Guide written by:
Michael, Professional and passionate welder, Sheffield
How many welders are actually in love with their torch? No one knows, but if there's one welding process loved and cherished above all others, it's flame welding. Let's follow the lovers and discover the art of flame welding. Fire ahead!...
Weld and welding: what’s the difference?
Welding involves uniting two or more parts into a continuous structure.
"Welding"refers to the process and "weld"tothe joint produced by this process.
I've had my wrist slapped before for forgetting the distinction... A first piece of advice, start on a good footing!
What's the anatomy of a welding torch assembly?
Everyone's heard the phrase, but there's an ocean of difference between the blowtorch held in one hand and used in plumbing or to caramelize a crème brulée and the dual gas blowtorch. We're talking about melting metal here!
Multi-purpose single-gas torch (also known as soldering lamp)
Consisting of either a cylinder or a disposable cartridge of butane or propane; a preset regulator; and a hose connected to a handle with a heating control knob, this has served plumbers for generations to braze, bend or tin-plate pipes. Through flame contact, an interchangeable burner lets you reach temperatures of up to 1600°C. The cartridges have a lifetime of one to two hours maximum, depending on the job.
Unlike the above mono-gas system, an oxidizer - oxygen - is added to obtain an optimum temperature of 2800-3000°C. Bi-gas torch sets are well-presented and compact, easy to store, and highly practical for small repairs in plumbing as well as for newcomers to autogenous welding. In addition, kit are supplied with extra-small nozzles for jewellery repair. Again, duration of use is limited.
Autogenous or oxy-acetylene welding
Another bi-gas setup used in industrial and modern plumbing applications, this set consists of:
- Bottled acetylene, dissolved at 17 bars, as fuel; the "warhead" (top of the bottle) colour-coded brown;
- An oxygen cylinder, pressurized to 195 bars, as an oxidizer; white warhead;
- Two separate adjustable pressure regulators;
- Two flexible hoses of different colours: blue for oxygen, red for acetylene;
- A specialized torch that ensures an appropriate mix of the two gases. Different levels of precision can be achieved with interchangeable nozzles of varying sizes.
Why oxyacetylene welding is a favourite with welders
There is a reason why welders prefer using an oxyacetylene setup: the flame produced by the torch has some excellent qualities:
- It's as hot as it gets, between 3100 and 3200°C - and produces three different heatzones: The tip, thepink plume (ooh pretty!) and the blue-coloured reducing zone, the crucial part of the flame for autogenous welding. I first learned that from a metalwork teacher donkey's years ago - you'll never forget once you've got the knack.
- It's easy to adjust, with a range of interchangeable nozzles provided on a star-shaped stand. These always come with the torch and are classified in terms of flow in l / min. They must always be kept clean to give a flawless flame tip: a good welder always has his welder's reamer in his pocket.
For safety reasons, a one-way valve, identical in colour to the hose in question, is placed on each hose as close as possible to the torch, to prevent the flame recoil into the gas bottles. This type of accident can result from a poorly maintained blowtorch, so take care.
How does a flame welder work?
For single gas setups, all you need to do is heat to the melting temperature of thefiller metal (e.g. tin or silver solder) without forgetting to use some stripper on your components beforehand.
In this case, the welded components themselves are not melted. Only the filler metal is melted in the welding process. Melting temperatures vary between metals; base your choice of equipment and operating settings on the properties of your filler metal.
Depending on the size of the component to be welded, different burners are used to concentrate the heat at the point of welding. For tricky welds, you can get dedicated nozzles that avoid the risk of damage to the surrounding area.
A single-gas torch can also be used to heat a component prior to shaping, strip paint from sheet metal or even make creme brulee!
The focus here is on autogenous welding, a process similar to bi-gas welding but a little more sophisticated.
How are welding torches classified?
Torches are classified by size, from smallest to largest. Of course, your choice will depend on the thickness of metal sheet or components you're working with. As a rule of thumb, a flow rate of 100 l/min per 1mmof thickness is about right; the wire diameter of your filler metal is equivalent to the thickness of your sheet metal. Clearly No. 2 below is more suited to heating pieces of metal to be forged!
Classification of welding torches
Nozzles from 10 to 40 l/min; small welding torch.
Nozzles from 50 to 200 l/min; most commonly used type of torch.
Nozzles from 250 to 1000 l/min; high-temperature torch.
Nozzles from 1250 to 5000 l/min; heavy-duty welding torch.
First-time use of a flame welder
So, the gas cylinders are connected, the pressure regulators set at a pressure of 0.05-0.1 bar for the acetylene (C
2) and 1-1.5 bar for the oxygen (0
Your torch will have two adjustable knobs, one for each gas, identifiable by their colour. First turn up the acetylene, followed by the oxygen (1/4 turn of bottle cock is enough); then ignite your torch with the dedicated gas ignition button and adjust your flame so it has a fine, sharp tip.
Have a go at heating some metal sheet to practise the art of melting - it doesn't matter if you make a few holes the first time round, you're learning!
Once you've mastered melting, move on to welding using an appropriate filler metal (diameter and type).
To begin with, while you're working out your settings, it's common for droplets of molten metal to fly around - so watch out for your work clothes! Repeat until you've got the right settings for what you want to do.
A piece of advice about your acetylene bottle: since the gas is dissolved in acetone,avoid running the bottle down completely and don't lie it down - both risk burning acetone in your torch, resulting in a rubbish flame and poor welding results.
If you want to be economical, you can get a device that starts and cuts off gas flow as soon as you attach / detach your torch.
Common accidents and malfunctions
Due to the nature of the device, malfunctions are not uncommon; however, more often than not there's nothing major to worry about!
Caused by a reduction in thepressure of one of the gases or bad condition of the torch.
Clicking / snapping noise
Either the opening of the torch nozzle is blocked - in which case you should clean it with a welder's reamer - or the nozzle is becoming overheated, in which case you should cut the acetylene and leave the oxygen running to cool it down.
Visible flames inside the torch
Caused by overheating of the nozzle; turn off the gas supply and restart.
This is when the flame becomes black and dirty. Make sure your gas flow is appropriately adjusted.
Tips for choosing...
To summarize, choosing a welding torch is about having a precise understanding of the range of what you need it to achieve. Having thus narrowed down the available options, you'll find an impressive range of products to suit you.
Just relax and let yourself be lured in by the beautiful coloured glow of your perfect welding torch... But don't get too close!
Learn more about welding equipment...
To find out more about welding equipment, follow our editors' advice and check out their other guides:
- How to choose your torch, cutter, pressure regulator and flame welding fittings?
- How to choose your electrode holder and earthing clamp for arc welding?
- How to choose your welding mask?
Guide written by:
Michael, Professional and passionate welder, Sheffield, 71 guides
I was trained as a pipe worker and a pipe-welder and after having traveled for 35 years working around the UK, I became the head a metal shop and then a designer and in the end the head engineer. I have designed and built a workshop where I make metal sculptures: I managed to find a piece of paradise where I can to let my imagination run wild. Auctions and garage sales are no secret to me. I find unusual objects and old tools there that I collect or transform into works of art. I also like decoration, painting on canvas, and gardening. I am developing new technologies concerning tools. To share my passion and humbly advise you in your choice of materials is a real pleasure.