Effects of Temperature

Summertime is here, causing an increase in the ambient temperature. Most plating shops are not air-conditioned and are impacted by this temperature increase. As most of you know, many of the process are greatly affected by temperature change.

Chemical Films, Cadmium, Zinc, Deoxidizes, Passivate, Conventional Brass, Tin/Lead, Pickles, Acid dips, Descalers, Acid Etches to name a few are adversely affected by temperature.

The chemical reaction rate of chemical films, chromates is increased do to the increase in temperature, which may be compensated for by reducing the immersion time. Some operators will reduce the concentration by about 15% in order to maintain the same immersion times especially if temperatures are excessive. Some operators have installed low wattage heaters, maintaining the solutions (Alodine, Iridite, cadmium, zinc, etc.) at a year around constant temperature. This allows the same immersion time year around with no alteration of chemistries. Most processing facilities generally do not consider this during the summer. The increase in deposition rate, porosity, etching, and coating weight has considerable impact on the corrosion resistance of a chemical film coating. In most cases, this increase in temperature is just enough to cause the coating to become micro porous in nature and there by reduce its corrosion resistance.

Some Descalers and pickles generate heat during use. In summer months, the starting temperature of these processes is higher and so will be the ending temperature. If pitting or smutting occurs, install a coil of appropriate material (chiller) in the tank and circulate water from a nearby fresh water rinse tank. This will stabilize the temperature to near normal with no increase in water usage.

Deposit color of Conventional Brass solutions change with temperature. These solutions are normally run at ambient. If the temperature becomes excessive, most of the problem can be eliminated by installing a small heater, maintain the temperature around 110 to 120oF, then readjusting the copper/zinc ratio and free cyanide to regain desired color. The temperature of the solution will be stabilized for summer and winter.

Acid etches tend to increase etch rate at higher temperatures. If the temperature becomes excessive the etch rate can be unacceptable for a given dwell time. Dwell times can be reduced or a chiller can be installed to maintain the temperature at a more acceptable level. Some proprietary etches tend to cause pitting if temperature becomes excessive. The temperature limits are generally reported in product literature.

Some processes require no drying between steps. During the hot summer months, long transfer times can be a problem due to drying. The drying can leave unwanted surface residue, passive surface and rewetting problems. Care should be taken to reduce the transfer times in order to reduce or eliminate this problem. One idea is install misters around the transfer area, these can be purchased at any garden or landscaping supply house and consume about ½ gallon per hour of water. They help keep the surface wet and at the same time reduce the ambient air temperature around the tank acting like an evaporative cooler.

We hope some of these suggestions might help eliminate or reduce some problems, which occur during the summer months.

Thank you,

Bruce
July 2008