AWJ for Surface Finishing of Marble
Abrasive waterjets (AWJs) are most common in cutting applications. Bortolussi et al.* presented a paper on their experimental study on using AWJs for surface finishing of marble. Here are the highlights.
As the last stage of stone processing, surface finishing has to meet aesthetic and durability requirements. Smoothing and polishing is the most common surface finishing method of stone elements used for interior decoration. However a smooth stone surface may present a slippery condition that becomes a safety concern. To address this safety issue, currently several processes are available for roughing up the surface, including bush-hammering, sand blasting, flaming, shot peening, milling, laser beam engraving, and waterjetting. Each of these methods has its advantages and limitations. When aesthetic values and safety are equally important, abrasive waterjets may present an opportunity to meet the requirements.
An experimental parametric study was done to determine the effects of AWJ process parameters on the stone surface. A well known marble material, “Bianco Carrara”, a metamorphic carbonate material rather homogeneous, was used in the tests. 300 tests were done by changing one of the 7 factors at a time. These 7 factors are: Pressure (100 and 330 MPa), Orifice Diameter (0.25 and 0.50 mm), Focusing Tube Diameter/Length (3/27.3 and 1.4/27 mm), Abrasive Flow Rate (55.4 & 158.7 g/min for coarse garnet and 78.5 & 183.2 for fine garnet), Traverse Speed (1000, 6000, & 10000 mm/min), Stand-off Distance (50, 100, 150 mm), and Average Garnet Particle Size (0.4775 – coarse & 0.2835 – fine).
The effects on the marble surface were indicated with the width of erosive bands, depth of kerf, and image analysis (scale of “Grey”). Based on these data, regression equations (refer to the original paper for these equations) were developed to relate “Outer Band Width”, “Inner Band Width”, “Depth of Kerf”, and “Density of Impacts” to the 7 factors.
The width of erosive bands is most significantly related to Stand-off Distance. Particle size has no impact. Other process parameters have some small effects. Depth of kerf is strongly related to Pressure and Stand-off Distance. Other parameters show secondary effects. Density of Impact is strongly related to all parameters except for Particle Size. Diameter of Focusing Tube has the highest impact. In fact it is the ratio of Focusing Tube vs Orifice that matters the most.
The authors concluded that it is possible to use AWJs for surface treatment, carving, and drawing, as a substitute to sand blasting.
* Bortolussi, A., Manca, M.G., Careddu, N., Ciccu, R., & Olla, S. (2002) Surface finishing of marble with abrasive waterjet, in Proceedings of the 16th International Conference on Water Jetting, Aix-en-Provence, France, October 16-18, p.425-435.
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