Copper wire question

Work hardened - soften by heating/cooling Gerry :-)} London, Canada

The alloy of copper used in the house is stiff. Ask anyone pulling 100' though a house.

For one, we can't afford pure copper, it conducts nicely but isn't strong to pull or hold up against much. Electrical grade copper is almost pure. Bus bars are that.

I have some bars and plan to melt them into bronze. Copper by itself is junk. They are 1/4" thick and 1/2" wide or so - won't hold their weight if stood on end with a slight angle. Only a bundle can 'stand'.

Martin

Ah, right. In a way it's true, since common copper has around 50-200ppm oxygen added to clean impurities and improve conductivity slightly, but that might as well be a trace. Doesn't count.

All copper wire *is* pure.

"Stiffness" is _hardness_. Stiff refers to how much a spring made of the stuff bends given a certain load, within the elastic range. If it's bent afterwards, it went into the plastic range and doesn't count. Hardness and strength refer to resistance to plastic deformation. Annealed copper is very soft indeed, though not as soft as say, 1000 series aluminum. Full hard copper is pretty strong, though I don't know how much off the top of my head. It work hardens an extreme amount, as this burner knows well:

silver soldered the jet tube to the mounting plate, so the copper was dead soft afterwards. After handling the burner by the shutoff valve a bit, the copper work hardened. Right now, it's strong enough to whip around nicely without bending.)

As for actual stiffness... I would guess, like most metals, the elastic modulus remains pretty much constant whatever the alloy (although...there are a lot of alloys), or at least whatever the hardness, work hardened or not.

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

Hmm. Elasticity and hardness are different material properties, or so I've heard.

Ya, that's why I put the misused term in quotes.

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

You were work hardening the material. Copper work hardens - when you bend it you are sliding the atoms back and forth across each other and eventually they start to chock at dislocations. If you anneal the wire (try a sample in a gas flame on your stove) the dislocations will anneal away and it will be butter soft again.

The ductility of materials like copper and aluminum are due in large part to the ease in which the atoms slip past each other. Add in some chocks like mechanical dislocations, or some small amount of impurity (for example, copper into aluminum) and the mechanical properties change remarkably.

Jim

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My dad, an auto mechanic of 30 years, tells me to heat used copper washers on banjo fittings before reinstalling them. Heat softens copper as noted by a few others. My dad also makes the occasional makeshift dowel pin or headless nail by securing some #12 copper wire and twisting the other end with a cordless drill, then cutting to length. Twisting 8 or 10 revolutions per inch work hardens the copper and straightens it too, making one long length of straight, hard material in a matter of a few minutes.

-- Bryce

Steve, Three kinds of copper are in use: hard-drawn copper, medium-hard-drawn copper, and annealed copper, also called "soft drawn." Copper wire is hard drawn as it comes from the drawing die. To obtain soft or annealed copper wire, the hard-drawn wire is heated to a red heat to soften it. Annealing, or softening it, reduces the tensile strength of the wire from about 55,000 to 35,000 lb per sq in.

Don

A more relevant property in this case is the yield strength, which can vary by 5x (~10ksi to ~50ksi) between annealed and heavily cold worked copper.

Ned Simmons

In my Metal Handbook there are pages and pages of copper alloys. Almost a whole page of hardness codes. Something like 28 pages of copper this and that codes.

Hard drawn copper is used. ASTM B 1 and B 105 are for electrical ASTM B 3 specifies soft or annealed copper. Square is ASTM B 48 - Soft square and rectangular... There are many others - those of standing, roping, Tin-coated and the like.

There are three general electrical categories : High conductivity coppers, high copper alloys and electrical bronzes.

Chromium tellurium beryllium and cadmium and zirconium are added where high anneal resistance is required.

Martin