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chromium. The thin, decorative bright chrome is the most
common form of chrome plating. Chrome plating imparts a
mirror-like finish to items such as metal furniture Chrome
plating is a kind of finishing treatment that utilizes the
electrolytic deposition of frames and automotive trim.
Thicker deposits, called hard chrome, are used in industrial
equipment to reduce friction and wear and to restore the
dimensions of equipment that has experienced wear. There are
two types of chromium plating: industrial and decorative.
Industrial chromium plating is also called Hard Chrome or
Engineered Chrome. There are two types of Industrial
chromium plating solutions: hexavalent chromium baths whose
main ingredient is chromic anhydride and trivalent chromium
baths whose main ingredient is chromium sulfate or chromium
chloride. Trivalent chromium baths are not yet common, due
to restrictions concerning color, brittleness, and plating
thickness. For decorative purposes, the best combination
would be chrome and nickel which offers the most protection
against corrosion. It will have a mirror finish that will
only be as good as the finish you put on the surface before
you put on the chrome. Hard chrome is plated in thickness as
required to take advantage of the extremely low chrome
coefficient of friction, or for wear build-up for functional
purposes. Micro-finished chrome will provide a coefficient
of friction lower than any other metal when used against
steel, iron, brass, bronze, babbitt, or aluminium alloys.
This is done when chrome is used as a bearing surface.
Chrome is a perfect set-up for longwearing working surfaces
because it is much harder than casehardened steel. It is not
advisable to use chrome on chrome. Chrome will resist mostly
all organic and in organic compounds and acids, except
hydrochloric acid. Chrome plate shall be uniform in
thickness on all surfaces. Plate shall be smooth,
homogeneous and free from frosty areas, pin holes, pits,
nodules, and other defects. Chrome plating is not a
difficult process provided that the part has been properly
cleansed and the following requirements met: Preparation of
the chromic acid (CrO3) solution, Temperature control of the
bath (plating solution),Preparation of lead anodes
(peroxide), Agitation method of the bath (bubbles), Plating
current density control and duration (controller),
Ventilation (for safety) Black chrome can also be plated in
the same way and still have similar characteristics to the
bright chrome. For aesthetic or anti-reflective
applications, it may be preferable in some cases. I have not
yet used it, but the formula is as follows: Having the
chrome plating facility right there when needed is very
valuable to the home machinist. Of course there is a
learning curve and some basic investment in dollars but this
investment is mostly non-recurring and will give you the
benefit of this process for quite a long time. In industrial
chrome plating the process is electrolysis. In the process
chromium metal is deposited on metallic surfaces submerged
in a chromic acid plating bath. The part to be plated is
made cathodic by connection to the negative terminal of the
rectifier. Inert lead anodes are made electrically positive.
When voltage is applied across the two, current flows
through the solution and metal is deposited. Proper control
of various plating parameters result in bright, hard,
adherent deposits. Coupled with other surface finishes such
as anodizing aluminum and the plating of other prime metals
such as copper, nickel, silver, or gold which we may yet
cover, we can really dress up and protect our creations.
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