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- - By transmissionman Date 10-29-2014 20:12
i'm having problems with some of the shafts I weld, they throw off sparks, form air pockets as if i'm welding too hot leaving the welded area looking like honeycomb, I tried lower heat and doesn't help, have asked a few at supply house and they look at me like a cow looking at a new gate, 1 welder I asked said certain alloys can make that happen but he was not sure which could make it happen, I tig weld transmission shafts repairing bearing surfaces, and splicing some to make most any trans hook up to most any motor, very few come through that that happens to, was wondering if anyone may have any answers about this thanks
Parent - - By Lawrence (*****) Date 10-29-2014 20:38
Three thoughts, all revolve around contamination.

If you are splicing a hollow shaft, the inside of that joint needs the same excellent preparation as the outside.  Anything but bright base metal can cause porosity.

Castings:  If you are joining to or repairing a casting, oil, soot and and grease can be impregnated into the base metal.  In some cases the casting can hold impurities from manufacture.

Shield gas.  A tricky torch angle can cause air to be drawn into the weld zone. A leak upstream of the torch will draw air into the line and cause porosity. And of course drafts will do the same.

The surfaces of castings may need to be ground/blended smooth prior to GTAW to a greater degree than other welding processes. Care of course must be taken when blending on rotating shafts to maintain balance, but this if often a key when doing build-up or repair with GTAW on castings.
Parent - By Milton Gravitt (***) Date 10-29-2014 22:09
Along with what Lawrence has said if the steel you are welding is 4130 it will spark like that if it gets to hot.

               M.G.
Parent - - By welderbrent (*****) Date 10-29-2014 23:18
Transmissionman,

WELCOME TO THE AWS WELDING FORUM!!

Great comments by Lawrence and Milton.  I think there may be one more idea here, so a question first:

Is this all the way around the shaft or more pronounced during the welding of the second half?

Now, either way, the gases inside the shaft are heating up, expanding, and then looking for a release port.  That is the area where you are welding and it will ALWAYS cause sparks and porosity.  Now, couple that with the possibility of grade of material and/or not clean of the greases and you have really added a toxic combination. 

Cure, a vent port.  This can be done several ways but on a driveline shaft you would mess with your balance so that limits us to a couple.  Drill a hole about half way up the shaft for the gases to flow through then weld your splice.  You can zap in the hole later to slowly seal it off or weld a small plate over the top of it but that will effect your balance.

But, Just from your post, my first suggestion would be to weld 75% of the way around, let it cool a little then slowly weld short sections at a time.  Very short.  And let it cool between welds.  Just get a small root in that will seal off the gap that is allowing the porting and then you can go over it with a good pass. 

Just my two tin pennies worth.

He Is In Control, Have a Great Day,  Brent
Parent - - By transmissionman Date 10-30-2014 00:11
the shafts are all solid, internal standard transmission shafts, 90% are used/worn out bearing surfaces that we grind .010-.015 and sometimes bead blast, then weld using pure argon on a low rpm lathe, less than 5% of these have the porosity problem, i think the oil impregnation is most likely the problem, but today we had new shafts that we are splicing and they have to be 100%, i tack then weld a lap and let it cool, by the 3rd lap or 1/4" thickness around center it starts fizzing and  large hole porosity
Parent - - By welderbrent (*****) Date 10-30-2014 01:17
Solid...shoots down the internal gas expansion theory  :lol:  :confused: 

We had a discussion here a while back about the effects of bead blasting and the residual "impregnated" impurities.  Especially for GTAW.  Somewhat sensitive to any such residues. 

Also, what tungsten are you using?  Don't remember seeing that yet. 

So, tungsten, gas flow (hose leaks? pressure- not too high, not too low), polarity -DCEN, Amps, grounding (on a lathe? ground should be straight to the welded part so you don't go through bearings for multiple reasons), clean (Stainless wire brush, Acetone is our friend, brush, Acetone is our friend, brush, did we talk about Acetone??), OH, what are you using for filler?  Is the base metal all the same and do you know the specs on it?

And, always a chance of contaminated shielding gas.  About once every couple of dozen cylinders depending upon which supplier I use.

Any one and/or combination of will cause problems as described.

He Is In Control, Have a Great Day,  Brent
Parent - By ssbn727 (*****) Date 10-30-2014 09:16
What type of media are you using for blasting?
Parent - By lo-hi (**) Date 10-30-2014 10:38
Wondering if they come from different manufactures, some being forged, some case hardened. Whenever you change the basic purpose of a mass produced part there may be engineering challenges. Maybe a quick shout to the supplier and see what they think, could help.  Perley
Up Topic Welding Industry / Technical Discussions / fizz

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