Text 21215, 124 rader
Skriven 2006-01-06 11:40:57 av Roy Witt (1:1/22)
  Kommentar till text 21181 av Michiel van der Vlist (2:280/5555)
Ärende: WTC fire         (was; La
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06 Jan 06 11:53, Michiel van der Vlist wrote to Roy Witt:


 MvdV>>> Have you ever done any brazing or welding yourself?
 >> Many times. I used to own a Miller 150 amp TIG welder. Sold it
 >> when I sold my shop. I also used the MIG welders that my welders
 >> used in that shop, although they owned them. After retiring in
 >> 1998, up until I moved from CA to TX, I owned an Oxy/Acetaline
 >> torch. I've done plenty of silver soldering and brazing with
 >> that torch, not to mention a lot of heat treating of tools.
 >> I still have the mixer and tips, planning on buying a
 >> new set of regulators and tanks one of these days. However, a
 >> MIG welder has priority for now.
 MvdV> Very nice.
 MvdV> I notice that this time you did not revert to a personal attack.
 MvdV> Thet tells me... no I won't give that away just yet. <evil grin>

That tells you that I know what I'm talking about...thanks. :o)

 MvdV>>> The normal brazing procees is very much like welding by wire
 MvdV>>> feed.
 >> No it isn't. You have to apply lots of heat to the material to
 >> be joined first, then you can do the brazing. A wire feed doesn't
 >> need the heat of the torch, as it's provided by the electric arc.
 MvdV> Language issue here. I thought hat by "wire welding" you meant
 MvdV> welding with a torch.

OK, I'll give you that one. We call that type of welding, with a torch,
using filler rod (here they're about 3ft long). Wire welding is with the
MIG machine and the wire is on a spool that is regulated by the MIG
machine.

 MvdV>>> You use a bronze wire instead of a steel wire. For the rest it is
 MvdV>>> pretty much the same. The temperature is a lower of course.

 >> Actually, in brazing, the tempurature is much higher than in
 >> electric arc welding. For instance, you have to heat the materials
 >> to be welded to a critical stage before you can expect any filler
 >> penetration. If you don't get any penetration, the weld is weak.

 MvdV> In welding, you have to heat the material above the melting point
 MvdV> of whatever you weld. In brazing you do not want the base matrial
 MvdV> to melt.

Correct. However, you do get the base material surfaces to the critical
stage, meaning it's near the melting point, but not quite there.

 >> Whereas, in electric arc welding, the depth of penetration is
 >> deeper and the only heat required is at the spot of the weld.

 MvdV> I see what you mean now. With arc welding the temperature is highe,
 MvdV> but only a small spot at the time is that hot. Yes, you may be
 MvdV> right that the overall heat rquired is less with arc welding.
 MvdV> Depending on the size of the object, etc etc.

BTW, the heat generated in arc welding tends to be absorbed by the whole
of the pieces being welded, similar to torch welding.

 MvdV>>> That tells me you never did any welding or brazing yourself.

 >> That tells me that you've never run into any exotic materials
 >> that are impossible to weld. For instance, tell me how to weld
 >> or braze together a car part or a toy made of pot metal.

 MvdV> Sorry, my language fails me. What is "pot metal"?

Usually the slag from any metal that's been used to cast other pieces. It
could contain aluminum, tin, who knows what else. It's very unstable as
far as welding goes. The way to do it is to set an acetalene torch to a
carburzing tip and flow carbon onto the material, then when you heat the
material to be welded, as the carbon disappears before your torch, it's
hot enough to add rod, but not hot enough to melt the parent material.

 >> One degree too hot and you'll melt the entire piece. How do you
 >> tell when the tempurature is correct, when the metal shows no
 >> sign of being heated? It can be done, but there's a
 >> trick to it that only an experienced welder would know.

 MvdV> I never claimed to be an experienced welder. In fact I am a lousy
 MvdV> welder.You may remember me and Jack Yates discussing welding and me
 MvdV> admitting to it. I am good at soldering though..

I never wanted to be a welder, because you can lose your eyesight very
easily. I've had 'sand' in my eyes more often than I care to. That's what
it feels like if you've been overexposed to the bright light of an arc
welder.

 MvdV>>> Penetration has nothing to do with strength. In fact deep
 MvdV>>> pentration may *weaken* the joint.

 >> Wrong, to a certain degree. All welding is penetration. Even
 >> when you're brazing, there is a minut penetration of the brazing
 >> rod into the parent material

 MvdV> Only a few molecules deep...

Yes. OTH, an arc can be as deep as a mm or more.

 >> (that's why you use a flux, heat the material and melt the rod).

 MvdV> The flux is to clean the surface and screen the material from the
 MvdV> atmosphere so that it does not oxidize.

Correct. That's what the gas used in MIG and TIG welding does. There is a
flux wire for the MIG, which means you pay more for the wire, but you
don't have to spend the money on gas.

 >> Otherwise, there would be no weld. And you're right about too
 >> deep penetration; that would occur if your weld burns holes
 >> through joint.

 MvdV> Which is why I am a lousy welder. I don't know how to properly
 MvdV> regulate it. Especially with thin stuf, I often burn through it.

That was my dad. He used to weld exhaust systems, using a torch and
clothes hanger wire, which could be made of anything. He burned a lot of
holes, but with persistance, he got the job done. But, once you learn to
use the proper wire, it's not that hard to weld thin stuff. Knowing the
tempurature colors involved in welding helps a lot.


Roy
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