A Study on Using Olivine Moulding Sand for AWJ Cutting
Olivine with large proportions of forsterite (Mg2SiO4) is commonly used as moulding sand. Can we use the moulding sand, a waste material in the process of steel production, as a source of abrasive in abrasive waterjet cutting? A rigorous study on using olivine moulding sand for abrasive waterjet cutting was done by Martinec, et al.* and the results will be highlighted here.
In this study, olivine abrasive was heated to simulate the properties of recycled moulding sand. Changes in olivine structure and properties after the heat treatment were analyzed using several instruments and methods. Abrasive waterjet cutting tests were conducted using these parameters: pressure 250 and 350 MPa, orifice 0.25 mm in diameter, focusing tube 1.0 mm in diameter and 76 mm in length, abrasive flow rate 250 and 300 g/min, and stand-off distance of 2 mm. Barton HP80 almandine garnet was used as a reference abrasive. Wedge shaped samples of mild steel and granodiorite (hard rock) were cut to determine the relative cutting depth --- using olivine abrasives vs using almandine garnet.
For cutting mild steels, the relative cutting depth is around 95% for olivine without heat treatment. It drops to around 88% with heat treatment.
For cutting granodiorite, the relative cutting depth is around 73% for the unheated olivine and around 63% for the heated.
The explanation is that grains of olivine tend to break up along a net of cracks that exists in the grain structure, during interaction with the high-speed waterjet. This net of cracks was developed even further under thermal effects. Higher pressure, thus higher speed of the jet, also intensifies the breaking-up. The finer abrasive tends to reduce the cutting ability. This effect is especially significant when cutting hard rocks like granodiorite.
Tests with 350 MPa pressure, 350 g/min abrasive flow rate, and 0.3 mm nozzle diameter were also run to compare the relative nozzle life. Mass loss was used to predict nozzle life for these tests. The results implied that nozzles last more than 9 times as long when using olivine as abrasive vs using almandine garnet.
* Martinec, P., Foldyna, J., Sitek, L., Bilkova, L., and Barcova, K. (2002) Olivine as industrial abrasive for high-speed water jet technology, Proceedings of the 16th International Conference on Water Jetting, Aix-en-Provence, France, October 16-18, pp 287-297.
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