Chapter 6

6. Wrought Iron Manufacturing Techniques used on Iron Ties. 1/5.

"Wrought iron is best described as a two-component metal consisting of high purity iron and iron silicate- an inert, non-rusting, glass-like slag. These two materials are in physical association (Fig. 6.1), as contrasted to the chemical or alloy relationship that generally exists between the constituents of other metals.

Photomicrograph of wrought iron

Fig 6.1. A photomicrograph illustrating the fibrous nature of wrought iron. The iron and slag are intertwined in close physical association but do not constitute an alloy. (Aston & Story, 1936).

In finished wrought iron the iron silicate or slag content varies from about 1% to 3% depending upon the type of product… This constituent is distributed throughout the iron base metal in the form of threads or fibres" (Aston & Story, 1936).

Wrought iron is the only ferrous metal that contains these non-rusting slag fibres and they are the reason for its tough, fibrous nature, making it ideal for working under the hammer (Fig. 6.2).

Fibrous nature of wrought iron

Fig. 6.2. A fractured wrought iron bar showing its fibrous structure making it ideal for working under the hammer. (Aston & Story, 1936).

The design of iron ties is dependent upon the manufacturing techniques used in forming them. An understanding of the processes involved in the manufacture of wrought-iron ties focuses attention on a range of diagnostic features that can provide a basis, in some cases, for distinguishing ties of different historical periods. Hand wrought iron is likely to be earlier than machine hammered iron and certainly earlier than milled stripwork.

6.1 Upsetting

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