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• Analysis of Vibration During Turning Process of Different Materials

  200-205

  Ádám Sarankó

  Gábor Kalácska

  Róbert Keresztes

  Views:

  254

  In this article, we would like to introduce the problems caused by vibrations in case of polymer turning processes. Nowadays there is a lot of research in this topic, to avoid the unnecessary phenomena of vibrations. The two most common methods are the Spindle Speed Variation (SSV), and the Vibration Assisted Machining (VAM). In case of SSV, the CNC machine can increase and decrease the speed of spindle continuously during turning which can significantly reduce the effects of chatter. This method is beneficial for longer workpieces when there is not any support except the chuck. Vibration-assisted machining can be used to minimise the problems caused by vibrations. VAM combines precision machining with small-amplitude tool vibration to improve the fabrication process. It has been applied to some processes ranging from turning, drilling to grinding. Based on the enumerated above we made some trial measurements about the basic vibrations of the turning tool shank. The tests were done on an NCT EUROturn-12B CNC machine which can found in the workshop of our institute. The tested material was Polyamide 6 because this is the most commonly used polymer in the industry. In the future, we would like to test some other basic and composite polymer materials too. The equipment was served by a specialist from SPM Budapest Kft. With these tests, our goal was to make sure that the equipment and the measuring setup are suitable for our future research.

• Temporal Changes of Pyrite Oxidation Rate in Bolivian Sulphidic Mining Wastes

  194-202

  Ferenc Móricz

  Ferenc Mádai

  Views:

  207

  Since the 70's, when huge sulphidic open pits were developed, the acidic rock drainage (ARD) become the leader problem of the sulphidic mining industry. Although the recycling is an essential technology, it cannot cover the demand alone, thus mining activity needs to continue. Acidity in mine drainage commonly requires most of the attention, but the main problem is the caused elevated level of metal mobility and leaching, which are generated by the increased rates of sulphide weathering under acidic conditions. The Itos mine is a polymetallic vein deposit in Bolivia, had been mined for silver and tin until 1990, leaving behind much and huge tailings and mine waste heaps, where quite often the pyrite content exceeds 10 %. Serious ARD effects take place in the mine waste heaps. These processes can be well characterized with the pH 1 or 2 of the seepage water, which forms serious alteration in the waste itself and the neighbouring rocks. In three consecutive years, the pyrite oxidation rate was investigated on the same 7 samples by humidity cell test. 5-6 months pauses were left between the humidity cell test periods, which mimics the alternation of wet and dry periods, typical for the place. The results give much more information, than the oxidation rate in the individual test periods, showing the changes by time. This applied method gave good result to characterize the behaviour of the waste in long-term. The column test was complemented with mineralogical analyses, such as electron probe micro analysis. The mineralogical and column test analyses show, that the changes of the pyrite oxidation rate split the samples into three different groups, one where the oxidation rate decreases, second where it increases with time and the third where oxidation rate is maximal and stays stable for several years.