Paper mills systematically inspect all the steam rollers about every 5-7 yrs for possible shell and head cracks due to the extreme service conditions, basically high temperature and pressure. Dryer head surface testing requires that it be free of scale, dirt grease, paint etc., in order to get accurate indication of possible cracks. Some dryer heads can build grease deposits that exceed 13 mm (1/2-in.) in thickness. In the case of excessive amount of baked-on grease, high-pressure waterblasting up to 138 MPa (20,000 psi) has been known to be the most efficient technique to remove the build-up thoroughly. In this paper, on the other hand, it is shown that the job can be accomplished at much lower pressures (≈ 50 MPa; 7,000 psi) using the patented forced pulsed waterjet technology. Complexities encountered during the dryer head cleaning job are also highlighted.
展开▼
