The titanium scraps can be fully recycled through SPS and microwave systems and synthesis time lower than 15 minutes (SPS) or 4 minutes (microwave).
The chips obtained through cryogenic machining are excellent (no oxygen contamination nor nitride formation) and allow to obtain titanium or titanium based powders for further reuse.
The collected data highlighted positive results in particular for the following indicators:
– Recycling of machined Ti chips in porous products by microwave heating: >70% using recycled or new Al powders
– Recycling of Ti chips in dense products by SPS: 100%
– Further possibility to valorize the chips by milling and converting in powders for powder metallurgy applications
If implemented on the large scale, the main environmental benefits concern the complete and easy recyclability of the chips, together with the no longer need of disposing of the lubricant. Oxygen uptake as a consequence of recycling is low, and multiple recycling operations are possible, for the same metal.
So important project results are:
– full recycling of titanium swarf that is no longer contaminated by organic lubricant/coolant, for an annual amount of 1500 kg, without any treatment prior to sintering;
– complete elimination of use of lubricants and coolants or their emulsions in titanium machining (up to 2000 Kg/year);
– no need to clean the chips (no use of soaps, detergents and pickling acids), or the machined components: liquid nitrogen just evaporates and returns to the air, without polluting;
– elimination of the costs of disposal of Ti swarf contaminated by lubricant/coolant.
Then, considering recent figures regarding the CO2 equivalent burden of oils that show that the production of virgin base oil requires 1156 kg CO2/Mg oil, which goes down to 676 kg CO2/Mg oil in case of regeneration, such worrying figures are nullified by the introduction of liquid nitrogen assisted cryogenic machining, which requires only the energy to separate and compress nitrogen from atmospheric air. So, only the project implementation permits to save up to 2500 Kg of CO2 emission per year.