Chrome is slang for Chromium, one of the 90-odd naturally occurring chemical elements. Chrome is a metal, but it is not useful as a solid, pure substance. Things are never made of solid chrome. Rather, when you hear that something is chrome, what is really meant is that there is a thin layer of chrome, a plating of chrome, on the object (the bulk of the object usually being steel, but occasionally aluminum, brass, copper, plastic, or stainless steel).
A cause of occasional confusion is the fact that people may tend to describe any shiny finish as "chrome" even when it really has nothing to do with chromium. For example, brightly polished aluminum motorcycle parts, electropolished stainless steel boat rigging, vacuum metallized balloons and helmets, shiny painted wheels, and nickel plated oven racks are sometimes called 'chrome' by the lay person. Indeed it's not always easy to tell chrome plating from other finishes if the parts are not side by side. When a decorative chrome electroplated finish sits right next to another bright finish, however, the other finish usually won't compare very favorably.
Chrome plating is more reflective (brighter), bluer (less pale, grayish, or yellowish), and more specular (the reflection is deeper, less distorted, more like a mirror) than other finishes. Put one end of a yardstick against a bright finish, and see how many inches of numbers you can clearly read in the reflection -- you can clearly see the clouds in the sky reflected in chrome plating. And there's a hard to define "glint" to top quality chrome plating that nothing else has.
Chrome plating is a kind of finishing treatment that utilizes the electrolytic deposition of 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 automotive trim. Thicker deposits, called hard chrome, are used to reduce friction and wear and to restore the dimensions of equipment that has experienced wear. These two types of chromium plating are called Show Chrome and Hard Chrome respectively.
The newest is called Vacuum Metallizing. During the process, metals are vaporized within a vacuum chamber and then deposited on to a surface. Once the vapor deposition process has completed, the substrate emerges from the vacuum chamber with a mirror-like highly reflective finish.The most common usage being with various grades of metal and plastics. Aluminum, steel, polycarbonate, zinc die cast, ABS, acrylic, nylon and polyester are examples of these.
Paints and Coatings
are commonly used in vacuum metallizing finishing for a number of reasons:
adhesion promotion, surface leveling and protection of the optical film after
deposition. These coatings are commonly referred to as vacuum metallizing
basecoats, topcoats and primers. It is very commonly used in the manufacture
of interior and exterior grade automotive, mirror fabrication and trim accessories.
Hard Chrome Plating
There are two types of Industrial chromium plating solutions: hexavalent chromium baths = main ingredient is chromic anhydride. And trivalent chromium baths = main ingredient is chromium sulfate or chromium chloride. Trivalent chromium baths are not yet common, due to restrictions concerning color, brittleness, and plating thickness. Hard chrome is plated to a thickness required to take advantage of the extremely low chrome coefficient of friction, or for wear build-up for functional purposes. Most people would not be very familiar with hard chrome plating. Hard chrome plating or Industrial Chrome is chrome plating that has been applied as a fairly heavy coating (usually measured in thousandths of an inch) for wear resistance, lubricity, oil retention, and other 'wear' purposes. Some examples would be rollers, piston rings or motorcycle fork stanchions etc. 'Hard chrome' is not really harder than other chrome plating, it is called hard chromium because it is thick enough that a hardness measurement can be performed on it, whereas decorative chrome plating is only millionths of an inch thick and will break like an eggshell if a hardness test is conducted, so its hardness can't really be measured directly. Hard Chroming is not as reflective as 'decorative chrome plating' and is not a finish you would want on say a bumper or a wheel.
Chrome is a perfect
plating for longwearing working surfaces because it is much harder than case-hardened
steel. 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. It is used for bearing surfaces. We recommend hard chrome as the best
choice for Morgan kingpins. Click HERE. 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.
|It is not advisable to use chrome on chrome.|
Show or Decorative Chrome
Decorative chrome plating
is sometimes called nickel-chrome plating because it always involves electroplating
nickel onto the object before plating the chrome (it sometimes also involves
electroplating copper onto the object before the nickel, too). The nickel
plating provides the smoothness, much of the corrosion resistance, and most
of the reflectivity. The chrome plating is exceptionally thin, measured
in millionths of an inch rather than in thousandths.
When you look at a decorative chrome plated surface, such as a chrome plated wheel or car bumper, most of what you are seeing is actually the effects of the nickel plating. The chrome adds a bluish cast (compared to the somewhat yellowish cast of nickel), protects the nickel against tarnish, minimizes scratching, and symbiotically contributes to corrosion resistance. But the point is, without the brilliant leveled nickel undercoating, you would not have a reflective, decorative surface .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.
Chrome plating should be uniform in thickness on all surfaces. The plate should be smooth, homogeneous and free from frosty areas, pin holes, pits, nodules, and other defects It is not a difficult process provided that the part has been properly cleaned and the following requirements met:
Triple Chome Plating
Triple chrome plating refers to decorative
chrome. It implies three layers of chrome but instead delineates the use
of three different metal layers as plating. Chrome is the final or top layer,
and nickel is always the second layer, providing most of the brilliance associated
with "chrome." The base or first layer fluctuates between steel, copper or
nickel or even aluminum.
Buzzwords: "Chrome Plating", "Double Nickel-Chrome", "Show Chrome", "Triple Chrome"
"Show chrome" probably means chrome that is good enough to be on a winning entry in a car show. Chrome-lovers believe that the key to "show chrome" is to copper plate the item first and then buff the copper to a full lustre before starting the nickel plating.
Whether you start with bare steel or buffed copper, at least two layers of plating follow -- a layer of nickel and a layer of chrome.
Salespeople are always looking for advantage, and they will use any good-sounding terms they can get away with! There are no laws that define what triple chrome plating actually means, so salespeople will be prone to call their service "triple chrome plating" if there are a total of 3 layers of any kind of plating, or "quadruple chrome plating" if there are 4. So those terms mean little.
Chrome plating is hardly a matter of dipping an article into a tank, it is a long involved process that often starts with tedious polishing and buffing, then cleaning and acid dipping, zincating (if the part is aluminum), and copper plating. For top reflectivity "Show Chrome", this will be followed by buffing of the copper for perfect smoothness, cleaning and acid dipping again, and plating more copper, then two or three different types of nickel plating, all before the chrome plating is done. Rinsing is required between every step.
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