De-stressing a piece of sheet metal (a reed) usually results in a change of shape. If you bead-blast a strip of cold-rolled metal, it curls up like a potato chip. If any significant amount of stress relief occurs in the ultrasonic bath, I would expect the gap to changeâby different amounts in different reeds. Have you checked the gap size before and after? Could the pitch change arise from gap change?
It seems intuitive that relaxing stress would lower the modulus of elasticity lowering the pitch. However, I havenât researched this.
I donât think that it is clear that the change in stress changes the modulus of elasticity. Elasticity is under the radical in the pitch equation so that a change of 2% in elasticity would produce only a 1% change in pitch.
Work-hardened brass would not seem to be a good candidate for VSR according to the following statement by Bonal, maker of VSR equipment:
"5) What are the limitations of Meta-Lax stress relief for metals? Meta-Lax stress relief is not effective on metals where mechanically induced stresses are dominant (for example cold rolled steel plates) where machine stability is the goal. Copper and high copper content metals do not respond consistently. â
The stresses in reeds are mechanically induced by machining (as opposed to unequal rates of cooling) and the copper content is high.
Vern