A Coulomb friction damper, consisting of a case-hardened roll-threaded collar resting against a reverse taper segment of drill rod, is studied for its noise-reduction potential. Axial impact causes the drill rod to be excited in many transverse bending modes of vibration, along with longitudinal and torsional resonances. Due to the inertia of the collar, simultaneous axial and rotational self-tightening motion occurs on the rolled thread. The collar consequently presses on the case-hardened tapered surface of the drill rod, inducing interfacial frictional rubbing, resulting in 5–45 dB of attenuation in peak acceleration of the modes of vibration, and reduction in decay time on the order of 10 seconds.

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