Welding stainless the MMA way. Pos or Neg?

[Drains]

Well that's what I thought. I'm going to have a good long hard look at that book and see what it's trying to tell me.
Maybe I need to stop drinking that absinthe...

 

[Weldingartisan]

I think the Audel book is American isn't it? So 'reversed polarity' will be + electrode, which I have been taught to use on stainless and most special alloys. W/A

 

[Weldingartisan]

Incidently, water expands 1/23rd of it's volume between 4 and 100 degC, not an insignificant amount, especially if you get it wrong when designing wet heating systems!

 

[Haze]

heating systems are pressure relieved, and should also be able to cope with a half decent amount of pressure.

 

[Drains]

I think the Audel book is American isn't it? So 'reversed polarity' will be + electrode, which I have been taught to use on stainless and most special alloys. W/A

Yes, it got me confused for a while. Reverse polarity is the normal state, or + electrode, which you'd use on most stuff, unless the electrode says so, or your knowledge tells you and you need to cut down the penetration.... I think!?

 

[Weldingartisan]

Thanks for that Haze, I've only been designing and installing heating systems for the last 35 years!

 

[Haze]

lol well tell me then how you could *get it wrong* as you put it

 

[Weldingartisan]

I did say 'if' Haze! And was of course refering to lesser mortals than myself!!!

 

[Haze]

heh, I cant imagine it to be possible on domestic systems, so then I must assume you are a commercial bod, probably a pipe fitter, and in my experience most work from plans drawn by the surveying company, so pipe sizing and expansion requirements are not generally dealt with by the pipey, but i bet your old school as heck shirt and tie welder xD

 

[dutch2u2]

Thanks for that Haze, I've only been designing and installing heating systems for the last 35 years!

Hi weldingartians

I gave up pipe fitting & welding nearly 30 years ago!!!

dutch.

 

[Weldingartisan]

Hopefully I'm not the oldest 'old git' on the forum then!
I now have a fab shop and do more ally and stainless work in that than pipework these days, it's opposite Brands Hatch so I get a bit of automotive as well, especially machining odds and ends for a touring car team up the road. Quite enjoy it all really. W/A

 

[dutch2u2]

I'm only about 5 miles along the A20 heading towards london from you then!!!

dutch.

 

[Weldingartisan]

Well, considering the global reach of the forum thats quite a coincidence really!
If you have hung up your helmet dutch2u2 and need something welded give me a PM! W/A

 

[dutch2u2]

I was thinking about blowing the cobwebs out of the mask & having a play this summer, just to see if my hands are still steady!!!!!!

As you said: 'considering the global reach of the forum' & we are 10 mims away from each other.

dutch2u2

 

[zzr1200]

I'm told that the +ve electrode attains a higher temperature than the -ve, although the total heat in the joint will be as you say.

You don't want thin metal to get too hot or it will melt away, hence -ve to workpiece.

I've been reading some oldish threads and decided to add some info, from my college days.

An AC Arc develops 4000 C in total, 2000 C at the -ve electrode and 2000 C at the +ve as the electrons change direction between the electrodes.

A DC Arc develops between 6000 C and 7000 C depending on the electrode covering and the length of arc, 2000 C at the -ve electrode and between 4000 C/5000 C at the +ve.

Hence if the work is DC +ve the work/weld pool temp is higher than if it is DC -ve. The weld pool shape and depth can be partly controlled by the gases produced by the electrode covering.

Some electrode coverings require a higher temp to work, ie: electrode +ve. or the burn off rate of the filler rod is required to be higher than if the electrode is DC-ve.

hth

John

 

[Axedieselman]

Stainless can be painless! (SMAW)

Just seen a post somewhere else saying you should reverse polarity when MMA welding stainless. Is this right? Whenever I stick weld stainless I notice the welds are usually smooth and low build. If I reverse polarity will the weld be higher? Will that affect penetration?

simondrains, 1st....stainless steel electrodes come with either a lime or titania coating. Lime is used only with DC electrode positive (DCEP), and titania can be used with both AC and DC electrode positive (DCEP) current. The lime coated electrodes produce flat or slightly convex fillet welds and the slag covers the entire weld, spatter is at a minimum, and the impurities are fluxed from the weld metal. The titania coated electrodes produce slightly concave type welds with a smoother and more stable arc than that found with the lime coated type. Remember to check the identification numbers on your electrodes. "E" indicates arc welding. The 3 digit number following the prefix letter indicates the type of stainless steel (e.g., 308, 410, 502, ect). The last 2 digits after the hyphen indicate the coating, current polarity, and welding position of each electrode.
>15 lime coating, DCEP in all welding positions
>16 titania coating, AC or DC in all welding positions
>25 titania coating, DCEP in horizontal and flat positions.
>26 titania coating, AC or DCEP in horizontal and flat positions.
This is the only way to properly (SMAW) stainless painlessly! Good Luck!