Wednesday, December 19, 2012

Iron to Wire? Some considerations on materials.

 As frequent readers know - I do spend (too much?) time every day on detailed answers / comments to various questions that come into me via e-mail. These pieces would be 'lost' if only sent to one respondent, and so often are modified to become the meat for postings here....

On 17/12/12 1:00 PM, Stephen **** wrote:
My interest is in replicating historical wire - iron, steel, and brass - for musical instruments. The research is done as part of my work at (named University), but it's also practical in the sense of replicating it for a niche market. I'm already selling iron wire and investigating the other materials. As you can imagine, production economics is a nasty constraint. A big problem is getting from cast ingots to rod stock. Historically this would have been hot worked by powered tilt hammer, which is probably not economically viable nowadays even with access to appropriate equipment. The wire drawing operations push up the $/kg production cost of the finished wire so there isn't a lot of $ room in the heavy stage production of the rods. I came across your 'bloom 2 bar' project and wondered what practical solution you might have come up with for converting your bloom iron to bar.
A couple of things in your message:

"I'm already selling *iron* wire"
Since you are being specific, I take it what you really mean is a modern Bessemer produced low carbon content *steel* wire. 'Black Iron' fencing wire one possibility. Getting 'soft iron rivet' material is another. A third would be the use of 'Electric' or 'French' iron. (All these are NOT the same as historic wrought iron material.)
I drone on about this endlessly, but actual *bloomery* iron / *wrought* iron is no longer available in commercial production. I have seen some hints that smaller amounts might be under production in China - but only as a material for specialized blade replicas. Other than that, these ancient / historical methods are only employed in very small scale - by people like me
(demented wackos) .

"historically hot worked by tilt hammer"
Most modern day professional artisan blacksmiths will have some kind of power assisted hammer in their shop. These fall into mechanical or air driven types. This does allow for the working of more massive bars.
I have both a 30 ton hydraulic press, designed for initial bloom compaction, and a 50 lb throw air hammer in my own shop for example.
The problem is actually on the other side - small diameter bar into wire. Few have the special equipment (or specific skills or experience) for drawing wire. I certainly have never done this.

"selling iron, steel and brass wire"
Wire of various copper alloys (tin and zinc alloys) is certainly available. A problem might be getting small enough order quantities against your business volumes.
*Steel* - as in modern produced simple iron plus carbon alloys will also be available in almost any combination you might require. I expect there that the purchase sizes may be much smaller, although some hunting might be required to find just what modern business might sell small amounts of exactly the specific alloy you might want. (Auto repair for example)

As you certainly are aware, actual *bloomery / wrought* irons are distinctive in their physical composition (this separate from alloy composition). They will contain some level of hard glassy slag, if only at a microscopic level. This will effect their mechanical properties, I suspect in ways that might be critical to your application as drawn wire in musical instruments.
These materials are also not consistent through their volume - the way modern industrial steel alloys are. This likely presents a huge problem for your specific application.

This all represents a major terminology problem - one that is not dealt with effectively (to my observation) by museums and academic researchers. "Steel" is used generically for any iron plus carbon alloy - reguardless of its method of production or physical structure.
In working from a natural iron oxide source ore into a working metal bar, there are effectively *three*  different factors that might effect the characteristics of the end product.

1) How the iron oxide was physically reduced down to a metallic iron mass.
This is the type and individual design of the furnace, related to the method of production, modified by the specific ore itself. Experience and skill of the iron master comes into play here.

2) How that iron mass is physically manipulated in secondary processing after it has been created.

3) The actual alloy chemistry of the starting mass, as potentially modified by the secondary processing. Primarily the single largest variation comes through changes in the carbon component of the metal.

In short, depending on the starting iron ore, different furnaces may produce different products, both physically and chemically. How the iron master controls the iron smelting sequence can also modify both.
It is quite possible to get radically different carbon contents from the same ore (even in the same furnace).
The resulting mass can then be manipulated in different ways during the 'bloom to bar' process. This may change physical structure and carbon content.
Carbon can both be removed, but also added during secondary or tertiary forging processes.

Often historic bloomery iron materials were effectively impregnated with additional carbon through surface diffusion. You can see how this would produce a material with a layered texture, including some degree of slag filaments, which then varied in carbon content from a higher C exterior fading to a low C interior. Compressed into a wire, this might seriously effect the performance of that wire musically.

I refer you to Lee Sauder ( A close friend and fellow researcher - and easily the most skilled bloomery iron master in North America. Lee also does sell both raw bloom sections and blooms worked to billets.

No comments:


February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

COPYRIGHT NOTICE - All posted text and images @ Darrell Markewitz.
No duplication, in whole or in part, is permitted without the author's expressed written permission.
For a detailed copyright statement : go HERE