Question: In our electroplating shop, discoloration repeatedly occurs when coating various substrates (stainless steel, copper alloys) with nickel, tin or gold. The components are both filigree small parts and more complex geometries, some of which are coated in drums and some on racks. The discolorations appear as yellowish or bluish streaks on nickel, matt grey spots on tin and reddish to brownish tints on gold.
The problem seems to occur depending on the batch, but not with every coating series. It is noticeable that rack goods are affected less frequently than barrel goods. We suspect that the water quality (ion exchanger or city water) could play a role. Could these discolorations actually be due to problems with the water and how can we check this for sure?
Answer: Your description suggests that there is an intermittent or variable cause rather than a permanent fault in the process. As these are different substrates, coatings, process technologies and therefore equipment, the most noticeable commonality is the water supply. This can affect both fresh water and demineralized (demineralized) water. As this appears to be an extremely urgent problem, we would suggest a two-pronged approach.
Water samples
Take samples from the last rinses, both fresh water and demineralized water, from all the systems concerned, which you must test yourself or have analyzed externally, depending on the laboratory. The main focus should be on organic and metallic contaminants. Possible causes include surfactants, additives and traces of oil as well as various metals.
Localization
The final rinse is usually a flow or hot rinse. Both are normally operated with demineralized water. Temporarily replace this water with fresh water at the system and preferably in the process in which you most frequently notice the problem.
There are now three possibilities:
- The problem has improved or is no longer occurring. This makes it clear that the cause is to be found in the demineralized water.
- The problem has worsened. This suggests that your fresh water supply has been contaminated.
- There is no difference.
Should the third case occur, there may be several causes. It is possible that the stains already originated in a previous sink. To test this, replace all sinks with demineralized water with fresh water between coating and drying. Make sure that the sinks are cleaned properly before refilling.
It is also possible that the parts still have stains, but that the number and shape or size of the stains are different. This can also be an indication of the possible cause. It is possible that not only the sinks but also the electrolytes are contaminated.
" Although the water quality in Germany is very good, there may be major fluctuations in quality "
Causes of fresh water
Although the water quality in Germany is very good, under certain circumstances there can be major fluctuations or even drops in quality. This may be due to the water itself or the supply network.
For example, work on water pipes can loosen deposits of iron, manganese or organic substances that would otherwise remain in the pipes. In addition, burst pipes or connections to old pipes can introduce dirt and foreign substances into the tap water.
In the event of accidents or illegal disposal, chemicals such as chlorides, sulphates, nitrates and organic compounds can get into the water supply. Disinfectants used in waterworks can also enter the network in excessive concentrations. If a backflow occurs from a connected system (e.g. heating, industrial water treatment), chemicals or foreign substances can return to the municipal water network. Similarly, sudden pressure drops in the network can cause contaminated media to be sucked into the supply network from connected pipes.
Precipitation, periods of drought or melting snow can influence the composition of the water (e.g. through increased levels of organic substances and minerals). In stagnant bodies of water that serve as a source of raw water, an excess of nutrients (e.g. phosphates) can lead to microbial activity and organic residues.
A water analysis should at least tell you which substance or group of substances is responsible for the stains. This can narrow down the search considerably. First check the inlet to the electroplating system. If no fault can be found here, contact the waterworks immediately. It is quite possible that your company is not the only one affected by contamination.
Causes with demineralized water
If the ion exchangers are affected, there may also be several causes. In older systems, it is plausible that the resins are defective or even clumped together. There may also be a problem with the regeneration of the resins. In order to find a solution as quickly as possible, you should contact the specialist company for the ion exchangers. They will be able to check the resins in particular as quickly as possible. The same applies to the regeneration process. It may even be a software error.
If it really is a demineralized water problem and this cannot be solved in the shortest possible time because, for example, all the resins have to be replaced, a mobile unit would be a conceivable interim solution. Such systems can be rented and quickly set up and integrated. Although this is not elegant, it is considerably cheaper than an indefinite loss of production.
Further effects
Depending on the source of the contamination, this can lead to far-reaching problems. Pre-treatment, post-treatment and electrolytes would be affected. In case of doubt, we recommend completely replacing the pre-treatment as soon as the cause has been found and rectified in order to prevent further carry-over into circulation systems and electrolytes. The same applies to post-treatments such as passivation.
The electrolytes should be examined in detail in the laboratory. Depending on the concentration of the impurity, you may not notice any difference and the impurities may degrade over time. It is best to contact the supplier of the bath chemicals and discuss the optimum procedure. If there are any effects, it may be possible to remove contaminants using selective cleaning or an adapted filter system.
"The close contact of electroplating plants can be an early warning system to detect problems in the fresh water supply "
Other possible causes
Although it is most likely that the problem stems from the water supply, this is not necessarily the only possibility. A problem with the drying process is conceivable if, for example, the drying air is heated at a central location and becomes contaminated here. Such problems are also known from contaminated compressed air.
There are also hygiene aspects. Organic residues could be caused by biofilms or microbial growth. Such residues are not always easy to detect and could be an indicator of a poorly cleaned pipe system or tanks. Organisms could originate in one place but spread throughout the plant via circulating water and disrupt the processes as described.
Another option would be deliberate sabotage. This possibility should be considered if, after the problem has been eliminated, the difficulties "suddenly" reappear and cannot be explained naturally.
Future measures
As the situation described is almost an existential problem, appropriate measures must also be considered, depending on the cause of the error, to prevent this from happening in the future.
In addition to one-off samples, continuous monitoring could be useful, especially if creeping contamination due to temporary events or fluctuations is suspected. Automated sensors could help with this.
Detecting changes at an early stage
In addition to testing fresh water and demineralized water, it could be useful to inspect the entire water pipes and circuits in the electroplating plant. Contamination could collect in dead pipe ends, filter housings or poorly rinsed tanks. This may not be the current cause of your problem, but could lead to a future problem.
If there is evidence of problems in the fresh water supply, other companies in the area may be experiencing similar difficulties. Talking to other electroplating or water-dependent companies could provide further clues. Closer contact between the companies can serve as a kind of "early warning system". If there is an underlying problem with the water supply, the companies can work together to exert greater pressure on the waterworks and the local authority responsible in order to bring about a change in the situation as quickly as possible.
