It is easy to become complacent as we run our businesses. As many say, “We get stuck inside our comfort zone.” To stay competitive, metal finishing operations must continually search for ways to improve their productivity to maximize profits.
Acid Zinc Chloride Plating Solutions
Many finishing companies operate acid zinc chloride (often called chloride zinc) plating solutions due to the faster plating speed achieved and the ability to plate directly on hardened steel. Yes, alkaline zinc offers you distinct advantages like excellent plate distribution as seen in the old, high cyanide bearing processes.
The Challenge:
Our customers often tell us that they have difficulty meeting their client’s demands without increasing their overall cost. Areas of focus for our customers are minimum plate thickness and production requirements. Rework, as a result of failing to meet their minimum thickness requirements, can often be a major challenge.
The Solutions:
Key fundamentals can be applied which can increase productivity and improve overall quality and maximize profits.
Increase the Bath Temperature
This increased plating rate can allow more parts to be processed in a plating barrel, or more parts can be plated on racks to achieve the same thickness requirements. Brightener cost may go up do to the higher operating temperature, but the potential overall production throughput should outweigh the drawback of the increased brightener consumption.
Chloride Baths
Increasing the bath temperature of the plating solution will increase the conductivity of the solution. As a result, lower voltage is required to obtain the specific current density (or adequate amperage) to meet production requirements. Cost for electricity is a big expense, which ultimately affects the bottom line. Not only is there an energy savings (less kilowatt hours consumed), but the parts plate faster, in many cases up to 20 percent or higher.
A mixed chloride bath containing Potassium Chloride (KCL) and Ammonium Chloride (NH4CL) or Potassium Chloride (KCL) and Boric Acid (3.5 – 4.5 oz/gal) electrolytes are commonly used. NH4CL contains 66 percent by weight CL ion compared to the 48 percent by weight CL ion in KCL. Less NH4CL will be required to increase the chloride concentration. NH4CL at 4-6 oz/gal concentrations are most common. Waste treatment issues could occur, but many customers don’t feel this is an issue.
Both Boric Acid and NH4CL buffer the pH and provide high current density burn control. In situations where NH4CL can’t be used, Boric Acid is used as the replacement. Pollution control systems can’t tolerate Ammonia because of its potential complexing nature, especially where multi-metals are being treated or where city water treatment municipalities impose limits. Full NH4CL electrolytes (30 oz/gal or higher) can also be used since they have a much higher current density tolerance (reduced burning characteristics). The increased production throughput is a key advantage because of its faster plating rate. However, the higher concentration can increase treatment and disposal costs. The advantages in increased production throughput offset the drawbacks.
Higher total chloride concentration (18 oz/gal – 22 oz/gal) will improve the coverage in the deep recesses or low current density areas (LCD), and improve the distribution of plate ratio of high current density (HCD) to LCD thickness. These ratios can be reduced (as seen with non-cyanide alkaline zinc), which will reduce the zinc buildup in the HCD and increase the zinc thickness in the LCD.
Solution Operation Temperature
Acid chloride zinc barrel electrolytes are highly wetted (as a result of organic brightener additives) which reduces the solution surface tension. Drag-in is greater than drag-out. Solutions often require bail out in the plating tank which can place a huge burden on waste treatment systems (i.e.-increased sludge, increased treatment cost, etc.).
Increasing the solution operating temperature will improve the evaporation rate of the solution. Many plating operations will utilize evaporators (i.e.- atmospheric, etc.) to ease the burden of solution growth and reduce metal in the rinse waters. Counter flow rinsing is utilized which reduces the zinc metal concentration being discharged to waste treatment.
If sufficient evaporation occurs in the plating tank the rinse waters can be returned back into the zinc bath. Operating the plating bath at a higher temperature (more than 110 degrees Fahrenheit) increases the evaporation rate.
Cloud point should be monitored. This tells you where the organic solubility point is with the plating bath. Oil-out can occur if the operating temperature reaches or exceeds the cloud point. Maintaining a high cloud point is important. The proprietary brightener package and proper solution maintenance are critical.
Asterion offers zinc systems that can operate at these elevated temperatures, thus allowing the customer to benefit from the increased temperature as outlined above.