Chromium Alloy Plating

Chromium alloy plating can be considered a subheading under trivalent bath, there is almost no alloy plating possible from hexavalent chromium solutions. There has been a great deal work, and some reviews are available, but nothing of commercial importance seems to have been developed. It appears likely that some fundamental problems of depositing chromium from trivalent baths remain to be solved, and that these are probably not made appreciably easier by introducing the added factor of alloy deposition. Alloy steel is one of good material as base plating metal for chromium electroplating.





One exception to the rule of no alloy plating from chromic acid baths is the work of Vagramyan and his collaborators. Alloys of up to 37% selenium, 15% manganese, 2% molybdenum, and 1 % rhenium were obtained with cold chromium deposits at about 20oC. These alloys are on the whole no longer obtained as the temperature is raised, so presumably they are alloys with the dull hexagonal hydride produced at low temperatures, and not with the bee deposits which form ordinary bright plate.

Much work has been done, mainly in France, to investigate claims of improved wear resistance of chromium-molybdenum alloys produced from chromic acid solutions. It appears that bright deposits generally contain less than 1% molybdenum, and this could possibly result from solution contamination of the deposit instead of alloying. Hard chromium plating baths are frequently a little low in catalyst due to too strict adherence to the 100:1 ratio of chromic acid to sulfate, and the improved wear resistance of deposits from solutions containing molybdenum compounds might be due to an effect on the catalyst balance of the solution.

Other Special Types of Chromium Plate

A "frosty" or satin-finish plate in between cold chromium and bright plate was found desirable for press plates. Such smooth-bubbly or natural rounded nodular plate has been found useful for handling textile materials. Some people used a special cold chromium plate produced in refrigerated electrolytes for printing plates. Black chrome plating can be obtained from immersing chromium deposits in molten cyanide acid.

Next articles:

• Nickel Plating
• Porous chromium plated 

To see other the video:

Power for electroplating

Electroplating need DC power source that can supply DC electric current in stable flow. For industrial company this may can supply by high power system that already make with perfect electric circuit, so DC electric current is not a problem anymore. For small uses like home industry this can be problem because their electric circuit sometimes is not perfect so that the current flow is not stable, in our country this always problem because electric source that supply from government still don’t stable the range is too far for example from 170 volt to 210 volt, this can make difficult to arrange even use current controller.

The quality of deposit coated metal such as in chrome plating is very dependent on the electric stability. The brightness and the regularity of thickness can be not even if the electric source is not stable flow. For small part may can result in evenly coated thickness but for wide part this can be problem if electric current flow is not high enough or less from the limitation. The DC current electric source should be able to supply electric current 5 A per sq ft of object to coat by chrome ion. If the electric current up and down to wide span, this can be difficult to arrange.

So the problem on chrome plating itself is not just from the preparation of base metal such as electropolishing but also from the DC current electric flow also should be stable. If any certain disturbance while running process the chromium deposit can be very brittle or too soft, out of the standard quality.

The usage of chrome electroplating

Chrome electroplating is a coating process on the surface of metal use chromic acid or chrome substance use electrolysis method. Chrome electroplating is more prefer to be applied in any metal because some reason like, electroplating product have good looking, chrome plating product stand to corrode better than other substance coated, chrome plating can be plated easily by using low electric current so that this process can use efficient electric power.

Chrome electroplating can be work with efficient chemicals usage because the thickness only in micron so that for a wide m2 area only use small chromic acid is enough. Different with electroless plating, plating area can’t wide area with use small substance, and the coating substance can’t stick evenly in all surface. Chrome electroplating can plated in wide area with homogen thickness and similar quality of chrome layer.

Process of electroplating should be doing in several step in order can get high quality product. These are the step of chrome electroplating should be done:

• Preparing Chrome Plating Base Metal
• Cleaning Base metal as Cathode
• Preparing Bath solution for chrome plating
• Water cleaning and rinsing
• Polishing of chrome plated surface

Operating Conditions

Operating Condition of Electroplating Process

Bright Plate can be reliably obtained by properly coordinating temperature and current density within definite limits, taking into account the chromic acid concentration of the bath. The operating condition for bright plate should be on the temperature range of 25– - 55 C degree with current density range between 5 -– 25 A/dm2 for solution containing 250 g/l CrO3. For example to produce a bright plate deposit from a solution containing 250 g/l chromic acid and 2.5 g/l sulfate at a temperature of 40 ^oC, use cathode with current density between 3.1 and 15.5 A/dm2 but at 45 ^oC use current density about 50 % higher.

Plating at higher temperature and current densities has been proposed for hard chromium plating and porous chromium plating. This idea has been applied successfully to plate a small articles, but the power required for plating larger objects may be prohibited or unavoidable.

Chromium plating speed was vary depend on the chromium concentration on the bath. Billfinger suggests the use of higher temperature and current densities, combined with lower ratios of chromic acid to sulfate, to obtain higher plating speeds for hard chromium plating.

Throwing Power

Both the throwing power and the covering power of chromium plating bath are poor compare with copper or nickel plating bath. The conductivity is high but reduced by such impurities as iron and copper. The cathode polarization during chromium deposition is relatively constant and substantially the same as that obtained during electrolysis of the same concentration of pure chromic acid without chromium deposition. The major variable connected with throwing power in bright chromium plating are the current efficiency and the bright plating range. If a given set of condition gives the widest possible bright plate range and the plating is done at an average cathode current density near the upper limit of current density for this bright plate range, the optimum throwing power will be attained.

High Throw Bath

High-ratio baths containing relatively high concentration of organic acids have been developed which exhibit remarkable throwing power or covering power over bright nickel, almost as good as that of bright nickel bath themselves. These solution operate at lower current efficiencies to produce thin bright plates of good decorative value. It is a characteristic that the coverage increases with the time and the plate continuous to spread into the low-current-density area with longer plating. Thus plating times as long as 5 to 10 minutes are recommended instead of the 2 to 3 minutes often used for decorative plating.

Other articles:

• The best metal for chrome plating
• Plating small parts 

The Best Metal for Chrome Plating

Metal want to be plated can be vary some of recommended from plating service industry can use aluminum alloy, Brass, Bronze, copper, mild steel, stainless steel, zinc die-casting, pewter. The chrome plating process itself can be do as follow sequentially:

• Polishing (preparation for plating)
• Soak Cleaning (can use alkaline cleaner)
• Surface activating
• Copper plate
• Nickel plating
• Chrome plating

The result of chrome plating is depend on the base plate condition before electroplating process applied. Poor adhesion of chrome plating can be happened because of the bath solution concentration or because poor base plate plating. Preparation of base plate is needed in order can best chrome plating. Bath concentration of the chrome plating bath should be checked before the plating is running, this is part of quality control of laboratory person job. Poor adhesion result of chrome deposit will immediately separating from the substrate after the object take out from the chromium bath. This can occur from peeling or blistering of chrome layer.

Bad Chrome Plating Deposit Causes

To test the quality result of chrome deposit usually by immerse on boiling water, until the object temperature up to reach boiling water temperature. Poor adhesion will likely show up as blister in chrome deposit surface. Other method to test the deposit quality is by grinding the deposit with 45 degrees angle and and examining the edges under microscope for to see if any flaking. Poor adhesion can also occur if the electric current flow is too high. Some deposit fail can cause of some of the following problems:

• Improper cleaning, some grease can withstand the molecule adhesion on the plate. For perfect cleaning can use organic and inorganic cleaner.
• Bad plate surface activation, see on the electrocleaning (cathodic cleaning) and chemical cleaning for pretreatment object preparation.
• Not perfect rinsing, make some dirt still stick to the object
• There is oil or organic material on the bath function
• Bad electric conductance on the process can because of any intermittent electric connection
• Anode already rubbed and dissolved on the bath solution
• Too little concentration of electroplating additive
• Bath temperature not in optimum condition check for this in baht temperature control
• Temperature, bath concentration of chrome plating operating condition should be controlled properly
• Postplating treatment after chromium plating can also make bad result of chrome plated.

Chromium (VI) must be Controlled

Worker must be provided with complete safety equipment in order can work in health condition for long time in chrome plating industry. Chromium plating is purpose to covered metal in order have good properties and stand for long time period. Chromium plating on the process will expose chromium fume. The problem when chrome (VI) or hexavalent chrome also vapor even this gas can cause severe health effects include lung cancer if long time exposed. Exposure limit from OSHA’s for Cr VI about 5 µg/m³ maximum 8 hours exposed. Chromium VI on the bath can be created by the temperature increase that can be affected by the electric current that flow on the bath solution. The character of hexavalen chrome is more easily to vapor compare to chromium III that more stable on the bath solution.

How to control the concentration of Cr(VI) 

To overcome the availability of Chromium (VI) we must know what or where this substance come from. Several source that developing Cr(VI) on the workplace.

Full Face Masker

Masker

1. This electroplating process is use electrodes (anode and cathode) that is connected to DC electric current source make each electrode developed gas and this gas then merge to the surface bring chrome substance Cr (VI) together, causing bad smell and make chromium concentration drop because vapor to atmosphere. The increasing number of chrome gas will generate higher electrical current in bath, longer plating time, higher surface tension and bad chrome coated in the subject. Chromium vapor can take out using fume hood to remove gas in the workplace and then gas is treated first before blow out into atmosphere.
2. To much vaporization can make spill and make more chromium vapor. This can be controlled by reduce the electric current that applied on the process.
3. Use other raw material in order not produce Cr (VI) too much, for example chromium (III) is less toxic than Cr (VI), for this purpose, supplier of chromic acid may can talk much more about the quality of this substance.
4. For person who work in this plant must use Personal Protective Equipment (PPE) for this purpose must use masker or full face masker.
5. Use hands glove on working with chrome plating process to avoid direct contact with skid, and use special chemical cloth for work that usually is designed special for working in chrome plating areas.
6. Put all dangerous sign and hazard symbol like use gas masker or must use hands glove for work and so on.

Chrome Plating Failure Can Make Aircraft Accident

The Story of Aircraft Accident

Chrome plating is good metal surface protection, but it should be used in correct place and application. We can’t coat all metal using this method because its look like better performance. Nowadays people like to crome their motor bike engine and all of part of their bike in order look good performance. This is not wrong but can not be applied to all part like engine parts. This can be dangerous, you can see the story of aircraft accident because of their engine part apply of chrome plating.

aircraft accident

The story are as follows; aircraft with four engine, propeller driven transport plane had just touched down when the left main wheel assembly separated. This plane slewed off runway and fire merge on the wing and engine of the left side. However the result of detail investigation, inter granular fracture was observed without evidence of fatigue striations. It was concluded that trunnion arm had failed because of corrosion and cracking.

Trunnion arm was made from a fine grained, through hardened and tempered 4340 steel. It had been subjected to excessive wear in repair, and during the overhaul it was known that already chrome plated to bring the dimensions can fulfill the specification. After use and worn trunnion arm back to the original level. Found that beneath the chrome plating and adjacent to the fracture, a regular pattern crack was found, but don’t continuous to the chrome plated, this indicate that this were not due to plating crack. The crack actually just 0.5 mm in depth, which caused by overheating occurred during grinding before hard crome applied. So chrome plating need perfect prepare before applied so some fist treatment like grinding is must be done before it being chrome.

Black and Color Chromium Deposits

Many attempts have been made to produced "black" chrome plating, and such deposits have been used commercially. They are usually dark grey rather than black, however, and all dull or mat chromium deposits color seem to turn bright metallic rather readily if exposed to much abrasion or wear, in spite of the hardness of the metal. Oiling and other final treatments give grey or dull deposits a blacker appearance. An early "black" chromium plate was produced by using a high current density in a cold bath containing principally chromic acid and acetic acid.

Modification of this process for "black" chromium plating has been proposed. Current interruption and sulfate-free chromic acid with fluoride or complex fluoride catalyst have been used. Some practical of this process should be make trial for several changes in parameter in order feel confidence on produce black color of chrome deposit. For other color of chromium deposit should use different bath chemicals solution rather than chemicals for black color deposit. For color chrome deposit should find other kind bath solution that can produce color chrome deposit like for decorative chrome deposit. The method to produce color chrome deposit can be in two stage, for example by first plating using nickel plating than the subsequent plating using chrome plating, or the first layer use copper substance that the subsequent layer use chrome plating.

Trivalent Chromium Baths

Historically, trivalent chromium baths have been the first and favorite approach to chrome plating, but they have always failed to match the reproducibility and dependability of chromic acid solutions, as has already been discussed in the section on theory.

The United States Bureau of Mines developed a process for the electroplating of pure chrome to meta from the ore from ferrochromium. Using a mixed bivalent and trivalent chromium sulfate solution, but the process has not been adopted successfully to plating purposes. A two-compartment cell is used at the Union Carbide Corporation, Marietta, Ohio, plant, and continuous operation on a large scale seems necessary for good result. In another review of the operation that low efficiencies always prevail during the startup of a cell.

Success was very limited in effort to utilize such baths for electroplating. A chromium ammonium chloride solution was used for brush plating. Better results in brush plating were obtained with Gregory's salt, ammonium chromium oxalat.

More recently there has been an effort to commercially the use of chromium chloride solution in or containing, organic solvent. The deposits are darker than those from chromic acid solution, and some chlorine gas is generally evolve at the anode. Only decorative deposits are being considered.

Chromium Electroplating

1. THE PRINCIPLES of ELECTROPLATING

Article Contents:

The Principle of electroplating

Decorative of hard chrome plating

Thickness Control of Plating Deposit

Preparation of chromic acid

Bright Chrome Plating

Black Chrome Plating

Temperature Control

Chrome Plating Result

Dull White, Black, Bright Black, White and Gold Color

Chromium Electroplating or people just say chrome plating is a process of metal coated using chromium substance or chromic acid. Why use chromium substance to cover metal surface? Chromium is a metal substance that resistant to corrosive while other metal like steel are easily to corrode affected by wet air. Chromium can’t be deposited from solution only chromic acid (CrO₃) and water. There must be present in bath one or more acid radicals which act catalyst to bring about or aid in the cathodic deposition of chromium. The purity of chromic acid used is often not specified or established and yet the nature. The end of the process chrome will coated the surface of metal.

Chrome plating is not difficult covered on the part has been properly cleansed using the following requirements met:

• Preparation of the chromic acid (CrO3) solution..(Do not acquire the hydrogenated ( H₃CrO₄ ) chromic acid crystals)
• 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)

All that remains is the requirement of time - so don't let the apparent complexity of the task discourages you because the results are very worthwhile, indeed.

I have studied the industrial processes involved, reduced them to pint-size applications for model engineering, and experimented enough to be able to tell you what works. We have a lot to learn and the process has been laid out for you in ten easy steps. So, here we go!

2. DECORATIVE OR HARD CHROME PLATING

All chromium is about the same hardness; 800 to 1000 VHN - very hard! The main difference lies in the thickness of the deposit of chrome coated on the metal.

For decorative purposes, chrome sits best on nickel which itself adheres very well to copper - this combination also offers the best corrosion protection resistance more better. Decorative chrome coating thickness will vary from a few hundredths of a mil to 1 mil. The mirror finish will only be as good as the finish you put on the surface before you put on the chrome.

For functional purposes, to take advantage of the extremely low chrome coefficient of friction, or for wear build-up (bearing surfaces or pistons, as examples), hard chrome is plated in thickness as required from 1 to 50 mills.

When used as a bearing surface. Chrome must be micro-finished (more on this later) and will then provide a coefficient of friction lower than any other metal when used against steel, iron, brass, bronze, babbitt, or aluminium alloys. Do not use chrome against chrome. Because chrome is also much harder than casehardened steel, we then have a perfect set-up for longwearing working surfaces. Chrome will resist mostly all organic and in organic compounds and acids, except hydrochloric acid (muriatic).

3. CONTROL OF THICKNESS OF DEPOSIT PLATING

Given fixed parameters for temperature, plating solutions, anodes, set-up, and current density, thickness is a function of time. Expect around .75 to 1.2 mil per hour of plating time.

I have plated up to 20 mills successfully at home - admittedly this was by accident because I was aiming for 3 mills deposit to refinish a piston! It had previously taken six hours using a particular chromic acid solution to deposit 3 mills of excellent chrome. I thought to shorten plating time I would increase the current density from 600 mA to 800 mA and the temperature of the solution was tweaked from 450 ^oC. to 500 ^oC. (113 ^oF to 122 ^oF). I then plated, with agitation, for five hours and wound up with an hour-glass shaped piston, due to a 13 mill chrome deposit measured at mid-skirt level and 21 mils on the edges (formed by the bottom of the skirt and the piston crown).

Let that be a lesson to all of us: Never change more than one parameter at a time. Subsequently, grinding of the same piston was successfully carried out; which attests to the excellent adhesion of the chrome to the base metal (steel) as prepared earlier.

Of course, the piston was then lapped to a perfect fit in the re-lapped bore (no rings involved in that 0.020 cu.in. engine). We'll come to the grinding and lapping notes later. Chrome will lap to a superb finish, to a degree of precision obtainable by no other method and limited only by the machinist's patience and skills.

4. PREPARATION OF THE CHROMIC ACID BATH

NOTE: The chemical formulations given in this article are in avoirdupois ounces per gallon of solution (avoir. oz./gal). To convert these to metric measure, simply multiply the oz/gal number by the conversion factor of 7.5 to obtain grams per litre.

4.1 BRIGHT CHROME PLATING

The formula for Bright Chrome Plating use the basic formulation of 100:1 chromic acid/sulphuric acid proportions:

• Chromic acid crystals = 33 oz. (936 grams)
• Sulphuric acid fluid = .33 oz. (9.36 millilitre)
• Distilled (or demineralized) water to make 1 gallon (3.79 litre).

Of course, you can vary these proportions in accordance with the quantity you wish to make up. So, to make up one pint for small work, simply divide everything by eight The dilution ratio of the sulphuric acid as purchased has to be taken into account and the amount used in the bath must be one of pure H₂SO₄ to 100 Cr0₃.

Be very accurate in this process; and:

ALWAYS ADD ACID SLOWLY TO WATER -- NEVER ADD WATER TO ACID

If you have access to demineralized water from your home dehumidifier (of course, clean filter if required). This is a good substitute for the recommended distilled water.

Also, I recommend the use of surgical rubber gloves when handling any of the chemicals called up in this article. Pharmacies (Chemists) carry them and they are much easier to replace than the skin of your hands.

The chromic acid crystals yield about 52% pure chrome metal. For reasons, which must remain unexplained at this stage, a freshly mixed solution will only deposit passably good chromium. The same solution, like a good wine, improves with age... So use it for experimentation when first mixed, before you undertake any serious plating - I keep mine in a sealed glass container and it is good for years. Filter as required between uses - plating current will be around 0.75 A/sq.in. For bright chrome and up to 1.4 A/sqin. for dull 'hard chrome'.

4.2 BLACK CHROME PLATING

Black chrome plating 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:

• Chromic acid 33 oz (936 g)
• Acetic acid = 28.2 oz (800 g)
• Barium acetate =1.0 oz (28 g)
• Distilled (or demineralized) water to make 1 gal. (3.79 litre).
• Operation of this bath will be at 90 ° to 115 °F (32.2 °C. to 46.1 °C.) and at a current density of 0.25 to 0.63 AIsq.in. (More on how to set this up later). 

Find Chemicals Supplier For Electroplating Solution:

4.3 TEMPERATURE CONTROL

Temperature is critical for good (or any) results. This is best maintained automatically by using a thermostatically controlled electric heater right in the bath. A simple and cheap expedient for this requirement is to use a tropical fish-tank heater available at any pet store. And, while you're there, pick up a fish tank air pump, plastic piping to suit, and one air valve control, too.

The 115 V heater comes in a quartz tube with a temperature control knob on top. This acts on a bi-metal strip contact tension and can easily be cranked up to maintain the required 45 °C. to 50 °C. (113 °F. to 122 °F). A thermometer covering this range is also required.

It is important this temperature range be maintained throughout plating times.

Note: the above article I get from old literature but I forget to write the source. I also ever try to use the formula but not working smooth because use simple tools that I made by myself.

Result of Chrome Plating or Chrome Coating and Product Applied

The product variety can be as on the picture below:

1. Dull White Color Chrome Plating

The process of chrome plating coloring is just the setting in variety of voltage and ampere of electric  current and additive substance to make bright or smooth on coloring deposit.

Dull White Color Chrome Plating

2. Bright White Chrome Plating

Bright Chrome Plating

3. Gold Color Chrome Plating

Gold Color Chrome Plating

 

Gold Color Chrome Plating

4. Dull Black Color Chrome Plating

Dull Black Chrome Plating

5. Bright Black Chrome Plating

There are two different tipe of black chrome color from the chrome plating process, there are trivalen chrome plating process and hexavalent chrome plating process. Through trivalent chrome plating just can result semi black dark color, but this product have advantage of more stand to corrode. See black and color chromium deposit.

Hexavalent chrome or Cr (IV) plating process can result true dark deposit color, very dark, smooth and non reflective. Hexavalent chrome is not good for goods that purpose to stand in corrosive environment because the layer is not strong enough stick to the surface layer.

Bright Black Chrome Plating

Find of Bright Chrome Plating Service Company:

Example of Hard Chrome Plating:

Hard chrome applied on industry usually in their hydraulic shaft, this hydraulic need maintenance in certain period time need to coating again to repair the surface coating and adjust the hydraulic clearance.

Hard Chrome on Hydraulic Shaft

Beside on hydraulic shaft, industrial uses also apply hard chrome on rolls use for certain uses like in transfer material in production process.

Hard Chrome in Rolls

Hard chrome vanadium usually apply as coating on tools, this tool need hard surface in order not easily scratch when use to tight of open bolt from equipment.

Chrome Vanadium on Tools

Bath Function on Chromium Plating

Bath Function for Chromium Plating

There only two essential constituents in conventional chromium plating bath; chromic acid and one or more catalyst acid radicals or anions. Chromium metal will not serve satisfactory as anode, owing two high solubility, insoluble anodes are used, generally lead.

Bath function on the chromium plating usually serve as Anode. Chromium metal is also appreciably more expensive if use as anode. The chromium to be deposited is introduced into the bath as chromium trioxide, CrO₃ (Chromic anhydride), commonly called chromic acid. It is reddish brown, hygroscopic material, easily soluble in water to give solution containing mainly H₂Cr₂O₇. Many manufacturers, now aware of the effect of even small amount of catalyst acid radicals, furnish a pure grade of chromic axid especially suited for chromium plating. The chromic acid is made to meet specification which require that it contain not more than a small of percent of sulfate and be free from other catalyst such as chloride.

To convert a pure chromic acid solution to a chromic plating bath a catalyst is necessary. With given set of conditions of bath temperature, current density, and chromic acid concentration, too small amount of catalyst will result in either no plate or in brown anode stains. Too high catalyst contain will result in either partial plating with poor throwing power or no plate at all, owing to depolarizing action or easy formation of chromium (III) at the cathode. The essential criterion of bath composition in chromium plating from the conventional chromic acid-sulfate solution is the ratio, by weigth, of chromic acid to sulfate. The ratio should be kept within the limit of 50:1 and 250:1; and preferebly at about 100:1. A ratio of 90:1 is common; ratio of 70:1 to 80:1 are common in hard chromium baths especially at higher temperatures.

A typical formula for a chromium plating bath using sulfate as the catalyst acid radical is

• chromic acid (CrO₃), 250 gr/lt.
• sulfate (SO4⁼), 2.5 gr/lt.

Electroplating Legal Patent

The extension of legal patent of certain patent is no longer needed, is this mean that we are no need permit to use the process of electroplating? May be because of many people in the world already use use this Chromium Electroplating Process without patent anymore or patent payment is not effective anymore. People don't want to pay of that certain patent process so that patent is no longer need to be extended.

Some important point on the patent you can read as bellow, so that you can develop your process in order can optimize of your electroplating process:

A plating process for plating chromium metal onto substrates is disclosed. The process uses a trivalent chromium plating bath with a sulfate and/or sulfonate matrix. The process also utilizes insoluble anodes. An addition of manganese ions to the plating bath inhibits the formation of detrimental hexavalent chromium ions upon use of the plating bath.

The present invention relates to a chromium plating method which utilizes trivalent chromium ions in the plating bath and insoluble anodes. An additive is proposed for the chromium plating bath which will minimize the creation of hexavalent chromium ions at the anode while the plating bath is being used.

The present of hexavalent on electroplating bath often disturb the formation of smooth layer on the metal. With additional of manganese ion like dissolve manganese metal into the sulfuric acid bath can help to prevent on the formation of hexavalent chromium ions.

Chrome plating aluminum wheels

Chrome plating aluminum wheels will create a corrosion protected part, but not make the wheel stronger. It's depend on the raw material use for car wheel. Chromium plating aluminum wheel is involved in two kind electroplating method. The first should know the chromium process itself and the second one must understand how chrome electroplating can work on the aluminum surface.

Look more about Electroplating:

• Chromium Plating
• Alloy Plating
• Plating small parts

Problem on Plastic Electroplating

The basic problem of plastic electroplating is in attempting to electroplate onto plastics substrates is, of course, that they are electrically non-conductive and cannot be immersed in a plating solution and coated in the way that metal objects can. Some method was therefore needed whereby a conductive film could be deposited onto the plastics surface to provide the basis for subsequent electrodeposition. It was, of course, vital that this surface layer, in addition to being electrically conductive, should adhere well to the substrate if the final coating system was to show good adhesion.

Substrate Etching

Early processes, using conductive paint or chemically reduced silver on surfaces roughened either mechanically or by solvent attack, did not provide adequate adhesion. In the mid 1960s, etching solutions based on chromic acid were developed which could successfully be used with acrylonitrile butadiene styrene (ABS) copolymer. Use of these solutions resulted in selective removal of the butadiene phase from the resin to give a micro-etched surface providing bonding to the subsequent conductive layer.

Electroless Plating

This development came at a time when great improvements were also being made in the technology of electroless nickel plating and electroless copper deposition. These advances in electroless plating combined with the development of the etching technique gave rise to a system that provided a highly conductive coating exhibiting satisfactory adhesion to the plastics surface.

Problem on Hard Chrome Plating

Pollution problem on electroplating process become general problem encountered by electroplating industry. The other problem of electroplating process is especially for hard chrome electroplating. The problem showed that the high surface tension was greatest up to 22 dynes/cm.

By adding some surfactant solution to electroplating baths this tension can yield considerable lower surface tension. This using of surfactant can make a pollution problem on their fluid waste. As it turned out, the tensiometer yielded considerably lower surface tension readings, which in turn has allowed the facility to substantially reduce the frequent additions of surfactant solution to the baths. Overall usage is down approximately 80%, which translated to a savings of close to $1000 per year in operating costs. The company owner’s anxiety level has also dropped substantially as he now feels more confident that they are complying with the regulation.

Those problem can source not just from the bath but sometime also from the instrument or electroplating equipment that easily broken because of corrode. By using of good tensionmenter on the bath will can operate electroplating in accurate procedure. In addition, maintaining higher concentrations of the surfactant due to inaccurate surface tension readings could, in some cases, result in pitting problems with the chrome finish if the facility is doing thicker hard chrome plating.

Electroplating Business

In Indonesia many small workshop spread in side of road especially in Jakarta of Electroplating Service that can treat your spare part or appliance to be electroplated. These workshops are applied a simple electroplating method, but the method is not use a standard that should be intention on this process, so the product will not get an optimum electroplating product. The product is not durable and easy to abrade, so the genuine metal will looked and corrode. They don't consider the durability and the quality of electroplating result, even don't treat the metal before electroplate.

Electroplating in industry use special method and use qualified raw material, industry really intense on the process order that they should follow. They don't have purpose for small customer and hope can build a long relationship with their customer, so they are very consent to the professionalism and continuous to create the product with more qualified result. Beside they use pretreatment for metal that will electroplate, they also don't electroplate directly with chromium to the metal, because this chromium can't strongly stick to the metal for long time. Other base substance electroplating must be treated to this metal before chromium electroplating. Nickel base electroplating is better and stronger plated on iron or other steel. Nickel plating also easy to plate and enter into the small hole that may available on the metal, so nickel plating will cover the entire surface better and smooth than chrome.

After the base electroplating is treated to metal, they do with chromium electroplating to get a bright surface. Chromium plating also more easily plate on the nickel than to the steed or iron directly. These all cycle of electroplating will need more time and cost so don't like apply for small business like that. The quality will better and more durable and have longer lifetime and will tight stick to the metal. This why, if you do electroplating in small workshop will have short lifetime and easily corrode.

Porous Chromium Plate

This name have been given to modified chromium deposits with oil-retaining properties, used on internal combustion engine cylinders and piston rings. Such deposits were used especially during the war on aircraft and diesel engine cylinders for salvage and to make engines last longer. Three main of porous chromium plate have come into common use.

The first is the mechanical type, produce by grit blasting the basis metal, chromium plating, and finally finishing to size by grinding, honing, or polishing. The second and third types of plate are those with pitted and channel porosity. Both of the later are obtained by treating the chromium deposit in an etching solution. The type of porosity obtained depends on careful control and regulation of the condition of deposition. Numerous publications and patents describe the production of all these types of porous chromium plate and the result obtained with them.






Another variation is to etch pits into the surface of the deposit through a plastic mask or photoresist. Etching by ion bombardment trough a screen and with alternating current are proposed. Plate process at extremely high current densities from 232 to 1160 A/dm2 at 30 to 55 oC to produce a porous deposit directly. Still another variation is to impregnate the porosity with Teflon to provide the possibility of dry lubrication, but this does not seen to have become important commercially.

The "pit" type of porous chromium may be produced, for example by plating under ordinary hard chromium plating conditions, such as in a bath containing 250 g/l chromic acid and 2.5 g/l sulfate, at 50 oC and to 46 to 54 A/dm2 for a minimum of 2 to 3 hr to get a deposit at least 10 μm thick, and treating the resultant deposit as anode or cathode in a suitable etching solution or by simple immersing in acid. A typical anodic treatment is about 150 A-min/dm2, but this may prolonged or repeated if it is desired to removed more metal or to obtain deeper porosity. After the deposit has been heavily attacked, numerous crack are found to be eaten away, and a surface crust of undermined metal remains. When this crust is ground? Honed, or polished away to the extent of 25 to 50 μm numerous pits remain in the chromium plats.

Good condition for producing the "channel" type of porous chromium plate are 60 oC and the ratio of chromic acid to sulfate of 115:1. The usual current densities of 46 to 62 A/dm2 are employed for a deposit thickness of at least 100 or 125 μm. After treatment in the etching solution, the deposit does not have a loose surface crust but only a network of fissures, so that grinding, polishing, or honing off about 25 μm leaves channels, with dense chromium "plateau" or "land" between.

Other articles:

• Chromium alloy plating
• Etch prevention on chrome plating 

Etch Prevention in Hard Chromium Plating

The self-regulating baths have a disadvantage common to all baths containing fluorides or complex fluorides, a tendency to corrode or etch recesses which do not cover with chromium. This tendency to etching is especially noted on steel, commercially, the ordinary baths with sulfate catalyst hate a strong tendency to etch copper and brass. This etching tendency is especially marked in over catalyzed bath, and can be overcome to a considerable extent by keeping the bath in balance, or operating at as low a catalyst concentration as possible. In higher ratio of baths, overcome this etching by prefilming the surface to be plated as cathode in a plain chromic acid solution.

Chromium Etching and pitting of the brass metal is sometimes encountered in hard chromium plating even in ordinary baths with only sulfate catalyst, if stray current is permitted to leave non plating area such as the exterior of cast iron diesel cylinder liners being plated on the inside only. This can be prevented by greater care in maintaining full insulation on racks and fixtures, or by insulating the surface to be protected.

By the immersion deposits of noble metals such as platinum and palladium on steel would prevent the etching that occurs in low current density recesses, particularly in baths containing fluoride catalyst. Such immersion deposits of noble metals create a low over voltage condition on the steel surface that favors hydrogen evolution and tends to prevent other reactions. They may even prevent chromium deposition at higher current densities.

Other articles:

• Porous chromium plated
• Hard chrome plating 

Hard Chromium Plating

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The success of chromium plating in industrial applications may probably be attributed to its unique combination of properties not possessed by any other one material available commercially. The most important of these are hardness, adhesion, corrosion resistance, non galling and non wetting qualities, and low coefficient of friction. In many instances all these properties are important for successful commercial applications. The properties of hard chrome plating process produce a metal with hard chrome plating.

The hardness alone would not be sufficient to secure widespread use, become a number of other hard materials or hardening process are available. It is the combination of very great hardness with extremely good corrosion resistance (equal or superior under most conditions to that of such noble metals as gold or platinum), and very low coefficient of friction or unique surface qualities, which has given such remarkable result in many applications of chromium plate. To this should also be added relative ease of application and control, which ensures the maintenance of fixed standards of quality and durability, together with moderate cost. There is also be ease of stripping permissible limits.






The benefit of the hardness of chromium deposits is not effectively obtained unless the coating is deposited on a sufficiently hard basis metal and to a satisfactory thickness. Generally, hardened steel is used for the basis metal. Even a relatively heavy deposit of chromium may be crushed or indented if applied over a soft basis metal such as copper. The best possible adhesion is also important in many uses where the surface may be subjected to severe stress or shock, and any chipping of the deposit would be injurious.

Sometimes a bright deposit is applied to a smooth surface and used without further mechanical treatment. By means of careful operation it is possible to plate to size within very close limits. Worn machine parts are salvaged by chromium plating oversize and grinding back to size.

The stable wetting agents used to control fumes from chromium baths were found to encourage the formation of pits in heavy hard chromium deposits more than 35 micro meter thick, at basis metal defects. Some fume suppressants or wetting agents partially overcome this difficulty.

Other articles:

• Etch prevention on hard chrome plating
• Postplating treatment 

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Postplating Treatment

Postplating treatments are not commonly used on chromium plate, as the great passivity and tarnish resistance of the metal usually make them unnecessary. The normal “air passivity” of the metal can be considerably increased by treatment with anodizing agent such as nitric acid, where this is practical. Treated thick deposits with hot nitric acid, chromic acid, or permanganate solutions for many hours, and stated that the passive chromium would no longer dissolve in hydrochloric acid, and was more noble than platinum. Except for nitric acid, such treatments tend to discolor the chromium surface.






Electrodeposited chromium foils 250 micro meter or more thick, produced by stripping the brass basis metal from them in concentrated nitric acid and then baking overnight at 165 OC. resisted corrosion for 2 hours in concentrated hydrochloric acid. It should be noted, however, that this is an unstable condition, and any slight disturbance or handling may result in the sudden violent attack of the chromium by the hydrochloric acid with evolution of hydrogen.
Although treatment in a sodium hydroxide-sodium nitrite solution has been recommended for improving the corrosion resistance of thick chromium deposits on steel, other workers have disputed the efficacy of this procedure. Electrolytic polishing of the steel before chromium plating was effective to give hard chromium deposits of greater corrosion resistance.

To improve the corrosion coating of chromium-plated parts with supplementary surface films applied by cathodic treatment for about 1 min in a solution of 50 g/l sodium dichromate and 1 g/l chromic sulfate at 85 to 95 OC and pH 2.0 to 2.5 using 0.32 to 0.64 A/dm2. The extent and permanence of the improved corrosion resistance are not clear. There are indications that the effect tends to be lost after a year or two of outdoor exposure.

Other articles:

• Metallic impurities
• Hard chrome plating 

Metallic Impurities

Cations that may commonly be present in chromium plating baths include chromium (III), iron, copper, nickel, zinc and sodium. Chromium (III) usually result when baths are operated with too large a cathode area and too small an anode area or when organic matter is introduced. The chromium (III) content can be kept down by increasing the area of the lead anodes used relative to the cathode area, or, where this is not practical, by electrolyzing the solution for a time with a relatively large anode area and a small cathode area.

Iron, copper, nickel, zinc and other metallic impurities may be introduced into the bath in various ways; if permitted to accumulate, they cause an increase in the resistivity of the bath. None of the cations discussed has any noteworthy beneficial effect on the operating characteristics of the bath.

Chromium (III) particularly is detrimental, although contrary statements have appeared. The tradition that a small amount of chromium (III) is beneficial when added to a new bath may have grown up due to making such additions in the early days in the form of chromic sulfate or chromium hydroxide precipitated from chromic sulfate and containing some sulfate, thus affecting the catalyst content of the bath. A number of very painstaking investigations have failed to indicate any improvement in new baths with the addition of small amounts of chromium (III) and there is no need to electrolyze made up new bath for this purpose.

The next article is about how to maintain and to control of chromium plating.

• Post plating treatment
• Preparation of basis metal