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Work hardening of piano wire

  • 1.  Work hardening of piano wire

    Registered Piano Technician
    Posted 12-22-2017 14:00
    I am intrigued about the idea that piano wire becomes "work hardened" over time making it stiffer and more brittle. Some have suggested that the tuning process accelerates this.  I also remember being told that this occurs with SS wire. Hmmm...

    Can someone explain this process adequately? What is actually going on?

    Is it also possible that vibration alone over time can accomplish this, or have some other detrimental effect?

    Pwg


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    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
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  • 2.  RE: Work hardening of piano wire

    Posted 12-22-2017 20:42
    Maybe that is what this tuner was referring to back in 1933? This is in a Knabe upright built in the late 1880's.





  • 3.  RE: Work hardening of piano wire

    Posted 12-22-2017 21:08
    Barbara,

     The consequence of rapid local fluctuations on a molecular scale in a homogeneous phase that is in a state of metastable equilibrium must first take place before  the nucleus acts as a convergence point (if unstable due to supersaturation) for molecules of solute touching – or adjacent to – the crystal so that it increases its own dimension in successive layers. 

    So how could that determination be made on site by a piano tuner?

    Answer: He made it up most likely.
    -chris
    #caveman




    ------------------------------
    A hunter's drumbeat steers the stampeding herd,
    His belly growls in hunger to what he sees.
    The mammoth aware blows his mighty trumpet,
    But alas, the caveman tickles the ivories.

    chernobieffpiano.com
    865-986-7720
    ------------------------------



  • 4.  RE: Work hardening of piano wire

    Registered Piano Technician
    Posted 12-22-2017 22:20
    Translation please...

    Pwg

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    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
    ------------------------------



  • 5.  RE: Work hardening of piano wire

    Posted 12-22-2017 22:27
    Hi, Peter,

    Wellllll...it sort/kinda made sense until we got to "solute"...which in the soggy mass that passes for my mind has to do with ‎a/the small/minor component in a solution...i.e., dissolved in a solvent...and, reading that produced a brainfart while I try to work through what about a piano string might be in solution, except in some peculiarly solid state...

    Cheers!

    Horace


      Original Message




  • 6.  RE: Work hardening of piano wire

    Registered Piano Technician
    Posted 12-22-2017 23:29
    Peter, here's a link to Wikipedia explanation of work hardening.  Work hardening - Wikipedia
    Wikipedia remove preview
    Work hardening - Wikipedia
    Work hardening, also known as strain hardening is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material. Many non-brittle metals with a reasonably high melting point as well as several polymers can be strengthened in this fashion.
    View this on Wikipedia >

    Please note that work hardening increases the brittleness, hardness, yield strength, and tensile strength, but not the stiffness.  Stiffness/modulus of elasticity/Young's modulus is a constant for a given chemistry of steel, and is not changed by work hardening, heat treating, or any other hardening/softening/tempering process. 

    A lifetime of alternating dry weather pitch raises and humid weather pitch lowerings will repeatedly bend and straighten the wire at the point where it leaves the tuning pin, eventually becoming so brittle that it cannot survive another bending/straightening, so it breaks.

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    Michael Spalding RPT
    Fredonia WI
    262-692-3943
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  • 7.  RE: Work hardening of piano wire

    Registered Piano Technician
    Posted 12-23-2017 01:09
    Today I did a 5 CPS pitch raise on a newish piano (Yamaha GP1) in a retirement home that I did a pitch lowering to in August.  Why do we insist on pitch raises and lowerings (I prefer not to myself) when allowing the piano to naturally cycle around an acceptable pitch would be much better and safer for the piano?

    This amount of cycling is due to heating and air conditioning and a lack of humidity control.  Aside from my recommendations (which will probably be ignored) there is little I or we can do.

    On a related note, my brother called me yesterday to report he heard 3 strings breaking on his old Wurlitzer grand at his home up in the mountains.  I had him check the strings and none were broken.  I then had him shine a flashlight from under the piano and he found several new board cracks (more developed within a few minutes).  His area just experienced a dramatic drop in temperature and humidity; I recommended a bucket of water under the piano.

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    Blaine Hebert
    Duarte CA
    626-795-5170
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  • 8.  RE: Work hardening of piano wire

    Registered Piano Technician
    Posted 12-23-2017 08:44
    Blaine,

    Can they even tell that it's above pitch or below pitch? Who cares?  😆😆😉🤣


    Michael,

    Interesting. I had already read that in Wikipedia.  My confusion I guess was over the fact that somewhere, someone (cannot recall) connected work hardening with increasing stiffness. So in trying to reason this out, plus the fact that I don't know alot about metallurgy, I got to wondering how this tiny little movement could affect the wire so much.

    However, if what you say is true, then we now have another very good reason to suggest humidity control for pianos, since compensating for extreme changes in humidity (in addition to all the other detrimental effects) work hardens the wire, contributing to premature string breakage.  Makes sense.

    I still wonder what is actually going on inside the wire to produce this effect. Chris's explanation doesn't quite cut it for me...I can't 'wrap my head around it'...it might be a bit of a 'stretch' to say that I now understand.

    Pwg

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    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
    ------------------------------



  • 9.  RE: Work hardening of piano wire

    Posted 12-23-2017 11:15
    The author of this post from 2002 (Craig Brougher) not listed in the current PTG membership database, though it appears that at the time of this writing (2002) he might have been a member.

    I haven't looked up the entire discussion in this archive (yet), but in light of the discussion that is taking place currently here, this posting in the "Mechanical Music Digest" may be of interest to others as it was to me.  Besides, it starts with an amusing cartoon appropriate to the holiday season: http://www.mmdigest.com/Archives/Digests/200204/2002.04.02.08.html.





  • 10.  RE: Work hardening of piano wire

    Registered Piano Technician
    Posted 12-23-2017 11:19
    When mixed elements are in a liquid state, they exist in a state of solution. So molten alloys are solutions.

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    Edward McMorrow
    Edmonds WA
    425-299-3431
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  • 11.  RE: Work hardening of piano wire

    Registered Piano Technician
    Posted 12-23-2017 15:32
     

    The simplest way to understand work hardening for our trade is to rather understand the effects of work hardening to piano wire in the strung piano. When a metal is stretched or bent beyond its elastic limit, meaning it has deformed into a permanent shape, work hardening has taken place. Along with hardening comes brittleness; imagine taking a wooden dowel and, after rubbing it hard with a burnisher (i.e. work hardening it), magically tuning it into a piece of chalk.

    Although a gross analogy, this is what happens when metal is work hardened. Most of us have restrung entire pianos, or at least replaced a broken string. You will have noticed, after the coil has been removed from the tuning pin, how easy it is to break the small becket length off of the coil. That sharp bend represents serious deformation of the wire, hence work hardening and brittleness.

    Those locations where piano wire is has been work hardened and deformed exist at the tuning pin and all termination and deflection points such as the capo bar, counter bearings, bridge pins and the hitch pin. These points are clearly visible upon removing an old string. Every deflection or bend in the wire represents a point of compromise due to "atomic dislocations", meaning that the natural internal crystalline structure of the metal is beginning to separate at internal boundaries of the structure.

    We sometimes repair a string broken at the tuning pin by pulling the string around the hitch pin. The bend at the hitch pin, considered a serious deformation and work hardened segment, is also pulled around but never really straightens out. Dislocations in the crystalline structure have occurred there and represent a possible future failure. But if that tight little bend, now being asked to go straight, should exist in the speaking length of the string a complete failure is almost certain. 

    Now, very important: Repeated flexure causes work hardening. Take the modern airplane. It must be designed to,

    "evenly distribute flexure, which can lead to work hardening and in turn stress cracking [especially where the long wings attach to the fuselage, NG], possibly causing catastrophic failure. For this reason modern aluminum aircraft will have an imposed working lifetime ... after which the aircraft must be retired." (Wikipedia)

    Like the aircraft, piano wire is subjected to repeated to-and-fro flexure and at very high levels of repetitions per second. Think of removing the aluminum tab from your Pepsi; you flex it back and forth causing work hardening, then brittleness, followed by "catastrophic failure". Thus higher-frequency notes in the piano scale are subjected to a more serious repetitious work hardening mechanism (primarily at the capo bar) as compared to notes lower in the scale. Failure at the tuning pin exists for similar reasons of stress and release, stress and release. Piano wire work hardening occurs less so at the bridge pin due to the yielding of the soundboard.

    Notice in the above quote that an "imposed working lifetime" is assigned to an aircraft. Same is true in piano wire depending on the mileage it receives. Piano wire simply wears out, and the more that wire is pressed into service the more quickly it wears out.






  • 12.  RE: Work hardening of piano wire

    Posted 12-23-2017 16:35
    My experience with Pure Sound on a Steinway M (scaling recommended by Juan mas Cabre):
    Within a few hours of stringing and pulling to pitch, wires in the capo sections began breaking spontaneously at the hitch pin. (I restrung the capo section with Mapes International Gold wire.)
    There was no spontaneous breaking in the agraffe section. After a few weeks, strings in octave 3 broke at the front bridge pin during playing. Very rapid work hardening at the termination point. Probably a sharper bending at the pin than at the agraffe.
    It was such an easy wire to string on a piano, soft and easy to work, made beautiful coils, and was was a pretty silver color....
    I restrung the agraffe section with Mapes IG, too.

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    Ed Sutton
    ed440@me.com
    (980) 254-7413
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  • 13.  RE: Work hardening of piano wire

    Posted 12-23-2017 17:17
    In my experience, having used  Paullelo 2, 1, O and M, re the breakage issue,  especially and 1 and O...zero breakage even in high use studio service. I do not have 2 in service in modern grands...only in a square...but the rest are all grands, 5' to an S&S C. Been using it for about 6 or seven years . 

    If Pure sound SS and 1 are relatively equivalent tensile strengths, what is the functional difference. I have not heard breakage stories with any of the Paullelo wires from other quarters as well...so though the numbers for 1 and pure sound look similar, there is a difference in the working charactistics of the wire...what would that be?.

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    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
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  • 14.  RE: Work hardening of piano wire

    Registered Piano Technician
    Posted 12-23-2017 23:05
    Nick,

    Your dissertation helps me grasp this much better. Interestingly, aircraft was precisely what I had in mind as an illustration. 

    Correct me though if I am wrong, but it sounds like in addition to the bending deformation and the back and forth tuning activity, the actual oscillation of the wire through use does in fact contribute to the work hardening of it. Yes?

    I also now better understand the atomic dislocation. That was hard for me to grasp. 


    Jim,

    I think the Puresound SS is just plain weaker all the way around as a function of the mix of molten metal so as to be stainless. Isn't it chromium that they add to make stainless? SS screws seem to be inherently weaker than comparable steel screws.

    Pwg

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    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
    ------------------------------



  • 15.  RE: Work hardening of piano wire

    Registered Piano Technician
    Posted 12-24-2017 10:08


    On Sat, Dec 23, 2017 at 9:04 PM, Peter Grey via Piano Technicians Guild



    --
    Nick Gravagne, RPT
    AST Mechanical Engineering





  • 16.  RE: Work hardening of piano wire

    Registered Piano Technician
    Posted 12-24-2017 10:19
    Did I miss something?

    Pwg

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    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
    ------------------------------



  • 17.  RE: Work hardening of piano wire

    Registered Piano Technician
    Posted 12-24-2017 11:09
    Hi Peter --- you should be seeing per below:

    Nick,

    Your dissertation helps me grasp this much better. Interestingly, aircraft was precisely what I had in mind as an illustration. 
     
    How interesting, RE the the aircraft illustration. 

    Correct me though if I am wrong, but it sounds like in addition to the bending deformation and the back and forth tuning activity, the actual oscillation of the wire through use does in fact contribute to the work hardening of it. Yes?

    Yes, absolutely. Imagine cold-working a piece of ductile steel rod by pounding on it with a large hammer. The rod will flatten to a noticeable degree because the hammering force has dislocated sections of the crystalline structure; i.e. the boundaries of the structure have permanently slipped apart as plastic deformation has occurred, but not so much as to fracture. More hammering produces more flattening, more dislocations, a shinier surface and material hardening, especially at the surface. The hammered steel will be more difficult to drill a hole in.

    Now each time a hammer blow is delivered to the steel rod, energy is delivered as well. The repeated introduction of energy upon energy upsets the in-place dislocations with additional dislocations, and the build up continues. In the end repeated hammering will shatter or split the flattened steel rod.

    So, then, each time a piano hammer hits a string, a similar mechanism takes place. Energy upon energy is introduced to the string. Forces of flexure are seriously concentrated at the most immovable points of termination (agraffe and capo bar) causing additional dislocations to pile up there but not necessarily drastically so, meaning that a sort of wall of resistance or equilibrium has been reached allowing the string to not fail catastrophically. But should the piano hammer grow harder through use, or reshaping or artificial hardening and / or should the piano now be in the hands of a more forceful player or piano tuner, the piano wire dislocations may indeed increase to the point of terminal string fatigue and failure.

    Like the hammering of the steel rod, the crystalline boundaries can take only so much slippage before they sever. So, yes, "the actual oscillation of the wire through use does in fact contribute to the work hardening of it." But in addition to the "sine wave" oscillation there exists also longitudinal (in-line axial) pulsations as well.

    Decades ago a well-known piano mfg., so as to cure chronic string breakage, advised restringing sections of the scale by going up a half-size wire (e.g. 16 to 16.5). Inharmonicity and tonal issues aside, it was correctly argued by scale designers in our trade that such a scheme was pointless as the breaking percentage remained unchanged. True, but the reason the half-size up works (to a degree) is that the larger diameter wire simply contains more bulk and is thus more resistant to these internal dislocations (a thicker tab on your Pepsi can will take more to and fro oscillations to break).

    ng






  • 18.  RE: Work hardening of piano wire

    Registered Piano Technician
    Posted 12-24-2017 16:53
    Nick,

    Outstanding clear explanation!

    And, I have long known that hard hammers will contribute to early metal fatigue and breakage. Now I actually understand the processes involved.

    Thank you

    Pwg

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    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
    ------------------------------