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Welding trivia...

A

Anonymous-0

Well-known Member
Instead of a tool challenge I thought I'd put up a welding related question that was on the Interprovincial test I did years ago. Let the non welders take a shot at it first. Hint: I asked an instructor about this particular question after the test and he was going to look into it. Here goes. Dave

What is the purpose of having the shielding gas continue to flow for several seconds after the completion of a TIG weld?

A. To prevent the tungsten from becoming contaminated while still hot
B. To cool the TIG torch
C. To keep impurities out of the weld
D. None of the above
 
i'd guess A. you're already off the work with the torch, so either letting it still flow keeps the impurities off the tungsten, or the gas company wants you to waste gas!!!!
 
I just wanted see if non welders could come up with the correct answer first. I thought it was kind of a trick question based on what they taught us in school and an instructor agreed with me. Do you know why he agreed with me? Dave
 
I don't really think it was a trick question. The tungsten gets hot not molten so rule out A.

The torches are either air cooled or water cooled so rule out B.

When I was in school many years ago the instructor taught us to hold the torch on the end of the weld during the post flow.

The machine builders like Miller, Lincoln, and Hobart don't sell gas so they would not put that feature on a machine to encourage you to waste gas. So rule out D

You recieved a couple of correct answers so I hope this did not ruin your triva question. Hopefully the test is over.
 
Post flow is intended to protect the weld 'puddle' from oxygen at the end of the weld to reduce/eliminate the possability of oxidation and carburization of the metal while the metal is above critical temperature, ie: molten. A very critical practice for stainless in perticular. Face purge (torch) and back-gassing are rules #1 snd #1A, Post purge is #2. Anybody that claims to be a stainless welder and doesn't apply the basic rules of gas application should be suspect.
 
I say it is all above.
B only applies to air / gas cooled torches, a water cooled torch doesn't need the gas to cool the torch. :wink:
 
Stainless piping usually has to filled with argon on the inside to prevent carbide precipitation and crystalization of the weld metal. They make special dams for this so the whole pipe doesn't have to be filled. As far as the question goes, there are 2 correct answers. That's why I questioned an instructor after the test. I picked the right answer but it was a real toss up. I think I spent more time debating this question than any other on the test although I did get a few questions wrong(92%). It is very important to have post flow so the tungsten doesn't get contaminated and then contaminate the next weld. They really stressed this at school. It is also very important to have post flow on the weld until it cools for several seconds to keep oxygen and other impurities from compromising the weld while it is still hot(orange/red in the case of steel). Both answers A and C are correct but according to the test, C was the best answer. I thought there should have been an E answer on the test. Both A and C. I can't remember if the test had the B answer I posted but it was something very similar. It wasn't an easy test even though it was multiple choice. If you ever watch a GOOD TIG welder, you will see that he/she holds the torch over the weld for a few seconds even though they have finished their weld. Most TIG machines have pre and post flow timers that can be adjusted for the size of the tungsten and/or the size of the weld. Having it on longer doesn't hurt anything and preflow is also common so there are no flaws at the beginning of the weld. Thanks for participating. Dave
 
I just put the B answer in to throw a curve ball in the question. There were a lot of questions with more than one right answer. The challenge was picking the best answer. On this particular question, I finally decided that the weld itself was more important than the tungsten. I got somewhat lucky but I also don't think that anyone who chose A should be marked wrong. An instructor said I made a legitimate point. Dave
 
The tungsten does get red hot and contaminated at this temperature. This contamination could be transferred to the next weld. When the weld is finished it is not still in a molten state. The tungsten and the weld can both become contaminated immediately after the weld by not having post flow. In that regard I thought it was a trick question and should have included another answer for both A and C. It didn't ruin the test at all. There was answer for all four of the possible answers. That's why I thought it was an interesting question. Didn't you like my question? Dave
 
The answer they were looking for was C but there should have been another answer listed that included A and C. It is 6 of one and half a dozen for the other as both are equally important. While the post flow is protecting the weld, it is also protecting the tungsten and vice versa. Dave
 
Because I was right. He's one of the instructors that was always stressing the importance of post flow till the tungsten cooled off. Dave
 
I had no problem with your question. The book I have from years ago in the paragraph on post flow makes no mention of contaimating the tungsten only the weld. I just checked another book from the 70,s. Before the post flow feature on machines,(I think, I can't remember that far back)

To stop the arc, lift the electrode holder quickly until the arc is broken or use the foot control to reduce current flow. Always keep the gas flowing until the tungsten is cool, or the tungsten will become corroded and will be consumed too rapidly. This gas flow will also protect the weld puddle until it has cooled sufficently.

Someone could have changed their ideas since the books I have were printed.

Have a great day
 
JOB whenever you get ready to update your library, this is a fantastic book on Tig welding. :wink:

GTAW.jpg
 
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