La Necesidad de Control de Proceso en Sistemas de Galvanoplastia

This does not mean that the other baths are unimportant; they are crucial as well. However, the plating bath has the highest priority. An unhealthy plating bath consistently results in poor quality deposits, higher rejection rates, and escalated production costs.

Fortunately, the hexavalent chrome bath is quite tolerant of reasonable impurity levels; in fact, it is one of the most forgiving of all electroplating processes. But that does not mean it should be mistreated. Quite the contrary, the chrome bath operates best when its ingredients and impurities are controlled within fairly narrow limits. The worst mistake a plater can make is to wait until a problem develops before testing the bath.

Critical Bath Ingredients

The hard chrome bath operates with only two main ingredients, chromic acid and sulfate. High-efficiency baths may include 1-2 additional catalysts, but nevertheless, chromic and sulfate levels are the most critical. These two components require frequent testing and control. It is very common for excess sulfate to enter the bath unbeknownst through water supply and impurities in the chromic acid used. Increased sulfate disrupts the chrome:sulfate ratio, resulting in a series of plating issues.

Sulfate is a true catalyst, meaning it is not consumed during electrolysis. Its concentration increases only by drag or addition to the bath. The sulfate level never decreases; it is naturally lost only through drag, a tank leak, or overflow. This, coupled with its huge impact on plating quality, is why it needs to be monitored and controlled closely.

On the other hand, the level of chromic acid gradually decreases in relation to the amperes-hours plated. The consumption rate of chromic acid is typically around 100 lbs every 400,000 amperes-hours of plating if Zero Discharge Recovery is employed for rinsing and venting systems. It will be significantly higher if Zero Discharge is not utilized.

Common Practices

Many hard chrome shops lack internal analysis capabilities and fail to see the need for closer bath control. This is a major mistake because maintaining the proper CrO3:SO4 ratio is incredibly important. Without this control, deposit quality, and therefore the profitability of the operation, decreases rapidly.

Old-school platers simply relied on a hydrometer to measure the Baumé (or density) of the bath as an indicator of chromic acid levels. This practice is entirely inadequate because the Baumé reading includes impurities in the bath, such as trivalent, iron, and copper. Therefore, the chromic acid level will always be lower than what the Baumé indicates. This disrupts the critical balance of the supposed chrome:sulfate ratio.

Another mistake is that many custom and captive hard chrome platers rely solely on their suppliers to conduct bath testing. This is problematic on several fronts:

• The time from when a bath sample is taken, received at the external lab, and results returned typically spans several weeks, with 2-3 weeks being common in many cases.
• The bath has changed significantly with ongoing production during this time. The results obtained, therefore, are irrelevant as they do not reflect current conditions. Accordingly, chemical additions made based on these reports are never correct, and the bath continually remains out of balance.
• To make matters worse, it is common for some shops to wait until a quality problem arises before conducting a bath analysis. This worst-case scenario leads to enormous production, product quality, and profit issues.

Our laboratory specializes in hard chrome bath analysis and receives samples from all over the United States and abroad. Over the past thirty years, the experience indicates that many bath samples were sent in to resolve quality problems that directly related to the chromic:sulfate ratio imbalance. This would not have been the case if these shops had their own internal analysis capabilities.

What Needs to Be Done

At a minimum, a chrome shop should have the capability to test its chromic acid and sulfate levels internally. The frequency of bath analysis is based on maintaining the desired chemical balance within 2%-5% limits, with a 2% variation being more desirable. Most operations will find that doing this once a week meets that requirement.

The equipment required for an internal lab is not excessively expensive relative to the benefits gained. The space needed is not prohibitive either, and 4-5 bath samples can typically be processed in an hour once the operator is familiar with the procedures.

Higher production operations may also want the capability to test their secondary catalyst, trivalent, and impurities like iron, copper, and chlorides. However, these tests require additional equipment and operational expertise. Typically, using an external lab to verify these items is viable since their levels do not change rapidly, and minor changes do not affect plating quality. This does not mean that their concentrations can be ignored; quite the contrary, it simply means that having them tested monthly is generally adequate.

Who Should Do This

The task of taking a bath sample, conducting the analysis, and making additions to the bath should be delegated to a single person. Utilizing multiple employees for this invites confusion and potential issues. The best person for this is often the primary shift foreman or plating supervisor.

Laboratory Requirements

Old-school box test kits are inadequate for today's process control requirements. Professional lab equipment is more durable and provides better results. There is a massive difference in the accuracy obtained between using a test kit and using a dedicated lab with reagents, glassware, and professional quality procedures.

The internal laboratory does not need to be excessively large or complicated, but it is better to use a small enclosed room. An area of 10 x 10 is sufficient if used solely for testing chrome and sulfate. Ideally, this would be located near the plating line but away from any polishing or machining operations so the lab remains free of airborne waste. Ideally, this room should be air-conditioned. This lab setup does not need to be elaborate; generally, all that is needed is as follows:

1. Several work tables with kitchen-style cabinets below to store laboratory glassware. Ideally, the surfaces of the tables would be covered with durable plastic; a 1/4 PVC coating is ideal. Having a backsplash and a top shelf along the back of the work tables is a good idea.
2. Several cabinets or wall racks to store various reagents.
3. Good fluorescent lighting, hot and cold water, and a small deep sink with a gooseneck faucet.
4. Several double electrical outlets, or power strips, distributed along the walls behind the work tables.
5. A desk and file cabinet to store lab records, a small computer, and a calculator.

Backup Testing

It is also recommended that bath samples be sent to an external lab regularly for backup analysis. This is necessary to test other bath ingredients, as well as the catalysts used, and to verify the accuracy of internal chromic and sulfate tests. This lab should also test chloride, trivalent, iron, and copper impurity levels. It is highly recommended to use a lab that specializes in hard chrome technology for this.

The frequency of conducting backup analysis will vary with the amount of plating work and tank volumes. Most shops find that doing this monthly is sufficient. The goal is to track the accumulation of impurity levels before they cause plating problems. This prevents the huge peaks and valleys in quality that some shops experience. The result is the consistent production of high-quality deposits from month to month and year to year. It can also eliminate or significantly reduce the volume of rework required.

The level of chlorides is critical because it is a very potent contaminant. It should always be below 50 ppm, and it is recommended to keep it below 20 ppm.

Aside from creating plating problems, these impurities also decrease process efficiency, thus increasing plating time and AC electrical costs.

The level of trivalent chrome is also important and should be maintained at around 1% (as a percentage of hexavalent chromic acid); it becomes an impurity when it exceeds much beyond 2%.

Iron and copper impurities become problematic when they are above 5 g/l individually or 5 g/l total when combined. In fact, copper has a much stronger negative effect than iron, so it should be kept as low as possible.

One reason these impurities cause problems is that they form chelates (bind) with hexavalent chrome, thus upsetting the usable sulfate ratio. They also increase the electrical resistance of the bath, requiring either an increase in voltage or reduced amperage. Besides causing plating problems, these impurities also reduce the efficiency of plating, increasing the plating time and AC electrical costs.

For instance, a chrome bath sample was recently sent to our lab in hopes of resolving a significant plating quality issue. It was a seven-year-old bath containing 5% trivalent and 23.2 g/l of combined iron and copper, resulting in a TCL of 28.2. This is almost 4 times the maximum recommended TCL and equates to 348 pounds of stray dissolved iron and copper in the 1,800-gallon solution. It is no surprise that it could not successfully plate anything. Unfortunately, that bath had to be disposed of and redone because there was no economical way to save it. The high cost of replacing that bath significantly impacted the company's profits. Its high operational costs, poor quality, and loss of customer satisfaction could have been avoided if that shop had simply utilized better process control. A properly operated and controlled chrome bath can last over fifty years and still perform high-quality electroplating.

But you cannot control your impurities, or other bath ingredients, without conducting routine bath analysis and monitoring impurity levels.

However, many hard chrome platers do not make a serious effort to control the impurities in their bath, allowing them to accumulate to a level that creates serious plating problems. At that point, they stop using that bath or dispose of and redo it, a very costly matter. In the meantime, their quality, efficiency, and profits continuously decline, and they may have lost one or two customers along the way. All of this could have been prevented simply by keeping their TCL between 4.8 - 7.2.

But you cannot control your impurities, or other bath ingredients, without conducting routine bath analysis and monitoring impurity levels. TCL should be tracked over time so that treatment can occur once it reaches 7.2. That is why it is so important to have the internal capability to test the basic ingredients of the bath and then regularly use a qualified external lab to check catalyst and impurity levels.

The cost of this service is compensated many times over with improved plating quality, reduced rework, and significantly lower operating costs. Using an external laboratory for backup and support testing should not be viewed as an expense; it is an investment in quality control that pays off multiple times with a better market position and increased profits.

The Benefit

Rework due to bath imbalances and excessive impurities is a very costly issue because the piece must undergo stripping, reconditioning, and re-plating. This cost is at least 3 times greater than getting it plated correctly the first time, and probably even more. This additional cost cannot be passed on to the customer, and therefore must be absorbed.

Hard chrome platers controlling their bath ingredients within a 2%-5% variation and managing their impurity TCL within the 4.8 - 7.2 range have significantly lower operating costs, higher production efficiencies, and reduced rework rates. These factors directly relate to increased profitability and even long-term sustainability.

The 21st-century industry demands on-time, high-quality deliveries. One of the best ways to meet these objectives is to take control over the electroplating bath and keep it healthy. Platers who adhere to this concept will thrive, while those who ignore it, well, not so much.

All that is needed for this operational improvement is better process control. The cost of doing so is compensated enormously, and it pays off many times over. It is not just a quality issue; it is also logical and makes business sense.

Eric Svenson Sr. is CEO of Plating Resources, Inc., in Cocoa, Florida. Visit www.plating.com or