1022 rod...

[R.G.]

Annealing 1022 adds a bit more bass, and levels out the Mids, and gets a nice sizzle on the topend- Its nice with A5 mags, Pe and a resistance at about 15k . ALso takes away from the honky highs ; )

Can it give us a velvety finish with a hint of parsnips?

[David Schwab]

Hey, getting back to cast iron... I was looking at a photo of my friend's new table saw... they call that cast iron. So what is that stuff exactly? Mild steel?

[corduroyew]

Real cast iron has enough carbon in it that you can't easily machine it because it's too brittle and you can't easily drill it because it's too hard. Is has to be cast, hence the name cast iron. It's nothing like mild steel.

[black_labb]

Hey, getting back to cast iron... I was looking at a photo of my friend's new table saw... they call that cast iron. So what is that stuff exactly? Mild steel?

cast iron is around 3.5% carbon, much higher than steel. the carbon is there so that the melting temperature is low enough that it can be melted relatively easily (around 850 degrees c as opposed to 1500 for steel) it is harder but more brittle than steel.

dont get comfused that it is being called iron, it is less pure than plain steel.

[R.G.]

Cast iron is a schizophrenic material. It varies from quite soft and easy to machine to hard enough to chip bits off carbide tools, depending on the rate it is cooled.

Cast iron is what comes out of a basic iron ore blast furnace. Grind up iron ore for the iron oxides, limestone to act as a flux, and coke or charcoal mix well and dump into a blast furnace with an intensely hot region at the bottom. The blast and coke burn to provide heat; the heat dissociates some of the coke/charcoal into CO; the CO has enough affinity for oxygen that it literally pulls the oxygen off the iron leaving molten iron and melted nonmetallic slag. Also excess CO, used for fuel gas to preheat the incoming air. When molten cast iron and slag build up on the bottom, they're tapped off - usually into railway car sized crucibles.

The molten iron has about 3.5% carbon in it, as black_labb says. But it's not just ends of pencil leads in there. It's bound up in the iron in two ways: one as a solution of carbon in molten iron like sugar in tea, and two as iron carbide, which is what puts the "hard" in all carbon steels. Cast iron is the original carbide engineering material, from the cementite (FeC) in it.

If you cool it slowly, the cementite forms little isolated grains isolated by iron with carbon atoms in solution. The iron is soft, so it can be machined easily, the tool cutting and peeling back the separated grains. Cool it quickly and you get "chilled cast iron" which is a semi-continuous matrix of cementite in tough ferrite. This stuff is very hard to machine. Breaks things. Machinists all know that the outer "rind" of an iron casting will have hard spots which need to be gotten under quickly to avoid breaking tools.

Aside from the chilled spots, cast iron is relatively easy - if abrasive - to machine and drill.

Cast iron has very low tensile strength compared to steel, and is brittle, so it fractures on impact relatively easily. The puddling and blast furnaces were developed to further burn the carbon out using iron oxides as a source of oxygen, giving wrought iron with very little carbon but some residual slag.

Humanity has had a number of "learner" materials. Copper, as it occurs as the metal naturally; bronze, as it's easily made from copper and other stuff at low temps; and cast iron, which casts into metal objects easily. That list properly includes Germanium, which is much easier to refine to semiconductor purity than silicon and also much easier to diffuse. When I was in college, there was a refrigerator-sized Germanium-transistor oven in one of the labs and some of the semiconductor guys would occasionally whip up a batch of them for some thesis or other.

[David King]

OK since you guys seem to have all this info at your fingertips, what's the metal that is used inside the big ceramic donut magnet on the back of a woofer? I have been collecting chunks of this stuff for years but its not exactly in a shape I can use inside pickups. I could cut it up but I'd rather just go out and buy some in the sizes I want. I'm thinking it's the same stuff I see inside relay and solenoid cores.

[black_labb]

OK since you guys seem to have all this info at your fingertips, what's the metal that is used inside the big ceramic donut magnet on the back of a woofer? I have been collecting chunks of this stuff for years but its not exactly in a shape I can use inside pickups. I could cut it up but I'd rather just go out and buy some in the sizes I want. I'm thinking it's the same stuff I see inside relay and solenoid cores.

usually speakers are ferrite/ceramic magnets, but not nessesarily. may be neodynum magnets as well, depending on the speaker.

[David King]

Sorry, I didn't make myself clear, I'm not talking about the magnets themselves but the iron core that forms the inside of the gap where the coil sits. These are shaped like a mushroom and are glued onto the back of the magnet so they can't shift. They look to be some kind of steel, usually with a yellowish-greenish zinc plating to keep them from rusting.

[black_labb]

ahh, im not sure about that. i thought that you would have some idea about the magnet material. im not sure about that part. my guess is it would be a magnetically porous material of some sort, but i dont know anything for sure.

[R.G.]

OK since you guys seem to have all this info at your fingertips, what's the metal that is used inside the big ceramic donut magnet on the back of a woofer? I have been collecting chunks of this stuff for years but its not exactly in a shape I can use inside pickups. I could cut it up but I'd rather just go out and buy some in the sizes I want. I'm thinking it's the same stuff I see inside relay and solenoid cores.

Good question.

Ideally, it ought to be 4% silicon transformer iron. Transformer "iron" is a special iron? steel? used for building transformers, so it's produced in great quantity. There are various admixtures to get the BH curve right, and the 4% silicon is to raise the resistivity and thereby lower the eddy current losses.

But I suspect it divides by speaker price - the high end speakers using the good stuff, the lower end speakers using low carbon steel for price and ease of fabrication.

The plate on the back is to gather the M-field flux from the back of the ferrite donut, the plug carries it to the the plate at the front of the magnet, and the plate on the front of the ceramic donut sets up a region of more-or-less constant flux in the gap for the voice coil to work in. So what's needed is a high permeability flux path and a not-too-variable M-field.

Since I obviously don't know exactly what the stuff is, a good way to find out is to hit the phone books in your town for analysis labs and buy a spectrographic analysis of the alloy. Cut them a chunk and have them laser-vaporize a spot and produce the run of elements, just like they show you on CSI. It'll cost you probably $100, but it gets you the direct answer.

If you had a friend who happened to be a professor of chemistry at a local university, you MIGHT, for the price of some backstage passes and a few sixpacks, get this analysis done out of mutual interest. If you have the luxury of picking friends, a professor of metallurgy would be nice.

[pilotjones]

ahh, im not sure about that. i thought that you would have some idea about the magnet material. im not sure about that part. my guess is it would be a magnetically porous material of some sort, but i dont know anything for sure.

Magnetically porous? What does that mean? That's the first I've heard the term.

[R.G.]

Magnetically porous? What does that mean? That's the first I've heard the term.

I took it to mean "highly permeable" or "high permeability".

[pilotjones]

Thanks.

[nickt]

One thing they can't duplicate is Damascus steel. They've tried too, and they can't figure out exactly how they made it.

Saw an article on this recently (think it was New Scientist) the theory was it contains carbon "nano-tubes". Wierd eh!

Edit: just found another link that talks about nano-toobs http://archaeology.about.com/b/2006/...scus-steel.htm

[EtLa]

I've already mentioned the capped iron pipe approach.

Thanx Joe! I tried annealing cold roll with the capped iron pipe in a fire and it work like a charm but just one thing, after the heating process the cap is tough to unscrew. The cold roll sample I heated (annealed) is now very soft.