American Welding Society Forum
Attempting to repair a cracked air dryer filter base, I don't know the type of aluminum involved. The unit resembles a conventional oil filter base but with multiple threaded inlet/outlet holes. The piece was degreased prior to carbide grinding the cracked area to shiny metal, recleaned with nonchlorinated degreaser and ss wire brushed. The part was preheated for an hour or so around 120 deg. Using prepurge to fill the recessed area to be welded, using 5356 rod and 3/32 tungsten. The metal blackens almost immediatly after the arc is struck and although the molten puddle is evident underneath, the filler rod balls up and refuses to join. (argon shielding, same tank and rod used without previous problems) Although the unit did not directly handle petro products, I suspect contamination from the crack is surfacing as the material is heated ? I reground the surface as before and heated the crack with oxy/act gently to remove this possibilty with no success. Also tried 4340 rod. The part has already been replaced with a new base, so this is more academic than necessity but I would still like to complete the weld if possible. Sorry I can't identify the material type, I realize this is a critical point and may be the real cause of the problem.
Thanks for your input, I will repost if any suggestions improve the result.
Sounds like there is still some contamination and the part has not been heated enough. Why purge the aluminum? It does you no good as the aluminum oxides melt at a higher temperature than the aluminum.
Cleaner/degreaser has a tendency to migrate deep into the opening (crack) taking any other contaminants with it and can be difficult to completly remove by conventional methods.
Try preheating at a higher temperature and really sticking that filler metal into the puddle. Slow wire feed in the vicinity of the arc often results in the condition you mentioned ("balling up").
It's probably not aluminum as welders know it. It used to be called pot metal. I have had sucess using an aluminun solder. The solder isn't like any other solder I have used. It doesn't need any flux! The direction say to use a propane torch. Some times it works and some times it doesn't. Some welding supply houses carry it or try Home Depot, Lowes.
DGXL hit this one on the head.
Surface prep on aluminum castings is huge.
100% of the crack must be routed out. Dye penetrant (Flourescent or red) is suitable to verify crack removal. Even the smallest residual crack left in a casting will hold impurities, (oil and degreaser in your case,) which will foul any attempt at a repair weld. You just need to grind until the bad stuff is gone.
Here is a tip for you casting repair folks.
When grinding with a carbide burr, spot facer or even a wheel. The addition of a bit of parafin wax will stop the tool from loading up. This will make the work go more than twice as fast and you won't make an enemy out of the guy shelling out $15- 30 bucks a piece for burrs.
you may want to check and see if the part is magnesium, this can be done by a flame test, by dropping some of your metal shavings through the torch flame, if it is magnsium it will spark or burst a little bit like a firework. Just curious but is it a bendix air dryer base?
The purge I was refering to in the first post involved preflow of argon to fill the cavity containing the cracked area, the oxy/fuel preheat was intended to burn off the suspected contamination contained in the crack.
I most likely reduced it to ash which promptly floats to the surface as the area melts. Grinding out the crack in the bottom of the recess will be difficult without resorting to a dentist drill. The sides form a U grove about 1/2" wide with the crack running across the bottom and part way up the sides. Using about 3/4" stickout and 3/32 tungsten I can't keep the arc directed to the bottom of the U. Tried 1/16" but could not develop enough heat. I will cut out the blackened weld ( carbide cutter with wax !) and after flame checking the grindings, try again.
It is a Bendix dryer base from a school bus. Once again, the unit will not likley be returned to service, but has provided a good lesson in real world repair, dirty and difficult to access.....
An increase to 300-350 degree F. Preheat with a good long soak time as you mentioned above will also help as you initiate fusion. (some old salts may run a 50/50 argon helium mix to get a bit more heat) If necessary, sometimes you need to remove more material to gain access to the root area. Aluminum builds up nicely and there are times when to salvage a badly damaged part that you will need to remove what seems to be an extraordinary amount of material... This will most likely have a negative effect on your temper conditioning. Wrapping the part in an insulating blanket right after oven removal and only exposing the area to be welded will also help. If you are making multiple passes its also wise to allow heat to dissapate after a few passes. This can be done by simply covering with the blanket for a few minutes or placing the part back into the oven for a time.
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