The Good, The Bad, The Ugly: A Welding primer for homebrew
Posted Feb 02nd 2014 | By:
After seeing many threads on this topic I've decided to chime and give my two cents about welding.
I am a professional welder, NOT a professional writer. Every time I see pictures of these welds posted in these forums I cringe and would be embarrassed to put my name on them. I know more than most but not ALL, so for you experienced welders out there, feel free to nit pick me at the end!
Let's get started. First off, what does a good weld look like and what does a bad weld look like?
Well, if it is clean and the same color as the base metal (your pot/fittings etc) inside and out
that's a good start. If the weld bead is pleasing to the eye inside and out,your on the right track.Personally I like a bead that looks like what we call a "stack of dimes."
It should be uniform and the word of the day is: CONSISTENT.
Consistency is biggest problem I see everyday at the shop I work in. If you have thirty fittings welded to the same kettle, or thirty different kettles, they should all look the same.
This is not a guarantee nor prerequisite, but it shows an experienced hand welded your product.A weld that looks really bad probably is,but not necessarily. CWI's (certified weld inspector say every day..."just because a weld looks bad, doesn't mean it is." And that is true for structural steel and the like. But what we're dealing with here, in my opinion, if it looks bad it is.
Now a large part of these discussions include bits about purging or back-purging. They are the same thing. Back purging is exactly that, purging the back side of the weld with a gas equal to the shielding gas running through the welder. There are several gases and mixtures used for stainless steels and vary by application, method, and sometimes welder preference. I will only talk about pure Argon and GTAW (TiG) process because GMAW(MiG) and FCAW(flux core) have no business near your pots and kettles, PERIOD.
The following example is not stainless steel, but shows how simple and easy (read wrong if your weld shop does not do) back purging can be, plus look at the nice, CONSISTENT weld bead.
For large pots and kettles, a bit foil or cardboard fitted over the top with a purge hose taped through a hole will suffice. I recommend 10 CFM for the purge line. Argon is heavier than air so where ever it naturally vents out of the set up should not be the lowest point. It should push air out, not suck it in.
If you notice any dark gray "sugaring" or crystallized look to the inside or non-welded side of the joint...
You are looking at an incorrect and non-sanitary weld. If say, a pipe is welded, two pieces end to end and you look down inside and it looks just like the outside, as if it was actually welded on the inside as well, it was properly back purged. The following shows both purged and non. The bead in the foreground is purged, the latter is not...
It may be not so easy, depending on application to get back-purging to specific areas. There are other means such as purge blocks:
Other things to be considered are equally important for sound, quality sanitary weld.
The weld side of the bead also must be taken care of in regards to the shielding gas. Under no circumstance should the HAZ(heat affected zone) be exposed to ambient air when it is above 800F. Technique and machine settings can take care of this. Basically, travel speed should be low enough that the metal loses the cherry red before you travel half the diameter of the Tig torch cup. Or weld a distance equal to half the diameter of the cup and stop, allowing "Post flow" ( a machine setting that allows gas to be expelled for
a preset amount of time after the arc is terminated) to cool and keep the weld shielded. Other equipment such a trail shields are use. They leave gas behind as the torch progresses forward...
Their are also several styles and types of cups used on Tig torches. If a "gas lens":
is NOT used, I would definitely use the trail shield, however I do not recommend welding without the lens. Gas flow is greatly controlled and focused for that CONSISTENT clean weld.
Above on the left is flow with a lens, on the right is without. The difference is clear and speaks for itself.
If your weld shop doesn't mention any of these techniques or equipment or you don't see them in their shop,they better have one of these...
A glove box can eliminate all of the above mentioned equipment but is a bit more difficult for most welders to use because it greatly reduces maneuverability and welder's hand stability. Other terms you might mention or inquire about when at your weld shop could be DCEN( DC electrode negative) or "straight" polarity.
Proper tungsten electrodes should include:
- Yellow=Lanthanated (multipurpose and most common)
- Red=Thoriated /
These are all alloys of tungsten and all are usable, however I would recommend them in the order of red,yellow, then gray. Gray being the least used. Your shop will probably say yellow.
The welder should wear "doctor exam" gloves when handling clean parts and welding rod. Parts should be cleaned with NON-metallic scrubbies and if they need be ground, grind with new fresh abrasive pads/wheels etc that have not been used. Used pads could have been used on carbon (ferrous) steel or even picked up bits from dirt
and dust containing them. A quick wipe down with acetone and lint free rag after grinding or scrubbing prior to welding is a good bet. Wipe down the welding rod as well. Even the oils on your hands can contaminate a weld area and cause porosity and other rejectable defects.After welding, the area should be cleaned well, inside and out.
Some talk of "passivation" has floated around here as well. Passivation is simple really. It is the removal (in stainless steel) of ferrous metal particles from the surface of the affected area, to inhibit rust. There are several chemical treatments that involve strong acids and temperature controls.These methods usually deal with machined parts of aerospace components
and electrical devices. For our purposes and thankfully the cheapest yet still effective method, is the clean method.Chances are, if the weld has been cleaned already, using the NON-metallic scrubbie and no discoloration is present, it is naturally passivated. Scrubbing removes the softer ferrous particles and the oxides (discoloration) and leaves the harder, purer, higher chromium content of the alloy on the surface and the instant these parts of the alloy are exposed to free oxygen in the air, they oxidize forming the hardest layer of highest chromium content material.
This should leave your kettle virtually rust/corrosion free!
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