空气等离子弧切割电极烧损机理

通过空气等离子切割电极烧损量与电极端面电镜形貌的对应试验,探讨了电极烧损机理。烧损主要发生于再引弧时,烧损量与熄弧后电极端部的氧化物和氮化物层厚度有关,熄弧时处于高温的铪极表面继续与空气中的O2、N_2、作用,使氧化物、氮化物层变厚,厚的氧化物、氮化物层在再引燃电弧时被烧损掉,导致电极寿命随引弧次数的增加而减少。研究表明,在铪极中加入石墨,使电极端部形成具有良好导电性、抗氧化性、耐蚀性及难熔性的碳化铪,成功地限制了铪极的烧损并延长了电极的使用寿命。

A STUDY ON THE MECHANISM OF EROSION OF HAFNIUM ELECTRODE IN AIR PLASMA CUTTING

In air plasma cutting conditions, the life of the electroed has been the key to reducing the operating cost and realizing the process automation. The mechanism of electrode erosion has been studied by the correspondence tests between scanning electorn micrograghs of the ends of the electrodes and the losing weights of them. As the arc extinguishes, the surface of the electrode under a high thermal load is oxidized and nitrided continuously in the air medium. This makes the original oxide film thickening and cracking while it is rapidly cooling. During the reignition, the cathode spot is developed on the end of the electrode rapidly, and the thickende film is thinned by cathodic cleaning. Finally, a thickened film becomes a thinned one in each and every reignition, and this results in a short life of the electrode.Further studies state that adding carbon to the hafnium electrode will form hafnium carbide film on the end of the electrode in stead of oxide film. It has splendid conductance and is more refractory than the oxide film. There is no more change in the thickness of the shield film. Now an advanced experience has becn presentcd to limit the erosion of hafnium electrod and prolong its life.