Beginner Help - Blowing Through 0.8mm bodywork

[Myles1970]

Pre flowing the gas is more something you do with a proper torch rather than one with the gas valve in the torch. With a proper torch MB15/25 etc the gas valve is usually in the machine and you'll have quite a length of pipe before the tip, so lots of room for contamination from air thats replaced the shielding gas in said pipe. With the valve in the torch there is only about 4 inches of air to contaminate which gets blasted out pretty much instantaneously when you press the trigger.

Do you mean purging the gas line? I thought pre-flow was intended to shield the weld area?

 

[prepman]

One thing I have on my MIG set is voltage adjustment, which effectively sets the arc length and that does have a big effect on thin material. Spent many a happy hour under old bangers making 'porcupines', whilst listening to the wax hissing my ears. The others have covered all the other aspects. I've found that if possible it's better to replace a substantial section rather trying to patch small areas with varying thickness. i.e cut back to good stuff, as rustonium is a very difficult material to master for welding.

 

[pedrobedro]

Sorry, not enough context. You wrote:



Valves that are in the torch are generally hand operated - turn the gas valve on then press the trigger. In other words, the gas flow is unrelated to the trigger operation and there is a long preflow from opening the gas valve to operating the trigger.

I have not seen a torch that contained a solenoid but then, there are a lot of things I haven't seen.

The trigger and manually operated valve are in the torch handle so when you pull the trigger you open the valve at the same time. More sophisticated units have a switch in the torch which operates an electrical solenoid in the welder to flow the gas

 

[Popcorn]

Thanks pedrobedro, thought I'd lost the plot for a minute

 

[DickyDoDah]

I use SGS and there are a few distributors in your area. The popular sizes are nearly always in stock and most places are open on Saturday mornings. I have a 5% for MIG and a bottle of Argon for TIG. you always get 100% of your deposit back if you return the bottles so whilst it is a bit of a layout to start with it does improve your welds no end.

SGS Gases | We stock a wide range of rent free welding gases

www.sgsgases.co.uk

I would also agree with others that you need to cut out more metal as the rust on the back will be more extensive than you think. I've learnt to cut out at least twice the size of the apparent rust. I spent ages chasing holes

 

[Seadog]

And you get a forum discount on your first bottle.

 

[Burdekin]

For your patch use thicker gauge steel and weld towards it. And then back towards the weld when moving forward if worried about blowing through. I weld hot and that means a fast weld, it may seem weird but a lower amp weld means you are probably putting more heat in to get the metal to fuse. Hot and fast. When grinding the welds, grind from the thicker patch metal onto the weld so to minimise thinning the weld any more. Probably only leave .5mm gap when fitting up thin stuff.

 

[stichill99]

I am on the same process with a mk1 golf and have had the same issues. I do think your gap is too big with the patch panel. I have used copper backing heat sink with success. Some of that old veedub tin just melts when you look at it though!

 

[AKN]

I don't know why more welders don't have a preflow setting. Many have a postflow setting so a very brief nudge of the trigger gives a 3 (or so) second post flow without creating a long stickout. A preflow would also get rid of the gas surge that is so common.

I use an Oerlikon Solomig M260C that definitely has pre-flow about 1/2 second, bugs its owner but doesn‘t bother me. It does weld nicely on bodywork though.

 

[Jack Ryan]

I use an Oerlikon Solomig M260C that definitely has pre-flow about 1/2 second, bugs its owner but doesn‘t bother me. It does weld nicely on bodywork though.

Fairly easy to get used to I would have thought. Some have a fixed preflow like yours, some, like the Millermatic 252, have a semi-fixed preflow. I forget the sequence - poke out your tougue, lift your left foot and power on to a special programming mode where the preflow (and postflow) can be set. Others, like my ESAB, have menu settings for pre and postflow.

It would cost very close to nothing to add that feature and yet it is not provided. It is even harder to understand the omission when the functionality is already there in TIG mode. Some organisations and some individuals spend real money mitigating gas surge - here is a no cost solution.

All the best