镀锌层彩色钝化常见问题及对策.doc

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镀锌层彩色钝化常见问题及对策

来源：   文章发表时间：2008-10-28
    镀锌层在以铬酐、硫酸、硝酸等组成的溶液中进行化学处理，使其表面形成一层铬酸盐薄膜，这一过程简称钝化。钝化膜具有下列功能：
    (1)提高了锌镀层的抗大气、二氧化碳、水蒸气腐蚀的作用；
    (2)改善外观色彩，有一定的装饰效果。
    目前钝化多采用低铬钝化工艺，按工艺配方浓度只占原配方浓度的l/30～1/50，大大减轻了环境污染和原材料的消耗，但对熟练掌握技巧、维护溶液正常进行也提出了新的要求，操作稍有不慎极易出现差错，应予以高度重视。
    1、钝化膜易脱落
    除了钝化溶液中硫酸浓度失调和镀件表面附有残留的添加剂未彻底剔除干净之外，操作不当也会造成钝化膜脱落，例如：
    (1)钝化后在未经干燥之前触碰物体；
    (2)钝化后未经吹、晾干之前直接进入烘箱烘烤；
    (3)在高湿度条件下未能及时晾干；
    (4)晾晒时镀件的下端及孔眼等处的积水未能及时除去
    (5)二次钝化件，即钝化后自认膜层色泽欠佳再经补钝化的零件发生脱膜；
    (6)经钝化并冲洗干净后，有时工件虽经晾干，但又受到挂具上流下的水所润湿而发生部分膜层脱落；
    (7)钝化溶液温度过高，钝化时间过长而引起的膜层过厚，影响到膜层的结合力。
    对于氯化钾光亮镀锌件，若钝化之前未经预处理而脱膜，则必须先经预处理，这是因为氯化钾光亮镀锌件表面附有添加剂，若添加剂未能彻底清洗干净，钝化后必然会引起脱膜，为此，钝化前尚需在沸水中煮3～4min，经冷却后再钝化，这一脱膜问题就能得到解决。
    为减少因脱膜而造成返修，在镀件钝化后尚未烘烤之前应做一次检查，当发现有脱膜的应当立即在稀盐酸中退除，用流动水冲洗后重新钝化，这样可以大大简化返修工序。
    2、根据钝化溶液温度调节钝化时间
    溶液温度偏低时成膜速度缓慢，所获的膜层薄，光泽性差，有雾状，需要延长钝化时间，尤其是延长空气中的停留时间才能有所改善，但仍难免“地图”形的花纹出现。
    溶液温度偏高时所获钝化膜虽较光亮，色彩自然，但钝化膜结合力差，要防止因钝化时间过长而引起膜层脱落。
    钝化溶液温度过高时工件离开液面极易快速干燥，从而影响膜层的结合强度，为此不宜在高温下操作。
    3、不同形状工件的钝化实例
    (1)长串件的钝化。长串件钝化时镀件的上、下端进出钝化溶液中的时间有先后，同时工件在溶液中摆动时，镀件的下端摆动幅度比上端大得多；另一方面钝化后在空气中停留时，溶液由上端往下流，下端镀件表面要比上端镀件附有更多的溶液，下端与溶液有更多的化学反应时间。这些都使得下端钝化膜的颜色深于上端。为减轻色差，这类零件进、出钝化溶液时建议横向出、入(下端用一挂钩钩起来)，并防止使用的阳极过长。
    (2)长条零件钝化。长条零件钝化时如钝化槽容纳不下，可采取临时措施，利用砖块或木条加工一个能容下镀件的框，框内衬以塑料布，注入钝化溶液后即可使用，采用此法既方便又可避免膜层不均匀或产生衔接印痕等质量问题。
    (3)平面件钝化。一般平面件钝化时由于在钝化槽中摆动时边缘部位与钝化溶液接触会比中间部位剧烈，而引起此部位钝化膜的色泽过深或不均匀的现象，此问题可采取压缩空气搅拌来解决，效果很好。
    为提高钝化膜的均匀性还需注意镀锌过程中的电流分布均匀性，必要时镀件的边缘予以屏蔽，以防该部位因电流过大而出现镀层粗糙，影响钝化膜的色泽。
    (4)表面光洁件的钝化。表面光洁件钝化后，由于表面光滑，钝化溶液在其表面较难吸附，很快流失，故钝化时在溶液中和空气中的停留时间都要适当延长，否则该工件的钝化膜显得较淡。
    (5)易兜水件钝化。要避免兜出溶液，以免引起钝化溶液过多损耗、污染环境，也可以保证该部位钝化膜的质量。
    (6)小件钝化。可把整串所绑扎的工件放在塑料篮筐内钝化，以免钝化时因抖动而脱离群体，掉入槽内造成返修。
    4、钝化溶液简便有效维护
    溶液经一年左右使用后所获钝化膜的颜色会逐渐陈旧，呈暗绿色，这是溶液中积聚的金属杂质或三价铬浓度超过允许值而引起的；需采取必要的措施予以调整，具体方法如下。
    取转为H+型的“732”强酸性阳树脂5kg左右，装在耐酸的布袋内，直接浸泡在钝化溶液中，隔一定时间提一下布袋，使布袋内、外的溶液时时得到交替更新。当发现袋内树脂的颜色变深时，说明树脂已吸附饱和，再无交换能力，需要再生，此时可将布袋由溶液中取出。经清洗后在硫酸溶液中再生，再生后可继续使用，一般在1～2天内即能使300l左右的钝化溶液中的有害杂质吸附干净，使溶液恢复透明的鲜红色，所获的钝化膜也即由原来的陈旧暗绿色变为鲜艳的彩虹色。使用过的树脂经硫酸再生后浸泡在清水中下次仍可继续使用。
    采取上述方法处理低铬钝化溶液无需停产，无需专用设备，不损耗溶液，从而既能避免对环境的污染，又能节省添置设备所需的费用。
    5、钝化溶液的调整和材料补充
    低铬钝化过程中由于溶液对基体锌层无抛光作用，钝化前镀层的抛光依靠浸稀硝酸来完成。硝酸出光有利于除去锌层表面添加剂分解后黏附于工件表面的有机物质，镀件进入钝化槽后钝化液直接与光亮的锌层表面发生化学反应，产生钝化膜，钝化对溶液中各组分的消耗是甚微的。由于铬酐含量低，溶液在镀件表面黏性小，随镀件带出的量也很少。因而溶液中有机、无机杂质的带入也大大少于高铬钝化工艺，相对来说溶液比较稳定，无需像高铬钝化那样须经常调整。
    经一定时间使用后如发现成膜速度逐渐减缓，所获得的钝化膜色彩慢慢变得浅淡，说明溶液中的成分有较大消耗，需要补充材料，此时可按如下方法补充。
    补充事先配制好的母液，每次加10ml/l左右。母液中铬酐和硝酸的浓度按工艺配方20倍，硫酸按工艺配方22倍配制，这是因为低铬钝化是液相成膜。经验证明，作为活化剂的硫酸其消耗量略大于其他成分，又硫酸具有维持溶液中pH值的功能，在保证必需的pH值条件下能促使钝化膜光亮细密，呈鲜艳的彩虹色调。但硫酸也不能过量，否则将会影响膜层的结合力。
    每加入10ml/l母液相当于提高原工艺配方浓度的20％，在一般情况下，材料补充后溶液即能恢复初期配制时相同的使用效果，如溶液浓度有较大变化，适量增添甚至整槽重新配制时，均可采用此法。采用此法可避免临时计算、领料、配制、溶解等忙乱事情的发生。
    6、由锌层出光溶液老化引起的质量故障
    某厂镀锌钝化工作量较大，钝化前的硝酸出光溶液很少更换。错误地认为出光溶液效果差是硝酸浓度低引起的，只要加点硝酸就可以了，结果浸出来的工件表面出现灰雾色，误认为是镀锌溶液有问题。实际上这一现象是硝酸出光溶液中锌离子浓度过高引起的，更换新溶液之后钝化膜灰雾问题随即得到解决。
    为摸清出光溶液中锌离子的允许浓度与浸亮件质量的关系，经小试得出锌离子约达4g/h浸出，工件经钝化即有灰雾状。
    在洁净的出光溶液中浸亮还能验证镀锌溶液被污染原因：出光后工件表面出现褐色膜，这是镀锌溶液被重金属杂质污染的现象；出光后工件表面出现白雾，这是镀锌溶液被有机物污染的现象。锌层出光溶液浓度较低l％～3％，氯化钾光亮镀锌件的出光液可用l％浓度的稀硝酸，费用相对较低，使用过于陈旧的稀硝酸，还可能由此而污染钝化溶液。
    7、钝化膜出现发花
    某厂镀锌钝化多为钣金件，工件面积较大，钝化膜的色彩显得不够均匀。为解决这一难题，采取了压缩空气搅拌钝化溶液的方法，结塑膜层色彩的均匀性虽有改善，却出现了发花现象。
    原来该厂使用的压缩空气未经油、水过滤。压缩空气中的油、水随空气直接进入钝化溶液，在液面处清楚可见有一层油膜，当工件入钝化溶液时会粘在工件表面。从而出现了发花的钝化膜层，油膜厚处甚至无钝化膜的形成。’
    提出如下两点解决方法：1)制作一个小型的油、水过滤器；2)未使用油水过滤器之前，钝化溶液表面的油膜及时用粗纸附着液面吸附掉.
    引起钝化膜发雾的5点重要因素。
    锌层低铬钝化后出现发雾的原因众多，常见的有以下几种。
    (1)与镀锌层质量有关。当镀锌溶液中积聚过多的有机质时(多由添加剂的分解产物引起的)，镀出锌层易发雾，在此锌层上钝化，所获钝化膜必然会出现雾状。
    (2)浸亮溶液中锌含量过高。这一现象在碱性镀锌工艺中尤为多见，碱性镀锌溶液中碱含量高，工件表面残留溶液较难洗脱，较易带入到浸亮溶液中去，从而致使浸亮溶液中锌离子浓度过快积累。
    (3)钝化溶液使用过久积聚过多的三价铬离子。钝化溶液中积聚一定量的三价铬离子时，钝化膜易出现雾状。
    低铬钝化溶液中各组分浓度低，多次以补充材料方式来延长溶液的使用寿命，三价铬离子必然会越积越多，在这种情况下要定期用732阳树脂进行处理，使低铬钝化溶液长期保持鲜艳的、清澈的红色(溶液呈暗绿色说明三价铬已超标，不能再继续使用)。
    (4)浸亮溶液浓度过稀。碱性镀锌溶液中碱含量高，不易洗脱而带入浸亮溶液之中，结果浸亮溶液中的硝酸很快被中和，起不到浸亮作用，由于低铬钝化无抛光能力，从而出现钝化膜光泽性差，细看似呈雾状。
    浸亮溶液的浓度也不宜过浓，否则锌层损耗过多，有必要时可选用氯化钾光亮镀锌来满足装饰上的要求。
    (5)前处理工艺不彻底。未经擦刷或电化学除油，当工件表面不亲水或有轻度氧化膜时，镀层的上镀期必然有先后，从而也就必然会出现不均一的镀层质量，由于镀层下污物的存在，也必然会有雾状出现。
    8、由一水多用引起镀锌钝化膜恶化故障
    由一水多用引起的质量故障较为多见，这是对清洗水水质与镀层质量并溶液关系重视不够引起的。清洗就是为洗去工件表面的污物，不让下道工序的溶液遭到污染，如果清洗的水本身不洁净，在此水中再洗也是洗不干净的，现举3个实例说明清洗水水质与镀层质量和溶液维护方面的重要关系。
    某厂镀锌白亮钝化和彩色钝化后的清洗合用一只清洗槽，结果白亮钝化层表面总是难以获得理想的银白色钝化膜。某厂仿金镀件与镀镍件也都在同一只清洗槽中清洗，仿金镀件干燥后当即变色，而镀镍件镀铬也难以沉上均一洁净的铬层。
    还有更为严重的，如氰化镀铜后的清洗水与中和后的清洗合用一只清洗槽，致使大量含铜水带人镍槽，造成镍槽不能正常工作，在这种情况下还可能引起因氰化物与酸作用而引起氢化氰中毒事故的发生。
    上述类似问题在某些厂家并不少见，其实这样做是得不偿失的，只有改变用水方法，如采用多级逆流漂洗等手段，才能充分清洗，保证清洗质量，同时还可节省用水，达到两全其美的目的。
    9、严格掌握钝化过程中色泽变化规律
    镀锌层钝化膜的耐蚀性能与钝化膜外表的色彩有着十分密切的关系，以彩钝为例，钝化膜的形成是根据钝化时间的长短来掌握，彩色钝化膜的色泽变化大致如下：
    淡蓝略带红色一蓝、红色一深蓝紫色一淡红色一桃红带淡绿色一艳绿色一金黄色一黄褐色。
    根据耐蚀性试验，以艳绿色和金黄色的钝化膜致密性最好，耐性也最好。
    10、钝化膜的合理老化
    锌层钝化后的老化工序很重要，采取合理的老化工艺即50～160℃，l0～15min烘烤时间，即可排尽钝化膜中多余的水分，增加光亮程度和抗蚀性能，但若老化温度超过70℃，尤其高于80℃时，钝化膜中所含的结晶水将会分解出来，此时钝化膜将会出现裂纹和孔隙，抗蚀性能随之降低，膜层的变色速度也会加快。
    11、保证钝化膜结合强度的种种措施
    锌层低铬钝化工艺中如何保证膜层的结合强度是关键的。重点要注意以下几种情况。

    (1)镀锌溶液中有机质含量较高。镀层中夹有过高的有机杂质时会严重影响钝化膜的结合强度。若钝化之前先在下列溶液中进行洗烫，则能获得良好的效果。
    氢氧化钠5g/l、碳酸钠5g/l、硅酸钠5g/l、温度70～80 ℃、时间0.5～1min。
    (2)钝化溶液中pH值过高。应按比例适量添加硫酸和硝酸。
    (3)钝化溶液老化。锌离子2g/l时需要更换，最好维持在0.5g/l左右。
    (4)硫酸根含量偏低，适量加入硫酸盐。
    (5)铬酐含量偏高。高于8g/l时成膜过快，易脱膜，但也不能太低，当铬酐含量低于3g/l时难以获得丰满的彩虹色，需要延长时间，且这时也容易引起脱膜。
    (6)钝化时间过长。钝化时间越长，膜层越厚，膜层越厚越容易脱落。
    (7)钝化溶液温度过高。温度过高，膜层离开溶液时会快速干燥，容易引起脱膜。
    (8)钝化溶液中pH值过低。成膜速度快，膜层结合力差，易脱膜。
    (9)钝化方法欠妥。离开液面观察时间过长，形成双层、三层膜。
    (10)钝化后在空气中停留时间过长，膜层干化后易脱落。
    (11)钝化膜未经吹干即进烘箱老化，钝化膜层易成片状脱落。
    (12)钝化后清洗不彻底或水质差。钝化膜层含酸性或碱性成分，引起钝化膜溶解。
保证的概念：保证人和债权人约定，当债务人不履行债务时，保证人按照约定履行债务或者承担责任的行为。保证人，有代为清偿能力的法人、其他组织或者公民，可以作为保证人。法律禁止作为保证人的情形romoting the construction of rule of law, but also the most basic development environment. Despite my good social order in General, but there are law-abiding consciousness, social order is not standard, regardless of faith, Twining visit visit and other outstanding problems. We want to actively promote the field of multi-level governance according to law, promote the continuous improvement of the social environment. To promote universal compliance. Actively foster the rule of law culture, carry out law publicity and education on honesty and trustworthiness, guide the masses and consciously abide by the law, failing to find method, problem-solving method, method of gradually changing the world, he is not looking for but someone "unspoken rules", formed all law law, abide by the good atmosphere. To strengthen the comprehensive management of public security. Deepening peace xingan construction, strongly against violence crime, mafia and serious criminal offences, to protect the legitimate rights and interests of citizens, legal persons, carry out criminal policy of temper justice with mercy, the maximum stimulating social vitality, and earnestly safeguard social harmony and stability. To resolve social conflicts by law. To further smooth channels of reporting social conditions and public opinion, improving regulation, arbitration, as wellGrass-roots governance according to law is an important foundation for promoting the construction of rule of law, but also the most basic development environment. Despite my good social order in General, but there are law-abiding consciousness, social order is not standard, regardless of faith, Twining visit visit and other outstanding problems. We want to actively promote the field of multi-level governance according to law, promote the continuous improvement of the social environment. To promote universal compliance. Actively foster the rule of law culture, carry out law publicity and education on honesty and trustworthiness, guide the masses and consciously abide by the law, failing to find method, problem-solving method, method of gradually changing the world, he is not looking for but someone "unspoken rules", formed all law law, abide by the good atmosphere. To strengthen the comprehensive management of public security. Deepening peace xingan construction, strongly against violence crime, mafia and serious criminal offences, to protect the legitimate rights and interests of citizens, legal persons, carry out criminal policy of temper justice with mercy, the maximum stimulating social vitality, and earnestly safeguard social harmony and stability. To resolve social conflicts by law. To further smooth channels of reporting social conditions and public opinion, improving regulation, arbitration, as well as dispute resolution mechanisms, implement fully the petitioners ' cases "third-party" hearings and supervising system of letters and calls, and to resolve the involved law lawsuit into the orbit of rule of law, vexatious, Twining visit visit, disturbing social order and other malicious extortion, resolutely crack down. Five, improving cadres Vitale, provide strong protection for forest development XI General Secretary stressed that the comprehensive revitalization in Northeast China, needs a high quality, solid style, cadres of the dare to play. Cadre cadres is a pledge, should want to do work and able to do good, enthusiasm is paramount. Treat party cadres, it is necessary to Strict management, and warm care, enable the broad masses of cadres work hard work, this is two parallel principles. In strict accordance with the standards of good cadres selection and appointment, the real officers, dare officers, those who want to play, good as excellent cadres at all levels of leadership in the past. At present, some leading cadres work initiative is not high, beyond political, idle, lazy governance governance, not as, slow, messy and a phenomenon still exist to varying degrees, affected and restricted economic and social development. We must mobilize the enthusiasm of cadres as an urgent task, adhere to combination of incentives and constraints, and adhere to the strict management and warm care, practical solution "for the officers not to" problem, motivate cadres and better lead the masses to an undertaking, the cadres and create the new achievement in a dare to play, good at shows as new. To identify the problem, accurate pulse