Nickel Plating

The Electro Nickel Plating is also called the Nickel Electro deposition and has become a very popular process recently for various manufacturing applications. The process basically makes use of an electrical current in coating a conductive material, most especially those that are made of metal and with thin layers of nickel. Other metals that are utilized for electroplating are copper, stainless steel, zinc, as well as platinum.

Generally, the electroplating process helps to improve a wide range of characteristics that are not often present on the base material.

Benefits of Nickel Plating

The plating comes with several benefits and among these are the following.

• Improved ductility
• Improved hardness
• Increased resistance to corrosion
• Resistance to wear
• Superior strength

Nickel is popularly used for electroplating metals since it offers superior ductility, hardness, and great corrosion resistance. The process of electro Nickel Plating can also help to improve the brightness of a product, as well as its external appearance. Various plating chemicals are being incorporated into the process in order to deliver a semi bright to fully bright cosmetic effects, as well as pearl, matte and satin finishes.

How Electro Nickel Plating Works

In order to properly transfer Nickel to the surface, a negative charge should be applied against the base material. To make this possible, the product will have to be attached to the rectifier and other power supply with the use of a conductive wire. As soon as it is attached, a nickel rod will be connected in the same manner to the positive side of the power source.

After all the initial steps are completed, the base material will then be submerged to a solution that consists of salt and chemical makeup and includes the electroplating metal. With the electro Nickel Plating, the solution comprises of nickel chloride salt and water. Because of the electric current found on the solution, the nickel chloride salt will dissociate with the negative chloride ions as well as positive nickel cat ions. The negative charge of the base of the metal will then attractive that of the positive nickel ions and the positive charge of the nickel rod will attract the negative chloride anions. As a result of this chemical reaction, the nickel that is on the rod will oxidize and dissolve to a solution. From this, the oxidized nickel will be attracted to the base material and will end up coating the product.

Current Density of Electro Nickel Plating Process

The process of Electro Nickel Plating will involve various density levels. The current density will directly determine the deposition rate of the Nickel towards the base material, more especially because the higher current density, then the quicker the deposition rate will turn out. The current density will affect the plating adherence as well as the quality of plating where higher current density levels deliver poorer result. As such, the optimal level of the current density will depend on the base material type as well as the specific type of the result that the final product will require.

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The History of Nickel Plating

Nickel Plating has already been used for several hundreds of years now. Its main purpose is to help in strengthening metals against corrosion and wear and tear and to add aesthetic value to a dull appearance of the metal as well. There are several different kinds of plating methods available and these methods make use of either the chemical or electric method of dispersing thin layer of metal coating to metal substrate. The electric processes make use of a slight metal current right off the chemical bath. When the electricity passes through the wire and into the substrate, the oxidation process will disperse metal flakes and salts to an even layer coating. The electro less process will simply make use of a chemical reaction in producing similar and more stable results.

The Invention of Plating

The actual invention of Nickel Plating started during the early 1800s when the electrochemical piles have been developed, which helps to pump current through the wires. Such innovation has been found little application at first, but experts describe the electro deposition of the nickel chloride and sulphate on Platinum. Such process results to a thin crust of nickel off the platinum substrate and soon after, some experiments were done that proves nickel chloride, and nickel ammonium sulphate and nickel are also suitable for the process of Nickel Plating. The nickel ammonium sulphate also known as the double nickel salts solution has become an industry standard in the next seventy years in the industry of commercial products.

Patenting of the Nickel Ammonium Sulphate Bath

The nickel ammonium sulphate bath has been patented in the United States during the year 1869. One of the theories is that the electrolytic bath must be neutral and should be free from any soda, potash, alumina, nitric acid and lime as well as any alkaline or acid solution. Experts have engaged themselves in an aggressive marketing campaign in both Europe and the United States which results to a near universal acceptance by various industrial countries.

The experimentation and innovation of Nickel Plating has progressed, which attempted to incorporate the citric or benzoic acids to nickel sulphate and to the electrolytic bath in an effort to develop alternate process of plating. Some of these have been caught on, however, others garnered small to no following.

The air agitation and temperature level varies greatly in the US and in the UK for quite some time until such time that the international standards have been developed during the 1930s. Such standards comprise of increasing the bath’s temperature from the previously used room temperature and then introducing the air agitation shake up of the bath.

Ancient Plating Theories

Nickel plating process is being used during the ancient times, however the more recent and still current methods have been developed and greatly improved all throughout the 19th century. Such changes are a result of experimentations with the chemical composition of the bath used to plate and new methods of isolating chemicals and metals from one another. In the current time, plating processes have been well refined such that they can be done by large industrial companies and even home hobbyists within their garage.

The Process of Pickle Passivation

When the stainless steel is being welded a scale is often formed on the either side of the weld and such side is a heat affected zone will vary in color from blue to black depending on the welding condition. Such area is enriched with metal oxides that consist of very little corrosion resistance and readily allows corrosion to commence. Such effect extends way beyond the areas that are affected by the change of color. This area is very reactive and will easily rust in only a short period of time. Since this is not fully understood, it’s normal to see severely corroded areas wherein the stainless steel can be found on site. This is most unfortunate because the method of avoiding such corrosion is easy and is in fact, inexpensive and this is by means of Pickle Passivation.

Pickling

Pickling is the process of removing a thin surface layer off the stainless with the use of an acid solution which is often a mixture of hydrofluoric and nitric acid. In order for the Pickling to be effective, the surface should be clean and be clear of oils and greases. The process of pickling can help to remove embedded iron, heat tint, surface iron contamination, as well as weld scale. Pickling can also help to produce a dull matt and uniform grey finish during the process of Pickle Passivation.

Iron Contamination

A major cause of the corrosion on service is the iron contamination and this could arise from a wide variety of sources. These will include using tools that are made of constructional or mild steels, abrasives that contains iron and any tools that have been previously used on steel that are non stainless. A cross contamination can also take place from debris and grindings as a result of working near the steel either on site or in the workshop. Furthermore, iron contamination is not always obvious. If it is expected, it can be detected with the use of the ASTM A380 or ferroxyl test. This is a type of rapid test where a solution will turn to blue during the presence of iron. Pickle Passivation is an effective process of taking off the iron contamination off the surface.

Heat Tint and Weld Scale

The heat tint is produced through the welding process and is not only unsightly but the thicker oxide layer will include chromium coming from the metal surface, which lowers its corrosion resistance. Pickle Passivation both removes the oxide layer and will trigger color tints and a thin layer of underlying metal that restores the original properties.

The stainless steel has owed its corrosion resistance from the formation of the chromium oxide surface layer and is then being called as passive. This happens naturally and it spontaneously provides enough oxygen. Even the aerated water will provide enough oxygen for such process to occur. The material that is supplied by the producing mills fully passivated and further Pickle Passivation is rarely needed. But if the oxide is stripped off, perhaps by means of picking, then the oxide layer will take a short time to be able to reach its full thickness.

The Process of Phosphate Coating

The process of Phosphate Coating the steel and aluminum parts is often considered as a type of conversion coating since the process will involve the removal of metal as being part of the reaction. However, the process is not similar to anodizing or black oxide where the phosphating is often due to a precipitation reaction. The final surface will be a layer of very fine phosphate crystals that adheres right to the surface of the metal.

When it comes to the paint as well as powder coatings, the Phosphate Coating will have two functions. First is that it provides an improved adhesion for the paint and power coating because the phosphate crystals will act as organic coating anchoring the sites. Second, the phosphate layer will act as corrosion barrier in case the organic coating will be scratched. When it comes to rust creep testing, the rust creep will be reduced if the phosphate is present right below the paint layer or the powder coat layer as compared to no conversion layer right below the organic coating. The Phosphate can be used as either a standalone coating for other purpose like lubricity on parts forming, but other functions are way beyond the scope of this article.

Most Common Phosphating Chemistries

The most common phosphating chemistries are zinc phosphate, iron phosphate, as well as manganese phosphate. There are also several other phosphating chemistries like  Plaforizing, which is nontraditional when it comes to their chemistry as well as their application because they are a single step and are usually known as an organo phosphate that will react in both organic contaminants as well as the metal surface.

Lessen the Temperature Requirements

The main thrust in the recent years when it comes to improving the Phosphate Coating process is to lessen the temperature requirements used for the phosphate bath. Some other chemistry was developed in order to work well at a certain room temperature. Generally, there have been trend coming from high temperature, which is from 90 degree Fahrenheit to as much as 200 degree Fahrenheit, up to much lower temperatures, such as 70 degree Fahrenheit up to a maximum of 140 degree Fahrenheit that results to energy savings.

Phosphating Lines

Most of the Phosphating lines are the single tank, which are a three step and five step processes. The three and five processes are the following.

Three Step Process

1.    Clean or Phosphate
2.    Rinse
3.    Rinse and Seal

Five Step Process

1.    Clean
2.    Rinse
3.    Activated Rinse
4.    Phosphate
5.    Rinse

The single step process is more conservative on both energy and water as compared to the three and five stage processes. As for the Enviroprep of the Calvary Industries, the chemistry will be phosphate free, yet it still serves as surface preparation stage for powder and paint coating.

The three and five step processes of the Phosphate Coating can often be made with more water efficient to flow optimization of the rinse recirculation, rinses, rinse counter flow and in some instances, reactive rinses. Both of the three and five step processes can be made of energy efficient by changing to the lower temperature phosphating chemistry.

Picklel Passivation

Stainless steel could corrode in service if there will be contamination right off the surface. Picklel Passivation is a type of chemical treatment that is being applied right towards the surface of stainless steel in order to remove contaminants and at the same time help in the formation of continued chromium oxide. Passivation and pickling are two types of acid treatments and none of them can remove grease or oil. If the process of fabrication will attract a lot of dirt, it will be necessary to make use of detergent and alkaline right before the passivation and pickling.

Pickling

Pickling is basically the process of removing high temperature scale as well as any adjacent low chromium layer of metal off the surface of stainless steel through a chemical process. Where steel is being heated by means of welding, heat treatments and other means, to a point where the colored oxide layer will be seen, there will be a chromium depleted layer that will be found on the surface of the steel right below the oxide layer. The lower chromium content will provide lower corrosion resistance. In order to restore the most excellent corrosion resistance, the damaged metal layer should first be removed in order to expose a fully alloyed surface. The process of mechanical removal could leave abrasives as well as other particles embedded, and thus, chemical process is being employed by means of Picklel Passivation.

Passivation

Passivation is the process of treating surface of stainless steel, which is usually done by means of an acid solution or paste in order to remove contaminants and to encourage the formation of passive film to a freshly created surface.

The usual passivation treatment will also include nitric acid solutions and pastes that will clean off the steel surface and free it from iron contaminants. Utmost care should be taken in choosing and using passivation treatment in order to ensure that the chosen treatment will target the contaminants. Picklel Passivation also helps in the rapid development of the passive oxide film right on the steel’s surface. Passivation will not usually result to a marked change on the appearance of the surface of the steel.

Heat treatments such as welding and annealing will usually lead to discoloration and scaling. This will not only cause deterioration on the appearance of the component but also its ability to be corrosion resistance as a result of the presence of the ferric oxides. The continuous passive layer of the chromium oxide will not be formed here, and thus, it should be metallically clean and must be a pure surface by pickling right before the passivation.

Safety

The process of Picklel Passivation makes use of dangerous acid that could trigger damage on the environment as well as on the operator, if the process is not handled well. The stainless pickling is highly corrosive to carbon steel. The process makes use of strong acids and the usual precautions to safety must be adhered to. It is a good idea to consult the materials safety data sheet as well as the product packaging for a more detailed advice when it comes to Picklel Passivation.

Phosphate Coating and the Process of Phosphating

Phosphate Coating is a type of crystalline conversion coating that will be formed in a ferrous metal substrate. The coating is used for the main purpose of pre-treatment that will be done right before painting or coating and for increasing corrosion protection as well as for improving the friction properties of the sliding components. In some instances, the Phosphate Coating is being applied on threaded parts and it is being top coated with a specific type of oil in order to add an anti-galling characteristic as well as rust inhibiting characteristics for the metal substrate.

Process of Phosphating

The process of Phosphating basically relies on the basic pickling reaction that will occur on the metal substrate if the process solution will come in contact with metal. The biggest benefit that Phosphating can give is corrosion protection and strong adhesion. Just like Phosphate Coating, the process of Phosphating is being used for steel parts although it is also sometimes being used for aluminum.

Manganese Phosphating

In some cases, companies that offer Phosphate Coating also offer Manganese Phosphating. This process is basically used as a corrosion protection and for giving a metal part a lubricity and anti-galling properties. Of the various Phosphating process available, it is the manganese Phosphating that is considered to be the hardest as it provides unbeatable abrasion and corrosion protection. Just like with the Zinc Phosphate Coating, the manganese Phosphating offers a continuous wear protection right after the breaking of components that are being subjected to wearing. The coatings can also be applied by means of immersion and the use of Manganese Phosphating will include the production of bushings, bearings, fasteners as well as other common industrial products. Manganese Phosphating is very useful for those projects that will require the sliding of parts, like the automotive engines as well as transmission systems.

Zinc Phosphating

As mentioned, another process of Phosphate Coating is called the Zinc Phosphating. This process is being used as a means to rustproof ferrous metals. They can be applied through a process called immersion also known as spraying. As you know, Zinc Phosphate is a lighter alternative to Manganese Phosphating and provides resistance to harsh elements that could wear products very quickly.

Process of Application

The application of Phosphate Coating will require the use of Phosphoric Acid while taking advantage of the low solubility of the phosphates in medium or high pH solutions. Zinc, Manganese or Iron phosphate sales are being dissolved to a solution of the Phosphoric acid. If the iron or steel parts are being placed on the Phosphoric acid, the Classic acid as well as metal reaction will take place that locally depletes the H3O+ or hydronium ions which increases the pH and cause the dissolved salt to fall off the solution and will be precipitated right on the surface. The acid as well as the metal reaction will also create iron phosphate locally that might also be deposited. In the event of depositing the Zinc or Manganese Phosphate, an additional Iron Phosphate could become an undesirable addition to the process of Phosphate Coating.

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Electroless Nickel Plating and Large Nickel Plating

Electroless Nickel Plating is a process of applying metallic coating to other metals or non-conductive substrates like plastic without the use of electric current. This is an auto catalytic, chemical bathing method from small to large nickel plating that has developed to be very benefiting for the manufacturing industry. The process happens through a controlled chemical reduction that is catalyzed by a metal or an alloy. Optimum quality is reached dependent on the success of maximum and uniform coating adhesion to the material. Electroless nickel plating has a lot of advantages such as: being free from flux-density, electric power issues, consistent plating and it prevents wear as well as corrosion. Moreover, even if the substrate structure is of complicated geometrical form, electroless nickel plating can still deliver a seamless finish to the plated product. Large nickel plating is one of the toughest yet achievable challenges of this technology. With time, bigger structures have been featured to be successfully plated by the process.

Historically, the plating of metallic nickel from a liquid chemical using hydrophosphite as the catalyst was first noted in the 1800s and it started to be developed during the 1940s at the time of the World War II. This technology had its full bloom in 1981 when it became industrialized to be the better option over electroplating. The other advantages of this technique are no sophisticated jigs required, flexibility in plating volume and thickness, complex filtration method is not required and matte, semi-bright or bright finishes can be achieved. There is a bit of challenge on the chemicals used since their shelf life are short, hence waste treatment is very costly. Aside from that, ENP is just the best option for small or large scale nickel plating. Some good examples of products are doorknobs, kitchen utensils, bathroom fixtures, office equipment as well as electric and mechanical tools. Also, since the coating is so strong it can be used to save corroding and worn parts of materials as well. Lastly, electroless nickel plating is also extensively used in the manufacture of hard disk drives, the layers of coating protect the magnetic layer should R/W head lose its air cushion and make contact with surface.

The process begins with pre-treatment wherein the material to be coated is thoroughly cleaned in series using different kinds of chemicals and most importantly water. Soils are removed first, then grease and after the material is treated with acid to also remove scaling. Each and every after one step the material is rinsed two to three times to make sure that none of the chemicals per step is left. The pre-treatment phase of electroless nickel plating is highly important since this determines the quality of the finished product. After this, activation is commenced with a weak acid for metal substrates or a propriety solution for non-metals. For finishing, the material needs to be also treated with an anti-oxidation and anti-tarnish chemical such as chromate and then rinsed again very carefully to prevent staining the finished nickel coat.