Single pulse detachment is challenging on the thick coatings used in marine vessels. An ablation-detachment hybrid process, however, is able to produce high-efficiency removal.
In the hybrid process, the first few overlapping pulses aim at reducing the coating thickness on a pulse to pulse basis (patent pending GB1710188.2). When enough radiation can be transmitted through the remaining thickness to kickstart detachment, the rest of the material is removed at high efficiency (Figure 1b).
Again, higher energy pulses typically above 100 mJ at 50 to 100 ns, unlock the non-linear efficiency growth threshold demonstrating removal rates in excess of 40 mm3/kW-min.
Figure 2 : Example paint removal efficiency thresholds for hybrid detachment of 300μm and 600μm thick semi-transparent paints
Figure 2 shows the increase in process speed for white paint on primer for a 300 μm thick coating and 600 μm thick coating. The onset for high-efficiency removal is observed at 180 and 260 mJ respectively. Average power is maintained at 1.5 kW, and the process is optimized for spot size and overlap. Pulse duration changes from 114 ns to 42 ns as the pulse energy increases. Pulse shortening only contributes to a linear increase in efficiency and has not been observed to achieve a non-linear efficiency boost without the accompanying increase in pulse energy. Results obtained using a Powerlase Rigel i1600e Q-switched DPSS Nd:YAG laser.