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选用锈蚀等级为B级的Q235碳钢板作为试验对象,将钢板切割成尺寸为100 mm×100 mm×6 mm的样件。为了消除样件表面初始锈蚀层对实验结果的干扰,样件表面打磨抛光后,被浸泡在质量分数为3.5%的NaCl溶液中100 h,随后测得样件表面锈蚀层的厚度约为80 μm,根据拉曼测试,激光除锈前,锈蚀层成分主要由Fe3O4、γ-FeooH、α-Fe2O3等组成。文中采用的激光除锈设备主要由激光器、扩束准直系统、扫描振镜系统、聚焦场镜、二维位移台及计算机控制系统等组成,如图1所示。所用激光器为纳秒光纤激光器,激光器波长为1064 nm,最大平均功率为200 W,脉冲宽度为60 ns,脉冲重复频率范围为20~50 kHz,聚焦场镜的焦距为160 mm,聚焦后光斑直径约300 μm。
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在除锈过程中,激光器发出的脉冲激光束经扩束准直后进入扫描振镜系统,计算机系统通过控制激光的开启关闭以及扫描振镜镜片的摆动,使入射的点光斑经反射后转变为光斑快速扫描运动的线光斑,点光斑运动的速度为激光扫描速度,线光斑经场镜聚焦后照射到锈蚀层表面,同时通过X、Y二维位移台及计算机控制系统调控除锈区域的形状和大小,激光除锈光斑扫描运动过程如图2所示。
图 2 激光除锈过程中光斑扫描运动轨迹示意图
Figure 2. Schematic diagram of spot scanning trajectory in laser derusting process
激光扫描速度直接影响到锈蚀层去除质量,其中激光扫描速度
$ v $ 、脉冲频率$ f $ 、光斑直径$ d $ 和光斑搭接率$ \eta $ 的关系为[14]:$$ \eta =\left(1-\frac{v}{f \cdot d}\right)\times 100 {\text{%}} $$ (1) 式中:在脉冲频率
$ f $ 和光斑直径$ d $ 不变的情况下,光斑搭接率与激光扫描速度成反比关系。激光除锈过程中线间距为图2中各行之间的距离,线间距不同,各行之间光斑搭接率不同,文中试验过程中,保持光斑在X、Y轴的搭接率一致,根据扫描线速度确定光斑搭接率以及线间距。文中主要开展激光扫描速度对除锈效果的影响规律研究,在整个除锈过程中,计算机控制系统通过控制板卡和振镜控制卡来实现激光输出功率、频率、扫描速度、脉宽等参数的调控。此外,利用体视显微镜进行形貌分析,拉曼光谱仪分析试样表面成分,白光干涉仪测试样件面粗糙度Sa和Sq。
Effect of laser scanning speed of the removal quality of rust layer on carbon steel surface
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摘要: 采用光纤激光器开展了碳钢板表面锈蚀层激光清洗研究,通过白光干涉仪、光学显微镜、拉曼光谱仪等研究了激光扫描速度对锈蚀层去除质量的影响。研究表明,当激光扫描速度小于2 000 mm/s时,因光斑搭接率高,热累积效应强,试样表面出现基材熔化重凝现象,同时试样表面发生二次氧化,生成了复杂的铁的氧化物膜层,此时试样表面粗糙度最小。当激光扫描速度增加到3000 mm/s时,试样表面锈蚀层去除干净,露出金属基底本身色泽,基材表面二次氧化减弱。当线速度继续增加时,因光斑搭接率低,锈蚀层吸收的激光能量少,仅有部分锈蚀被去除,试样表面开始出现残留锈蚀层,且随着线速度的增加,残留锈蚀层和试样表面粗糙度增加。通过调节扫描速度可以获得较好的除锈效果,工艺优化后,激光功率为120 W时,除锈效率达到1.5 m2/h。Abstract: Laser cleaning of rust layer on the surface of carbon steel was studied by fiber laser, the effect of laser scanning speed on the removal quality of rust layer was studied by white light interferometer, optical microscope and Raman spectrometer. The results show that, when the laser scanning speed is less than 2 000 mm/s, the high spot overlap rate and strong heat accumulation effect, lead to the melting and recondensation of the substrate surface, and a secondary oxidation occurs on the sample surface, which result the formation of a complex iron oxide film, at the same time, the surface roughness of the sample is the smallest. When the laser scanning speed is increased to 3000 mm/s, the rust layer on the surface of the sample is completely removed, the color of the metal substrate is exposed, and the secondary oxidation on the surface of the substrate is weakened. When the scanning speed continues to increase, due to the low spot overlap rate, the laser energy absorbed by the rust layer is less, only part of the rust layer is removed, the residual rust layer begins to appear on the surface of the sample, and with the increase of scanning speed, the residual rust layer and surface roughness increase. Better rust removal effect can be obtained by adjusting the scanning speed, after optimization the process, when the laser power is 120 W, the rust removal efficiency reaches 1.5 m2/h.
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Key words:
- laser rust removal /
- laser scanning speed /
- rust layer /
- surface roughness
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