Rounding everything off are sections on common workshop skills – drill sharpening, the use of taps and dies and basic blacksmithing.
Of course, a book can take you only so far. A good practical course is the best way to improve; check out local colleges and training groups.
Farm and Workshop Welding is based on articles which first appeared in Power Farming and Farmers Weekly magazines. Weld examples were produced by the author, by the Welding Institute’s ex-chief instructor Max Rughoobeer, by ESAB’s Welding Process Superintendent Mick Andrews and by plastics specialist Dave Tucker. The Welding Institute provided sectioned weld pictures. Blacksmithing techniques were demonstrated by Sussex smith Frank Dean, who sadly passed away in 2004. The advice and help of all is much appreciated!
ANDREW PEARCE
January 2007
Don’t Take Risks
Here’s the line taken on safety throughout this book. Today’s duty of care requires that businesses and individuals both do, and are seen to do, the right thing regarding safe working practices.
I don’t intend to witter on at every turn about staying safe. Adults must pack a sufficiently well-developed sense of responsibility to look after the well-being of others, of children and of livestock.
If a risk or hazard exists that might not be obvious, I’ll try to point it out. Nevertheless, the responsibility to use good, sensible and legal working practices rests entirely with the reader.
When welding, cutting or grinding use protective equipment – eye shields, fireproof clothing, footwear and respiratory protection – as specified by Occupational Safety and Health (OSHA) guidelines, or the equivalent in your country. Advice on safe working is readily available: ask your welding equipment supplier, the equipment manufacturer or contact the OSHA directly. Be aware of the presence of children and livestock, and the possible risk to them from hot material, flying grit and ultra-violet radiation. Assess whether your skills are up to the fabrication or repair that you’re about to undertake, and think through the safety implications if it fails in service.
The bottom line is this. If you’re not 100% sure about how to do something and/or not 100% confident about the outcome, don’t do it.
First Things First
Just what is welding?
It’s the process of joining materials using heat. In fusion welding, joint components are heated until they melt together or are positively fused by pressure. Blacksmiths use heat and hammer blows, but here we’re more concerned with getting heat alone to do the work.
This heat will come from either an electric arc, a gas flame, or in the case of plastics, from a hot air gun. Filler is usually added to the joint from an electrode or separate rod. Non-fusion welding techniques like braze (or bronze) welding and soldering use heat too, but not enough to melt the metals that form the joint.
ANY OLD IRON?
METAL IDENTIFICATION
This book deals mainly with welding mild steels. Yet, as not all bits found under the bench or prised from the scrapheap will be mild steel, it might be good to start with a run through of materials and their weldability. Although accurate identification of steel is a complex business, the main classes can be sorted out with a file, a grinder and some basic ground rules.
Wrought iron is no longer very common, but in the past has been used extensively for chains and hooks. It’s very low in carbon, and malleable.
Mild steel is the common user-friendly stuff. It doesn’t usually harden when heated and cooled, and is easy to bend and weld. Black mild steel is what you’d normally buy: as strip it comes with rounded edges and retains its coating of mill scale from hot-rolling.
Bright mild steel in its flat form has square edges, is shiny and is more accurately sized than mild steel. It’s made by cleaning and cold-rolling black mild steel, leaving the metal stronger but less ductile.
Silver steel looks like bright steel but is much harder. It contains chromium but, oddly, no silver and is usually sold in short lengths.
Black and bright mild steels are easily filed and give off long, light yellow sparks under an angle grinder. Both are readily weldable. Silver steel is not.
Adding more carbon to steel makes it harder, and logically enough, produces carbon steels (Table 1). As the carbon level climbs, so does the end product’s hardness, brittleness and difficulty of welding.
After being formed to shape, carbon steels are often heat-treated (tempered) to boost their resilience. Welding heat can destroy the tempering effect, leaving the joint zone hard and brittle until it’s re-treated. Springs are a classic example.
The more carbon in steel, the harder it is to file – and files themselves have a very high carbon content.
So here’s a quick test. If an unknown material can’t be filed, it’s probably not weldable.
The exception can be cast iron; see below. The grinding spark pattern also changes with carbon level. As it rises, the sparks get shorter, bush out closer to the grinding wheel and may be darker yellow in color. If in doubt, compare sparks from the unknown metal with those from a chunk of mild steel.
Alloy steels. Although heat treatment will improve the resilience of carbon steel, really spectacular gains come from adding small quantities of exotic elements to produce alloy steels. All sorts of metals – nickel, tungsten, manganese, molybdenum, cobalt, vanadium – can spice up the mix, and the end result is usually heat-treated to maximize its properties.
Alloy steels turn up wherever toughness, resilience and corrosion resistance is needed. Typical applications are springs, gears and transmission half-shafts. Stainless steel is a variant using chromium to beat corrosion, which for the metalworker is both good and bad news. Although stainless is slow to tarnish, that reluctance to oxidize means it can’t be gas-cut. While many stainless steels are non-magnetic and weldable, if a magnet sticks to the bit you want to use don’t try welding it – cracking is very likely.
Two jobs using a dissimilar steels electrode: a sash cramp’s cast iron endplate welded to the central mild steel beam for more rigidity (left), and a slurry pump’s cast steel shear plate resurfaced to near-original dimensions (right).
Table 1. Materials and their weldability
Sorting an alloy from a carbon steel is largely a matter of application, though stainless stands out readily enough thanks to its satiny bright finish. Think about cost too: a cheap hand tool is more likely to get its hardness from a tempered carbon steel than an expensive alloy one.
Castings can be recognized by their complex shapes, generally rough surface finish and any raised surface lettering. But is the bit in your hand cast iron or cast steel? Application and a grinding test usually supply the answer.
Grey cast iron breaks very easily if bent or shocked to leave a grainy surface. Yet it stands compression loads very well, so turns up in machine beds, bearing housings, electric motor bodies, belt pulleys, engine blocks, manifolds and such. Heat treating grey cast iron produces the much tougher malleable cast iron, which is close to