smaw

By Lawrence (*****)

Date 02-03-2006 13:19

It will take some sorting out because I believe "Slope" is a non-standard term that gets applied across several processes nowadays

I believe your class discussion might have been talking about an adjustment on Constant current power supplies that is called "Arc Force" or "Dig". If your supply was CC/CV the same knob would also control "inductance" during CV Mig operations.

The "Arc Force/Dig" control is used to influence penetration in SMAW most specifically in open root welds. The higher the setting the greater arc density and greater penetration. You can really see the difference in Arc Force settings with open roots and E6010 electrodes.

The "Inductance" has an influence on penetration primarialy during Short Circuit transfer mode, this is especially noticable with open roots and straight CO2 gas. The higher the inductance setting the greater the penetration.

CV power supplies of an older vintage also sometimes come with multiple taps for the work clamp for better arc performance in either short circuit and spray transfer... I believe this is the more proper common place to find the the term "Slope" control

By aevald

Date 02-03-2006 15:05

Hello Lawrence, I've got a question for you. When you are using the SMAW process on a CC power source the voltage will increase with lengthening the arc length and will decrease with shortening of the arc, the current will stay relatively the same. I have been led to believe that as the voltage increases relative to the current this essentially gives the arc more heat and as the voltage decreases relative to the arc it provides less heat. This is how I've been led to believe that pipe welders and others that run open root welds will allow for variances in fit up and still be able to control root penetration and fill. Now back to the "slope", As you stated one setting will cause a digging characteristic the opposite setting will essentially provide a smooth sort of characteristic if I have interpreted this correctly. I have thought that a slope or inductance control allows the Volt/Amp curve to be altered relative to one another as opposed to being fixed according to the design of the machine, offbase or somewhat close on this train of thought? Would appreciate your thoughts on this. Thanks and regards, aevald

By 357max

Date 02-03-2006 15:31

Whip and pause technique which you describe produces the following: With a SMAW long arc the voltage increases. Voltage Affects the height and width of the weld deposit. High Voltage flattens the weld/Low Voltage piles up the metal. A shorter arc length requires less voltage because their is less resistance. Decreasing the arc length may (dependent on slope(volt/amp curve) of the particular welding machine) produce an increase in amperage. Amperage has the greatest affect on the penetration.
Whip out - increase arc length/increase resistance increase voltage and decrease amperage/decrease penetration, whip in - decrease arc length/decrease resistance/decrease voltage increases amperage/increase penetration.

By Lawrence (*****)

Date 02-03-2006 15:56

Aevald

I knew this thread would go in all directions because folks apply the term to CC and CV, GMAW and SMAW.

Back to your question. I understand SMAW current vs voltage the same way you do.
As far as pipe goes, I'm not an expert, Hopefully JTMc will read this and offer his knowledge, he is really sharp. Anyhow. Yes a slight adjustment in length will help somewhat control heat in open root welds. The Hobart school teaches a whip and pause method with open roots and E6010 and I respect them to the point of using their training materials, DVD's etc for SMAW, GMAW, GTAW and FCAW. However, I was taught by an old pipeliner who burried the 5P right into the groove and dragged it slightly and made adjustments in depth of penetration guided by sound. The guy was like a stick welding Yoda. I teach both methods and don't argue with success as long as it's within the parameters set forth in the WPS.

I have a nice Ed Craig training video on GMAW and as I recall he deals with Inductance and Multi-tap slope as seperate items.

A little more looking takes me to Larry Jeffus Welding Principles and Appplications 5th ed where he says:

"Although GMA Power source is said to have a constent potential (CP) it is not perfectly constant,.... there is a slight decrease in voltage as the amperage increases within the working range. The rate of decrease is known as slope. ...... A machine slope is affected by curcuit resistance. Circuit resistance may result from a number of factors, including poor connections, long leads, or a dirty contact tube. A higher resistance means a steeper slope. In short circuiting machines, increasing the inductance increases the slope. This increase slows the current's rate of change during short circuiting and arcing intervals, Therefore, slope and inductance are synonymous in this discussion."

There is more to it than that, but that helps a bit I hope.

By 357max

Date 02-03-2006 15:15

I believe this slope (volt amp curve) is the term used with variable voltage constant current motor generators. Selecting a coarse range selection and then selecting a fine current setting will change the OCV and the slope. A low fine current adjustment near zero on the rheostat will produce a flatter volt amp curve and a digging aggressive arc for cellulose (XX10-11s). If a range selection is made where the fine current adjustment is made near 100% of the rheostat setting a drooping volt amp curve is produced which is great for the low hydrogen electrodes. This slope provides a high open circuit voltage which low hy electrodes needs.
Use a volt meter and tong amp meter and measure the voltage values available at different coarse range selections for the same amperage values. The voltage changes will become apparent with welding at the same amperage with different (variable voltage) voltages.
The new printed circuit board controlled machines have the variable additional dig amperages at low welding voltages but the voltage value is controlled by the arc length.

By aevald

Date 02-03-2006 19:27

Hello all, I appreciate everyone's input on this subject. I know for myself that a lot of information that seems to be available on this topic doesn't clearly explain it as far as I'm concerned. When you check many of the reference books they seem to dance around on the subject. All of the responses that I've seen on this thread have been very good and helped my understanding greatly. Also a thankyou to cryogenicshaun for asking the original question. Thanks and regards, aevald