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What is 'Chrome'Chrome is slang for Chromium, one of the 91 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). |
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Chromium Plating, Weiner & Walmsley |
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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.
What's the difference between "Chrome Plating", "Chrome Electroplating", "Chrome Dipping", "Chroming", etc.?Nothing. Chrome is always applied by electroplating, it is never melted onto parts in the fashion of chocolate on strawberries, or applied in any other way than by electroplating. Note the previous paragraph, though, that everything that is somewhat bright is not necessarily electroplated chrome.
Is all chrome plating about the same, then?Not quite. There are two different general applications for chrome plating: "hard chrome plating" (sometimes called 'engineering chrome plating') and "decorative chrome plating".
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Hard Chrome PlatingMost people would not be very familiar with hard chrome plating. Hard chromium plating 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 hydraulic cylinder rods, rollers, piston rings, mold surfaces, thread guides, gun bores, 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 onlt 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.
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Hard Chromium Plating, Robert K. Guffie |
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Hard chrome plating is almost always applied to items that are made of steel, usually hardened steel. It is metallic in appearance but is not particularly reflective or decorative. Hard chrome plating is not a finish that you would want on a wheel or bumper. There are variations even within hard chrome plating, with some of the coatings optimized to be especially porous for oil retention, etc. Many shops who do hard chromium plating do no other kind of plating at all, because their business is designed to serve only engineered, wear-type, needs. If a shop says they do 'hard chrome only', they have no service that most consumers would be interested in.
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Decorative Chrome PlatingDecorative 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 chromium plated surface, such as a chrome plated wheel or truck 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. By the way, there is no such thing as "decrotif chrome plating". That is just a misspelling of 'decorative'.
Buzzwords: "Show chrome", "Triple Chrome Plating", "Double Nickel-Chrome""Show chrome" probably means chrome that is good enough to be on a winning entry in a car show. Although most OEMs rely on the "self-levelling" property of nickel plating to give sufficient reflectivity to roughly polished steel, 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. But high quality plating requires a minimum of two layers of nickel. 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. The most important issue for durable chrome plating for outdoor exposure such as on a vehicle is that it MUST have at least two layers of nickel plating before the chrome: namely semi-bright nickel followed by bright nickel. The reason for this involves galvanic corrosion issues. The bright nickel is anodic to the semi-bright nickel, and sacrificially protects it, spreading the corrosion forces laterally instead of allowing them to penetrate through to the steel. OEMs demand very close control of this factor, and there is a test (the Chrysler developed STEP test) which large shops run daily to insure the right potentials. Careful control of this issue is probably the principal reason that today's chromium plating greatly outlasts the chrome plating of earlier times. Experts argue whether copper plating provides any additional corrosion resistance at all, but with or without copper plating, chrome on top of a single layer of nickel will not hold up to the severe exposure of a vehicle! Industry professionals call the two layers of nickel "duplex nickel plating", and that would be a much better term to use than "triple chrome" and such. 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.
Restoration WorkWhen an item needs "rechroming", understand what is really involved: stripping the chrome, stripping the nickel (and the copper if applicable), then polishing out all of the scratches and blemishes (they can't be plated over and any scratches will show after plating), then plating with copper and "mush buffing" to squash copper into any tiny pits, then starting the whole process described above. Unfortunately, simply replating an old piece may cost several times what a replacement would cost. It's the old story of labor cost. The new item requires far less prep work, and an operator or machine can handle dozens of identical parts at the same time whereas a mix of old parts cannot be processed simultaneously, but must be processed one item at a time. If a plater has to spend a whole day on your parts, don't expect it to cost less than what a plumber or mechanic would charge you for a day of their time.
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Aluminum How-To, Robert Probert ASM Metals Handbook vol. 5 Surface Cleaning, Finishing, and Coating Electroplating Engineering Handbook, Lawrence Durney The Canning Handbook: Surface Finishing Technology Standards and Guidelines for Electroplated Plastics, ASEP Electrodeposition, the Materials Science of Coatings and Substrates, Jack W. Dini Practical Electroplating Handbook, N.V. Parthasaradhy |
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Peeling chrome?If your chrome plating is peeling, this is virtually always a manufacturing defect due to insufficient adhesion of the plating to the substrate. Although exposure conditions can certainly harm chrome, they don't make it peel. It can be very difficult for the plating shop to get good adhesion on some things (specifically on aluminum wheels) because they are not pure aluminum, but if they can't do it they shouldn't sell it. If your parts have peeling, you should complain and you should not be deterred by nonsense about chemicals in your garage, how frequently you wash the wheels, etc. We'll say it again, peeling chrome is virtually always a manufacturing defect.
Do it yourself?The best way to chrome plate something is to take it to a chrome plating shop. The industry is very 'job shop' oriented, with experienced people ready to handle your parts. Before thinking seriously about doing it yourself, here's some food for thought--
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RegulationsElectroplating was our nation's very first categorically regulated industry. So, what does "categorically regulated" mean? It means that all of the waste products from this industry -- even very dilute rinse water -- are, as a matter of law, regulated, even if the particular substance is actually harmless. Mix the waste in with other waste, and the whole mass is by law hazardous waste (see EPA 'mixture rule'). Make another product from it and (with some exception) the product is hazardous waste (see EPA 'derived from' rule).
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Water and Waste Control for the Plating Shop, Kushner & Kushner |
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In turn this means you can't discharge a single drop of hose water without pretreatment and permits; it means you can't take your bad solution anywhere without hazardous waste manifesting; it means you can't accumulate it without permits either. Finally, it means you are legally responsible for it forever regardless of how much you spend to get rid of it. But are you subject to these regulations? If you are selling plated parts or plating services, absolutely! See EPA CFR431 and try to find an exception -- you won't. If you are doing it solely as a hobby, maybe you can get away with it if you stay lucky. But if the sewer authority wants to impose an assessment for upgrading the piping, and your neighbors know that you are plating, they will probably turn you in in a heartbeat. Read the fine print on your sewer agreement: you're forbidden from putting these wastes down the drain and both your neighbors and the sewer authority would dearly love for you to have to bear the cost of repairs or upgrades. Is it going to happen? Probably not. Can it happen? Certainly.
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Chromic AcidChrome plating is done in very highly concentrated (about 32 oz./gal) chromic acid, H2CrO4 -- "hexavalent chromium" -- the stuff that made Erin Brockovich a household word. If a neighborhood child develops cancer from any cause whatsoever and his/her parents find out that you were chrome plating, God help you. Factories that use this stuff require exhaust scrubbing, they require fume suppressants that are monitored every day. The workers require medical surveillance (frequent blood tests for absorbed chromium). If you do illegally dispose of chromic acid you will probably be caught because it leaches through the ground very readily and turns up in the aquifer, and it is not only easily detectable but actually visible at 1 part in a million, and all wells and water supplies are monitored for chromium. Dropped a beaker on the garage floor? That could be enough to poison all of the wells for a few city blocks in every direction, and you do not have "pollution insurance" in your homeowner's policy. |
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On top of all this, many city councils have a written or de facto ban on chrome plating. Finally, chrome plating is notorious for hydrogen embrittlement. If you don't know how to immediately and properly bake the parts to relieve the embrittlement, you can turn hardened steel parts like springs, steering linkage, and fasteners into brittle glass.
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Current Solutions to Hydrogen Problems in Steels, Interrante & Pressouyre |
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AlternativesThere are things that are easier and safer than chrome plating. If your parts are aluminum, you could learn to polish; polished aluminum can look very good indeed. If you want an easier route to brightness than chrome plating, the new generation of "chrome like paint" is much better than what was available even a few years ago. If you insist on electroplating, there are proprietary plating processes based on other metals and alloys like tin-cobalt that are still electroplating, and can still get you in trouble, but at least they don't carry the baggage of carcinogenic hexavalent chromium.
Still With Us?Think about this: suppose you wanted to open a restaurant without ever having worked in one. It would be a risky business, but at least you've spent hundreds or thousands of hours in restaurants in your life. So you know what a menu is and what appetizers and soups and salads and entrees and desserts are. And coffee and tea and soft drinks. You know what a hostess is and what she does. You know what a waiter or waitress is, what the cook does, what the busboys do, what the dishwasher does. You know about tables and chairs and tablecloths and silverware and glassware and dishes, pots and pans, stoves and ovens. You know about flowers and candles and romantic music and soft lighting. Vending machines, restroom requirements, no-smoking areas. You know about insects and vermin, and that you need to cook pork and eggs thoroughly. You'd recognize food poisoning or a customer choking. You know all these things from a lifetime of experience and and take them for granted. Now, imagine that a Robinson Cruesoe type, raised from infancy on a desert island, has never seen a kitchen or a restaurant of any type, and asks on the internet how to get started in the restaurant business. You would shake your head and say, "Sorry, there is just too much to explain and no starting point; you need to spend some time in restaurants first". If you've spent no time in a plating shop, you're like a castaway wanting to open a restaurant. If you are interested in chrome plating, you need to read a couple of books from our "must have" book list, subscribe to a couple of journals to begin acquiring a feel for the industry, start attending monthly meetings of the AESF and a few conferences and exhibitions, take a plating course through AESF (www.aesf.org) or Kushner Electroplating School. and visit a few chrome plating shops. But the best way to learn chrome plating is to work in a chrome plating shop for a little while. Think of it this way: if you couldn't land a job as a journeyman in a plating shop due to lack of experience, are you ready to compete in that business against the shop's supervisors and boss? Why not get some hands-on training while someone else pays for your mistakes? We're NOT saying you should not take the dare and grab for a piece of the American dream -- PLEASE DO! (this industry needs new blood) -- but educate yourself as well as possible first to give yourself a fighting chance!
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Please feel free to ask specific questions on our Hotline-Letters page! In your inquiry please tell us that you've already read this page, as that will save time and lost motion. Good luck!
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