Quality Waterjet Newsletter 7/5/2005

Review On Surface Preparation with Waterjets --- Part Two

There are several traditional ways of doing surface preparation.  As the new kid on the block, waterjetting is a technology that needs to be proven to be effective in this industry. People want to know its advantages, as well as its limitations. Trotter wrote a paper* summarizing the study he and his colleagues did to compare hydroblasting with the other technologies. The following review will highlight their findings.

A Pulp Mill in Brazil (the largest in the world) was undertaking a depainting and surface preparation project. To answer the owners’ concern on product contamination, a research project was launched to study and compare four different surface preparation methods: a) Abrasive paper with pneumatic grinder; b) Pneumatic needle; c) Copper slag blasting, and d) ultra high pressure hydroblasting. The hydroblasting was done at 1,700 bar of pressure with a nozzle rotating at 2,000 rpm and aiming at the surface at 15° and 50 mm away from the surface.

Tests were done using these four methods and the results are displayed on the graph to the left. Hydroblasting gave the best results (0 mg/cm2), in terms of the remaining amount of contaminates.  The pneumatic needle gave the worst results (65 mg/cm2). The reason why hydroblasting worked the best was because it gave the surface a “deep cleaning,” especially at the craters and pits (where other methods could not work effectively).  The reason why pneumatic needle did not work so well was because the needles drive steel oxide as well as all kinds of salt contaminants into the surface and keep them buried in pockets.

Although hydroblasting was proven to be the most effective technology, the surface after hydroblasting showed flash rust within a few hours. Therefore the surface should be painted within two hours of hydroblasting.

* Trotter, E. L. E. O., “Comparison of surface preparation using different methods,” Proceedings of the 11th American Waterjet Conference, Minneapolis, Minnesota, August 18-21, 2001, Paper 57.


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