浅析真空自耗电弧炉锭子断面形状与电气控制的关系

真空冶金 李宏 西安石油大学

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  本文结合某单位实际生产过程中出现的不同形状的锭子断面,分析影响锭子断面形状的[1]因素及其与电气控制的关系。

1、直流电弧炉工作过程及电气控制要求

  直流电弧熔炼通常分3 个阶段完成,即起弧、熔炼、补缩或浇铸阶段。系统具体的工作过程为:在炉内真空度满足要求的前提下系统投入运行,当给正负极加上直流电源时,作为负极的金属棒与水冷铜坩埚底部的起弧料触发起弧。随着电弧的正常触发和电流的迅速增大并达到设定值时,电极末端迅速熔化,坩埚内的液态金属高度逐渐增加,金属电极长度逐渐减小,系统则进入真正的熔炼阶段[1]那个棋牌信誉好。此时对电气参数和物理参数的控制最为重要,适当的控制这些参数将能有效的避免形成不合理的锭子断面。

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2、影响锭子断面形状的因素及其形成原因分析

  在实际的生产过程中熔炼锭子断面一般会出现以下三种形状:(1)锥形;(2)内凹形;(3)平整形由以上分析可以看出影响其断面形状的因素大致可以分为四类:一是电气参数的控制,主要包括熔炼电流的大小、电弧的弧压、电弧长度、稳弧电流等;二是物理参数的控制,主要包括真空度、电极杆水压、坩埚水压、冷却水温、熔化电极直径与坩埚内径的比值等;三是直流供电系统自身所产生的磁场,由于磁场的作用和电流的电磁力的作用产生的偏弧。四是电弧的发热和传热。其中最为关键的因素有:(1)弧压的高低;(2)稳弧电流的大小;(3)坩埚冷却水温的高低;(4) 熔化电极与坩埚电极的比值

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熔炼时电弧分布示意图

那个棋牌信誉好TU1 RONGLIANSHIDIANHUFENBUSHIYITU

  真空直流电弧熔炼过程中熔炼弧压对熔池与自耗电极(熔炼锭子)间的弧长有直接影响,弧长的变化通常会影响熔化速度和熔池温度,这是形成各种锭子断面的关键因素。当δ 一定时,如果弧压过低,则弧长缩短,极易引起短路;但弧压又不能太高,如果弧压过高,则弧长拉长,将会引起侧弧、爬弧使得熔炼锭子的边沿和底端同时熔化,且熔化的速率不一致,导致锭子形成了如图3 所示的圆弧断面。此时就需要设备操作人员及时做出调整,避免击穿坩埚而造成重大生产事故的危险。从图2 弧压与弧长曲线关系可知,弧压U 在弧长L 较短时两者之间有明显的依附关系,当弧长超过一定值后,弧压的变化趋于一稳定值。因此,这就要求直流电弧熔炼应选择短弧熔炼模式[3]

电弧电压与电弧长度关系曲线图

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  (2)WENHUDIANLIUDAXIAODEYINGXIANG

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  熔炼锭子直径与坩埚内径的比值(俗称坩埚比)若d 表示熔炼锭子直径,D 表示坩埚内径,则坩埚比可表示为σ=d/D。在熔化电压、熔化电流、稳弧电流相等的条件下,坩埚比越小即σ 越小,图1 中所示的δ 越大。由于坩埚外部的水冷套内通有不断循环的冷却水,δ 长的空间距离内为空气,从电弧的发热和传热的角度来看,图1 中的电弧中心区的发热量起着主导作用。据相关资料表明电弧中心区的发热量在电弧发热总量所占的比例高达96%以上,所以δ 越大,坩埚自身散热加快[4]。再者,坩埚内部通有不断循环的冷却水,进回水的温差较大。一般冷却水温的要求为进口温度不低于+5℃,而出口水温不高于60℃。同时为保证炉内的真空度,炉体的真空系统那个棋牌信誉好不停的抽真空,更加速了δ 空间的散热速度。由此导致熔炼锭子靠近坩埚边沿的温度低,而锭子中心温度高,引起锭子中心熔化速度快,外壁熔化速度慢,使图1 中的ΔL 变的很大,导致熔炼锭子断面形成了如图4 所示的内凹形。

熔炼锭子断面

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3、工程实验验证

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4、结论

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CANKAOWENXIAN

  那个棋牌信誉好[1] 李宏. 常用电力电子变流设备调试与维修基础[M].北京:科学出版社,2011.

  [2] 孙足来,党哲鹏,杨洪帅,等.真空电弧炉和真空感应炉的研究[J].真空,2008(4):6- 12.

  那个棋牌信誉好[3] 卢新昌.铸钛工业与机电一体化技术[J].钛工业进展,2006(1):38- 41.

  那个棋牌信誉好[4] 乔兴武. 直流电弧炉的传热[J]. 河北冶金,2002(2):13- 16.

  那个棋牌信誉好[5] 苏德良.炼钢电弧炉引起的电压波动,闪变抑制措施探讨[J].黑龙江冶金,2000(2):31- 35.