Welding stainless the MMA way. Pos or Neg?

[cobminor]

Quote "You don't want thin metal to get too hot or it will melt away, hence -ve to workpiece." unquote. So what about thick metal?

 

[cobminor]

Have any of you arc guys tried this yet?

 

[rtbcomp]

According to the manual I quoted earlier, electrode packets state which polarity the electrode should be used with, for example the NiCl electrodes I have say AC (OCV>50) & DC(+) (OCV = Open Circuit Voltage)

 

[TechnicAl]

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.



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

I meant at night

 

[Drains]

LOL technicAl

Wot ho folks. Been trying to use lo hi's on an ac set 48v open circuit, but the packet says ac 70v, dc+. And man, it's impossible to keep the arc going! Have I answered my own question?
Rgds
Si

 

[rtbcomp]

I meant at night

Of course! I should have realised LMFAO

 

[Alex]

I think water can get hotter than 100 degrees, if its under pressure and contained, not intially sure though.

 

[rtbcomp]

I think water can get hotter than 100 degrees, if its under pressure and contained, not intially sure though.

Yes, water boils at 100 degC at atmospheric pressure. Increasing the pressure increases the boiling point. Impurities do the same.

Also water can become superheated above 100 deg without boiling in a microwave. This is why when sometimes you put a spoon or a bit of sugar in hot water out of the microwave it seems to explode, it actually boils vigorously.

 

[Alex]

Like on mythbusters when they heated water in the microwave and then poured some distilled water in it and it boiled violently.

 

[Justme]

Yes, water boils at 100 degC at atmospheric pressure.

Almost

At atmospheric pressure at sea level. Go higher up & the lower presure of the air causes the boiling point to move.

justme

 

[Alex]

as does the volume of liquid change with different pressures.

If its critical they weigh it.

 

[rtbcomp]

as does the volume of liquid change with different pressures.

If its critical they weigh it.

The change in volume is negligble as liquids don't compress, gasses are different altogether.

[pedantic]Pure water boils at 100 degC at 1 atmosphere pressure[/pedantic]

 

[Justme]

Quick some one pass me a tin opener need to open a new can of worms....

 

[Alex]

liquids will expand though, especially if they are heated, though it is tiny.

 

[marknotgeorge]

[stick in oar]
Actually, you can have liquid water at 100C and 1atm. You need to add extra energy to get it to boil. This is why, in those school experiments where you stick a beaker over a bunsen burner and put a themometer in it and do a graph of temperature over time, the graph goes flat for a bit. Then the water boils and the beaker explodes.
[remove oar]

 

[rtbcomp]

[stick in oar]
Actually, you can have liquid water at 100C and 1atm. You need to add extra energy to get it to boil. This is why, in those school experiments where you stick a beaker over a bunsen burner and put a themometer in it and do a graph of temperature over time, the graph goes flat for a bit. Then the water boils and the beaker explodes.
[remove oar]

Exactly - thats why they don't use thermostats in electric kettles, as soon as 100 deg was reached the kettle would switch off and the water wouldn't boil. They detect the water vapour instead, because when vapour is released the water is boiling.

 

[TechnicAl]

http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/examples/kimcon.html

This is the phase diagram for steel. Look at alloy A and basically it shows there is not much difference between the liquidus (top line) and the solidus (2nd line) . The area in between is the mushy zone.
Temperatures above the liquidus will result in volatalisation so the metals composition changes.
Where am I leading, well when you are welding there is always a chill effect and the metal wont stay molten for long so yes the temperature can exceed the melting point but only for a split second and in a very localised area.
By the way the diagram is plain carbon steel, additions of Manganese etc will alter it.

 

[rtbcomp]

I'll look at that again when I'm sober I think !!!

 

[Drains]

Now then Laddies
Wondered if we might be able to return to the question in hand, viz, polarity whilst welding MMA (stainless or no. As TechnicAl said, read the box)

My question is now, Does DC+ mean electrode positive or work positive? Obvious, you might think. A silly question, you might think, but the Audel welding reference manual is putting major confusion in my tiny mind. Can anybody clear this up?

Best regards etc my knowledgeable friends...
Si

 

[rtbcomp]

DC+ means electrode positive