What causes backfiring?

[culp]

Hi

I'm just starting out oxy-acetylene welding. With the help of the assembled experts here I'm now getting a good flame and able to melt the metal and get the whole weld-pool thing going.

I'm getting beckfiring; now I know that its caused by getting the torch too closed to the weld pool. To be quite honest I'm a bit scared of the whole process and tend if anything to have the flame too far away not too close yet I'm still getting backfiring?

What causes it?

 

[hotrodder]

Backfires (pop, pop, pop) are typically caused by the tip overheating allowing the flame to regress back into the nozzle. As well as getting the tip too close (overheating it, especially with a fillet weld) or touching the tip to the work, a dirty/partially blocked tip can cause 'em as can incorrect gas pressures.

 

[bawjaws]

and impurities in the steel, has to be cleaned first, had a try on a lightly rusted exhaust yesterday, its a no go!

 

[Delboy]

Big bangs that make you jump look at pressures.

 

[Paul.]

As Hotrodder says, usually backfiring is caused by overheating the nozzle, a partial blockage such as spatter, or a burr on the nozzle will also give problems by interrupting the flow of gas, some proper OA tip cleaners are a must.
Flame adjustment is critical, always a neutral flame for welding steel, If the nozzle overheats it can be quenched in a can of cold water, always keep a trickle of oxygen flowing to keep water out of the nozzle, (thats also a useful tip for cutting torches),
Backfires in the nozzle are normally not too serious, but if you see a stream of black smoke coming from the nozzle, its reached the mixing chamber of the torch, and can damage the torch.

 

[the snooper]

i agree with del boy pressures, just like turning the oxy to high crack and its blow out

 

[Jake SS]

Can also be dodgy tip, mixer o'rings (if fitted)