Re: Copper Casting In America (Trevelyan)

From: Eric Stevens (eric.stevens_at_sum.co.nz)
Date: 07/04/04 

Date: Mon, 05 Jul 2004 11:44:08 +1200

On Sun, 04 Jul 2004 08:03:46 -0400, Gary Coffman <ke4zv@bellsouth.net>
wrote:

>On Sun, 04 Jul 2004 22:14:36 +1200, Eric Stevens <eric.stevens@sum.co.nz> wrote:
>>On Sun, 04 Jul 2004 05:07:36 -0400, Gary Coffman <ke4zv@bellsouth.net>
>>inadvertantly omitted:
>>
>>On Sun, 04 Jul 2004 02:36:09 GMT, Seppo Renfors <Renfors@not.com.au>
>>wrote:
>>
>>> ---- snip ----
>>
>>>>> "It is the sudden impact pressure that causes the
>>>>>molecules to move rapidly, that causes FRICTION, which in turn causes
>>>>>heat and if sufficient sudden pressure is applied (eg hammer blow to
>>>>>already hot metal) it CAN melt the material. To "weld" something by
>>>>>definition requires bringing part of it to a liquid state - ie melted
>>>>>in the portion being welded.
>>
>>... when he quoted my response to it.
>
>Actually, there was nothing inadvertent about trimming the message
>of older quoted material which anyone with a proper threaded newsreader
>has already seen, and can access again if they care. It is just good
>netiquette to only quote enough material to show the statements to
>which one is responding.
>
>Not doing such trimming is poor netiquette, and results in deeply nested
>reposted material, causing posts to be of excessive length, which are
>tedious to wade through to find the relevant new material. Some participating
>in this thread seem prone to do that. It is bad form.
>
>Any nesting of quotes greater than two levels is generally excessive, with
>rare exceptions. (Complaining about excessive quoting is one of those rare
>exceptions.)
>
>Now on to the factual dispute.
>
>>>>On Sun, 04 Jul 2004 18:06:21 +1200, Eric Stevens <eric.stevens@sum.co.nz> wrote:
>>>>How do you explain the well known welding at ambient temperatures of
>>>>precision slip-gauges made of hardened steel? Leave them in contact
>>>>overnight and you will be lucky to get them apart in the morning.
>>>
>>>No. While true cold welding can occur, that's not the mechanism(s)
>>>responsible for wringing gage blocks together.
>>>
>>>Frankly, the exact details are still in dispute. Part of it is atmospheric
>>>pressure differential between the outside and the area where air has
>>>been forced out from between the blocks. (up to 14 PSI) Part of it is
>>>often due to the stickiness of oil on the blocks. (roughly 2 or 3 PSI)
>>>
>>>But neither mechanism is strong enough to account for the amount of
>>>force typically needed to separate the blocks. (typically on the order of
>>>100 PSI)
>>>
>>>Most experts believe that Van der Waals forces (the same forces that
>>>give water surface tension, or make solder adhere) are responsible for
>>>the bulk of the effect. Others now point to the Casmir force (a quantum
>>>effect). Lively disputes still continue.
>>
>>You are discussing the underlying welding mechanism.
>
>No, I am not. I'm telling you welding is *not occurring* when gage blocks
>are wrung. Perhaps I need to use smaller words and shorter sentences
>when trying to communicate with you.
>
>>>A true weld is as strong as the parent materials. (up to 200,000 PSI for
>>>tool steel gage blocks).
>>
>>That is very rarely the case.
>
>It may be the case when an incompetent is doing the welding, but any
>sound weld is as strong as the parent material.

There is NO weld technique which produces a weld with metallurgy
identical to the the parent metals. ANY weld technique leads to a
discontinuity in material properties in or around the weld zone which
ALWAYS results in a propensity for the welded structure to fail in or
around the weld zone rather than the parent metal.
>
>>> When you break a true weld, parts of the parent
>>>materials are ripped out. That doesn't happen when separating wrung
>>>gage blocks. So that's not an example of actual welding.
>>
>>It depends upon how long you leave them together.
>
>Leave them together until hell freezes over, they still aren't welded.

They are merely immovably stuck together in such a way that it may
require an electron micrscope to detect the interface.
>
>>>To do an actual weld, the atoms of one piece of material have to be
>>>brought as close to the atoms of the other piece of material as the
>>>atoms of one of the pieces are to each other. At room temperature
>>>this requires a lot of force, on the order of the yield strength of the
>>>material.
>>
>>So?
>
>So, wringing gage blocks doesn't produce forces that even remotely
>approach the levels necessary for pressure welding to occur. I thought
>that would be obvious in context, but if you need it spelled out in smaller
>words, I'll try to oblige.

This phenomenon only occurs with precision gauge blocks for the simple
reason that their faces are so flat that the atoms of one piece of
material brought very close to the atoms of the other. When the
interface is broken an electron microscope will show the tears where
the asperities of one surface have welded to another before
separation.

No sudden impact is required to create such a weld. Neither is heat,
friction or any other mechanism to cause melting.
>
>>>This is a few thousand PSI for relatively low yield materials like copper,
>>>or more than 100,000 PSI for materials like tool steel. Of course, as
>>>you increase the temperature, the yield strength of the material declines,
>>>and less force is needed. When a material melts, the yield strength goes
>>>to virtually zero, so little or no force is required to achieve a weld.
>>
>>But we (Seppo and I) were discussing welds at ambient temperature. See
>>http://www.twi.co.uk/j32k/protected/band_3/ksedn002.html
>
>Indeed, and you used the wringing of gage blocks as an example. It is a
>faulty example, as I explained.
>
>I didn't bother to "me too" your good example of copper electrical line
>splices, since such piling on is considered bad netiquette.
>
>The pressure generated by the hydraulic swaging tools used by linemen
>is sufficient to cold weld clean copper. That was a good example. But your
>choice of the wringing of tool steel gage blocks as another example of cold
>welding was not. No welding at all is occurring in the latter case.

Electron microscopy says you are wrong.

Eric Stevens

Relevant Pages

  • Re: Copper Casting In America (Trevelyan)
    ... >of older quoted material which anyone with a proper threaded newsreader ... >>You are discussing the underlying welding mechanism. ... There is NO weld technique which produces a weld with metallurgy ... and you used the wringing of gage blocks as an example. ...
    (sci.archaeology)
  • Re: Wanna-Be Weld needs help!!!
    ... You would need to have your products anodized after welding them, which requires finishing the weld and heat affected zone. ... The anodizer needs to be able to process pieces as big as your finished products. ... This is not a good home based business so consider the cost of commercial shop space too, in addition to the welder, gas, electrodes, etc. ...
    (sci.engr.joining.welding)
  • Re: welding technique for clusters
    ... part of the welding process. ... stick or TIG) or create your ... Harry, ... A cracked weld is common with TIG, ...
    (rec.aviation.homebuilt)
  • Re: Tried running some 6011 electrodes
    ... > ring welding to a piece of flat bar to create an anchor point. ... but striking the arc ... > I also tried the drag rod technique with 6011. ... > bead was rough, the rod stuck, and the weld metal ended up on one side. ...
    (rec.crafts.metalworking)
  • Re: Brown soot whilst MIG welding
    ... I'm welding hot rolled steel with the mill scale removed. ... I'm getting a lot of brown soot around the weld bead. ... consistent gun angle, avoiding jerky movements of the gun. ... wire while you are moving. ...
    (sci.engr.joining.welding)