Why Oxy-Acetylene is the Ideal Brazing Gas


13 July 2015
A-Gas Managing Director John Ormerod on high temperature work and how the regulations have changed surrounding this topic. 

Brazing pipes is an integral part of the job for fridge and air conditioning engineers. Oxy-acetylene provides the highest temperature for this line of work which makes it a popular choice for installers. This mixture delivers a temperature of approximately 3500°C which is ideal for work with larger copper pipes. ​
Why oxy-acetylene is best for brazing - ACR Journal
Why oxy-acetylene is best for brazing
As engineers know, the heat input rate for brazing is important for proper penetration of the filler materials around the joint. With the growing use of high pressure gases like R410A and CO2 this is becoming particularly relevant.  

Copper is an excellent conductor but takes away heat from the area being worked on. Larger pipe sizes need more heat to get the filler material to flow adequately in the joint and to provide a very strong leak-proof weld. So having a high temperature oxy-acetylene gas is a key requirement to ensure a first class job. 

Cheaper alternatives, like Methylacetylene-propadiene propane, are suitable for smaller pipe sizes up to and around 5/8th of an inch. Propane and Propylene gases also fail to reach high temperature levels. Oxy-acetylene has the edge here because it can be used for pipes in excess of 2/8th  of an inch.  

Without doubt high temperature oxy-acetylene gases are crucial if you want your work to be of safe and of good quality. The Braze-A-Gas® range of oxy-acetylene gases from A-Gas meets the demands of high temperature jobs by delivering  around 3500°C. They can also be used with a range of metals including copper and steel. 

High temperature oxy-acetylene gases are very flexible. You can put in a very small amount of heat – or large amount – depending on the size of the job. This means you get more efficient brazing and less heat waste. 

Regulation changes

There have been changes in the law affecting the use of oxy-acetylene units. The new Acetylene Safety Regulations have simplified the regulations but have done so without reducing protection for the user. This is good news for installers whatever industry they are working in.  

But a key part of the new regulations, and one which engineers in the fridge and air conditioning industries should know about, is the use of flashback arrestors in oxy-acetylene work. The use of flashback arrestors was formerly covered by best practice – to my mind not always a good yardstick – but it is now a legal requirement. Flashback arrestors are mandatory when using portable cylinder equipment – the type favoured by fridge and air conditioning engineers – and this is a very sensible move. 

It always seemed bizarre to me that flashback arrestors were not compulsory. They are a key feature when tackling any job, whatever the size. The route to a flashback can begin if there is a problem with the brazing torch or regulator; or the engineer may have closed off one valve and not the other or possibly there has been a failure of the non-return valve.  

In these circumstances it is possible to get a flammable mixture forming in the tube. If ignited this could, in extreme circumstances, find its way back out of the cylinder, causing a fire or explosion. 

The flashback arrestor is a very important last line of defence – ensuring that the installer is not at risk – and that’s why one should always be in place and used. There are no short cuts here. This is not regulation for the sake of regulation but a change in the law which could save your life. 

Most fridge engineers will probably be aware of the need to use flashback arresters. They are supplied with all reputable brazing equipment, so there is now no excuse not to use them. 

Safety emphasis

As for the industry generally, there is now a greater emphasis on safety in brazing work. There is also an increased focus on getting better joints, driven to some extent by the F-Gas Regulations. This means we are moving in the right direction.  

Oxy-acetylene is easily available these days; as a supplier we focus on small, portable cylinders. We’ve listened to the industry and know that fridge and air conditioning engineers find this more useful than using large cylinder packs. These pack sizes are available through A-Gas national wholesalers.  

The bulk of acetylene production goes to large cutting applications. The fridge engineer is never going to be tackling jobs on this kind of industrial scale, so small, portable packs really are ideal. 

If you are working on a roof or in the tight confines of a cellar, the size and weight of the cylinder is going to make a difference. It could save you time and money. A fridge engineer’s job is demanding enough, so anything to make it easier has got to be welcomed. 
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