten manuscript. The team at The Crowood Press, editorial and production, were, as always, an un-alloyed delight with whom to work.

My thanks also to the following people. Ian Stansfield for providing the post-accident frame ‘experiment’ on page 17 in Chapter 1 (don’t try this at home!). TLJ Welding of Macclesfield, who generously gave their time and facilitated the pictures of a modern SME in the demanding field of high-integrity fabrication in exotic alloys; and Advanced Metallurgical Services (AMS) of Oldham, who similarly provided access to their scientific and technical facilities in material testing and failure analysis. To Graham Tindell (my brother) for his expertise in all things vintage Indian, not forgetting some epic riding. To Peter Wileman for his professional photography – the Banbury Run in 2019 (page 81). To the late Jim Caunt of Lincoln, creator of the unique JCS 250 and 175. And to Open Access (www.gov.uk), for the use of the Flixborough Report; the Stockport Model Engineering Society (SMES); the Veteran Cycle Club (VCC), Cheshire section; the Vintage Motor Cycle Club (VMCC), Manchester and High Peak section; and the Innominata Mountaineering Club (IMC) – all of whom have provided source material and great experiences. To all those not mentioned who have helped this book on its precarious way, whilst responsibility for all errors, omissions and general incongruities remain mine. And finally, to Phil Roberts for his patient consideration of the manuscript, one based on our shared formative experiences probing the mysterious world and enigmatic characters in the metallurgy and engineering departments of 1970s UMIST.

Thank you all,Henry Tindell.

Preface

Joining metals … so what’s the big deal?

Well, on the one hand, indeed no big deal – drill a hole and pop in a bolt, any bolt that fits. Or weld together with the omnipresent manual ‘stick’ welder, and any electrode. Perhaps just fix with a dab of super glue. What could possibly go wrong?

This may well do the trick, perhaps applying all three methods for a ‘belt, braces and baler twine’ result as an ‘agricultural’ solution – no disparagement of adventurous agri-repair farmer friends intended!

However, this rather narrow view of today’s world of joining metals fails to see that most familiar objects could neither function, nor be successfully produced – being significantly more sophisticated than our initial premise allows. The fact that all engineered products are fine until they fail is shown in the examples of some very well-known, and lesser known, jointing failures that led to disaster. And so, it turns out that this is actually an intriguing subject that perhaps deserves a second thought.

August 2021,Cheadle Hulme

List of abbreviations

AISI

American Iron and Steel Institute (material certification)

Al;CP

aluminium (element); Commercial Purity (CP Al)

Ag

silver (element)

Au

gold (element)

ASME

American Society of Mechanical Engineers; (design codes)

ASTM

American Society for Testing Metals; (test codes)

AWS

American Welding Society

BS

British Standards; BSEN (current Euronorm standards); BS EN (e.g. EN19 T) – superseded material standards, still widely used in UK

BSF

British Standard Fine (threads)

BSW

British Standard Whitworth (coarse threads)

C

carbon (element)

CE

Carbon Equivalent (relates to weldability of steel)

CCT

Continuous Cooling and Transformation (heat treatment diagrams)

CFRP

Carbon Fibre Reinforced Plastic

CI

Cast Iron

Co

cobalt (element)

Cr

chromium (element)

Cu

copper (element)

DPI

Dye Penetrant Testing (NDT)

E

either heat energy (J), or Modulus of Elasticity (stress/strain e.g. N/mm

2

)

ECA

Engineering Critical Assessment (use of Fracture Mechanics to assess material and fabrication defects

ESAB

leading multi-national welding and consumable manufacturer

FCAW

Flux Cored Arc Welding (AWS)

Fe

ferrous, iron (element)

FL

Fusion Line (interface weld metal to heat affected zone)

G

free energy, e.g. in corrosion; or Modulus of Rigidity, in material strength analysis

G48

widely used accelerated corrosion test for stainless steel in seawater

GMAW

Gas Metal Arc Welding (AWS)

HAZ

Heat Affected Zone (of weldment)

HSFG

High Strength Friction Grip (bolts)

IIW

International Institute of

Welding

IQI

Image Quality Indicator (radiographic interpretation tool)

ISO

International Standards Organisation

K

c

Fracture Toughness value

K

IC

Plane strain fracture toughness

Mg

magnesium (element)

MIC

Microbially Induced Corrosion

Mn

manganese (element)

MnS

Mn-sulphide (inclusion in steels)

MS

mild steel – low C steels

MPI

Magnetic Particle Inspection (NDT)

Nb

niobium (element)

NDT

Non-destructive Testing

Ni

nickel (element)

PM

Parent Metal (base metal, adjacent weld)

PWHT

Post Weld Heat Treatment (stress relieving after welding)

Qu & T

Quench and Temper (e.g. heat treatment low alloy steels)

RT

Room Temperature (20°C)

SAW

Submerged Arc (AWS and BS)

SMAW

Shielded Metal Arc Welding (AWS), Manual Metal Arc (MMA – BS)

S-N

Stress – Number of cycles (fatigue graph)

T

g

‘glassy’ transition temperature, (non-metals)

Ti

titanium (element)

TWI

The Welding Institute, Cambridge, UK

UNC

Unified National Coarse (threads, USA)

UNF

ditto, Fine

UT

Ultrasonic Testing (NDT)

WM

Weld Metal

XRF

X-ray fluorescence (NDT)

Zn

zinc (element)

ΔT

8 -5

cooling interval time of a metal or weld from 800°C to 500°C, typically steels

Symbols

σ

stress (e.g. N/mm

2

)

ε

strain (unit-less)

τ

shear stress (e.g. N/mm

2

)

γ

shear strain (unit-less)

υ

Poisson’s ratio (unit-less)

µ

coefficient of friction (unit-less)

ρ

density (e.g. g/mm

3

)

E

modulus of elasticity (e.g. N/mm

2

)

G

modulus of rigidity (e.g. N/mm

2

)

Introduction – background to joining metals

Wherever metals are found in the home workshop, not to say in the world at large, there exists a need to connect various pieces to produce a functioning whole. So self-apparent is this, and ubiquitous the use of ‘joining’, that the subject is often overlooked and thus assumed simple – or even trivial – which may be a great mistake!

Not unusually as one begins to focus on the subject, the opportunities, complexities and potential pitfalls become even more intriguing. Take the case of the humble bicycle (seeCase study 1); and the catastrophic collapse of an offshore oil rig (Case study 4). These contrasting examples illustrate a wide range of joining applications and consequences following joining choices and decisions, and unintended consequences, such as in the Flixborough disaster inquiry (Case study 3) – from the everyday to extreme environments.

There is a natural tendency, in metal joining, to concentrate on the immediate practical aspects, at the cost of neglecting fundamentals. Whilst this may often suffice when dealing with the familiar mild steel, whether used in non-failure-critical items, or for critical work, case studies 1, 2 and 3 illustrate some dramatic consequences.

Whilst mild steel is generally regarded as a familiar, strong and forgiving material, all around the modern world we encounter other steels (high-carbon, low alloy, stainless); cast irons (grey, white, ductile); copper-based alloys (brass, bronze); and the light alloys (aluminium, magnesium, titanium). The light alloys particularly illustrate the potential vulnerability to injudicious choices in methods of joining, such as welding, where a strong material can be rendered weak or brittle, or a perfect joint produced, as in Case study 1.

Ironbridge, Shropshire – built in 1779, the world's first iron bridge.

Cast irons are still in great demand worldwide and can be found in a wide variety of compositions and mechanical properties derived from the original castings of the Industrial Revolution, perhaps well illustrated in the world’s first all-metal (cast iron) bridge at Ironbridge in Shropshire. Built in 1779, it is still standing, high over the River Severn. This non-ductile material has been successfully employed by using mechanical joints (bolts and pins) to effect purely compressive loading in the structure. It therefore avoids the danger of any member being in tension, and thus subject to potential brittle failure. Notably, this was a feature well understood by the great engineers of the Victorian era, who carefully avoided use of cast iron where tensile forces could occur, such as in pressure vessels. Instead, they often demanded the newly developed mild steel for their ground-breaking projects.

Classic tractor – automotive metal joining heralding a farming revolution.

Steam traction engine at Coalbrookdale, Shropshire.

Steam locomotive at Foxton Railway Centre, Cheshire.

Nineteenth-century steam loco, Foxton.

Steam at Foxton – symbol of the first industrial revolution.

Detail of Victorian metal joining: mechanical joints.

Steam crane at Foxton.

Model railway in full steam, Stockport MES.

In motion at South Park, Stockport MES.

Engine room, miniature steam loco, Stockport MES.

This is beginning to indicate that a fundamental understanding of the properties of the materials to be joined is of paramount importance, not only for the method of joining – the three fundamental categories of the joining of metals are mechanical, metallurgical and chemical – but also for the design of the joint, in detail, and as part of the whole structure, as in Case study 3.

Steels are widely used and found in a great variety of forms, as noted earlier and discussed in more detail in Chapter 2, but even the common mild steel cannot be taken entirely for granted. It is necessary to be aware of limitations such as increased thickness, reduced temperatures, or restraint – the joint or structure can be rendered crack sensitive and vulnerable to brittle failure!

The basic understanding of these various families of alloys is pursued in Chapter 2, following the historical perspective in Chapter 1. Chapters 3 and 4 describe the practical methods for effecting joining, such as by bolting, welding and adhesives. Design of joints and structural aspects are explained in Chapters 5 and 6, whilst joining limitations are examined in Chapter 7. Degrading of metals through corrosion is discussed in Chapter 8, and testing methods by Non-Destructive Testing (NDT) is seen in Chapter 9. Finally, case studies 1 to 6 review some of the limitations and documented failures involving metal joining.

1 A history of joining metals

HISTORY OF THE BOLT

As a means of effecting a jointing of metals, the male bolt, along with its female nut, provide a critically important mechanism, the details of which are explored in Chapter 2.

The origin of the bolt, and the realization that the ‘inclined plane’ could be adapted to circular form as the screw thread, has been attributed to the Greek philosopher Archytas of Tarentum. Around 400BC he is said to have invented the screw thread, as utilized by Archimedes (287–212BC) in his famous water-raising screw, a principle still being used in water-driven turbines for local electricity generation. However, it is likely that the ancient Egyptians were already familiar with this as a method for land irrigation and the pumping of water from ships.

It seems likely that the concept of the threaded bolt, mated with a nut (or an item with an internal thread), did not reach significant utilization until the Middle Ages. Originally, it was in the form of the ‘non-threaded’ bolt, deployed by the Romans for fastening hinged doors or flaps in the manner of ‘bolting a gate’. The Romans also developed an early thread that was applied to cylinders or bars, by hand filing a helical groove into, typically, bronze. Another method was to wind and solder a wire around the bolt, to form a crude threaded device.

By the fifteenth century the use of threaded bolts and nuts for generating clamping forces was being utilized by Johannes Gutenberg in his printing press. Thence, the nut and bolt became critical in the development of weapons of war, and clockmaking. From his late fifteenth-century sketchbooks, Leonardo da Vinci produced designs of what have been described as early screw thread cutting machines – characteristically far-seeing of da Vinci, as accuracy and precision are critical for successful bolting manufacture.

Birthplace of the great Victorian engineer.

In France, Besson produced an early machine for making bolts. Improved in 1690 by the English engineers Hindley of York, with a screw cutting gauge for lathes, this found wide adoption as Britain headed into the Industrial Revolution. By 1760, J&W Wyatt had developed a machine for mass production, but this only led to a proliferation of different screw threads, given the choice of the variables of diameter, thread form, thread pitch, and materials. A great problem arose with compatibility of thread forms, and the difficulty of interchangeability with replacements.

In 1840, the great engineer Joseph Whitworth produced the first ‘standardized’ screw thread: the eponymous ‘Whit’ – widely used for manufacture until the late twentieth century, and still forming the current world standard in camera tripod attachments, as ¼” BSW (British Standard Whitworth).

Whitworth used a thread angle of 55 degrees (seeChapter 2) and a fairly coarse pitch (threads per inch), with radiused tops and bottoms of the thread. In the USA, William Sellers, in 1864, opted for a 60 degree thread angle to produce the original UNC and UNF (Unified National – Coarse and Fine). It was found that by taking the best form from Whitworth and Sellers, a flat top and radiused bottom profile produced the best fatigue results.

In Germany, in 1919, the original DIN standard was based on the American thread form at 60 degrees, thus producing the ‘metric’ coarse and fine. Adopted by the ISO (International Standards Organization) it is now the most widely used thread standard.

The ISO standards also designate material and provide detailed information on dimensions, bolt strength and load holding parameters, to enable safe selection and design. However, the ISO system is not the only one – several others are still in common usage, especially when restoring items such as historic vehicles and machinery. So, a basic understanding of the thread remains as important as ever.

HISTORY OF WELDING

The etymological origins of ‘welding’ arise in the Old English word samodwellung, based on samod (joining), rooted in the Swedish valla (heating), as Sweden had a large iron export market in the Middle Ages, likely imported during the Viking Age, as are many Scandinavian words into English.

The Middle English word welling also meant joining, first appearing in the 1590 version of the Christian Bible. In Middle English, the verse Isaiah 2:4 was written as …shallen welle togidere her Swerdes-in-to-sharris, meaning ‘shall weld together their swords into ploughshares’.

The practical origins of welding are common to the Bronze and Iron Ages, as documented by Herodotus of the ancient Greeks in his ‘The Histories’. He wrote that Glaucus of Chios had invented iron welding in 5BC (presumably by forge welding), but the method of joining by ‘casting-on’ was also used in the ancient world. A well-known example of this early welding comes from India in 310AD, as the 5-tonne Iron Pillar of Delhi.

In Europe during the Middle Ages, forge welding was being widely and skilfully employed by blacksmiths, to join wrought iron parts by heating them in the forge to red heat (800°C), and then hammering them together. This contrasts with modern fusion welding, the former being based on an enhanced diffusion (non-fusion) process, as discussed in Chapter 2. The early metallurgical treatise ‘De la pirotechnia’ by Vannoccio Biringuccio, published in 1540, describes the forge welding method as used by the Renaissance craftsmen in Italy.

But it was not until the Scientific Age of the nineteenth century that welding developed towards the many processes that we recognize today. This began in 1800 with Sir Humphry Davy, who discovered the ‘short pulse’ electric arc, followed in 1808 with the ‘continuous’ electric arc, and the subsequent development of the major field of ‘arc welding’. In the meantime, the Russian Vasily Petrov had independently produced the continuous electric arc in 1803, recognizing its potential use for melting metal.

‘Electric arc welding’ was invented by the Russian and Polish workers Nikolai Bernardos and Stanislaw Olszewski using the continuous arc produced between carbon electrodes to provide an intense localized heat source capable of generating a weld pool. Consumable electrodes were tried by the Russian Slavyanov in 1888, and by the American C Coffin in 1890. This was followed in 1900 by the English A. Strohmenger with the flux-coated metal electrode, providing the technique that has continued to be developed up to the present day – its coating providing the shielding slag, with alloying additions for today’s SMAW (shielded metal arc welding, from the widely used American Welding Society (AWS) designation).

A number of entirely different methods of fusion welding began to appear during the nineteenth century. Edmund Davy’s discovery of acetylene in 1836 eventually led, following the development of a suitable torch to mix compressed oxygen with acetylene, to ‘oxy-acetylene welding’ in 1900. The resultant flame, circa 3,000°C, provides sufficient concentrated heat to produce a weld metal pool, or the lower heat required for brazing (seeChapter 2). It made this a popular, low-cost and portable process. Widely used in industry until the mid-twentieth century, it is still invaluable as a method for the smaller-scale and specialized work often found in the less highly industrialized environments of small business and the home workshop.

‘Resistance welding’ was patented by Elihu Thomson in 1885, later finding widespread use in highly automated industries, such as the automotive industry, from the mid-twentieth century. In 1893, ‘thermit welding’ appeared, a process of employing a rapid chemical reaction to generate an intense heat source, and has long been used for the in-situ welding of continuous railway lines.

The impetus of re-armament upon industrial production for the 1914–18 and 1939–45 wars produced further rapid welding advances, the inter-war years seeing the world’s first all-welded ship (the British Fullagar), and a road bridge that crossed the Sludwia River near Lowicz in Poland, in 1928. Also prior to WWII, in 1930, ‘stud welding’ was developed – an adaptation of resistance welding. Around this time, forms of automatic welding began, based on continuous wire feed through a special gun, thus providing critical gas shielding to avoid the porosity that beset early work, and now forming the important processes known as ‘semi-automatic’, with a solid or flux-cored wire fed through the welding gun. Providing automatic arc-length regulation, these are now known as GMAW (AWS designation for gas metal arc welding invented in 1948) and FCAW (flux-cored arc welding, 1957). SAW (submerged arc welding), invented in 1930, remains vital for heavy engineering and high production rate, high-quality, welding.

Even underwater welding became possible, of great value to subsequent offshore oil exploration, following the work by Russian Konstantin Khrenov in 1932. In 1941, the GTAW (gas tungsten arc welding) process was successfully established. The heat source is produced from an inert gas shielded, non-consumable tungsten electrode, with a hand-fed consumable wire electrode being introduced, as is for oxy-acetylene welding. GTAW has become the pre-eminent technique for manual, low production rate, and specialized welding of the highest quality.

Developments continue to the present day, from notable advances, including diffusion bonding by Russian N.F. Kazakov in 1953; electro-slag welding (ESW) in 1958; electron beam welding, also in 1958, particularly for small gap, large thickness and difficult material combinations, but at high installation costs; laser beam welding, in 1980, after the invention of the laser in 1960, with significant recent applications. Friction stir welding, a 1991 invention by Wayne Thomas of The Welding Institute, based in Cambridge, England, has provided many direct applications, especially in the highly automated industries. It also provides the basis for a potential replacement of the rivet, one of the earliest metal joining processes …c’est la change!

HISTORY OF ADHESIVES

Adhesives, or ‘glues’, have their origins in the beginnings of human activity and civilization. Traditional glues comprise colloidal solutions in water, providing a hard adhesive film on drying of the water base. Protein collagen provides a glue derived from animals via boiling of their hides, bones and horns. Vegetable glues, such as latex rubber, gum arabic and starches, are derived from organic sources. Inorganic natural glues, including ‘pitch’, produced from coal tar, are further examples of materials that were available in the pre-historic era. Extensively used, even in industrialized countries until relatively recently, such natural products have been largely superseded by modern synthetic adhesives. These synthetics fall into the two major categories of ‘thermoplastic’ and ‘thermosetting’ (seeChapter 2).

The earliest documented examples of adhesives used by man come from central Italy, with the finds of ‘tar-hafted’ stone dated to the Middle Pleistocene period, some 200,000 years ago. Birch-bark tar was used as the joining material, a glue recently found to have been simply produced from the burning of birch-bark under certain conditions – within the experimental capability of these ancient humans.

More sophisticated compound adhesives have also been discovered in stone axes, of plant gum and natural iron oxide (red ochre). These tools are dated from 70,000BC, amongst finds from South Africa. Ancient burial sites of 4000BC have revealed the use of adhesives for rebuilt clay pots, buried with dead tribesmen. Three resins were employed for this early repair work, presumably enabling the living to pragmatically retain the undamaged earthenware!

A particularly well-researched item of adhesive use dates from 3200BC, known as Ötzi’s axe, the Tyrolean Iceman. This early tool was reconstructed after preservation in a glacier on the Austrian–Italian border. Flint arrowheads, and copper axes with wooden handles, have also shown evidence of pitch as an organic adhesive, to affix stone or metal to wood using pitch made from the pyrolysis of birch-bark.

From 2000BC, there are records of use of adhesives from the ancient Egyptians, such as the wood and glue casket from King Tutankhamun’s tomb. The Egyptians also employed lamination to improve the performance of their bows and in the manufacture of furniture. They developed milk-based glues, as ‘casein’ for these items, as well as starch-based glues for fixing papyrus to clothing and moulds.

In the period up to AD500, the Greek and Roman empires produced important advances with their animal and fish glues, enabling fine marquetry and veneering of a high standard. Gold leaves were bonded with adhesives based on eggs and vegetables. Whilst the Greeks employed slaked lime as mortar, the Romans developed their cements with lime, sand and volcanic ash. ‘Pozzolanic cement’ was famously used for building the Roman Colosseum. The use of beeswax and tar for caulking their wooden shipping is also attributed to the Romans. After the fall of the Roman Empire, the armies of the vast Mongol Empire of Central Asia, by AD1000, are considered to have received a significant advantage from the adoption of Genghis Khan’s powerful bows, formed by gluing laminated lemonwood and bullhorn.

It was not until the two centuries from AD1500 that the Europeans began to invent wood glues, thus assisting in the magnificent work from the craftsmen–designers such as Thomas Chippendale. This led to the modern era of adhesive development with the first industrial production of animal-hide glues, from a factory in Holland, established 1690. Britain’s first adhesive patent was filed in 1750 for a fish glue, followed by production in Germany and Switzerland.

Natural rubber was being used as an adhesive in 1830, which later led to the extensive use of rubber-bonded metal for automobiles in 1927 with a process for solvent-based thermoplastic as the adhesive. In 1847, USA postage stamps were issued with starch-based glues, with the derivative Dextin patented in the USA in 1867. Casein glue was patented in the USA in 1876.

An important family of rubber-based adhesives, later used as a backing for the ubiquitous electrical and surgical tapes, was first established with Henry Day’s USA patent in 1845.

The synthetic plastic development of ‘Bakelite’, a thermoset phenolic, led, in 1910, to phenolic resin as a plywood coating, and by 1930 these phenolics had spawned an important sector of adhesives. In the period to the mid-twentieth century, many new adhesives were created, including those for the joining of high-strength, lightweight metals. These enabled materials previously found difficult, impractical, or even impossible to join by methods other than mechanical, to now be fixed with adhesives. This was the case for metal to non-metal joints, where adhesives now offer a unique solution. It will surely empower the continuing development of this field for the foreseeable future.

CASE STUDY 1: THE BICYCLE – A STUDY IN JOINING METALS

The evolution and development of the bicycle from the early nineteenth to the early twenty-first century provides a useful illustration of the design-enabling power of metal joining. The origins of the bicycle are generally agreed to arise from the ‘Hobby Horse’, also known as the ‘Draisine’, invented in 1817 by Karl von Drais of Karlsruhe in Baden-Wurttemberg. A simple two-wheeler without mechanical drive, it was propelled by ‘paddling’ along – just like the present-day child’s ‘balance bike’. The frame, steering gear and seating were all based on the wooden beam from which the wheels were suspended. Although temporarily popular in contemporary society, it was soon abandoned as a serious means of transport, to be replaced almost fifty years later by the ‘Boneshaker’, or velocipede, the earliest pedal cycle, from France. This began to resemble the modern bike, albeit with wooden wheels, spokes and a front wheel with direct pedal drive, like a child’s tricycle. The beam frame and forks were now made from wrought iron, rather than the wooden beam of its forerunners.

However, bicycle design then veered off at a tangent with the Boneshaker, developed by increasing the front and reducing the rear wheel diameters. It resulted in the infamous – the first, but not the last, fast but potentially dangerous two-wheeler – the Penny Farthing, known as an ‘Ordinary’ or ‘high bicycle’ to the aficionado. This short, but somewhat epic, period lasted only fifteen years until the penny dropped and sanity prevailed with the, aptly named, Safety Cycle in 1885. The iconic ‘Rover Safety Cycle’ by J.K. Starley, with its curved, all-metal frame and solid tyres, was a pointer to the ‘final solution’ (see Diagrams 1 and 2).

‘Draisine’ (Hobby Horse), circa 1820.

Velocipede (Boneshaker), circa 1860.

The ‘Ordinary’, (Penny Farthing) circa 1870.

The Early ‘Safety’, circa 1900.

This appeared in 1888 with the world’s first pneumatic tyre, patented by John Boyd Dunlop of Ireland, and, combined with the ‘diamond frame’, provided the essence of a design that prevailed worldwide for the next 80 years, and still retains a significant part of the growing cycle market to the present day.

From the early nineteenth to mid-twentieth century, the two-wheeler’s frame and associated parts were connected from a very limited range of joining choices. As the Hobby Horse was wooden framed, so traditional woodworking techniques were employed for its manufacture. The limitations of wood as a structural material meant that these machines were inevitably heavy and inefficient. The Boneshaker was an improvement, with its front wheel pedals, but was still not designed to harness the potential of metal for a more efficient construction of a better strength-to-weight machine.

The Penny Farthing required an all-metal design, but the huge front wheel enforced the use of long members for forks and spine of the frame. Metal joining in this period was still very basic for this simple but heavy design concept, drawing more from the methods of the blacksmith than from lightweight engineering. Then suddenly, with the dramatic design change to the diamond frame Safety Cycle, the elegant and efficient triangulation of lightweight tubes called for equally efficient joining methods (see Diagrams 3 and 4).

In the early days of the Hobby Horse, Boneshaker and Ordinary, metal joining still relied on woodworking and blacksmithing, using screws, bolts and pins to fasten crude and heavy lugs of one part to another. Towards the latter part of the nineteenth century, mild steel had begun to replace wrought iron and cast iron for structural work, including bicycles. The great Victorian engineers, such as Brunel and Stephenson, fully appreciated the transition to this cheap, strong and ductile material for civil, ship and railway engineering; but road transport was still horse-drawn, the province of the blacksmith – apart from the bicycle. In 1898, John Reynolds founded his steel tubing company, to produce his patented double butt-end tubes, perfect for the new diamond frame bike. This enabled the use of lighter tubes, made with thicker section ends to facilitate joining. Use could now be made of the lightweight lug design and joints made by soldering these lugs. Despite the lower strength of the filler material in shear, the large area of this lap joint enabled sustainable stresses. This method became so successful that it was continued as the most popular way to produce these frames throughout the twentieth century.