Welding stainless the MMA way. Pos or Neg?

Drains · Mar 6, 2007

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?

cobminor · Mar 6, 2007

I was told this some years ago by a proper welder and I have had it confirmed recently by my college tutor. You get more heat in the positive electrode and stainless is a poor conductor of heat. To get some heat in to the weld the positive goes to earth. I have not tried it yet but I am sure there are guys on here that will be trying it tommorow now it has been brought up.

lexi · Mar 6, 2007

Never have a problem getting heat with my Sip 210 arc and 316 rods just with standard arrangment. I may try it though .
Alex

Justme · Mar 6, 2007

I assume that arc & gasless mig are basicaly the same process so why dont all arcs use poss earth?

Justme

rtbcomp · Mar 6, 2007

Don't forget a lot of cheap arc welders are AC so swapping the leads over won't make any difference.

Drains · Mar 6, 2007

Justme said:
I assume that arc & gasless mig are basicaly the same process so why dont all arcs use poss earth?

Justme

Migs are always rectified, hence polarity is important.

MMA sets though. Hmm. Inverters are usually dc. I thought "normal' MMA sets were AC. Even oil filled are just a transformer without rectification. :confused:

I shall be trying it tomorrow, whatever...

rtbcomp · Mar 7, 2007

I suspect there always have been DC MMA sets, as welding rods are specified as being for AC and/or DC, with a recommendation for polarity, long before inverter sets became available.

DC arcs are easier to sustain than AC, I made an external rectifier for my Mono welder to (try) to weld some thin steel.

lexi · Mar 7, 2007

I aint tried the MMA function yet on my Inverter. Remember Frosts and a few other people were selling little boxes for thin metal stick welding. Were they not little Inverters? Was it not an add on to an Arc welder?
Alex

rtbcomp · Mar 7, 2007

lexi said:
I aint tried the MMA function yet on my Inverter. Remember Frosts and a few other people were selling little boxes for thin metal stick welding. Were they not little Inverters? Was it not an add on to an Arc welder?
Alex

If it was an add-on to an arc welder it would most likely have been a rectifier.

Remember those Rawlplug welders that ran off a battery? They incorporated a buzzer coil that vibrated the rod.

Alex · Mar 8, 2007

simondrains said:
Migs are always rectified, hence polarity is important.

Not on the SIP Handymate gasless there not. Utter crap, they expect you to MIG weld steel with 50hz.

Drains · Mar 8, 2007

The SIP Handymate gasless isn't a mig! I think you may agree with me there...

Alex · Mar 8, 2007

It's junk, thats what it is

TechnicAl · Mar 9, 2007

Back to Stainless MMA
The polarity to some extent depends on the make of the rod and what you are doing with it. You should read the instructions on the box, I think you will find most quote DC+ because you may not get full penetration using the DC-. Some use DC- for the root run in plate.
If in doubt use DC+

Drains · Mar 9, 2007

I'd hoped you'd turn up TA. For the sake of us mere mortals, can you expand on cobs post re heat into weld via work, not electrode. Only because I don't have a scooby and we all need to learn.
While your about, I saw a thread on ukwelder where you put a list of rod codes and apps (which I now can't find). I know i'll seldom have any reason to use anything other than 6013, but would you mind putting the list in here, and i'll reference it away, just cos.
Frankly TA, you should start running internet courses on welding, as this sometimes feels like the blind leading the blind. I've been at it for 25 years on and off and know Nothing.

TechnicAl · Mar 12, 2007

DC- is normally used on thin materials or on the root pass of a butt weld. This is because the DC- provides less penetration than DC+. Basically you only use DC- if you are likely to burn through.
As for putting more or less heat into the joint. The heat input or energy is calculated by Volts X Amps x Time divided by distance welded = Joules/mm. There is no differentiation between DC+/- or even AC. Using the DC- will be slower so it will be higher heat input compared to same settings on DC+.

rtbcomp · Mar 12, 2007

TechnicAl said:
..The heat input or energy is calculated by Volts X Amps x Time divided by distance welded = Joules/mm. There is no differentiation between DC+/- or even AC. Using the DC- will be slower so it will be higher heat input compared to same settings on DC+.

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.

TechnicAl · Mar 12, 2007

simondrains said:
I'd hoped you'd turn up TA. For the sake of us mere mortals, can you expand on cobs post re heat into weld via work, not electrode. Only because I don't have a scooby and we all need to learn.
While your about, I saw a thread on ukwelder where you put a list of rod codes and apps (which I now can't find). I know i'll seldom have any reason to use anything other than 6013, but would you mind putting the list in here, and i'll reference it away, just cos.
Frankly TA, you should start running internet courses on welding, as this sometimes feels like the blind leading the blind. I've been at it for 25 years on and off and know Nothing.

here is your list
http://www.lincolnelectric.com/knowledge/articles/content/awsclassification.asp

I was hoping I could find it somewhere, didnt fancy typing it out

TechnicAl · Mar 12, 2007

rtbcomp said:
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.

Im not sure. Ive always believed that the arc is similar to the temperature of the sun and I think that is around 3000 oC (someone will know).
Also the melting point of the particular steel / alloy is the melting point, it cannot be changed so a higher temperature would lead to volatalisation (I think)

As I said Im not sure but I cannot think why the temperature would be higher.

Drains · Mar 12, 2007

TechnicAl said:
here is your list
http://www.lincolnelectric.com/knowledge/articles/content/awsclassification.asp

I was hoping I could find it somewhere, didnt fancy typing it out

Thanks TA. I shall spend the next few days studying the Lincoln site. Good to have some homework!

rtbcomp · Mar 12, 2007

TechnicAl said:
Im not sure. Ive always believed that the arc is similar to the temperature of the sun and I think that is around 3000 oC (someone will know).
Also the melting point of the particular steel / alloy is the melting point, it cannot be changed so a higher temperature would lead to volatalisation (I think)

As I said Im not sure but I cannot think why the temperature would be higher.

The temperature of a molten metal can be higher than the melting point, like water can be at a higher temperature than ice until it boils.

From "Basic Engineering Craft Studies"

".......arc has a temperature of up to 3600 degC ..........."

".... heat generated is split into 2 parts, 2/3 goes to the positive pole and 1/3 to the negative pole........"

It actually states "heat" rather than "temperature"

According to Wikipedia the surface temp of the sun is 5500 degK

Welding stainless the MMA way. Pos or Neg?

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