Rotordynamic Analysis of Carbon Graphite Seals of a Steam Rotary Joint

Abstract

In the present paper, a carbon graphite mechanical seal under low speed (< 1 m/s), low pressure (3 to 7 bar) and high temperature ($120\mbox{ \textendash }17{0}^{\circ }\mathrm{C}$) conditions has been analyzed. Paper manufacturing machines, where the process fluid steam transfers the heat to rotary drum for drying of paper-pulp, use a floating arrangement of such mechanical carbon graphite seals. A good design of floating ring seal permits relatively low clearance (to minimize leakage) without rubbing contacts, but in the absence of a reliable rotor dynamics tool, often floating rings are subject to excessive vibrations and subsequent brittle failure. To avoid unpredictable seal failures it is always essential to estimate reliable static and dynamic characteristics of floating seals. The present paper describes a numerical procedure for computing the static and dynamic characteristics of floating ring seals accounting for all radial and axial forces. The dynamic characteristics are predicted, based on the perturbation analysis and a finite-difference scheme. The analyzed results have been utilized to modify the geometric design of seal rings. Finally, comparative experimental studies performed on the modified and existing seals have been presented to validate the modified seal design.