We report the results of a study on the influence of oxygen in the plasma gas used in the plasma arc cutting process on cuts obtained in mild steel plates. Experimental results of shapes of kerfs and the leading edges of the cut front formed while cutting a 6 mm mild steel plate at 100 A with nitrogen, air and oxygen as plasma gases are presented. These results are discussed in the light of the overall energy balance of the process. It is found that the exothermic reaction of oxygen in the plasma gas with the iron in mild steel enables the cutting of mild steel at higher speeds with both air and oxygen than the maximum cutting speed attainable with nitrogen. A comparison of the melting rates for oxygen with those of air reveals that although oxygen can produce more exothermal energy by oxidation, oxygen is not superior to air in melting metal near the bottom of the kerf formed at high cutting speeds.The study shows that the dross formed at the bottom of the cut is determined by the shape of the cut-front surface over which the molten metal from the cut front flows to be ejected at the plate bottom. Any improvement of metal ejection to be gained with oxygen as the plasma gas may be the result of enhanced superheating of the metal melted from the cut-front surface.
The effect of high-energy (50 MeV) Li 3+ ion beam irradiation on polypropylene (PP) film has been studied in the fluence range 2⋅ ⋅4 × 10 12-1⋅ ⋅5 × 10 14 ions/cm 2. The a.c. electrical properties of PP films were measured in the frequency range from 0⋅ ⋅05-100 kHz, and at temperature range between 30 and 140°C. This study indicates two peaks at 60°C and 120°C with comparatively high magnitudes. There is an exponential increase in conductivity with log of frequency and the effect is significant at higher fluences. The loss factor (tan δ δ) vs frequency plot suggests that PP film based capacitors may be useful below 10 kHz. The capacitance is constant over a wide temperature range up to 130°C. FTIR spectra of the PP films before and after irradiation indicate that intensity of C-H stretching vibration at 2900 cm-1 is modified. The presence of many new peaks with the increase of fluence suggests the formation of alkanes and alkynes which might be responsible for the observed changes in the dielectric and electrical properties of PP films.
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