Prevent Plating Problems with Critical Inspections

Q: We are continuously reprocessing a lot of scrap work. An issue pops up, we fix it, then something else goes wrong. Everything is reactive, and we are running behind because we cannot run consistently. How can we get things back in order?

A: Every reworked part will cost the company money through time lost on the original run and the time it takes to strip and send them back through. What is the first thing you do whenever a quality issue occurs on your plating line? Action must be taken quickly, but where should you start? The best course of action is usually taken before a problem arises. Tanks and their contents should be regularly inspected visually and analytically where possible. Analytical results of the chemistry should be logged and ranges where your process produces parts of the best quality should be recorded. When a quality issue arises, you should be able to quickly pinpoint where the main issue is occurring by checking which parameter is out of line.

Common issues with coating quality can manifest as blistering or flaking, often caused by problems in pretreatment. Acid and alkaline pretreatment tanks should be monitored for concentration, temperature and dip time. Oil slicks in the corners of alkaline pretreatment tanks could indicate the chemical concentration is too low or the end of life of the bath has been reached. The surfactants within the cleaners can only hold so much oil before becoming completely saturated and will not hold any more, despite additions of chemistry. An oil split test and alkalinity titration could help diagnose the problem. Alkaline cleaning chemistries are often operated at elevated temperatures to remove oils, soil, and so on. Something simple like noticing the lack of steam coming off a soak or electroclean tank could save time in the event of an adhesion issue. The heater may have gone out, or it was not turned on at the start of the day.

In an electrocleaner, running parts with too much current can cause discoloration and subsequent adhesion issues. However, applying too little current may not effectively scrub the surface of the part in the time allotted. Make sure the amperage or voltage is where it should be when an issue pops up. Like most chemistry, pretreatment tanks need time to effectively clean the part’s surface. Running parts too quickly, whether intentional or not, might not allow enough time for the chemistry to do its job. Conversely, an extended dip time could adversely affect parts coming out of the acidic tanks. This adds additional contaminants into the pickle solution and generates smut on the surface of the part and lowers the lifespan of your tank.

Other problems, such as a cloudy finish, low thickness, treeing, star dusting, pitting, and so on can often be traced to the plating bath itself. These chemistries should also be monitored visually and analytically as often as possible. Attributes such as solution color, clarity and temperature are quick and simple checks that can be done several times a day while passing the tank. Many of the chemical analyses required for good process control can be done through titrations on the line or in the lab. But some analyses cannot be determined on site due to instrumentation requirements or an unknown analysis method.

What should you do if your process is producing an out-of-spec product and everything else checks out in the plating tanks, or you don’t have the ability to analyze it? For example, parts coming out of the bright nickel tank are flaking. Review the known acceptable ranges for each process tank and compare them to those you checked in the current samples. Start the troubleshooting process with the pretreatment tanks because adhesion issues are often caused by pretreatment issues. However, the cleaners and pickle tank are operating properly both visually and analytically. A good quality system and analysis records would indicate that the last time there was flaking of your bright nickel parts, the nickel carrier was low. The analysis for nickel usually requires a UV spectrophotometer, so you cannot check it now. However, the last few analyses from the outside lab show the carrier trending downward, close to the lower limit. A small carrier addition is made to bring it within acceptable range and the flaking dissipates. Send a sample to the lab for analysis to fine-tune the chemistry concentration as soon as possible.

When things seem to be within acceptable ranges on the chemical side, the search must expand as chemistry is not the only variable in the plating equation. All equipment that goes into a plating line must operate effectively for proper plating. Get eyes on how the hoists for your racks and barrels look. Some things to consider: if the racks or barrels and their connections are worn down and by how much; if there are any spots where racks might get caught; or if there is enough grease on the track to keep things moving but not too much to drip into the tank.  

Rectification is a crucial piece in the plating process. How often are your rectifiers inspected and checked for ripple? Plating functions best when alternating currents are kept to a minimum. Some newer plating baths, like trivalent chrome, can only tolerate an extremely small amount of ripple before issues start to manifest on parts. Keeping records of the current and power applied to the process can diagnose many issues quickly. For any ultrasonic cleaning process, when was the last time the transducers were checked? They can fail periodically, and it is not noticeable until there is an adhesion issue on the line.

If you like automation in your process, there is likely a feeder pump set up somewhere on the line. These feed liquid chemistry to your tank. The feed rate can be based on amp-hours (the number of amps that occur in a one-hour period), pH, ORP, and so on, depending on the tank type. The tubing will become loose over time in these automatic pumps. Therefore, regular inspections and calibration checks of this equipment are critical to ensure the desired amount of product is being added whenever it kicks on. This can be done simply by gathering a graduated cylinder or beaker, artificially turning on the pump and measuring the amount of liquid delivered in that cycle. This is critical when feeding brightening chemistry into a plating tank, as they will often cause quality issues if over or underfed. A proper preventative maintenance schedule will assist in avoiding most of these equipment-related issues.

Familiarity with the process and good recordkeeping can usually help solve an issue quickly, even before it happens. Take notes of issues whenever they occur. Tie those notes with past analysis and you will quickly recognize and remedy a situation before it manifests itself onto the parts you’re plating. When in doubt, contact your chemical or equipment vendor or get one of the many plating handbooks concerning your finish. They are fantastic references and will give you a leg up on solving any issue.

We could keep going with different specific examples, but the point is this: “An ounce of prevention is worth a pound of cure.” – Ben Franklin.