喷枪阳极结构对等离子射流及粒子行为的影响

Effect of Anode Inner Structure on Plasma Jet and Powder Particle Behavior

摘要:

喷枪阳极是等离子喷涂系统中的关键部件之一，其通过电弧的运动行为直接影响等离子射流流动及粒子的加热加速历程，最终决定了涂层的综合性能．为了深入理解大气条件下锥形Laval和标准圆柱形阳极喷嘴制备涂层性能之间存在较大差异的原因，在前期制备涂层工作的基础上继续开展相关的数值模拟工作．基于计算流体动力学理论针对等离子喷涂过程建立包括喷枪内外区域的数学物理模型，系统探究两种阳极产生等离子电弧、射流特征及喷涂粒子的飞行行为．结果表明：在相同的喷涂条件下，锥形Laval阳极内产生的等离子电弧电压低、消耗电功率小，大电流密度区和等离子速度明显较标准圆柱形阳极的小；在喷嘴出口处，标准圆柱形阳极具有更高的等离子射流温度和速度，但锥形Laval阳极的等离子射流在喷枪外具有较小的衰减速率和较大的空间尺寸；在相同喷距位置，锥形Laval阳极的喷涂粒子速度要比标准圆柱形的小得多，但相应的升温和降温速率却更大，熔化也更充分．因此，标准圆柱形阳极适合制备致密且结合强度高的涂层，而锥形Laval阳极则更适合用于制备高沉积效率的多孔涂层.

Abstract:

Anode nozzle is one of the key components of plasma spraying systems. Movement behavior of plasma arc directly affects the plasma jet characteristic， and also the heating and acceleration process of sprayed powder particles， which determine the quality of deposited coatings. This work aims to further understand the reason for the large performance difference between the coatings prepared with conical Laval and cylindrical anode nozzles under atmospheric conditions， the numerical simulation work is continued based on the previous experimental work. A numerical model of the plasma spraying process including the inner and outer space is established to study the plasma arc and jet characteristics and the flight behavior of sprayed powder particles. The results show that under the same spraying conditions， the value of plasma arc voltage generated by conical Laval anode is small which corresponds to lower electric power consumption. At the anode nozzle exit of the cylindrical nozzle shows a higher plasma jet temperature and velocity， while the plasma jet of the conical Laval nozzle has a smaller deceleration gradient and larger spatial diameter. At the same spraying distance， the spraying powder particle velocity of conical Laval anode is smaller than that of the cylindrical anode， but the heating and cooling rate of powder particles is greater and the melting is more sufficient； In addition， spraying powder particles with small particle size in plasma jet has the characteristics of faster heating acceleration and cooling deceleration.