Aluminum outboard skeg repair (bigger one this time... with He mix)
I replaced a broken off skeg off a fairly large outboard motor. This was a physically larger motor (higher horsepower) and skeg. Larger skeg, and thicker material than I'd done before.
Here is my previous skeg repair (happened to post a thread about it too) :
http://www.everlastgenerators.com/fo...(TIG-aluminum)
Although the skeg repair was technically "harder" this time around, it seemed to go easier, perhaps because I refined my approach in the solution a bit.
The customer bought a replacement skeg, and it wasn't quite a perfect fit. For one, it didn't have the perfect contour, but more significantly, it's thickness was 1/2", while the thickness of the remainer of the original skeg (the broken off "stub") was 1/4".
On the previous go-around doing a skeg repair (in the link above) I used product called "heat fence", which was sort of a clay or putty. It would go on moist, and as it encountered heat, it would absorb it heat and dry out in the process, as water inside it evaporated. The main thing I don't like about it is, it's messy and not something you want to touch your clean gloves on. I ended up supplementing it with extra water last time, so this time I just skipped the messy heat fence and went straight to using a water-wetted cotton towel for heat control.
Also, this time, I used a Helium-argon mix, which I now have access to. For this thick material, I wanted an instant puddle, to weld "hot and fast", to minimize heat input into the work as much as possible. This approach seemed to work great!
To prepare, first I ground the pieces to match contours. I generally left as much "meat" in the part with the oil and gears (and prop) as much as possible. I removed material from the replacement skeg instead of the "stub" as much as I could.
Then, I ground the sides of the replacement skeg into a Vee shape. This is important on many alloys for reducing hot cracking (and also makes more fully penetrating easier.) I have an aluminum 4.5" angle grinding wheel that is the right tool for this job - doesn't load up.
Then time for the tack welds. Sometimes it's really tricky just getting that first tack weld on there with the parts oriented in the right position. I got it done this time by bending a filler rod and propping the filler rod up in the weld groove - so gravity would feed the filler rod automatically as soon as I made a puddle in the appropriate spot. That freed up one hand to hold the pieces in alignment. It worked like a charm!
I followed up by putting a couple more tack welds on it, and then I start running a stitch weld bead. I stopped after each stitch, let it cool (cool to the touch and welding "hot and fast" with the helium, I was surprised it didn't heat up that much even right after the first stitch...)
...then I'd ran another stitch section. Cooling with a water soaked rag helped a lot, to quickly cool it when it got .
I got water down into the groove at one time, which caused a problem because you can't weld something that's wet (without hydrogen porosity) compressed air came to the rescue drying it off.
After repeating the stitch, I'd then cool it down to the touch, and do the same over a few times, then flipped it over, checked the vertical alignment of the skeg was doing okay, and did some stitches on the other side.
At one point, one of the stitches cracked from the heat expansion and cooling contraction of the other stitches. I would go over it a second pass, trying to melt through deeply and quickly, with the hot, high helium mix. I also used a second pass to straighten the skeg as needed into neatly perfect vertical alignment. (To be honest I can't remember if this picture was before straightening or after. But the photo may have been off to the side which makes it look crooked even if it's not.)
Here is how it looked after it was done being welded:
Some info on the welding settings used for this:
Based on the thickness of the material, I stepped up the Helium mix percentage, to about 33%. 10cfh argon, 5cfh Helium. I kept on the #6 gas lens cup I had on these, along with the 1/16" tungsten. (2% lanthanated.) Since this work was large enough that I didn't feel like dragging it up on my table (also the water cooling operations are more easily done with a lot of room), I ended up welding it down on the floor and not on my bench, and I set up the torch switch instead of the footpedal. I set the current up to get me as close to "wide open" as my machine can do with the torch switch, which is about ~190 amps or so the way the knob works on my machine (Foot pedal, I can reach 198 amps according to the digital readout, but the panel knob can't quite reach that.) Anyhow, I used my usual 20% AC Balance, and no pulse.
I didn't set any downslope, but in hindsight, probably should have set at least a little bit, to taper off the current at the end a bit.
(Next post... grinding)
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(That was kind of my goal.)
Originally Posted by Cippee
