Meeting Thickness Requirements in Bright Nickel Systems

Q: We are having frustrations with our bright nickel system, especially with corrosion in the low-current density areas (LCDA) of parts. Do you have advice on why we are not meeting minimum thickness requirements in the normal cycle time?

A: I had this same situation come up during a recent trip to a decorative plating shop. They were even starting to look at switching nickel chemistries in order to fix the problem. The first thing we did was review the chemistry and make sure that all the bath components (NiSO₄, NiCl₂, H₃BO₃, Carrier, pH) were at optimum. We then ran hull cells to review the overall appearance of the deposit. Next, we measured the surface area of the part to ensure they were plating at the proper amp per square foot. Finally, we went out to review the line and that is where we found many things that were helping create these problems.

The first thing we noticed was salt formation covering not only the anode rails but also the flight bar. The first flight bar that we came to in the loading area had salts that were almost an inch thick underneath the rack head. As we came up to the nickel tanks, we noticed that the anode bags were completely brown and looked like they were plugged. After talking to the plating technician, he said that they only change the bags 1-2 times per year, and that they pressure wash them once per month.

We recommended having them clean a few flight bars and change the anode bags in one cell of the bright nickel to see if this makes a change. Afterward, their thickness increased by 25 percent (allowing them to meet their minimum requirements) and the corrosion issues in the LCDA went away.

In today’s world, most plating shops do a very good job of analyzing and controlling their chemistry, but what separates the great shops from the average shops is the attention to the systems around the chemistry that make plating work. Here are five areas outside of the chemistry where plating shops can benefit greatly by giving them a little attention:
Chemistry Feeders and Probes: Like any technology, they are great when they work, but can create nightmares when they don’t. In order for them to work properly, they should not only be maintained by changing tubing, cleaning and so forth, but they should also be calibrated and audited. A good rule of thumb for pH probes is to verify the pH by using a hand-held meter at least once per shift. Then have the probes removed, cleaned and calibrated once per month as part of your maintenance plan. For feeders, I like to audit them once per week. This can be as simple as pulling the line from the tank and having it pump into a graduated cylinder to ensure that when the pump says it is delivering 100 ml, that the correct amount is being delivered.

Anodes, Anode Baskets and Anode Bags: Node maintenance is critical to producing a consistent, quality finish. Anode rails should be covered (or periodically cleaned) to prevent salts from drying on them and creating electrical resistance. Anode baskets should be filled during maintenance to ensure you have the proper anode surface area. This is typically done on the weekends. Anode bags should have the proper fit and be cleaned or replaced when needed. The timing of this will vary from shop to shop, but a good rule of thumb is to replace bags when they are torn or when you can notice a difference in the time it takes the anode bag to drain.

Filters: Filtration is a key factor in the success of many plating shops. Not only does filtration allow you to remove particulates from the plating solution, but it also allows you to purify the bath by adding carbon to the filter. A flow meter on the discharge of the filter is an easy way to ensure you are getting the number of bath turns per hour that you expect. You can also schedule your maintenance and filter change outs based on pressure readings. This is because as the filter begins to fill with particulates, the pressure inside the chamber will increase. For nickel plating, it is also a good idea to periodically add smaller amounts of carbon throughout the week, instead of adding it all at one time. This will allow the solution to continually see fresh carbon while it is filtering.

Racks and Barrels: These should be maintained based on your shop’s requirements for quality. A POP shop’s rack stripping∕maintenance requirements will be much higher than someone who is rack- or barrel-plating acid zinc. The coating of the racks should be periodically inspected to ensure there are no holes and the contacts aren’t broken from the splines. Barrels should be inspected to make sure the perforations are not plugged and the electrical connections to the danglers are sound. If any problems are noted, they should be corrected as soon as possible.
Rectifiers and Electrical Connections: Many shops take rectification for granted and assume it’s always the same. But just because the display on the rectifier is saying that it’s producing 2,000 amps, it doesn’t mean you are getting those amps at the workload. You can lose current from numerous places, but a common place is due to resistance in the bussing. It is wise to include cleaning bussing connections and saddles as part of your maintenance plan. I recommend cleaning the saddles weekly during your maintenance activities and having the maintenance department disassemble and clean the connections in the bussing once per year.

In my experience, another thing that has worked is to have your maintenance department invest in a thermal imaging camera. This will allow you to scan your electrical system and determine where you are generating hot spots—which are a sure sign of resistance in the electrical system. Once you identify where the problem areas are located, you can take the proper steps to fix them.