Hi All, Does anyone know the mechanical properties (more or less) of the brass used in today's agraffes, or those of yesteryear? This probably varies with manufactures around the world. Brass is basically an alloy of copper (say 70%) and zinc (say 30%), but often includes other alloying elements such as tin or even aluminum in order to modify its properties for strength and workability (hot worked, cold worked, machinability). Something called High brass containing 65% copper and 35% zinc, has a high tensile strength and is used for springs, screws, and rivets. Seems as though High Brass would make sturdy agraffes. Of all the properties, I am most interested in tensile strength, both ultimate and yield (ultimate strength being at times significantly higher than yield). Also, how are agraffes manufactured today: extruded, blanked and machined, cast and machined? Tempered? I am asking because I would like to work up torque values for agraffes, whether re-installing the originals or replacing with new. Preloading refers to initial (safe) torque, this load is then statically increased by the up-pull of the strings, and is finally increased dynamically by the vibrating string (I would factor this in as a forte blow). I realize that many of you don't need these values as you have been successfully torquing up agraffes by feel for many years. I understand that quite well, but it would be nice to put some numbers on this and to consider safe limits for torque. Over-torqued agraffes plastically deform and develop strain-hardening just under the head and above the threaded stud, and this hardening causes ductility to drop. The over-torqued (torsioned) agraffe has passed the yield point and is now compromised. How much depends. If someone out there has already investigated this, or has data from anywhere, I would be interested in the findings. Thanks Regards, Nick Gravagne, RPT Piano Technicians Guild Member Society Manufacturing Engineers Voice Mail 928-476-4143 _____ -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech_ptg.org/attachments/20090329/13d09cb7/attachment.html>
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