Page 52 - CFCM Jan-Feb-2021_Neat

PLATING AND ANODIZING: AIR POLLUTION CONTROL EQUIPMENT

CONTROLLING AIR

EMISSIONS IN ANODIZING

AND PLATING

ontrol of emissions into the air is an issue for a broad range There are various types of wetting agents and fume suppres-
of industries. However, metals finishing has a unique set of sants in use. Surface-active fume suppressants go directly into the
Cproblems that need effective technologies to reduce their chromium plating bath.
potential health hazards. Some types produce a foam that helps suppress the mists
Metal ions themselves, along with the compounds formed produced on the surface of the bath, while wetting agents directly
from them, are constantly emitted into the work area, posing a affect the surface tension in the bath to reduce the misting effect.
potential threat to workers, and also to other businesses or homes Reducing the surface tension cuts the potency of the bursting of
close to the plant. Any anodizing or plating operation needs to the bubbles, resulting in less misting. Mist suppressants are
ensure it does not incur expensive legal penalties or civil organic compounds with components have opposing solubility
litigation through failing to protect its workers as well as its tendencies, typically an oil-soluble hydrocarbon group and a
immediate neighborhood. water-soluble ionic group.
The best known, and perhaps the most studied, problem today is Still, whatever measures are used to reduce the airborne emis-
emissions from chrome plating. While hexavalent chrome, the sions, some degree of emission still occurs. At this point, custom
most hazardous version of the metal, is being phased out of many extraction systems and specialty air evacuation methods need to
applications in favor of trivalent chrome, complete elimination is cut in, to ensure that safe levels of breathability are maintained
not really possible. throughout the manufacturing cycle.
Hexavalent chrome, or the chromic acid that is given off Viron International Corp. has been producing scrubber systems
from plating processes, is both toxic on its own and a recognized since 1971. Its Viro Chrome 9000 Series was designed to meet the
carcinogen. stringent California Hexavalent Emission requirements along with
Chrome plating is a process whereby a thin layer of chromium is US federal emission standards. The system, Viron says, has exceeded
deposited electrochemically onto another metal that serves as the these requirements of 0.006 mg/amp hour of chrome emissions.
substrate. The process results in significant gassing from the pro- The 9000 Series is available with the scrubber housings made in
cess tank, with the gases rising to the surface as bubbles (more than either PVC – (Type I, Class1) and fiber-reinforced plastic (FRP)
80 percent of the electrical energy used in plating produces is not modes. PVC is well established for its chemical resistance, and the
the actual metal deposition, but the gas bubbles). FRP version is made from Hetron 197 or its equivalents.
Most of these bubbles burst at the surface, forming aerosols (mist- Viron manufactures its scrubber housing utilizing a 10to 20 mil
ing) that are then released to the atmosphere. These aerosols consist veil liner followed by an 80 mil chopped corrosion liner. The
of the process liquid containing chromic acid, and without the use of a housing is then covered with a structural layer of FRP and a UV
mist suppressing agent, the environment becomes contaminated. inhibited gel coat.
The moisture eliminator uses a three-
stage knitted type mesh pad made of poly-
propylene. This series of mesh pad type and
configuration has been designed to meet
the California regulation.
PVC spray nozzles are employed in each
of the chrome scrubbers. These nozzles
spray the mist eliminator pads to keep the
chrome from building up and clogging the
pads. The spray nozzles will be sized for a
range of .25 to 1 gpm per square foot of mist
eliminator pads.
All spray header pipes from Schedule 80
PVC pipe. Each spray header has a Sched-
ule 80 true union, which facilitates removal
and maintenance of the spray nozzles.
A vertical scrubber from Mech-Chem. Mech-Chem Associates Inc. designs,
fabricates and installs scrubbers for all
types of chromium-using applications, in-
52 CANADIAN FINISHING & COATINGS MANUFACTURING JANUARY/FEBRUARY 2021