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| Electroplating is the coating of one metal on another by applying electricity in order to secure an improved appearance, resistance to corrosion and/or prevent rusting. This is usually carried out under an appropriate and suitable condition. There is tremendous market demand for electroplating solutions, especially in soldering, which is an important process in the manufacturing of modern hi-tech products like as (Tag, Terminal, Holder) Mobile Phones, Lcd Monitors, Pcs & Laptops. We are also deal with Automobile Industries (Locks, Clips, Handle, Holder, Reflectors, and Coil), Garment Indsutries (Button, Frame, Purse Frame, D-ring, Dog Hooks, Buckles, Rivet) Surgical Industries, and sand Metal Finishes. |
| In a strategic move by the founders to tap these increasing market demands in India and overseas, SreePadham Industries was established in 2000 as a reliable service provider. The company is a leading electroplating service/solution provider, principally engaged in the business of providing innovative electroplating solutions with specialization in the electroplating of tin, brass, and trivalent zinc, decorative & hard chrome to meet the needs of a host of industries. We are an affiliated member of the prestigious Small Scale Industry (SSI). |
Electroless deposition
Usually an electrolytic cell (consisting of two electrodes, electrolyte, and external source of current) is used for electrodeposition. In contrast, an electroless deposition process uses only one electrode and no external source of electrical current. However, the solution for the electroless process needs to contain a reducing agent so that the electrode reaction has the form:
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Effects
Electroplating changes the chemical, physical, and mechanical properties of the workpiece. An example of a chemical change is when nickel plating improves corrosion resistance. An example of a physical change is a change in the outward appearance. An example of a mechanical change is a change in tensile strength or surface hardness.
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Limitations
Obtaining a uniform thickness with electroplating can be difficult depending on the geometry of the object being plated. The plating metal is preferentially attracted to external corners and protrusions, but unattached to internal corners and recesses. These difficulties can be overcome with multiple anodes or a specially shaped anode that mimics the object geometry; however both of these solutions increase cost.
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ACID ZINC PLATING:
An acidic zinc electroplating bath comprising zinc fluoborate dissolved in an aqueous liquid containing as an iron- and metal oxide-deposition inhibitor a small effective amount of a mixture of a 4-hydroxy-, 4-alkyl- or aryl-, 5-acyl- or aroyl-piperidine and thiourea or N-substituted derivative thereof. The invention also includes an improved process for zinc-electroplating ferrous metals from such bath.
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Steps of Commercial Zinc Electroplating Process
On the commercial scale, zinc electroplating is done by the following steps.
1. Surface of the metal is cleaned in alkaline detergent type solutions, and it is treated with acid, in order to remove any rust or surface scales. Cleanliness is essential for successful zinc electroplating, as the molecular layers of oil or rust can prevent adhesion of the coating.
2. Next, the zinc is deposited on the metal by immersing it in a chemical bath containing dissolved zinc. A DC current is applied, which results in zinc being deposited on the cathode. Alkaline zinc baths are used by the finished products, to produce a more consistent zinc thickness, especially in recesses.
3. Hence an increased protection from corrosion is provided, as the corrosion of the deposited zinc is reduced. The zinc coating can increase the time required for the formation of white rust, by ten times. Finished Products also apply sealers, which are now commonly being specified by the automotive industry, further increasing corrosion protection.
4. It is very difficult to obtain a uniform thickness of coating, with electroplating technique. The thickness of the coating is very much dependent on the geometry of the object being plated, and it is preferentially on the external corners and protrusions of the metal body, hence not much of it is deposited on internal corners and recesses. Zinc electroplating process is used to make a clean, smooth and corrosion resistant surface. It also makes an excellent undercoat for powder coating or paint and can leave recesses on complex shaped components without sufficient zinc coating, in order to provide corrosion protection. |
Zinc Plating
Zinc coatings prevent oxidation of the protected metal by forming a barrier and by acting as a sacrificial anode if this barrier is damaged. Zinc oxide is a fine white dust that (in contrast to iron oxide) does not causes a breakdown of the substrate's surface integrity as it is formed. Indeed the zinc oxide, if undisturbed, can act as a barrier to further oxidation, in a way similar to the protection afforded to aluminum and stainless steels by their oxide layers.
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Tin Plating
The tin-plating process is used extensively to protect both ferrous and nonferrous surfaces. Tin is a useful metal for the food processing industry since it is non-toxic, ductile and corrosion resistant. The excellent ductility of tin allows a tin coated base metal sheet to be formed into a variety of shapes without damage to the surface tin layer. It provides sacrificial protection for copper, nickel and other non-ferrous metals, but not for steel.
Tin is also widely used in the electronics industry because of its ability to protect the base metal from oxidation thus preserving its solder ability. In electronic applications, lead may be added to prevent the growth of metallic "whiskers" in compression stressed deposits, which would otherwise cause electrical shorting
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Alloy Plating
In some cases, it is desirable to co-deposit two or more metals resulting in an electroplated alloy deposit. Depending on the alloy system, an electroplated alloy may be solid solution strengthened or precipitation hardened by heat treatment to improve the plating's physical and chemical properties. Nickel-Cobalt is a common electroplated alloy.
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Cadmium Plating
Cadmium plating is under scrutiny because of the environmental toxicity of the cadmium metal. However, cadmium plating is still widely used in some applications such as aerospace fasteners and it remains in military and aviation specs. Cadmium plating (or "cad plating") has technical advantages such as excellent corrosion resistance even at relatively low thickness and in salt atmospheres, can be dyed to many colors and clear, has good lubricity and solder ability, and works well either as a final finish or as a paint base.
• Zinc Plating • Acid Chloride • Alkaline Non-Cyanide • Cyanide • Zinc Nickel
Welcome to the premier industrial resource for Zinc Plating. The manufacturers and distributors featured in the following listing offer a broad range of Zinc Plating, including clear & black non hexavalent chromate & trivalent chromate processes, barrel & rack and salt spray protection. Also available on the extensive Thomasnet.com directory are Zinc Plating related services and products, from Zinc-Cobalt Alloy Plating, Zinc Die Casting Plating, Perforated Zinc, Plating Machinery and Zinc Plates.
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Electrochemically, alloys can be designed
to produce different corrosion potentials than their alloying elements. It is possible, therefore, to maintain the sacrificial protection of zinc coating over steel, but at a different potential, closer to steel, by alloying it with another metal, preferably more noble than zinc. As a result, the alloy corrodes at a much slower rate than zinc alone, affording better corrosion protection. Some of these alloys have been found to be excellent replacements for cadmium plating in many applications.
Zinc alloy plating technologies were introduced in the mid 1980's in the U.S. Although started in Japan and Europe some 10 years earlier, it was only recently that their acceptance and use on a commercial basis was felt in the U.S. and Canada. Several factors may have delayed the adoption of these technologies by U.S. industry, despite their documented success in Japan and Europe:
1. Our regulatory agencies have only recently restricted the use of cadmium as a protective coating. Finding a good substitute, therefore, became urgent. |
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2. The desire for improved quality and product reliability surpassing that of zinc plating.
3. The simultaneous introduction of several zinc alloys and processes required time to evaluate in order to sort out the best ones before new specifications were drawn.
The various technologies offered to the metal product finisher today include: zinc-iron, alkaline or acid zinc-nickel, zinc-cobalt, and tin zinc. |
Zinc-Iron
This process produces alloy deposits containing 15-25 pct iron. Electroplated strip steel adapted this process initially to improve its corrosion resistance. The deposit has good weldability and ductility that are needed in subsequent manufacturing steps. This alloy can be adjusted to improve adhesion of electroplating of formed steel components. Black chromating is the most suitable for this type of alloy. Although zinc-iron offers good corrosion resistance as plated and chromated, exposure to heat deteriorates this resistance rapidly. This makes it unsuitable as a coating for under-the-hood automotive components. |
Passivation and Post Plate Treatment
There are several hexavalent chromate passivation treatments for the zinc alloys, which are necessary to produce the enhanced corrosion resistance of these alloys. Recent developments have introduced trivalent chromate formulations as well as chromate free passivates in various finishes ranging from clear to iridescent and black. Inorganic and organic topcoats are also available to further enhance overall corrosion resistance and provide other properties such as lubricity and torque and tension.
As more industries worldwide respond to local bans on cadmium plating, and demands for improved functional coatings, zinc alloys offer the industry a viable alternative to conventional zinc and cadmium plating. The last few years have seen large scale installations of these technologies. The trend is continuing. Corrosion resistance of the various zinc alloy deposits is compared in Table VI. Zinc-nickel alloys maintain the highest corrosion resistance even after heat treatment. |
Zinc Alloy Plating
Electrochemically, alloys can be designed to produce different corrosion potentials than their alloying elements. It is possible, therefore, to maintain the sacrificial protection of zinc coating over steel but at a different potential, closer to steel by alloying it with another metal, preferably more noble than zinc. As a result, the alloy corrodes at a much slower rate than zinc alone, affording better corrosion protection. Some of these alloys have been found to be excellent replacements for cadmium plating in many applications.
As more industries worldwide respond to local bans on cadmium plating, and demands for improved functional coatings, zinc alloys offer the industry a viable alternative to conventional zinc and cadmium plating. The last few years have seen large scale installations of these technologies. The trend is continuing. Corrosion resistance of the various zinc alloy deposits is compared in Table VI. Zinc-nickel alloys maintain the highest corrosion resistance even after heat treatment.
Zinc alloy plating technologies were introduced in the mid 1980s in the U.S. Although started in Japan and Europe some 10 years earlier, it was only recently that their acceptance and use on a commercial basis was felt in the... |
What is electroplating?
Electroplating is the deposition of a metallic coating by putting a negative charge on an object and exposing it to a solution containing a metal salt. The positively charged metal ions in the salt solution are attracted to the object and reduced to metallic form upon it. |
How does it work?
Look at the figure above: We have a metallic object we want to plate with a metal. First we fill a cell with a solution of a salt of the metal to be plated. Most of the time the salt (nickel chloride in our example) is simply dissolved in water and a little acid The NiCl2 salt ionize in water into Ni++ ions and two parts of Cl- ions. A wire is attached to the object, and the other end of the wire is attached to the negative pole of a battery (with the blue wire in this picture) and the object is immersed in the cell. A rod made of nickel is connected to the positive pole of the battery with the red wire and immersed in the cell.
Because the object to be plated is negatively charged (by being connected to the negative pole of the battery), it attracts the positively charged Ni++ ions. These Ni++ ions reach the object, and electrons flow from the object to the Ni++ ions. For each ion of Ni++, 2 electrons are required to neutralize its positive charge and 'reduce' it to a metallic atom of Ni0. Thus the amount of metal that electroplates is directly proportional to the number of electrons that the battery provides. |
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This relationship is a reflection of Faraday's Law of Electrolysis. If you are advanced enough in chemistry (a high school student), that you've heard terms like gram molecular weight, mole, valence and Avagadro's number, but it's all a hodepodge to you instead of a cohesive whole, don't despair! Study Faraday's Law, and suddenly all of these disparate wacky terms will come together in a moment of enlightenment.
Meanwhile back at the anode, electrons are being removed from the Nickel metal, oxidizing it to the Ni++ state. Thus the nickel anode metal dissolves as Ni++ into the solution, supplying replacement nickel for that which has been plated out, and we retain a solution of nickel chloride in the cell.
As long as the battery doesn't go dead, nickel continues to dissolve from the anode and plate out onto the cathode. |
We used nickel chloride in the example chiefly for simplicity of explanation. First, because nickel always dissolves in the "+2" oxidation state (Ni++), whereas many other metals like copper and zinc can dissolve in either the "+1" or "+2" state and add some confusion; secondly because chloride is a simple one-atom anion whereas most anions like sulphate or acetate are far more complex. But we do not recommend that nickel be used for school science demonstrations because -- while the explaining is simple -- the plating is difficult
The first demonstration -- Zinc plating a penny
For the first demonstration, the cathode will be copper (pennies), the anode will be zinc, and the electrolyte (solution) will be zinc dissolved in vinegar and water.
Zinc anodes are available from boating stores
With a hacksaw a teacher or group can cut many slices from one anode .A second option is to sand down a modern U.S. penny (1983 or later) until the copper surface is removed and the underlying zinc substrate is exposed. |
| A third possible source of zinc is the shell of conventional carbon-zinc batteries (make sure not to use alkaline batteries like Duracell or Eveready Energizers, nor rechargeable nickel-cadmium batteries -- just the cheap 1-1/2 volt AA, C, or D plain carbon-zinc batteries). The science teacher can cut up such batteries and remove the black glop, and give the student the cleaned zinc. |
For the pennies that you wish to plate onto, any pennies will do, but if you start with a dull brown penny, you'll end up with a dull zinc plated penny. Try to find shiny new pennies for best results! Immediately before plating, clean the penny with toothbrush and toothpaste, or a gentle scouring powder like Bon Ami or Multiscrub, and rinse well after cleaning. Your hands are oily, so wear plastic gloves so you do not get fingerprints or other soils on the penny after cleaning.
A transparent plating container is best, a Pyrex beaker is excellent, but a glass dessert bowl can serve well. |
A recipe suggested by Tom Pullizzi, and found to work is:
Fill the container about half way with vinegar (vinegar is mild acetic acid). Put the zinc anode into vinegar and let it sit for several hours, allowing some of the zinc to dissolve.
Add 100 g/l of Epsom Salts (this salt helps make the solution conductive)
and 120 g/l of table sugar (this is called a "brightener")
Connect one flashlight battery (1-1/2 volts) to the penny and the zinc anode, and place them into the solution. Don't let them touch each other. With luck, within a few minutes you'll begin to get a bright silvery coating. Ted Mooney didn't have quite that much luck when he tried it, but did find that a reapplication of the toothbrush and toothpaste quickly polished the thin greyish coating he got to a fairly bright shine. |
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