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等离子弧粉末堆焊条件下粉末颗粒的热行为Ⅱ粉末颗粒与等离子弧之间的传热过程研究

Evaluation of Powder's Thermal Behavior in Plasma Transferred-Arc Space (Ⅱ)——Study on Heat Transfer Between Powder Particle and Plasma

    摘要
  • 摘要: 运用传热学理论对等离子弧粉末堆焊时Fe基粉末颗粒和B4C颗粒在等离子弧柱中的热行为进行了计算分析,结果发现堆焊时等离子弧电流对粉末颗粒在弧柱中被加热程度的影响要远大于对其输运速度的影响;对于Fe基粉末颗粒来说,当I=200A时,流经弧柱中心区内的粒径≤50μm的颗粒将在弧柱中被完全气化;对于粒径为50~150μm的Fe基颗粒,在弧柱中将被加热到完全熔化,而粒径>200μm时,颗粒尚不能熔化。在I=100A的小电流情况下,只有粒径<50μm的Fe基颗粒在弧柱中能被完全熔化;而直径大于该值的颗粒则不能被完全熔化;只有在弧中心处,少量颗粒可能被加热到熔化温度。而对B4C颗粒来说,其热行为与Fe基粉末颗粒则有较大差别,从平均水平看,在等离子弧柱中心区域,即使在200A的等离子弧中,也只有粒径≤50μm的颗粒才能在弧柱中完全被熔化,其它稍大粒径的颗粒在弧柱中的温升都达不到熔化温度,只能被预热。

     

    Abstract: The heating processes of Fe-base alloy and B4C particles in the plasma transferred-arc(PTA) space were theoretically evaluated in this article based on heat conduction theories.It was found that most of the Fe-base particles would be fully melted while they transporting through the central plasma field with 200 Asurfacing currents.And the particles with a diameter less than 0.5×10-4 m migth be fully evaporated.However,for the boron carbide(B4C) particles,only the one with a diameter less than 0.5×10-4 m could be melted in the same PTA space.Most of B4C particles are only preheated at its soild state when they were fed through the central field of PTA plasma when the surfacing current is equal or less than 200 A.When the arc current was smaller than 100 A,only the particles smaller than 0.5×10-4 m could be melted in the PTA space for the Fe-base alloy.Almost none of the discussed B4C particles could be melted in the 100 A PTA space.

     

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