低锡量镀锡板点锈原因分析和预防

Cause analysis and prevention of spot rust of low tin content plating plate

针对低锡量镀锡板点锈问题,测试了锡层孔隙率、锡层在基板上的截面分布、基板表面轮廓形貌以及Tafel曲线,从电化学腐蚀角度分析了点锈的原因。结果表明:点锈产生的原因与镀锡板表面漏铁有关,Fe的溢出与锡层产生电势差,为原电池的形成创造了条件。助熔剂对镀锡板的腐蚀性和溜平作用使锡层聚集在基板表面的凹坑处,加剧了镀锡板表面漏铁的概率。基板的表面轮廓越复杂,凸点数越多,越易导致锡层分布越不均匀,镀锡板耐蚀性越差。为此,对助熔剂进行了管控,高锡量镀锡板仍用助熔剂助熔,低锡量镀锡板改为水助熔,且当助熔剂槽切换为水助熔的时候,需要确保槽内无助熔剂残留。对平整工艺段的基板表面轮廓进行管控,通过改变工作辊的毛化参数,降低连退基板的凸点数,同时限定凸点数低于80个/8 mm的基板可用于低锡量镀锡板的生产,如凸点数高于80个/8 mm,则用于高锡量镀锡板的生产实践。

Aiming at the problem of spot rust of low tin content plating plate, the porosity of the tin layer, the cross-sectional distribution of the tin layer on the substrate, the surface profile of the substrate and the Tafel curve were tested, and the reasons for spot rust were analyzed from the perspective of electrochemical corrosion. The results show that the cause of spot rust is related to the iron leakage on the surface of the tinplate. The overflow of Feproduces a potential difference with the tin layer, which creates conditions for the formation of the galvanic cell. The corrosivity and smoothing effect of the flux on the tinplate makes the tin layer gather in the pits on the surface of the substrate, which aggravates the probability of iron leakage on the surface of the tinplate. The more complex the surface profile of the substrate and the more salient points, the more uneven the distribution of the tin layer and the worse the corrosion resistance of the tinplate. Therefore, the flux is controlled. The high tin content plating plate is still fluxed with flux, and the low tin content plating plate is changed to water fluxing. When the flux tank is switched to water fluxing, it is necessary to ensure that there is no flux residue in the tank. The surface profile of the substrate in the flattening process section is controlled, and the number of salient points on the continuous annealed substrate is reduced by changing the texturing parameters of the work rolls. At the same time, the substrate with the number of salient points less than 80/8 mm can be used for the production of low tin content plating plate. If the number of salient points is higher than 80/8 mm, it is used for the production practice of high tin content plating plate.