Pertinent Facts of Nickel Plating

Plating baths each provide specific benefits that, regardless of cost, have become necessary for various on demand finishes. These include: decorative, functional, wear resistance, and corrosion protection. Nickel encompasses many plating systems, each of which is very important to many aspects of metal finishing. Even though the prices of nickel anodes and related salts have been very volatile, the importance of nickel in plated finishes is still of great significance.

For industrial purposes, almost any metal can be nickel plated. The inherent properties of nickel can be combined with the unique properties of other metals. Some examples of metals commonly plated with nickel are: steel (high strength), brass (easily bent and formed), aluminum (impact extrusion), and die castings (design flexibility). Plastics, which have been treated for conductivity, are also commonly nickel plated. Nickel can be directly plated over several metals. This is typically performed directly over steel, brass, and copper. In some cycles, appropriate immersion treatments or pre plate deposits precede nickel. This is especially prevalent when plating a copper strike and copper plate over zinc parts before nickel. Aluminum, because of it’s unique electropositive nature, must first be conditioned by immersion zincating, before plating either electrolytic or electroless nickel.

The application of a suitable nickel deposit can be of significant benefit to the parts, ultimate quality of the finish, and meet or exceed specifications. These advantages can actually reduce related manufacturing costs, improve marketability, and increase production throughput. Depending on the finishing requirements or service life of parts, nickel contributes the following advantages:
Good electrical conductivity, low coefficient of thermal expansion, magnetic, and good heat conduction. Nickel can be plated as a soft deposit (not far off from copper) or almost as hard as chrome. In fact, nickel can be plated to almost any desired deposit hardness in between this wide range. Aesthetically, nickel can be plated in decorative applications to achieve a wide range of brightness and leveling, still retaining sufficient deposit ductility.

Finished parts can be assembled or mechanically formed into selected commercial products. Along with these benefits, duplex nickel forms an excellent corrosion barrier, especially in the plating of exterior automotive parts. Nickel forms an important barrier to prevent the migration of zinc on tin plated parts. In engineered finishes, nickel decreases contact, resistance and friction, improves solder ability and brazing, and improves resistance to galling and wear. Plating with nickel can salvage worn or miss-machined parts. Almost all nickel deposits can be machined. Incorporating nickel into the deposit, in place of solid metal, reduces some manufacturing costs.

As mentioned previously, nickel can be plated to provide rapid leveling, filling voids, eliminating microscopic “peaks and valleys”, while plating a relatively thin deposit. For this reason the base metal may not have to be mechanically polished, buffed, or mass finished. If this is acceptable, cost savings to prepare the surface for plating may be realized. Nickel can be plated from a variety of specific bath formulations (usually Watts and sulfamate types), to develop deposits that range from flat to dull to semi bright to bright. This affords the finisher the capability to provide nickel deposits that meet engineering requirements, corrosion protection, and aesthetic preferences. The Woods strike effectively activates stainless steel for subsequent nickel plating. Duplex nickel, as mentioned earlier, promotes exceptional corrosion protection, by plating a balanced ratio of a special semi bright and bright nickels. The Step Test is a specific quality control procedure for this application. In recent years Watts baths containing modified organic additives, have successfully replaced cyanide copper strikes over zincated aluminum. Decorative chrome, either trivalent or hexavalent, continues to be a specified finish over nickel. The chrome topcoat enhances overall appearance and maintains an excellent scratch resistant, hard finish. Although we commonly refer to the bright chrome finish, it is primarily nickel (usually bright) with a thin chrome flash. The combination of these deposits give the assembled parts a preferred pleasing appearance, along with exceptional corrosion and wear resistance. For several decades, the combination of bright nickel and flash chrome has been the best selection for plating parts subject to outdoors exposure.
Nickel can be plated as a very ductile deposit. In combination with a proper base metal conditioning and any preplate deposits, the finished items can be stamped, drawn, or formed in a variety of shapes. This is very common in the strip plating of continuous coils that will be used in the manufacture of different types of consumer and industrial goods. In this application, the organic brightener and leveling additives may be kept at lower levels, to achieve the required ductility. Final aesthetic appearance of nickel occurs in a short buffing cycle before optional chrome plating. Parts that require exceptional brightness and leveling may be stamped before the plating cycle.

Nickel can be plated to meet any thickness requirement. Industrial based coatings usually require 0.005 – 0.020 inch. For decorative purposes, nickel thickness may range from 0.0003 – 0.001 inch (or up to one mil). As indicated by the application ranges, there is a minimum that should be plated to meet the intended use of finished parts. As a guide, 1 lb of plated nickel is required for every 22 ft2 of intended parts coverage. Depending on the nickel bath and plating parameters, the deposit tensile strength can range from 50 to 220 thousand lb / inch2.

Nickel anodes, as we are aware, are quite expensive. Be certain a certificate of analysis confirms the quality. Anything less than sufficient purity material could result in severe contamination of the nickel bath. A typical assay is: Nickel (99.950%), Cobalt (0.03%), Copper (0.005%), Carbon (0.001%), Iron (0.001%), Sulfur (0.01). Anodes are provided in various shapes, including: spears, buttons, rounds (sulfur containing S and sulfur free R), and chunks.

There are many applications for plating nickel, using several types of process baths. The demand for nickel plating continues to be relatively strong. Although the prices for nickel anodes and salts have markedly risen, the consumer market for plated finishes keeps this plating service very active. Original and after market automotive finishes have “re-discovered” bright nickel / chrome finishes. The decorative plumbing industry is very positive on nickel / chrome and brushed nickel finishes. Clothing and apparel manufacturers now feature nickel finishes (ex. oxidized, brushed, under flash brass or gold). Nickel anodes and salts may not be cheap (compared to a few years ago), but decorative and industrial finishes for nickel are still in strong demand.

Filtering Cleaners: A Wise Choice

Last month’s blog described several filtration methods, along with equipment, purifying agents, and the overall benefits of filtration. The underlying message was how the subject, as related to plating baths, is so important. Most of us, through experience, can relate to the strong link between effective filtration and quality metal finishing of parts. One would be hard pressed to not see some form of filtration in a plating line. By walking the line backwards, how many cleaner tanks have you seen being filtered? Do you think it is a good idea? Is there any real benefit? From practical experience, using equipment and formulating specific cleaners, I know that filtering these baths is a good decision. Let us consider some reasons for filtering cleaners and available methods.

Is It Clean or Dirty
Obviously, the ideal condition for any cleaner is the freshly prepared working solution, just before immersion of any parts. After the initial dunk of parts, the solution becomes soiled; as should any good soak cleaner behave. As production use proceeds, the bath loads up with contaminants typically consisting of oils, grease, and fine particles. Perhaps you have noticed the tell tale signs: solution turns either a dark or tea brown, milky color, oils tend to separate and float (especially as the cleaner cools), grease rings form on the walls of the tank, sludge and particles build up on the bottom of the tank. Just how soiled does the cleaner become before it starts working against you? Why not try a couple of quick tests that might tip off trouble before it actually strikes.

• -Specific Gravity. Measure the cleaner bath specific gravity when first made up (no parts as yet immersed). On a scheduled basis, measure and record the specific gravity as the bath ages. During this time maintain the cleaner concentration at the initial make up. There will be a point at which the data coincides with a drop in quality cleaning. The specific gravity will have increased to a point that indicates how much oil, grease, and particles have built up in the bath. Corrective action may include making additions of the cleaner concentrate, cut the bath and replenish, or dump and replace with a new make up.



• -Performance Test. Immerse a clean panel (ex. Steel hull cell panel) in the cleaner bath for the same time as the parts. Rinse in cold running water for 60 seconds and examine for water breaks. Next, immerse in dilute acid (5% Hydrochloric or Sulfuric Acid) for 15 seconds, followed by rinsing in cold running water. Examine for water breaks. A positive observation of water breaks at either step would indicate deposition of soils from the cleaner bath on to the panel. Once again, corrective action may include making additions of the cleaner concentrate, cut the bath and replenish, or dump and replace with a new make up.



• -Oil Displacement. As the bath ages, the concentration of emulsified oily soils becomes more concentrated. Take a 50 milliliter sample of the hot cleaner and using care, slowly add to it 50 milliliters of 10% sulfuric acid. Mix the solution well for about 15 minutes. Pour the solution into a clean 100-milliliter graduate cylinder; adjust volume, if necessary, with water to 100 milliliters. Observe as the oils separate. Record the volume and multiply by 2 to obtain the %-displaced oils. As with the two previous tests, corrective action may include making additions of the cleaner concentrate, cut the bath and replenish, or dump and replace with a new make up.

These control examples confirm or predict at what point the cleaner, even with proper maintenance additions, and correct operating temperature, will approach its maximum service life. In most instances, adding more cleaner concentrate may restore quality cleaning, but perhaps only for a short time. We have only considered how to determine to what extent the cleaner is contaminated, with the same type of corrective action alternatives. In no instance has any consideration been given to removing the contaminants or minimizing their buildup. Can this be done? Yes, quite effectively. By filtering the cleaner, the following realistic benefits are readily obtained:

• -Extend cleaner bath service life. Less down time means longer periods of uninterrupted productivity.



• -Less bath dumps reduce the workload in waste treatment.



• -Minimizing contaminants in the cleaner helps to maintain the solution consistency closer to the new make up.



• -Quality cleaning results in satisfactory surface preparation, leading to quality finishing and post treatments.

The cleaner can be filtered using some different options.

Cartridge Filter. These are enclosed canister types that have a polypropylene center around which similar fiber material is tightly wound. The porosity of the filter medium can range from 100 microns to below 5 microns, based on the specific filtering requirement. Particles are retained in the media pattern. The polypro material absorbs oily solutions. The cleaner is continually pumped through the filter cartridge. It is a relatively simple, yet effective system to remove the typical contaminants found in the cleaner. The unit does not take up much floor space. When spent, the supplier can dispose of cartridges sometimes directly to a certified destruct facility.

Oil Absorbing Filter. This unit consists of an enclosed housing that contains polypropylene baskets containing special oil absorbing plastic type media. The cleaner is pumped through the enclosed system, where the media absorbs oils and grease. The saturated media is replaced as needed.

Bag and Indexing Fabric Filters. The cleaner is pumped through a large filter chamber, where oil, grease, and particles are retained. Takes up large floor space. It is a decent filtration system, but not applicable to systems cleaning large volumes of very oily parts.

Ultrafiltration. This is an interesting technology, using a somewhat permeable membrane system. The soiled cleaner is pumped through the (ceramic) membrane tubes. Molecules of sizes larger than water are blocked from passing through, diverted to a discharge. The aqueous cleaner solution passes through and returns to the process tank. Ultrafiltration provides a rapid, very dramatic filtering action. Of the examples given, ultrafiltration is by far the more expensive (approx. $20K and up). Considering a flexible or mobile unit that can be used to treat several cleaner tanks can offset the application, or rental as required.

Filtration can be supplemented by the application of mechanical oil removal devises. These units are quite cost effective and can be used in-tank. An overflow weir or side tank can collect cleaner solution, which cools down about 10-20 degF below the temperature of the cleaner, while oils separate to the top. The oils can be skimmed off using a disk or belt. A coalescer is another oil removing device. It channels the flow of cleaner, separating the aqueous from oily solution.

A final consideration to assist in the filtering of cleaners would be to consider the type of cleaners to be used. Displacement cleaners remove and release the oils for quick removal by the filter or separator. Another type of cleaner is what I refer to as the “mini emulsion”. Oils are kept emulsified as long as the cleaner is agitated (such as barrel soak cleaning). When the solution settles in dead zones or in a side tank, oils are released for suitable removal. Another choice is the emulsion cleaner, that releases significant quantities of oils by simple cooling (ex. from 160 degF down to 120 degF). A chemical additive can also be used for certain cleaner formulations. The mixture of agents selectively emulsifies the oils in favor of the heated cleaner, splitting out in mass with the oils.

Filtering cleaners offers the metal finisher several benefits. They include: quality, economics, productivity, compliance, and safety. The available filtration equipment provides the degree of treatment or sophistication that is preferred. Cleaning is the first step; in fact the most important step in a finishing cycle. By effectively filtering the cleaner, buildup of contaminating soils is kept at a minimum or controlled. Subsequently rinses and process tanks down the line are kept relatively free of contaminated cleaner solution drag in.

Filtering cleaners. Make the wise choice, your choice.

Filtration: It's a Must Have!

We associate cleaning, clarifying, and purification with the process of filtration. Many of us rise each day to enjoy a first cup of fresh brewed coffee that has passed through a filter. Perhaps a filter is running to condition the air we breathe. Start the car engine and efficiently operating oil and gas filters make the trip to work possible. These are a few examples of which there are many more that exemplify how essential filtration is to our daily lives. In fact have you ever wondered why our bodies sustain two operating kidneys to filter our blood and other essential fluids? That is how important these organs are to us. In fact, the kidney is so resilient that only one can do the job of two. Take proper care of your kidneys and they should provide many decades of trouble free service.

Let us consider some general facts regarding the importance of filtration in metal finishing. It should become clear how important proper filtration is to influence optimum performance and quality processing of parts. Water conservation, minimizing drag out losses, closed looping, and easing the burden on waste treatment, all place a critical burden on plating solutions. These are some contributing factors that make filtration so important. It is very common to filter plating solutions. This should also be done correctly and maintained on a fixed schedule. Routine maintenance of the plating bath should include analysis, hull cell, and continuous filtration. Minimizing contaminants in a plating bath greatly affects: meeting or exceeding specifications, salt spray and other wear resistance tests, and realizing anticipated field service life of finished parts. Routine analysis and continuous filtration to maintain sufficient purity, inherently influence the quality of the deposit. Some general considerations with regard to filtering plating solutions are listed. Specifics, focusing on more quantitative information, can be found in many informative publications.

• Carbon. Granular and powdered carbon have been found to be equally effective. Both of these forms of carbon can be used for purposes of continuous filtration. Initially, powdered carbon purifies quicker, due to it’s greater surface to volume ratio. This is why it is preferred for batch purification treatments. Granular carbon is much less dusty, generally cleaner, and much easier to work with. There are some commercially activated carbon grades available that have been chemically treated with special agents that improve adsorption activity and sequester some heavy metals.
  



• Diatomaceous Earth. These are generally forms of clay, which can be used as filtering media. They are commonly referred to as filter aids. In some instances particular organic contaminants may not be as susceptible to adsorption to carbon. Filter aids offer additional binding sites for better removal of these tougher organic contaminants. They also, in combination with carbon, help to remove fine particulates.



• Filter Cartridges. These are normally pleated, having different porosities. It’s beneficial to the plater by the ability to remove particles down to one micron in diameter. In this way, desired clarity is achieved. Deposit roughness and pitting are avoided. The unit may be a simple, single cartridge filter. Or, it could be a multiple chambered system, in which a carbon containing bag or cartridge may be inserted. Pleated or wound sleeves and discs may also be used. Very useful, especially to remove any trace floating floc, that may be flowing in the discharge to sewer pipe. An excellent application for the final polishing of water in waste treatment.
  



• Multiple Disks or Sheets. A very large, effective surface area can be achieved by precoating a series of multiple disks, sheets, or sleeves with alternating layers of filter aid or diatomaceous earth and carbon. The plating solution is continually pumped through the aggregate layers to maximize particle removal and adsorption of organic contaminants. The filter can be precoated with the filter aid of choice at approximately 2 ounces per ft2 of disk or filter surface area. Usually, one half to three ounces of carbon per ft2 of filter is sufficient. Filter disks can be precoated from a slurry tank in the progression of filter aid followed by carbon, with balance of filter aid. Equipment manufacturers will offer specific operating instructions for their specialized filtration units, to obtain maximum operating performance.



• Balancing Activity. Preferred solution turnover is factored with required purification, to obtain the optimum balance and effectiveness. A rule of thumb (general purposes) for nickel and other plating solutions is 1-2 solution turnovers through the carbon packed filter, on a continuous basis. The requirement to replace carbon in the disk chambers or precoat filter may be determined by monitoring the rise in unit pressure versus the decrease in return flow from the filter discharge. Don’t ignore these visual maintenance aids. I have pulled a few solution filter discharge to bath hoses and found a trickle, at best.

Plating deposit defects sometimes signal the urgency to perform a major purification treatment. For example, a nickel deposit may exhibit characteristics, such as: brittleness, pitting, roughness, dull, poorly leveled. The result may be plating rejects, resulting in shutting the nickel bath or an entire line, because of this one solution. How the bath came to this condition is one problem that must be corrected, to eliminate it from happening again. Of immediate priority is the need to purify the contaminated bath, returning it to a satisfactory plating system. The preferred procedure is the batch purification. The heated plating solution is pumped to a previously cleaned treatment tank. Depending on the contamination and magnitude, treatment with powdered carbon and sometimes an oxidizing agent (hydrogen peroxide or potassium permanganate to further breakdown organic contaminants or precipitate iron) is required. The step-by-step procedures are readily available. The addition of carbon may range from 1-5 LB per 100 gallons of the nickel-plating solution. When treatment has been completed, filter aid is added to speed settling of the carbon, iron hydroxide, and any other particles. The conditioned bath is then transferred back to the cleaned & prepared plating tank through a freshly packed carbon filter. Subsequent wet analysis, plating tests, with appropriate additions are made, before trial plating commences.

Once satisfactory production plating resumes, careful review of maintenance or lack thereof usually furnishes corrective action, to prevent repeat or additional problems in the short or long run. In the case of a nickel bath, there are three great maintenance friends the plater can count on: regular solution analysis, continuous carbon filtration, and dummy electrolyzing. Is too much or aggressive carbon filtration bad? My simple answer refers to the best definition of poison: too much. For example, in the case of a nickel bath, the anti pitting agents (wetters), reduce solution surface tension, preventing the formation of stationary hydrogen gas bubbles on parts, that would result in gas pits. These wetters are somewhat carbon sensitive. Overly aggressive carbon filtration will deplete the wetters to low levels, leading to the unwanted gas pits. It is recommended to follow instructions as given for types of carbon and filter aid along with surface area loading commensurate with plating solution volume.

In continuous plating operation, plating baths will always be exposed to some degree of organic contamination. This may for example occur by drag in of cleaners, oils & grease, thermal & electrolytic breakdown of bath additives, and the effects of closed looping. Effective filtration will minimize drag in of organic contaminants and in-tank breakdown products. Bath analysis, hull cell, and dummying will not correct these problems. Only filtration will provide the necessary purification to remove these organic contaminants and particles. I recently spoke with Jack Berg, who reminded me of just how important filtration is. It’s a must have!

Time is Valuable

Of all the measured parameters we deal with, time is perhaps the one that receives the most attention. Have you considered how fragile the success of organized and professional sports would be, without fixed times, to keep the action balanced? How exciting is a football game if the time to snap the ball is unlimited? Would the absence of a shot clock keep basketball exciting? How would unlimited time in soccer affect the penalty kicks, in deciding the game’s outcome? Activities revolve around time, acknowledging it to be a critical parameter to planning, execution, and review. We begin our day, conduct our work and social activities, eat, and sleep, all adhering to some degree of timeliness. If one is not careful, the anticipated schedule can easily be derailed. That is why compensation must always be an integral part of time. In the ‘90’s, time management was a popular phrase, intended to keep us on track. Date planners, electronic messaging, and post it notes, are some of the devices intended to help and remind us. Are these helpful? Certainly, if used properly and within the scope of application. If we do not consider the validity of time, then all efforts will quickly become wasteful.

In the metal finishing industry, the value of time is highlighted in many ways. No matter how inconsequential it may seem, it is surprising just how critical it is. Finishers and suppliers share in the responsibility to focus on the importance of time. It is so important, that the quality of finished coatings and treatments depend heavily on it. Typical processes we deal with include chemical immersion and induced reactions. These revolve around basic scientific principles. No matter how innovative, updated, or new systems are developed, time can be at the centerpiece of success. In another industry aspect, outside considerations from government and regulatory agencies incorporate time as an important factor. Let us consider some of these items, and how they interact with time as a valuable parameter.

Mass Finishing
The process incorporates the action of mechanical energy and chemical reaction to modify the surface of parts, obtaining the desired characteristics. The objective may be cut down, deburring, or burnishing. Any such cycle is dependent on chemical concentration, ratio of media to parts, operating conditions of the equipment (e.g. barrel or vibratory), temperature of solution, and time of the cycle. Solution temperatures do not vary much. It is generally room temperature, rarely warm. Chemistry is normally based on proprietary blends that will accomplish the treatment specified. Time is the allocated driving force to accomplish the end result. Modifying the other listed parameters will normally affect how long or short a period it takes to complete the cycle. This has a bearing on desired production throughput.

Surface Preparation
Cleaning and activation can be included, since there are distinct similarities. In both steps, unwanted surface materials are removed, thereby preparing the base metal for subsequent treatment. Soak cleaning is predominantly an immersion step. Parts are conditioned in an alkaline solution that usually includes surfactants, builders, inhibitors, and alkaline salts. Oily soils and grease are removed in this step. The concentration of this cleaning formulation is based on product development to accomplish the desired effect, in a particular time sequence. It normally meets the range of dwells programmed into automatic process lines. Concentration and temperature will modify the time according to an acceptable target. An old finisher’s measure is very effective: for every 20 degree rise in temperature of the cleaning bath, the required time for cleaning is halved”.

Electro cleaning adds mechanical scrubbing action to further enhance the effect of surface preparation. The applied current density generates a magnitude of gas bubbles (focus is primarily oxygen per anodic condition of the parts), to remove or loosen unwanted surface materials such as scale, oxides, and rust. Voltage requirement is affected by the solution temperature and concentration of the electro cleaning formulation. Desired time is contingent upon concentration and temperature. This electro cleaning surface treatment is usually allocated less than half the time of the previous soak-cleaning step. Time becomes a valuable parameter in cleaning.

Acid activation promotes the surface conditioning to neutralize alkaline films, dissolve oxides, scale, & rust, and activate the surface prior to subsequent finishing. The quality time required is based on the acidic solution concentration and it’s operating temperature. An optimum balance between these two parameters affects the required time for this final surface preparation step. In many instances it may be equal to in duration to the previous electro cleaning step or even half of it.

Electroplating
Every process bath used to deposit a metal or alloy conforms to Faraday’s Law: the quantity of electricity that is transferred per equivalent weight of an element or its ion. The quantitative value is approximately 96,500 coulombs. The desired or required deposit thickness is related to the applied current density and time of application. As the current density increases, the plating time for thickness requirement decreases. There is a balance to the relationship, by which related conditions and parameters are critical. Bath chemistry, permissible temperature and current density ranges, concentrations of chemical additives, and purity of the plating solution, are important to each system. Optimizing these conditions will allow the process to meet the plating requirements in the optimum time relative to it.

Post & Specialty Treatments
There are several types that can be mentioned. They include: chromates, phosphates, black oxides, and rust inhibitors. Optimized temperature and concentration of each specific treatment permits the use of the right time, for the best results. Quality time is valuable. If only occurs if the process is on target.

Our industry also acknowledges time as a valuable parameter in relation to mandates and changes. Regulatory agencies require adherence to specific limitations with regard to effluent discharges and handling of sludges. Any modifications to specific concentrations or materials allow a time period in order to maintain compliance. Manufacturing changes, such as the implementation of RoHS, grant a period of time for finishers and suppliers to conform to new requirements.

Time is a valuable part in any facet of the metal finishing industry. On time: manufacturing, finishing, packaging, and delivery, can only occur if every step in any process is optimized. In so doing, time is a most quality part of the system. There can be lots of time, if used wisely. The clock is ticking. Are you on time?