John Delacour wrote: > > Brief details of the tensions achieved in the good old days are to be found > in Alfred Dolge's book (Publ. Dover). Even in 1850 the strengths achieved > were higher than I expect from modern wire. By 1870-80 the results were > phenomenal. As a bass string maker I come across a lot of the old > Poehlmann wire and one day I will have it properly analysed and tested for > indications of the drawing techniques used which are obviously as important > as the actual alloy used. [...] > Comparing tensions is not enough to analyse the strength of music wire. Strain hardening is an important factor, as breaking stress is significantly increased for smaller diameter wires which require additional drawings. Perhaps the manufacturing process has now been `modernized' so that the benefits derived from strain hardening have been eliminated....could tell this by comparing breaking stress of tenor and treble wires of modern pianos, the treble should be significantly higher than the tenor. This might explain the differences noted for the older Roeslau wire in several earlier posts. In general the stress, or tension/cross-section area of the wire (units of MPa or psi), is the correct measure of the breaking strength of music wire. This is ultimately determined by the alloy and is independent of gauge, **except** for effects due to the drawing process, which tends to increase the strength of thinner wires if they are drawn more often (strain hardening). > > It must be remembered that the one factor that enabled the modern piano to > develop was the development of music wire. > This is true in the sense that it permitted a longer scale and thicker (and hence inherently weaker) wire to be employed, the additional strength being compensated for by the modern alloys employed. The lost benefits of strain hardening must ultimately be paid for. > I am a little sceptical when I hear talk of "fatigue" in piano wire. > Perhaps someone can explain how this fatigue manifests itself and what > scientific papers exist on the subject. I am not sure that metal fatigue > is a very significant factor in string breakage. > I agree with this observation. I'm sure almost all strings break because the breaking stress is exceeded for one reason or another. Bashing a string which is already close to breaking is often sufficient to break it. The only conclusion for these breaking treble strings is that they are too close to breaking stress. Check out the book by Goodway and Odell on harpsichord wire. The metallurgical facts are relevant to piano wire also. Stephen Birkett (Fortepianos) Authentic Reproductions of 18th and 19th Century Pianos Waterloo, Ontario, Canada tel: 519-885-2228 fax: 519-763-4686
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