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Up Topic Welding Industry / General Welding Discussion / GMAW Contact tip
- - By MRWeldSoCal (***) Date 06-19-2013 13:50
Question:  When a GMAW or FCAW contact tip gets over heated and starts to make the welding less smooth, what is actually happening to the copper the make that happen?
I mean I know if the wire has turned it into a hot dog in a hallway there is less surface area of the wire getting contact, Im just looking for the over heating reasoning, like when the tip turnes a bright gold.
Parent - - By jwright650 (*****) Date 06-19-2013 14:01
The natural spiral of the wire where it was wound around the spool will wear the tip, but if the tip overheats the hole in the tip closes up on the wire and that will also cause the tip to wear. The erratic feeding can be from the wire getting caught in the tip, or when the tip isn't making a good electric connection causing the wire to feel like it's jumping because of the wire melting, then stop melting, melting again, stop melting...etc at a fast rate.
Parent - - By MRWeldSoCal (***) Date 06-19-2013 14:44
what about the times when you use a brand new tip and maybe a really hot application like 26 volts on a hard wire and the tip is in great shape physcially but a new tip is smoother?  I guess its there something on a molecular level with conductivity?  Like maybe if it over heats it loses something to it, I cant tell you how many times I have just replaced what looks like a decent tip and have seen a world of difference when the hole was barely wore out.
Parent - - By jwright650 (*****) Date 06-19-2013 16:07

>a really hot application like 26 volts


IMHO, 26v isn't all that hot. You may have liner problems or some other issue with the feeder side. Make sure that you haven't tightend the drive wheels too tight, this can mis-shapen the wire where it can hang in the liner or the tip. An egg shaped wire traveling through a round hole may not feed very well.
Parent - By JMCInc (**) Date 06-19-2013 16:26
Is the polarity on the machine set correctly?
Parent - - By MRWeldSoCal (***) Date 06-19-2013 17:58
Im just talking in general, It happens on many machines.  Am I crazy?  none of you have ever had a tip that the hole was tight fitting still but the copper color was cooked and the new tip made a better current flow?  no one?
Parent - - By jwright650 (*****) Date 06-19-2013 18:05
Hmmm, I'm not sure what you're seeing to be honest...maybe I'm just not paying too close attention when I'm welding to notice it until it gets really bad and then I start investigating to find the problem. I've noticed the puddle fluttering before and usually I'm running something out of whack(ie..too much wfs for the voltage when trying to weld on the low end of the mfg's recommendations)
Parent - - By MRWeldSoCal (***) Date 06-19-2013 18:36
I mean you notice a new tip from an bad tip right?   Now picture you have two new tips but one was just barely use but over heated..  I thikn when it gets cooked to a certain temp the conductivity changes within the copper and instead of free flowing electricity it is pushing it through.   If you have a MIG that rips really good try and see if you notice a difference next time.

Weld it up!
-J
Parent - - By jwright650 (*****) Date 06-19-2013 19:52
You may be on to something....after a bit of googling, it seems that copper(actually all metals) tend to be less conductive as temperature rises within the material.
Another thing that may be part of what you are seeing is that the oxide layer that forms on the copper when exposed to high heat and free oxygen can't help conductivity from the tip to the wire even though many copper-oxides are conductive. I suppose a fresh, brushed tip will serve better than an old tip that has been heated to a temperature where an oxide layer has formed on the surface.
Parent - - By MRWeldSoCal (***) Date 06-19-2013 20:54
It makes me wonder then if the copper is taken to a certain point with heat that its perminantly changed chemically or electrically
Parent - - By Milton Gravitt (***) Date 06-19-2013 22:29
What type of material are you welding on. Some times it is worst on aluminum than it is on cs.

                                                                M.G.
Parent - By MRWeldSoCal (***) Date 06-20-2013 14:33
Im really only reffering to carbon steels and sometimes spray transfer fluxcore.. Mostly just short circut
Parent - - By ssbn727 (*****) Date 06-19-2013 23:24
Here's a decent article that covers contact tips from the Fabricator...

http://www.thefabricator.com/article/consumables/caring-for-your-contact-tips

In fact, this article should answer your questions.:wink:

This article was used as a reference in the previous article above and when you read the summary, it explains the reason which is relatively simple as well as offering a logical and practical solution:

http://www.boulder.nist.gov/div853/Publication%20files/NIST_Weld_Contact_Tube.pdf

This is from Superior Consumables:

http://www.superiorconsumables.com/copper-alloy-tips.asp

http://www.superiorconsumables.com/contact-tips.asp#tips

http://www.luvata.com/Documents/Special%20Products/Welding%20Products/Contact%20Tips/Luvata_ContactTips_8.5X11_English.pdf

In this catalog on page 67-68, you'll find a recent upgrade in contact tips where contact tips with a triangular orifice gives better conductivity:

http://catalogs.praxairdirect.com/issue/30867

These guys mfg & sell a decent product line:

http://www.dfmachinespecialties.com/products/consumables/mig-torch-contact-tips

Hope this helps you out.:wink:

Respectfully,(Most of the time:eek::lol:)
Henry
Parent - By MRWeldSoCal (***) Date 06-20-2013 14:41
wow that is some excellent information! thank you!
Parent - - By Lawrence (*****) Date 06-20-2013 12:56
I don't believe a copper contact tip can become overheated short of melting....  Just don't see that happening/    You can wear an oval shape in the end but that has nothing to do with overheat..

Copper oxidizing because it gets hot is no mater of consern at all.  The copper can get VERY hot, and when the contact tip cools it will remain the same without distortion.

Can contacts be inconsistant?   Yes...  Some made overseas are not consistant.

Also filler wire can be inconsistant... Have seen this with Hyundai solid ER70S-6 in a number of occations... Also some Hyundai sold as .035 and .045 is slightly different so it can be cross sold overseas in a different metric class I've been told.

Filler wire Cast and Helix can be inconsistant as well... The "spiral and lift" of the wire if you lay it on the ground... If the wire is not consistant in this way trouble can occur in feeding and at the contact tip.
Parent - - By MRWeldSoCal (***) Date 06-20-2013 14:24
Experimental measurements have revealed that contact tip operating temperatures at the front could be in excess of 500 degrees C. Exposure to such temperatures triggers microstructural changes that deter the original mechanical properties of contact tips

That was a pretty good article.  I know it had to be something close to that.
Parent - - By Stringer (***) Date 06-20-2013 22:45
They make heavier tips for high voltage applications. In 37 years of welding I've never seen anybody change out mig liners, tips, insulators as often as they need to.
Parent - By jwright650 (*****) Date 06-21-2013 11:31
We use the heavy 600amp guns so the tips are beefier than those in the lighter guns...they seem to hold up alot better.
Parent - By ssbn727 (*****) Date 06-21-2013 02:17
Two words...

Basic metallurgy.

HVC
Parent - By MRWeldSoCal (***) Date 06-24-2013 18:39
Im not talking about physical distortion per say, more a chemical or microstructural change that effect current flow from being as resistant or distorted.

-J
Parent - - By pipewelder_1999 (****) Date 06-24-2013 12:27
My opinion.  Copper expands when heated.  Hole gets bigger. The curve in the wire varies and changes the point of contact thus changing the electrical stickout. This is really noticeable in pulsed spray transfer mode. I have not measured one while it was hot though but am pretty sure the hole gets bigger.
Parent - By cddolan74 (**) Date 06-24-2013 13:55
Lawrence is spot on in regards to cast and helix. this should be more of your focus.
Up Topic Welding Industry / General Welding Discussion / GMAW Contact tip

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