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 Affects
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
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Over the years, we have found that many of our customers and clients,
requesting tests, did not know what they were, their purpose or what the
information could or would do for them. With that in mind, starting in
2008, we will be publishing a "newsletter" here covering the issues
listed below and more. If you have a question concerning a test or
procedure you would like to know more about, just
e mail us and we can include your topic.
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Taber Abrasion Testing
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Salt Spray Testing
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Analytical Protocol/Lab set up
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Preparation of Monthly Test Panels
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Reasons for test panel failures
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Passing Chemical Film salt spray
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Passing Type I Anodize salt spray
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Micro hardness failures on test coupons
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Conversion charts and graphs
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Various routinely used formulas
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Plating Alloys (Sn/Pb, Cu/Zn, Cu/Sn, Ni/Sn,
etc.
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