Chemical degreasing is an important process step in the electroplating process, and it is also a key process that determines the quality of the coating. Faults caused by improper chemical degreasing methods are also common. The following are the problems that the author has encountered and has been solved.
some technical issues.
1. Excessive water glass content in the chemical degreasing solution affects the bonding strength of the galvanized layer
Once it was found that the bonding strength of the galvanized layer was poor. At that time, whether the galvanizing solution will be polluted by oxidizing substances, whether its formula composition is within the process specification (exceeding the zinc content in the zincate galvanizing solution will affect the bonding force of the coating), whether the pretreatment of the workpiece surface Effectiveness and other aspects were explored, and the results were ruled out one by one. Finally, it was decided to find the cause from the source and check whether there were hidden dangers buried in the chemical degreasing solution.
When asked whether materials have been added to the chemical degreasing solution recently, the answer is that materials are often added, and a lot of . This is an excellent clue that when the concentration of water glass in the chemical degreasing solution is too high, the water remaining on the surface of the workpiece
The glass will inevitably increase accordingly. If the water glass is not washed out during cleaning, insoluble silica gel will be produced when it encounters acid, which will affect the bonding strength of the coating. According to the obtained clues and possible faults, after , the quality of the coating was greatly improved, and then the chemical degreasing solution was diluted!#! A glitch was finally resolved.
2. Excessive concentration of sodium hydroxide in the chemical degreasing solution affects the quality of the coating
When a factory prepared a chemical degreasing solution, because the cast sodium hydroxide was not easy to break, it put the whole large piece of sodium hydroxide in a snakeskin bag and hung it in the degreasing tank. It was originally intended to dissolve part of it and take it out. As a result, due to the heat release during dissolution, the dissolution rate is getting faster and faster. When it is about to be taken out, the sodium hydroxide has already been dissolved. According to calculations, the concentration of sodium hydroxide in the solution reaches 150g/L, causing a film layer to appear on the surface of the workpiece after degreasing, which affects the quality of the coating.
After testing, the effect of rinsing this workpiece in acid is not good. Although it can be brushed with a bristle brush dipped in furnace ash, it is impossible to brush all the corners. After diluting the solution sufficiently to the range of the process recipe, the problem was solved. It can be seen that the higher the concentration of sodium hydroxide in the degreasing solution, the better.
3. No surface inspection before chemical degreasing affects the degreasing effect
The chemical degreasing process has a good degreasing effect, which can not only emulsify mineral oil, but also saponify animal oil and vegetable oil. However, due to the limitations of process conditions and other factors, some workpieces with too much butter, paint
There is nothing that can be done to remove materials such as glue and even colloid. Therefore, the workpiece needs to be checked before chemical degreasing. When above-mentioned dirt is found, it must be removed by mechanical means or organic solvents. A certain unit just underestimated this process, and as a result, the workpiece was repeatedly repaired, which not only caused waste of energy, but also affected the work process.
4. The dirt in the screw hole affects the bonding strength of the outer coating of the screw hole
There are three possible reasons for this phenomenon.
There is oil in the screw hole. During electroplating, the oil stain dissolves and spreads out, forming a bright coating with a . Spiral before plating
When there is oil stain in the hole, wipe it with a cotton swab dipped in gasoline. After the oil stain is dissolved, the polishing paste in the screw hole can be wiped off. Polishing paste is more stubborn and difficult to wash off. It is better to use a knife to dig out , otherwise it will not only affect the quality of the product, but also seriously pollute the solution.
In the blind hole, the solution entered in the previous process cannot be rinsed off. If necessary, it can be sucked off with a medical syringe, or it can be shaken off forcefully.
5. Increasing the washing process is conducive to improving the cleanliness of the surface of the plated parts
Scrubbing after degreasing and derusting the workpiece is a traditional old process, which is no longer used in most cases, but this process indeed helpful for cleaning the surface of the workpiece, avoiding burrs on the coating, increasing the bonding strength between the coating and the substrate, and preventing plating
The appearance of "white hair" in the zinc layer has unique functions. Although the workpiece has been degreased and derusted, the decomposition products after treatment often remain on the surface of the workpiece, and it is not easy to automatically detach , but washing can play a unique role in this respect. For this reason, the author has intentionally carefully observed the "long hair" of the galvanized layer and the quality failures of peeling, blistering, burrs, and rust spots that appear too quickly on other coatings , and found that most of them are related to the cleanliness of the workpiece surface. For this reason, under possible conditions, it is , especially for poor surface cleanliness and sporadic fine parts.
6. It is not appropriate to replace chemical degreasing with a single scrubbing
For the sake of convenience, a certain unit adopts a single washing instead of chemical degreasing, because it is impossible to effectively wash away the oil stains on the corners, holes, slits, etc. of the workpiece, and the result is that the surface of the workpiece can be plated, but the parts that cannot be washed Places not only cannot be plated with metal due to dirt still present, but also contaminate the solution and require rework as a result.
7. The high temperature of chemical degreasing is not conducive to the utilization of energy
What is the appropriate temperature for the chemical degreasing solution? The author's opinion is that it should not be too high, and 70-80 ℃ (is more suitable . This temperature can fully meet the requirements of chemical degreasing. When the temperature is higher, although it can improve the solubility of saponification products, increase the speed of saponification and emulsification reactions, and accelerate The circulation of the solution reduces the viscosity of the oily substance, strengthens the convection of the degreasing solution, etc., but when the temperature is too high, the energy consumption will increase greatly, and the solution will evaporate faster, which is not conducive to the indoor environment and safe operation .
According to the author's suggestion, a factory changed the boiling temperature of the chemical degreasing solution to 70-80°C , not only the quality was not affected , but also the energy consumption could be saved by 1/4.
In order to further save energy consumption, the author also recommends switching to a normal temperature degreasing process slightly higher than room temperature, which is still in trial use .
8. There are fingerprints under the coating
There are two possible reasons.
The workpiece is not chemically degreased, but directly washed. When washing a large polyhedron, each side needs to be turned over by hand. When the hand touches the unwashed surface of the workpiece, it is stained with oil. For this reason, when washing such workpieces, in addition to avoiding dirty hands from touching , it is better to wash them again. When washing the second time, first wash the tools and hands first. Quality is a plus.
Hands were not washed during mounting (after degreasing), or workpieces were touched with dirty hands during plating.
9. Irregular crushed ice patterns appear on the surface of the galvanized layer
This phenomenon is caused by the ineffective degreasing of the workpiece and the expansion of the surface oil film to the surrounding during electroplating. The coating between "ice cubes" and "ice cubes" is bright white, and the surface of "ice cubes" is gray and dark (this is the case for nickel plating and galvanizing). When deplating, the coating layer between the "ice cubes" and "ice cubes" is removed first, indicating that there is more oil film on the base of this part, and the coating layer is gradually deposited later.
After a certain accident, two boards that had been degreased were taken, and one of them was additionally treated with a brush and galvanized under the same conditions. As a result, the quality of the two boards after plating was completely different. After supplementary washing, they were completely normal, but not After supplementary washing, there are still crushed ice-like patterns, which proves that the above analysis is in line with reality. To avoid such failures, degreasing in the pretreatment process needs to be effective.
10. Ineffective degreasing causes slow deposition rate of the coating, and marble pattern appears after plating
Insufficient pre-plating treatment process is directly related to post-plating quality. Quality problems all related to this. It is not easy to be plated because the surface of the plated piece is blocked by oil or oxide film. After the plated piece is energized for a long time, the marble-like coating appears. This kind of coating not only seriously affects the appearance of the coating, but also is thin and has high porosity, which makes it difficult to meet the quality requirements in terms of protective performance.
In this case, the electroplating should be stopped, the plated parts should be taken out, the pre-treatment should be carried out again after the coating is removed, and then the plating should be carried out again, otherwise the coating will inevitably fade.
11. There are rubbing marks under the coating
This phenomenon is left over during brushing. Generally, lye is mixed with white powder, cinder ash or brick ash as abrasives when brushing. This is conducive to the removal of dirt on the surface of the workpiece, but because these abrasives After wiping, the following measures need to be taken to remove it. Use a clean towel to evenly wipe the surface with rubbing marks in the water to completely wipe off the abrasives; rinse with pure hydrochloric acid to dissolve the residual alkaline substances on the surface. This kind of failure will no longer occur after the above method is processed .
12. Improper degreasing and rust removal make the coating appear yin and yang
A batch of sheet-shaped galvanized parts were plated by a factory, most of which only one side is good, while the other whole or part, there are also double-sided or part of the coating is either bubbling, or the coating is extremely thin, or even no zinc deposition, which is The first phenomenon is undoubtedly related to the fact that the workpiece is not dispersed and hung during degreasing and derusting .
It is understood that after the binding of these workpieces, dozens of pieces are hung together in the degreasing tank or derusting tank to complete the work. This does not meet the requirements. And the oxide film cannot be removed. In normal operation, the workpiece should be hung one by one, and the position should be moved once at a certain time. The factory has followed this requirement for many batches of tasks in the future , and this kind of quality problem has never happened again.
13. When degreasing, the workpiece exposed to the liquid surface affects the bonding strength of the coating
高温去油溶液的温度高达80-90℃，溶液易蒸发，这时工件在离液面较近的部位会先露出液面，并迅速干化，罩上含有肥皂等污物的碱膜，这层膜在酸液中是不易去掉，若电镀前未能被发现，镀上镀层后该部位必然暴皮。防备方法：要时刻注意去油槽液的液位变化，去油前补上过量的水，去油后的工件加强检查。
14、除油溶液配方单一影响镀层结合强度
化学去油溶液配方单一是不利于工件表面油污的有效除尽的。这是因为工件表面往往沾有多种性质的油脂，如矿物油、动物油和植物油等，为此化学去油要有既能使矿物
油脂的乳化，又能使动、植物油脂的皂化的双重作用。植物油中硬脂酸能与氢氧化钠发生皂化反应，但矿物油等非皂化油脂只能通过乳化作用才能除去。
某单位不According to油脂性质和去油要求，化学去油溶液中有什么料用什么料，结果常常因为达不到去油目的而发生镀层暴皮等质量故障。
防备方法：化学去油溶液需要According to工艺配方要求按比例配制，溶液中除氢氧化钠之外还需要配有具有良好缓冲作用的碳酸钠和兼有良好乳化作用的磷酸三钠和硅酸钠等相
配合，只有这样才能在互补的条件下除去工件表面不同性质的油脂。
15、除油温度过低影响镀层结合强度
常温化学去油效果是很好的，只是某单位单纯认为常温去油就是溶液无需加温即可除去工件表面的油污，当车间温度低于 !$%时仍在工作，结果由于温度达不到常温去油要求，难以有效除尽工件表面油污。
防备方法：采用常温化学去油的工艺方法时，室内温度低于 &’%时应将溶液适当加温，更好维持在 ($%左右。
16、工件在洗刷时未能移动位置而影响镀层结合强度
这一故障主要是在洗刷时未按先洗刷B面后洗刷A面（B面假设为工件的副面）有次序地进行和A、B面同在一只洗刷台上洗刷引起的，并与工件表面油污过多、事先未经有机溶剂洗刷等因素有关。
防备方法：在洗刷工件时要有序地进行，洗刷 * 面后不可在原地洗刷 + 面，否则留在台面上的油污会沾在工件的 * 面，前功尽弃；而且拿过未刷工件的手再接触已刷过的工件时也同样会造成二次污染。
17、电化学除油中程序错乱引起镀层起泡
某单位镀出工件严重起泡、掉皮，除油后的工件表面发灰，是什么故障呢？经多方寻找原因，最后在电化学除油工序中终于找到了答案。原来是正、负电极接错引起的。该厂在双向闸刀板上写（+）、（-）标志时位置写错，致使除油过程与工艺上实际要求的正、负极恰好相反。
除油工艺方法的利弊关系作如下简要剖析：
（1）单一阴极电化学除油的利弊。阴极电化学除油时阴极上所产生的氢气的体积是阳极电解除油时阳板上所产生氧气的 & 倍。为此，阴极电化学除油效果优于阳极电化学除油。阴极电化学除油的另一特点是不腐蚀基体，能有效地活化工件表面的钝化膜，对净化工件表面具有较好的效果。阴极电化学除油的不足之处是工件容易渗氢，引起氢脆，乃至镀层起泡、掉皮，当除油溶液中积聚过多的锡、铅、锌等金属离子时还会在工件的基体表面析出海绵状的沉积物，从而也严重地影响镀层质量。为此，According to上述利弊关系的比较，采取单一的阴极电化学除油是不适宜的。
（2）单一阳极电化学除油的利弊。阳极电化学除油时能将工件基体表面的有机物氧化分解，除去基体表面的残渣，不会发生氢脆。阳极电化学除油的不足之处是除油效果比阴极电化学除油差，有色金属不适宜采取此工艺方法，否则会产生严重腐蚀。当溶液中碱的浓度过稀或有氯离子存在时对钢铁件也会产生腐蚀。此外，若工件的狭缝等处进入的酸未能充分冲洗净时该处还可能出现棕色锈迹。故采取单一的阳极电化学除油也是不适宜的。
（3）先阳极后阴极电化学除油，因为阳极电化学除油时引起的弊端在阴极电化学除油时无法被遮掩，故此工序也是不可取的。故障实例举例如下。
某厂发现镀镍层常起泡、掉皮，撕下镍层基底呈灰黑色。开始以为是淬火件经酸洗后表面的游离碳未洗净，可是见到的除油后工件表面都很干净，没有氧化皮，表面污物也很少。于是，笔者取了几个工件简单的刷洗一下即进行镀铜、镀镍，镀后未见起泡、掉皮，说明镀铜、镀镍溶液都正常，问题很可能出在电化学除油过程中。由于该厂除油槽直流电源铜排未涂红、绿标记，无法辨认阴、阳极，铜排引出处又无法进入察看，为此笔者只好试着把电化学除油的极梗与直流电源铜排的连接处接触点对调后，让他们仍按原来的除油次序进行电化学除油，结果连续镀出三槽工件结合力都很好，显然该厂在工件电化学除油过程中阴、阳极除油次序颠倒，从而影响了镀层的结合力。
早期的电化学除油是在两个槽中分别进行的，即先在一个槽中进行阴极电化学除油，然后再在另一槽中进行阳极电化学除油，这样做在电化学除油全过程中绝少发生阴、阳极电化学除油次序倒错，也可避免处理时间的失控。近年来，为了减少车间占地面积、节省设备投资和日常生产中能源的消耗，二槽电化学除油方法已很少见，绝大多数是在同一槽内有序地改变电极极性来进行电化学除油，这种方法是可取的。阴极电化学除油与阳极电化学除油各有其作用和特点，但需要严格遵守先阴极电化学除油再阳极电化学除油的程序。
18、工件尖端部位无镀层沉积
工件的尖端部位无镀层沉积有以下两种可能：
（1）阴极电化学除油时电流过大。阴极电化学除油过程中电流过大时，工件的尖端部位极易沉上除油溶液中有机或无机杂质，有机质主要是油污，这些污物若在阳极电化学除油时，处理时间过短，则难以退尽，电镀时就可能出现上述情况。
（2）电化学除油溶液太脏。液面上漂浮着过厚的污物时，这些污物会随工件进出槽吸附在其表面上，若工件出槽后能在热水中漂洗，则污物极易被洗脱下来，若直接在冷水中洗，则由于油污会骤冷而紧附贴在工件表面，在后续的水洗、弱腐蚀过程中难以将其除干净，从而出现难以沉上镀层的缺陷。
解决措施：
（1）工件出槽前先在液下提几下（不要露出液面），使液面上的污物向四周扩散，在此瞬时之间迅速把工件提出液面，达到“出污泥而不染”的效果；
（2）加强溶液维护，液面上的污物用粗质无填料的纸吸附除去；
（3）适当延长阳极电化学除油时间；
（4）除油后先用热水清洗。
这类故障有时是因为电化学除油溶液蒸发，液面露出部分工件，这一部分工件因未能有效除油，从而无法沉积上镀层。
19、 弹簧件电化学除油后发脆
某厂镀出一批拉簧，轻轻一拉即断裂，邀笔者去找原因。一般情况下弹簧类材料镀后渗氢是有可能的，但不至于如此严重。先怀疑是酸洗时间太长了，据介绍并非如此，只酸洗14-2min，电化学除油与镀亮镍时间相同，约在15min 左右。据此情况，检查了电化学除油过程。原来电化学除油全在阴极上完成的，这完全违背了工艺要求。
最后调整了极性，并交待这一措施是针对该工件的。镀其他工件时需要要先阴极后阳极进行。这样弹簧件发脆问题得到了有效解决。
20、电化学除油引起工件腐蚀
电化学除油的工艺条件对质量影响较大的主要是溶液温度与除油时间，现就此两点分述如下：
（1）溶液温度
按常规工艺要求，溶液温度一般控制在60-70℃之间，由经验可知：溶液温度高虽然有其一定的优点，能加强工件表面油污的乳化作用，从而有利于提高除油效果。但溶液温度过高必然会引起室内碱雾弥漫，恶化环境，溶液蒸发加快。当溶液中含有较高的氯离子时还会加剧工件在电化学除油时的腐蚀，能源消耗也随之增加；溶液温度过低时除油效果明显降低，有时还可能出现锈蚀，为此，电化学除油溶液加温是必要的，温度过高又是不适宜的。
（2）除油时间
按常规工艺除油时间通常定为阴极电化学除油3-5min，阳极电化学除油 0.5-1.0min。在这个时间范围内完全能使工件表面的薄层油膜有效除尽，且对工件和镀层质量都不会产生影响。若在此基础上再延长，则无论对工件基材或镀层质量都是不利的，如阴极电化学除油时间过长引起渗氢，阳极电化学除油时间过长引起锈蚀等弊端出现。
本例质量故障就是未按上述电解除油的工艺要求，而是采取室温并长时间通电处理引起的。
21、电化学除油溶液维护不当引起的镀层质量故障
在电化学除油溶液的组成中，氢氧化钠浓度过低或硅酸钠浓度过高对除油质量影响甚大。
（1）氢氧化钠浓度过低时的现象。当氢氧化钠浓度过低时，首先是阳极区溶液的PH值下降，除油速度随之缓慢，放出氧气增加，工件表面开始遭到氧化，其表面出现附积物，甚至还会明显地出现棕色铁锈。故要定期进行化验分析或凭经验予以补充。
（2）硅酸钠浓度过高时的现象。电化学除油溶液中加入适量的硅酸钠有利于除油时工件表面油污的乳化，但当浓度过高时会吸附在工件表面，且极难清洗干净，结果必然会影响镀层的结合力。硅酸钠浓度过高多为加料时计算上的错误引起。可采用在稀释溶液后只补充其他材料的办法来解决，也可经电化学除油后用热水加强清洗来解决。
22、电化学除油槽中洗净剂过量引起镍层掉皮
某电镀厂因电化学除油用的抑雾剂断档，临时改用海鸥洗净剂。未曾料到工件除完油，离开溶液，通过液面上的海鸥洗净剂时，工件上迅速披上一层薄薄的海鸥洗净剂液。由于工件是在70-80℃的除油溶液中提出来的，表面温度很高，当即干化。有可能是由此干化，也可能是操作者蜻蜒点水似的操作方法，在清水和弱腐蚀溶液中均未能除去表面的洗净剂。结果镀出镍层连续掉皮，后来改在除油后加强在热水中洗烫，并增加弱腐蚀时间之后，问题终于得到解决。
23、电化学除油的对极不当引起的溶液故障
某厂电化学除油溶液犹如黄泥水，经了解该厂电化学除油的对极直接接在槽体上，工件在阴极除油时整个槽体就是阳极，槽体遭到氧化，溶液中低价铁离子也会由此而不断增加，最后导致出现这一污染现象。同时槽体作为对极除有上述不利因素之外，由于对极面积过大，当工件处于阳极位置时还会对工件引起腐蚀。
电化学除油更好选用镍板作为对极，也有用镀镍铁板的，但镍层要保持一定的厚度，较厚的镍层孔隙率低，鳞片状脱落的机会少。
24、电化学除油后工件的狭缝口堵有红褐色锈迹
这一现象经分析是工件酸洗时渗入到该处的酸未能有效冲洗干净，同时电化学除油又直接进入阳极除油而形成的。为避免上述现象，可将这类酸洗过的工件先在热水中浸泡，促使狭缝中的酸浸出来，同时改进电解除油程序，按正规的先阴极后阳极的除油过程进行除油，经此改变后问题得以有效解决。
25、电化学除油溶液表面的污物影响除油质量
电化学除油溶液的清洁维护重点首先是溶液的表面，在电化学除油的反应过程中，在分解油污的同时便会产生肥皂、甘油、硬脂酸酯等物质，这些物质及尚未与碱液起作用的游离油污悬浮于溶液表面，当工件进出溶液时即会黏附在工件表面上，严重地危害着工件的除油质量，这是引起镀层掉皮的重要因素。本例故障就是由此引起的，要除去这层漂浮物可用布网捞除，也可用粗质纸平贴液面吸去。
为防止这类事故再次发生，可在工件挂入除油槽时先在碱液中抖动几下，以漂去工件入槽过程中与碱液表面接触时黏附上的污物。工件出槽时也应先在碱液中抖动几下，并趁液面上的污物向四周扩散时迅速提出。
当发现槽底有污泥沉淀时，可先吸出上部清液于另一槽里，弃去沉淀物，洗净槽子后将吸出的清液吸回原除油槽中，补充不足部分的材料即可使用。
26、电化学除油后未热水洗而影响镀层的结合强度
工件在电化学除油后须经热水漂洗这是工艺上的需要，也是保证镀层质量的需要。因为工件经电化学除油之后表面留有碱液及油污被皂化、乳化后的产物，这些物质遇到冷水后会凝聚在工件表面。为此，经电化学除油后的工件需要经过80℃以上的热水清洗，只有这样才能有效除尽工件表面的污物，达到保证质量的目的。
27. Improper suspension of the workpiece during electrochemical degreasing affects the quality of the coating
A batch of box-shaped workpieces in an electroplating factory, after plating, the nickel layer with an inner corner was completely bubbling. According to the analysis, this phenomenon is caused by the presence of gas in this part during the electrochemical degreasing process. The nest gas affects the removal of oil at this part, and the nickel layer on the surface of the workpiece that has not been electrochemically degreased must be weak. During nickel plating, the cathode can be moved and the workpiece can be shaken continuously to prevent the adsorption of gas.
28. The workpiece is found to be rough after electrochemical degreasing
The surface finish of the electroplated parts in the electroplating workshop of a certain factory is greatly affected after electrochemical degreasing. The author was invited to participate in the discussion on this failure. According to this phenomenon, the influence of the low concentration of sodium hydroxide can be denied, otherwise it must be rust like corrosion, and it is impossible to be so uniform. Is it possible to be contaminated by chloride ions? If hydrochloric acid is mixed into the solution (generally, it is unlikely to be mixed in a large amount, and sodium chloride is added as sodium carbonate when adding materials, which should be easy to distinguish), it is difficult to check with silver nitrate, because the degreasing solution itself contains chloride ions It is prepared from tap water, and it is not worth treating if it is checked out. Finally, it was decided to prepare a new solution, and the replaced solution was used as a chemical degreasing solution.
