P.Gonfiotti – Investigation on GMA garnet recycling in Abrasive Water Jet Cutting
Chapter 10 – Conclusions and suggestions 143
10. CONCLUSIONS AND SUGGESTIONS
The first result of this work is understanding the main steps of the recycling process: first of all the importance of a proper drying, in order to have an effective screening of the very fine powders through the sieves. Even the separation of the metal chips from the abrasive has to be performed.
Another important conclusion is that the approach of recycling with the screening of particles smaller than a chosen optimal size value and a following recharge with new GMA is very effective and give back a sample that doesn’t lose its cutting capability for at least three times of recycling. The fact that the particle size distribution and shape remain practically constant with three steps of recharging allow to think that the abrasive can be used even more times.
The recycling with screening of fine powders and the recharge seems the best way to reuse the abrasive but it isn’t surely the only one: since the particles of the recycled samples are sharper than the new one’s, another approach could be to collect and mix the sieve classes from 106μm to 212μm that can be sold as garnet #120; in fact, the GMA garnet #120 is composed by mass fractions in that range. From the sieving analysis of the recycled samples comes out that about the 43% of the input mass could be sold as #120 with a performance that, if investigated, could be better than new GMA #120. Otherwise, the screened #120 sample, could be used in the same company for high precision edge applications that require smaller focusing tube size and abrasive particle size.
The cutting performance tests have shown that the maximum achievable depth of cut when cutting Aluminum 6061-T6 of the recharged samples is greater than with new GMA;
among all the samples with different screening size values the best performing has been the sample with particles greater than 90µm. Its cutting performance is about 10% better than new GMA. The tests on recycled samples have given even better results but are not comparable with the recharged abrasives because the pressure is different; anyway, even in that case the recycled abrasive samples performed better than new GMA.
P.Gonfiotti – Investigation on GMA garnet recycling in Abrasive Water Jet Cutting
Chapter 10 – Conclusions and suggestions 144 The investigation on multiple recharging (3 times) has pointed out that even the cutting performance remains practically constant in the three cycles of recycling. This result is very important for the evaluation of the effectiveness of the recycling, that doesn’t lose its economical advantage if the smaller particles are screened out.
The observations with the microscope of recycled abrasive on first, second and third step of recycling have exhibited how the particle fragmentation is great after the I cut, with very small particles respect to the fresh abrasive. On the other hand, the fragmentation after the II and III cut are less pronounced. The shape of the particles becomes sharper with the fragmentation and this seems to be the main reason because the recycled and recharged samples perform better.
The cutting quality of recharged and recycled samples, measured by the surface roughness and waviness, has resulted to be better than new GMA’s.
From the cost comparison of the abrasive sample comes out that the sample with particles bigger than 90µm is even the most cost-effective and is the best choice to get profit from the abrasive recycling. The savings can range from 10 to 18 % on the specific AWJC cost, depending on set up and working load.
The cutting test could be more reliable, with more levels of the cutting parameters and at least three replications to give a statistical reliability to the data, but, due to the need to recycle the abrasive by collecting, drying, separating and sieving by hand the preparation of the sample for cutting has been very time consuming.
The future developments of this work could be a deeper investigation of the cutting performance of recharged samples taking into account more levels of the cutting parameters. Moreover the particle fragmentation should be investigated, in order to develop a model for the fragmentation process that is still missing. In particular, the degree of fragmentation should be someway related to the water pressure and the abrasive load ratio of the jet.
Finally, the economics of the recycling of other kind of recycled abrasive (Barton, Indian garnet, …) should be investigated, because there is still lack of studies in this area.
