Copper Casting In America (Trevelyan)



Incorrect. Consult a good welding text such as "Modern Welding" by Althouse and Turnquist (the most widely used, and most authoritative, welding textbook).
It is true that fusion welding produces a HAZ (Heat Affected Zone) around the actual weld joint. This can significantly alter the properties of *some* materials, namely medium and high carbon steels, some alloy steels, and some aluminum alloys. But *part of the welding process* in those cases is post-weld heat treatment to restore those properties to their original pre- weld state. In other words, you haven't completed the welding process for those materials until you've done the post heat treatment.
For materials such as mild steel, the most commonly welded material, there is no such concern. The HAZ doesn't affect the material properties. That's because mild steel has too little carbon in the solid solution to produce the phase changes that could alter its crystaline structure. A *competent* welder will also choose an appropriate alloy filler material so that the fusion zone won't have different properties from the parents either.
It is well to note too that different welding techniques produce differing size HAZ. TIG welding produces less than arc, MIG produces less than either, and exotic techniques such as laser welding produce practically none at all.
Now you are postulating *cold welding* for the gage blocks, and that produces *no HAZ at all*. So the material properties surrounding the weld joint would not be altered *at all*. Of course cold welding isn't what's actually happening when you wring gage blocks together, but if it were, you'd still be wrong.
Gary
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wrote:

Right now I have consulted:
Metallurgy for Engineer's - Rollaston Mechanical Metallurgy - Dieter The Practical Use of Fracture Mechanics - Broek Pressure Component Construction - Harvey Creep of Engineering Materials - Pomeroy How Components Fail - Wulpi Practical Stress Analysis in Engineering Design - Blake Mechanical Engineering Design - Shigley A Procedure Handbook of Arc Welding - Lincoln Electric
... and none of them agree with you.

An analogous process is the natural welding by spontaneous adhesion of frozen mercury when constructing molds for precision casting.
Eric Stevens
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wrote:

I've already answered this but you deserve a better response than a mere battle of authorities.

OK, you have partly acknowledged my main point, that there is a discontinuity around the weld. In this case it is the 'heat affected zone'(HAZ). Now, not all HAZs need post-weld heat treatment, but HAZs still exist.
The metallurgy of the HAZ is visibly affected as can be seen in the micrographs in http://www.nuvonyx.com/catalog2/welding.html The variation of the mechanical properties of the material in the immediate vicinity of the weld can be seen in diagrams at the same site.
More information is available at the site of The Welding Institute at http://www.twi.co.uk/j32k/protected/band_3/jk48.html
It is a common view that the resulting weld will be strong if one uses a weld material that is stronger than the parent material. However fusion welding is a casting process and entails a puddle of molten material cooling down and solidifying. The resulting shrinkage requires local yielding of both the parent and weld material. If the weld material is too strong it will not yield and all the shrinkage has to be pulled out of the parent plate. Even if this does not cause cracking it leaves high residual stresses.
Someone will now say that you can relieve the stresses by heat treatment. That is perfectly correct but this further modifies the metallurgy of the weld zone and some of this may be adverse. Grain growth and embrittlement is a particular problem.
The reason why any discontinuity in properties at a weld results in a local weakness is that the mechanisms of failure are complex. Even ignoring any geometrical disturbances caused by the original welding, deformation will occur in the metal when stresses are applied.Tension applied to a plate will cause it to become slightly thinner and narrower. At low stresses the deforemation is elastic and the plate will return to its original shape if the load is removed. If the applied load becomes sufficiently high yielding (i.e. plastic ceformation) will occur in the material. If there are local variations in the material properties (e.g. at a weld) some parts will yield before others. This will result in a local redistribution of the stresses and the stronger parts of the material will end up carrying more load than they would if they had been surrounded by a material with a higher yield stress.
Now it gets really complicated. The local material is subject to a mixture of tensile and shear stresses. The interaction of these gives rise to 'principal stresses'. there is a principal tensile stress and a principal shear stress which acts at right angles to the principal shear stress. With some meterials it is the principal tensile stress which causes the failure and with others it is the principal shear stress which causes the failure.
The metallurgical discontinuities associated with a weld give rise to local disturbances in the stress pattern. These give rise to local variations in the principal stresses. Some will be higher than in the undisturbed parent plate. Others will be lower. Some parts of the weld zone will be less likely to fail than the parent plate but there will always be parts more likely to fail than the parent plate. It is at these latter locations that failure will commence.
That's why I say a weld is never as strong as the parent material.

Unless the weld is perfect, it still leaves an interface detectable by microscopy.

Its not just the properties 'around' but the properties 'at' which matter.

Eric Stevens
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Bwaa haa haaa haa.
I should check in on threads like this more often. A little bit of howling funnies is good now and again.
Jim
================================================= please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ================================================
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Eric Stevens wrote:

I suspect you snipped the wrong text there! What you left isn't mine.
But then explain how come each strand of a multi-strand cable can easily be separated from each other - even if very fine strands? Also electricity uses only the surface of any wire - so it isn't as if it holds the wire together either. I think you are confusing something with "welding".

Ahhhh..... nothing to do with welding at all. You are barking up the wrong tree - try simple air pressure. Two steel blocks each with a perfectly smooth surface, and you place those surfaces together - you can lift the bottom block solely by lifting the top one (momentarily at least). Air pressure, is what is holding them together. I have a set of dies made for me by a tool-maker mate that I can demonstrate exactly that with.
Not knowing what a "slip-gauge" was, I looked it up and they tell the same story.
http://homepage.tinet.ie/~jcelce/subjects/eng/pages/metrology.html "The measuring faces of Slip Gauges have such a good surface finish that when you place two gauges together with their measuring faces in contact, and slide one gauge over the other, they will wring together. Basically this means that they are almost stuck together, and that they will not slide off each other easily."
Nothing at all to do with welding.
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wrote:

The point is that they have not been forced together under pressure.

You are thinking of the 'skin effect' which applies to high frequencies. You can ignore it for DC of ordinary AC.

I bet they weren'r of grade 0 or 00 quality. If they were, you wouldn't want to leave them together overnight.

Eric Stevens
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Eric Stevens wrote:

If you add enough pressure to distort metal you cause friction and friction causes heat, the heat is sufficient to "weld" - whatever you are joining.

You tell that to my brother-in-law and nephew (both electricians), and they will have a good laugh..... of course it matters for both AC and DC - it governs the current the cable can carry. I refer you to fuse wire as an example.
[..]

A reference to a "set of dies" does rather tell you of harsh use - eg subject to impacts therefor excessively fine tolerances are not wanted/needed. Further to that the tools are much finer than commercially bought similar items. They are quite sufficient to demonstrate the effect.
[..]
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wrote:

Well done, Paul. Nothing like actually working with the metal to demonstrate its properties.
Gary
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a
started
.......
metal.
Possibly, probably. But more importantly, there is still an volume of gas bubbles trapped inside the ingot, that is equivalent to the volume of the blob sticking out of the upper left hand side.

Yes
They are a result of the small air bubbles trapped throughout the metal caused by melting it in less than controlled conditions. Pure copper, direct from the mill, melted in a vacuum furnace, or a void and inclusion free piece of native copper, would forge out as well as the upper alloyed sample.

not also depend on the

I have added a 4th picture to the above mentioned url to address this. It is of a forging made from manufactured bar. In fact it is made from the same bar that made up most of the cast piece.
The cast piece was annealed 8 to 10 times in the course of it's forging. That is a lot, considering it's length was only increased by 50%. But the large crack on right the appeared in the first round of hammering and I didn't want the piece to fall apart.
The piece made from manufactured copper was annealed twice. I probably could have done the forging with out annealing at all, but it was a small piece being held in my fingers. As the hammering hardens the metal, more vibrations travel up the metal and into the hand. It can be quite painful.

For the sake of orientation, the sectioned surface of the ingot is the small end of the forging.
The outer surface of the casting solidifies very rapidly, and is usually bubble free, the bubbles tend to be trapped inside. Subsequent forging would mash these shut (although not bond them together) making them difficult to see in a radiograph as they would either be smaller than the resolution or look like regular forging flaws.
This is why radiographs are inconclusive an any piece that may have been forged.

other
This is true, but as cast copper is as soft as it can be and needs a significant amount of hammering to harden it. For any edged tools or fish hooks or awls, this would surely display the tendency to fracture. Sheet goods also would require a lot of hammering. Heavier decorative items or ceremonial pieces would require much less work and cast preforms would work fine.

alloying
look
Yes, that appears to be the rub. And is an area in which someone should undertake some real hands on research.
Otherwise, it is like the old saw about the man who lost his keys late one dark night. He spent the rest of the night looking for them beneath the only street light that he passed, because if he lost them anywhere else, he wouldn't be able to find them in the dark.
Paul K. Dickman
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"Paul K. Dickman" wrote:

Yes I understood as much.

I can understand that during a melting process where molecules are at their most active, some reaction to air and a certain amount of mixing can occur. What I find difficult is that an annealing process causes bubbles -UNLESS it is overheated to a melting point locally. How else does something get INTO the metal to cause bubbles when it is pure to begin with?

Indeed, and that is because it has no inherent flaws with in it, to cause fracture points. Only it would appear, as I read various replies, than in certain circumstances "welding/forging" etc occurs without much temperature - Eric is even suggesting room temperature in one reply. Only when copper has been melted and has these gas bubbles occur, it can't be done - apparently.
I do understand the idea of oxidization, but that would result in embedded impurities more than wholly prevent welding to occur. Granted it wouldn't be as good a copper as modern melting techniques provides, but then such techniques and quality wasn't known about then and ignorance is bliss. They would have been happy with what they could do.

So it would appear that implied in the last statement is - the more frequent annealing the better the outcome (for shape). Of course, in this case you haven't trimmed the piece which might have been done in that sort of situation of a severe crack by the ancients.

That one I'm also familiar with - and it doesn't only apply to forging :-)

It is something I have been thinking as well.

Arrow and spear point are relatively small, and would want to be of a medium hardness only - so the tips of retrieved arrows/spears would be beneficial to NOT be too hard - so they will not break when missing the target - and so they can be restored again when bent.

Certainly in Mexico casting was used even for very small items.
[..]

Exactly :-)
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wrote:

At high temperatures oxygen is soluble in copper.
Eric Stevens
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Eric Stevens wrote:

So you say the copper has to be melted at that point, as you claim "soluble" - in a SOLUTION! As I thought...
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wrote:

Oxygen is soluble in copper at temperatures below its melting point. In much the same way hydrogen is soluble in iron at ambient temperatures. Look up 'hydrogen embrittlement' if you don't believe me.
Eric Stevens
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Eric Stevens wrote:

"Soluble" is a word that refers to something dissolving into a liquid mixture of (whatever). You cannot have something "dissolve" (also related to "solution") into a solid so it remains solid! Impossible!
SOLUBLE - adjective 1 (of a substance) able to be dissolved, especially in water - OED. DISSOLVE - verb 1 [no obj.] (of a solid) become incorporated into a liquid so as to form a solution - OED. SOLUTION - noun 2 a liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent). [mass noun] the process or state of being dissolved in a solvent. - OED.
QED [..]
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Seppo Renfors wrote:

http://www.thefreedictionary.com/solid%20solution
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wrote:

That's because your definition is wrong.

http://www.azom.com/details.asp?ArticleID 07 "Hydrogen embrittlement is caused by the presence of hydrogen atoms within the crystal lattice structure of a metal or alloy. In the galvanising process, hydrogen may be absorbed in the steel during the pickling process through contact with the hydrogen ions present in the hydrochloric acid."
The definition you quoted is correct for the world of cups of tea etc but has to be expanded to take into account the wider range of phenomena experienced in the real world.
Eric Stevens
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Eric Stevens wrote:

It isn't mine - it is merely the world authority on the English language you are saying is "wrong".

See, no mention at all of "soluble, solution or dissolve" even though a solution IS involved. This is because the are not relevant! Mind you I really would like to see "pickled steel" I wonder is it anything like pickled onions.... or gurkins..... still it has nothing to do with the actual subject - copper and annealing which is NOT "galavanising steel" involving "hydrochloric acid"!

The definitions *I* quoted are the accurate for the English language and they really ARE the "real world" you know. There does exits perfectly good words for other processed eg - as above "absorbed" - you do NOT need to abuse and misuse the language.
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Seppo Renfors wrote:

Seppo,
    Read and absorb:
http://www.thefreedictionary.com/solid%20solution
Including:
"Noun    1.    solid solution - a homogeneous solid that can exist over a range of component chemicals; a constituent of alloys that is formed when atoms of an element are incorporated into the crystals of a metal"
And:
"solution - a homogeneous mixture of two or more substances; frequently (but not necessarily) a liquid solution; "he used a solution of peroxide and water"".
Tom McDonald
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Tom McDonald wrote:

I already ignored that nonsense before.
CONTEXT - you missed the CONTEXT that governed the terminology and therefor its meaning.
Eric's reply was:
"At high temperatures oxygen is soluble in copper" to the question "How does the gases get in that causes the bubbles?" in relation to annealing.
Therefor it is NOT possible Eric was referring to the chemistry of a solid mixture containing a minor component uniformly distributed within the crystal lattice of the major component because:
(A) it doesn't "dissolve" into the copper because of annealing the reasons being (i) It requires the movement of the crystal structure to create spaces to "dissolve" into
(B) IF spaces exist there already is something in these spaces as a vacuum cannot exist. (i) It means the material is porous enough to use as a filter. (ii) The copper is not pure. (iii) If the substance in (i) is oxygen, then it would revert to a copper oxide in no time and couldn't exist as pure.
(C) Your term fails completely as in the annealing process it is NOT possible to get anything "uniformly distributed within the crystal lattice" of a piece of copper, as is required by the term you attempt to use.
(D) The (whatever) that is uniformly distributed within the crystal lattice has to be there from the moment of the crystal formation. (i) Then it cannot be the answer given by Eric. (ii) There is no proof there IS any space to contain anything in pure copper (remember it includes MODERN melted pure copper) in the aforesaid form.
All this is something that really needs no thinking about - it is self evident and obvious from the moment of seeing the term. Your attempt was another of those "Good morning - Axe handle" type cases.
[..]
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Seppo Renfors wrote:

    You're funny, Seppo. Don't ever change.
Tom McDonald
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