辊套材料的导磁性对铸轧区磁感应强度的影响
李晓谦,周伟华,郭运涛,郑益华
(中南大学 机电工程学院,湖南 长沙,410083)
摘要: 采用对比实验考察在新型材料辊套和合金钢辊套下铸轧区磁感应强度的差异;根据电磁场理论,研究上述2种辊套材料对铸轧区磁场的衰减和屏蔽效应。研究结果表明:合金钢辊套的相对磁导率为300,是新型辊套材料的300倍;合金钢辊套对磁场既具有衰减作用又具有聚磁效应,衰减作用使铸轧区的磁感应强度减小,聚磁效应使磁感应强度增大;合金钢辊套对磁场的聚磁效应比对磁场的衰减作用强,使铸轧区的磁感应强度增大5%左右。新型材料辊套对磁场只有衰减作用,使铸轧区的磁感应强度降低5%左右。当电磁感应器的励磁电流为10 A、励磁频率为13 Hz时,在合金钢辊套下比在新型材料辊套下铸轧区的磁感应强度大10%左右。从磁场利用的角度考虑,在电磁场快速铸轧技术中使用合金钢辊套比使用新型材料辊套更好。
关键词: 电磁场快速铸轧; 辊套; 铸轧区; 导磁性; 磁场衰减; 聚磁效应
中图分类号:TG249 文献标识码:A 文章编号: 1672-7207(2005)04-0621-05
Influence of magnetoconductivity of roller shell on magnetic induction in roll casting zone
LI Xiao-qian, ZHOU Wei-hua, GUO Yun-tao, ZHENG Yi-hua
(School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China)
Abstract: By adopting the contrastive experiments, the differences of the magnetic induction in the roll-casting zone were researched in different conditions between the new material roller shells and the alloy steel roller shells. And based on the theory of electromagnetic field, the attenuation and shield effect of the above-mentioned roller shells on the magnetic field were also investigated. The results show that the relative permeability of the alloy steel roller shell is 300, which is 300 times of that of new material roller shell. The alloy steel roller shell attenuates and congregates magnetic field. Attenuation diminishes the magnetic induction in the roll casting zone. However, magnetic congregate effect augments the magnetic induction by centralizing the magnetic field lines around the roll casting zone. Its magnetic congregate effect has an advantage over attenuation in the influence on magnetic field, which increases the magnetic induction by about 5%. In contrast, the new material roller shell only attenuates the magnetic field, which decreases the magnetic induction about by 5%. The magnetic flux density in the roll casting zone under the condition of using alloy steel roller shell is about 10% higher than that under the condition of using the new material one when the exciting current of inductor is 10 A and exciting frequency is 13 Hz. So it is better to use the alloy steel roller shell in the technology of high-speed electromagnetic roll casting in terms of utilizing magnetic field.
Key words: high-speed electromagnetic roll casting; roller shell; roll casting zone; magnetoconductivity; magnetic field attenuation; magnetic congregate effect
人们经过几十年对铝及铝合金双辊连续铸轧的研究,相继开发了电磁铸轧[1-5]和快速铸轧[6-9]等新技术,极大提高了铝带坯组织性能和深加工性能,提高了生产效率,增加了可铸轧的铝合金品种。电磁场快速铸轧技术集电磁铸轧技术和超薄快凝铸轧技术于一体,是一种崭新的铝及其合金加工技术,其轧辊辊套必须采用导热性优、承载能力强和抗疲劳能力强的材料,并要求该材料具有合适的导磁性,以保证在铸轧区获得足够的磁感应强度。新型材料辊套和普通合金钢棍套是用于快速铸轧和常规铸轧的2种辊套。新型辊套材料的相对磁导率仅为普通合金钢材料磁导率的1/300[9],但是,新型材料辊套的冷却能力为普通合金钢辊套的3~4倍[8]。作者采用对比实验的方法,在400 mm×500 mm(直径×宽度)铸轧机上研究了此2种材料辊套的导磁性对铸轧区磁感应强度的影响,根据电磁场理论分析了辊套在电磁感应器磁场中的衰减和屏蔽效应[11-19]。
1 实 验
1.1 实验原理和装置
采用如图1所示的实验装置,在400 mm×500 mm(直径×宽度)铸轧机上模拟电磁快速铸轧,将电磁感应器的线圈和铁芯固定在铸嘴区,通过交—直—交变频电源提供的交流电,使线圈产生稳定的准静态磁场[9]。由于电磁感应器的磁轭断开未闭合,所以,在气隙处磁力线发散,一部分磁力线穿过上、下轧辊辊套,产生一定的磁场能损耗,使该处的磁感应强度减小。
![17-t1.jpg](/web/fileinfo/upload/magazine/143/5375/image001.jpg)
图 1 铸轧区磁场测量实验装置
Fig. 1 Experimental device of measurement on magnetic field in roll casting zone
1.2 实验参数
2种辊套材料的机械、物理性能参数见表1[7,9]。
根据工业生产的要求[3],为了能在铸轧区获得一定磁感应强度的磁场,电磁感应器的气隙磁感应强度为0.05 T,因此,在实验中电磁感应器必须满足如下工况:励磁频率为13 Hz;三相励磁电流为10 A;环境温度为25 ℃。
表 1 辊套材料的机械、物理特性参数
Table 1 Mechanical and physical characteristic parameters of roller shell’s material
![17-b1.jpg](/web/fileinfo/upload/magazine/143/5375/image002.jpg)
1.3 实验步骤
实验前,对铸轧区进行如图2所示的网格划分,实验时采用实测法,用460型3通道特斯拉计直接测量、记录各节点的磁感应强度。
实验中分别换上新型材料辊套和普通合金钢辊套,测量各自在铸轧区中各检测点的磁感应强度,并将感应器退出时相应位置的磁感应强度进行比较。
![17-t2.jpg](/web/fileinfo/upload/magazine/143/5375/image003.jpg)
图 2 铸轧区检测点划分
Fig. 2 Division of the measure node in roll casting zone
2 结果及分析
2.1 实验数据
图3所示为实验测得的铸轧区横向磁感应强度分布图。可见,在普通合金钢辊套下,铸轧区的磁
![17-t3.jpg](/web/fileinfo/upload/magazine/143/5375/image004.jpg)
图 3 铸轧区横向磁感应强度分布
Fig. 3 Distribution of magnetic induction of horizontal node in roll-casting zone
感应强度比感应器退出时相应位置的磁感应强度大5%左右;而在新型材料辊套下铸轧区的磁感应强度比感应器退位置时相应位置的磁感应强度小5%左右。此外,电磁感应器的磁场为不均匀磁场。
图4所示为铸轧区自轧制线沿轧制反方向的磁感应强度分布图。
实验结果表明,使用普通合金钢辊套比使用新型材料辊套在铸轧区获得的磁感应强度大10%左右。
![17-t4.jpg](/web/fileinfo/upload/magazine/143/5375/image005.jpg)
图 4 铸轧区自轧制线沿轧制反方向磁感应强度分布
Fig. 4 Distribution of magnetic induction along reverse direction of rolling line in roll casting zone
2.2 讨 论
电磁感应器电磁场的边界为空气、磁轭和辊套(真空磁导率μ0=4π×10-7 N/A2),普通合金钢辊套的相对磁导率μr=300(μ=μr×μ0,μ为合金钢的磁导率),新型材料辊套的μr≈1,空气的μr=1。由于电磁感应器的激磁频率较低,为13 Hz左右,因此,可不考虑辊套的集肤效应和涡流效应。很明显,磁力线由空气进入新型材料辊套时,由于二者的磁导率几乎相同,方向不发生变化;而当磁力线由空气进入普通合金钢辊套时,由于合金钢材料的磁导率远大于空气的磁导率,磁力线发生折射[9](见图5),将有一部分磁场能损耗在辊套上。
根据电磁波有关理论可知,电磁场在介质中的衰减常数α与电导率γ、磁导率μ和激磁频率ω的关系为[9]:
![17-2.jpg](/web/fileinfo/upload/magazine/143/5375/image006.jpg)
考虑到新型材料的μr1≈1,γ1=107 S/m,ω=2πf=26π Hz;合金钢的μr2=300,γ2=0.6×107 S/m。由衰减常数易知,新型材料辊套的衰减常数为:
![17-1.jpg](/web/fileinfo/upload/magazine/143/5375/image007.jpg)
同理,可求得普通合金钢辊套的衰减常数α2=184.2 Np/m。从衰减常数可以看出,普通合金钢辊套对磁场的衰减比新型材料辊套的衰减大。
![17-t5.jpg](/web/fileinfo/upload/magazine/143/5375/image008.jpg)
图 5 磁感应线在介质边界上的“折射”
Fig. 5 “Refraction” of magnetic induction line on at boundary of medium
但是,实验结果表明,在普通合金钢辊套下铸轧区的磁感应强度较大。这可能是由于合金钢辊套的聚磁效应[11]引起的磁感应强度增加量大于衰减引起的磁感应强度的减小量,聚磁效应对铸轧区磁场的影响起主要作用。而新型材料辊套对磁场只有衰减作用。由电磁理论可知,磁场中若有介质存在,由于介质被磁化,产生附加磁场B′,叠加在原磁场B0上,使磁场分布发生变化,B=B0+B′。一般介质(顺磁介质或抗磁介质,如新型材料等)对磁场的影响很小,如图6(a)所示;但铁磁介质(铁、镍、钴及其合金,如普通合金钢等)对磁场的影响很大,如图6(b)所示。
由于辊套的聚磁作用,普通合金钢辊套下的磁感应强度反而比新型材料辊套下铸轧区的磁感应强度大。铁磁介质的普通合金钢辊套能把一部分发散的磁感应线“拉”回铸轧区。因此,普通合金钢辊套下比新型材料辊套下的铸轧区的磁感应线密,相应磁感应强度大,可能是由于辊套的屏蔽效应引起的磁感应强度的增加量比由磁场在辊套中的衰减作用引起的磁感应强度的减少量大。因此,在普通合金钢辊套下铸轧区的磁感应强度较大。相反,在新型材料辊套下铸轧区的磁感应强度比感应器退出位置时的要小。
![17-t6.jpg](/web/fileinfo/upload/magazine/143/5375/image009.jpg)
图 6 介质对均匀磁场的影响
Fig. 6 Influence of mediums on even magnetic field
3 结 论
a. 辊套材料的导磁性是影响铸轧区磁感应强度的一个重要因素。合金钢辊套为铁磁介质,它对磁场既具有聚磁效应,又具有衰减作用,其中聚磁效应起主导作用。新型材料辊套为顺磁质,它对磁场仅具有衰减作用。
b. 从磁场利用方面考虑,使用普通合金钢辊套比较好;但是,新型材料辊套的冷却能力为普通合金钢辊套冷却能力的3~4倍,从冷却效果方面考虑,使用新型材料辊套较普通合金钢辊套好。因此,在选择辊套材料时应全面权衡,综合考虑,既要保证在铸轧区有足够大的磁感应强度,又要求在铸轧过程中能快速冷却,在电磁场快速铸轧技术中使用新型材料辊套比使用普通合金钢辊套好。
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收稿日期:2004-11-08
基金项目:国家“863”高技术计划项目(2001AA337070-01)
作者简介:李晓谦(1958-),男,湖南双峰人,教授,从事冶金机械、金属材料制备及工艺研究
论文联系人: 李晓谦,男,教授;电话:0731-8876167(O); E-mail:meel@mail.csu.edu.cn