Metal Finishing Environmental Stewardship Benefits More Than Just the Environment

Advanced Plating Technologies has always taken a clear stance on the environment.  Since the beginning of the clean water act in 1972, APT has been committed to not only meeting but exceeding all local, state and federal environmental laws.  This record speaks a silent assurance that many “low cost” metal finishing suppliers cannot.  In fact, metal finishing companies with substandard environmental systems is a liability not only for their continued operation but for potential litigation down the road against themselves and their customers.

APT’s Modern Waste Treatment Facility

The metal finishing industry continues to be one of the most highly regulated industries in the country with new regulations and requirements added each year.  New regulations on PFOA and PFOS compounds and additions to the Toxic Substances Control Act (TSCA) are just a few of the latest impending regulatory restrictions. For this reason, APT continues to invest in improved treatment technologies and self-imposed compliance standards below permit levels as an example within the Industry.  APT’s leadership has been recognized with numerous local, state and national environmental awards from the Milwaukee Metropolitan Sewage District (MMSC), Wisconsin State Department of Natural Resources (DNR) and the United States Environmental Protection Agency (EPA).

The history of environmental compliance within the metal finishing industry is marked by various landmark laws that have far-reaching implications counter to what many would consider sound environmental practices.  In 1980 the Resource Conservation and Recovery Act (RCRA) mandated that the F006 wastewater treatment sludge produced by electroplaters shall be listed as hazardous waste categorically. This designation was applied without testing the waste product for its actual chemically hazardous profile using the TCLP methodology.  Thus, the applied arbitrary designation limits the ability of the waste to be recycled to recover the valuable metals contained therein. Since then, this legislation has come under increased criticism from many in the industry as it results in the waste of thousands of tons of valuable metals each year.

However, there have also been moments of true partnership in between agencies and industry towards a common environmental goal.  In 1994, under the Clinton Administration the US EPA launched the Commonsense Initiative which promoted cleaner, cheaper and smarter environmental standards. This initiative engaged several industries including the Metal Finishing industry. The Finishing Industry was challenged to propose a package of improved policies which were to be based on projects and discussions between industry and committee members. This resulted in the passing of an extension of the 90 day storage rule to 270 days for materials recycled and transported over 400 miles.

APT CEO John Lindstedt has been a principal leader within the metal finish industry in environmental compliance and sound legislation based on facts.  John has served on government regulation committees with local state and federal agencies, including 30 years work with the Government Activities Committee (GAC) for the National Associate of Surface Finishers (NASF).  Recently John was interviewed by Scott Francis of Products Finishing Magazine to discuss ways that current legislation could be improved to further promote recycling of valuable resources contained within the sludge by-product of many metal finishing shops.

Checkout the recent On the Line Podcast from Products Finishing to hear John discuss how current environmental regulations could be improved to benefit industry and the environment alike.

Download Article

The post A Discussion of Metal Finishing & Environmental Stewardship appeared first on Advanced Plating Technologies.

Deposit Thickness in Surface Finishing

By: J. Lindstedt, President.

In ordering a surface coating system to enhance the performance of an article in service, the use of standard finishing specifications is the established procedure employed by most manufacturing entities. The specifications most commonly referenced are ASTM, MIL Specs, AMS and unique corporate specifications.

Surface finishing specifications identify a number of parameters which evaluate the ability of the surface coating to perform its intended function. The most common coating requirements used to qualify a coating system are:

1. Deposit thickness: This parameter is often defined by a service class. Service class prescribes a deposit thickness as a function of intended use. Service classes are easily found in most ASTM specifications.Thickness is defined by several definitions, minimum, maximum, average and average range.
2. Deposit appearance: The appearance description is a generic narrative of the visual attributes of the applied coating.
3. Deposit adhesion: This parameter is defined by several methodologies. Most of these criteria will stress the coating/basis metal interface in an attempt to remove the deposit from the basis metal. These tests typically stress the coating metallurgical bond by mechanical or thermal means. The prevalent standard tests are found in ASTM B571.
4. Penultimate plating requirements: Often the coating system selected is a series of deposits to provide the required performance. This section will define the additional deposits below the final deposit, order of application and required thickness of any penultimate layer.
5. Secondary performance prerequisites: These additional testing protocols are most typically hydrogen embrittlement relief, solderability and accelerated corrosion testing.

Of all of these parameters the one which is the least understood and thus often incorrectly applied is deposit thickness. Unfortunately, this leads to confusion and the frequent over or under application of deposit thickness which results in needless delays in securing acceptable components.

Understanding Deposit Thickness Variation

Deposits as applied by electrolytic or electroless methodologies by barrel, rack or continuous strip plating techniques will all be normally distributed as defined by the Gaussian distribution curve. The distribution curve of deposit thickness is defined as a function of x(thickness) in Equation 1 below:

where:

x is the sample measurement i.e. deposit thickness

x-bar is the arithmetic mean of x data points

σ is the population standard deviation

This function is shown graphically as

Figure 1: Normal Gaussian Distribution Curve

In this graph it is clear that the thickness of a deposit at a single measurement location is not a single repeatable value but a distribution of numbers that cluster about a central value, the arithmetic mean, and the variation about that central value is defined by the standard deviation. The standard deviation is a measure used to quantify the variation or dispersion of a set of data values. The standard deviation is defined in Equation 2.

Equation 2: Standard Deviation of Population

where:

x is the sample measurement i.e. deposit thickness

x-bar is the arithmetic mean of x data points

σ is the population standard deviation

n is the number of data points

It is key to an understanding of deposit thickness on an article at a single measurement location is that it is not a single repeatable data point but a scattering of values that will accumulate around a central tendency, the arithmetic mean.

The breadth or width of the dispersion is defined by the variation of the process. It is the width of the dispersion that must be considered when designing an article. It is this variation in thickness that will impact mechanical fit of components, corrosion performance, solderabiliy etc. It is also critical to consider the process variation when defining quality acceptance criteria.

The percentage of data points that cluster about the arithmetic mean can be calculated by the techniques of integral calculus where the area under the curve is computed. Thus the area under the curve from plus infinity(+∞) to minus infinity(-∞) represents 100% of all data points in the distribution. The area under the left hand portion of the curve from -∞ to the mean represents 50% of all data points. The same is true for the right hand portion of the area from +∞ to the mean.

Similarly, any area between any two values of the x axis can be calculated and the area divided by the total area to calculate the percent of measurements that are contained between the two selected points. The percentage of data points in a normal distribution that exit between -1σ and +1σ is 68.26%. The data points that exist between -2σ and +2σ standard deviations is 95.44%, and similarly the data points that exist between -3σ and +3σ is 98.74%. This is shown in Figure 2 below.

Figure 2: Percentage of Data Points between +/- 1, 2 or 3 Standard Deviations

From Figure 2 several facts regarding the standard deviation of a process are evident.

1. The absolute value of the standard deviation is an important parameter to use in defining the range of thickness values which are to be expected from a surface finishing process. To completely define the thickness of a deposit on an article, thought must be given to the dispersion of data points. As the magnitude of the standard deviation increases the dispersion of data increases thus resulting in deposit thickness data points that can be very small or very large. Thus, fewer data points cluster about the central tendency and the range of deposit thickness increases. This has design considerations that need to be addressed.

Example:

If a process has a large standard deviation, special consideration in the use of maximum or minimum specifications must be evaluated. For example, if a supplier specifies a minimum specification which is defined as NO values below the stated thickness and there is a quality acceptance criteria of 2000 ppm (0.2% defective), this will force a supplier to select a targeted average deposit thickness that is at least 4 standard deviations greater than the specified minimum thickness such that no values are measured below the specified minimum value. This will have dramatic size implications on those data points that are in the right hand portion of the distribution curve. This resultant number of thickness values that are greater than the elevated target average thickness may be an issue as there will be articles measured at the mean plus 4 standard deviations. These data points certainly need to be considered in the use of the stated mimimum specification.

2. At +/- 3σ there still exits 0.26% of values that are significantly less than the mean or significantly greater than the mean. This has large implications in corrosion performance or in sizing concerns if a quality acceptance level of less than 2600 ppm (0.26% defective) is the requirement. While this represents a small percentage of product,0.26%, this level of unacceptable product is often an issue in the automotive, medical or aerospace industries.

Modification of the Magnitude of the Standard Deviation

As shown above, deposit thickness in surface finishing is composed of two main elements, the arithmetic mean and the dispersion of that data about the mean, the standard deviation. Clearly it is critical to minimize the size of the standard deviation to more closely cluster as much data as possible about the central tendency. This provides a much more consistent and homogeneous thickness data set which facilitates product design and quality compliance.

Figure 3: Demonstration of Strong and Weak Central Tendency of Data Sets

Figure 3 demonstrates the variation in data with a standard deviation 50 % smaller than an alternate example. In the red data set 95% of the data will reside between 30 and 70 units. In the blue data set 95% of the data will reside between 40 and 60 units. If the parameter of concern is dimensional and the graph depicts deposit thickness the smaller tighter variance would be of value in providing a much more uniform and consistent article for fit and function. A similar discussion would follow if corrosion testing where of concern. The tighter grouped data of thickness would provide a more corrosion resistant product with many fewer articles at reduced thickess of less than or equal to 25 and thus reduced occurance of corrosion failures.

Reducing the Spread of Thickness Data – Electroless versus Electrolytic

The plating process can be selected and modified to reduce the magnitude of the standard deviation. All deposition processes either electrolytic or electroless are normally distributed with the electrolytic methodology having an intrinsically greater standard deviation than electroless plating processes. Therefore the first decision for a design engineer to make is to select an electroless process over an electrolytic one if there is a need to reduce the spread or range of deposit thickness. If that decision is not possible i.e. an electroless process is not available for the metal required then other choices need to be made.

The following choices will reduce the standard deviation for electrolytic deposition systems.

1. Selection of a plating system that deposits from a complexed cation versus a simple ion. An example of this would be to copper plate from a cyanide electrolyte rather than an acid matrix.
2. Reducing the current density used during processing.
3. Use of a barrel plating technique versus a rack plating technique.
4. If rack plating, the employment of shields will reduce standard deviation.
5. Operation of the chemical system at the low end of operational temperature range.
6. In barrel plating, techniques that enhance mixing i.e. barrel rotational speed, serrated barrel cylinder walls, breaker bars will assist in obtaining lower standard deviations.
7. Maintaining solution chemistry within 2% of optimal.

The following choices will reduce the standard deviation for electroless deposition systems.

1. In rack plating, use of enhanced solution mixing i.e. proper air flow, use of cathode bar agitation or both simultaneously.
2. In barrel plating, techniques that enhance mixing i.e. barrel rotational speed, serrated barrel cylinder walls, breaker bars will assist in obtaining lower deviations.
3. Maintaining solution chemistry within 2% of optimal

The post Deposit Thickness in Surface Finishing, the Misunderstood Variable appeared first on Advanced Plating Technologies.

By James Lindstedt, Manufacturing & Process Engineer

Rack Plating Introduction – A Metal Finishing Job Shop

Advanced Plating Technologies is a metal finishing job shop. What does that mean? A metal finishing job shop encounters the metal finishing demands of any industry that has a need for metal finishing. Metal finishing is a highly diverse industry serves the needs  of  a myriad of other industries. Although there is always common ground, every industry has its own unique set of needs and criteria for metal finishing. The conscientious metal finisher must be able to recognize these unique requirements, and reconcile them with the nuances of the plating methods and processes.

Rack Plating & Tooling

When quoting at a prospective job, some of the key factors to consider are:

• Part geometry
• End use
• Base material
• Part volume (EAU)
• Throughput
• Type Of Process (Electroless, Electrolytic, Immersion Only, etc)

There is one critical item that unites all of the above bullet points: TOOLING. Tooling is one of the most important inputs when we begin to put together a metal finishing solution. Often times a tooling charge may be incorporated into a quote as an effort to optimize the process at the onset of the job. In the context of metal finishing, tooling is the broad category of hardware that is required to apply the finish to the part. Tankage, bussing, power supplies, HVAC, plating barrels, plating racks, masking, agitation equipment, and material handling equipment can all fall under the umbrella of tooling. Rack plating is a particular area of concern with respect to tooling. Designing an effective plating rack often consumes a large amount of engineering bandwidth during the development of a new job.

Defining Rack Plating

The broad-stroke category of plating that Advanced Plating Technologies performs falls into a category known as “loose piece” plating. This term serves mainly to distinguish from continuous forms of plating, such as reel-to-reel. In loose piece plating, the goal is to apply the desired finish to an individual part – the “loose piece”. The loose pieces are processed as a load of varying degrees of size, using tools called plating barrels or plating racks. As such, when developing the finishing protocol, the finisher must choose a physical means with which to apply the finish to the loose piece. There are two principal subcategories of loose piece plating – barrel plating and rack plating. The first discussion of this two-part blog will cover the latter – rack plating.

Rack plating is a method that involves fixturing individual parts into an array that is mounted on a solid frame – the so-called plating rack. The plating rack serves the following purposes:

• To physically hold the parts in a secure manner
• To maintain electrical contact with and to pass DC current to the parts
• To orient the parts appropriately in accordance with the thickness specifications, part geometry, drainage, gas elimination, and quality requirements.
• To optimize throughput

Some representative photos of rack plating and the diversity thereof are shown below:

Figure 1.1 – Rack Plating Fixtures and Their Diversity

Rack plating can be configured to accommodate virtually any part size or geometry.  Racks can be made for a single part, or thousands of parts; a rack may be the size of a textbook, or the size of a garage door. In any case, rack plating requires careful consideration of plating process phenomena and the nuances of the part in question.

The Relationship Between Rack Plating And the Plating Cell

Electroplating is an electrochemical process. Driven by an external DC power source, metal cations, such as Ni²⁺, are reduced at the surface of the part (the cathode of the plating cell) to nickel metal (Ni⁰). The anodes in Figure 1.2 are the sources of new metal ions to replace the ions being plated on to the part. This process involves the physical movement of ions through the plating solution at a rate on the order of 0.01 centimeters per second. The rate of ion flow can be manipulated by what is referred to in the industry as current density – that is, the ratio of current supplied by the DC power supply to the surface area of the cathode (i.e., the parts being plated). The importance of current density as a metric in the industry cannot be understated, particularly with regard to rack plating. Current density manipulation is often a principal reason for developing a custom rack.

Figure 1.2 – A Schematic Drawing of a Rack Plating Cell (As Viewed From Above; NOT TO SCALE)

For a given array of parts on a plating rack, the current density is not distributed evenly across the parts; almost without exception, there will be a gradient.

Figure 1.3 – A Schematic Representation Of An Array Of Parts Configured For Rack Plating

Consider Figure 1.3 – a schematic representation a plating rack.  As illustrated in Figure 1.2, the parts around the perimeter of the array would be considered “high current density areas”, meaning that they will receive a relatively higher amount of metal deposition than the more interior pieces. So, other things being equal, a piece located at position A1 or G4 would receive a higher amount of plating buildup than a piece located at position D2 or E3.

Similarly, the portion of the part that is toward the interior of the plating cell, rather than facing the anodes, will have less plating buildup – this is a phenomena known as “shielding”. Just as a tree may provide shade from the sun, physical objects between the anode and cathode of the plating cell will shield metal deposition. In addition to shielding, a surface that is facing the anodes will have less plating buildup in holes, recesses, cavities, or other internal features. These tendencies can be mitigated through sound rack design. Parts may be oriented on the rack in such a way that critical features are facing the anodes.  In more technical applications, a plating rack may even be developed with an auxiliary anode inside of the parts to generate the required current density in a hole or other recessed feature.

Figures 1.4 through 1.6 are exaggerated rack plating illustrations showing the relationships between part geometry, current density, and plating thickness.

The following table is a summary of the advantages and disadvantages of rack plating:

Conclusion

Rack plating plays a very key role in developing effective metal finishing protocols. It is the responsibility of the conscientious metal finisher to recognize the customers’ needs, and to reconcile them with the often-misunderstood idiosyncrasies of the plating process. When considering the factors that have been discussed above, often the most appropriate method of processing reveals itself. Other times, several iterations of trial and error may come to pass before the solution becomes clear. Regardless, in rack plating it is always advisable to develop a custom tool for the application. This will ensure that the process is optimized and parts are being processed in a manner that in consistent with good plating practice.  Advanced Plating Technologies has vast experience in designing in building plating racks. A staff of Manufacturing and Process Engineers work directly with customers from the quoting phase all the way through to full scale production. This ensures that the unique needs of the job are being met from a tooling and processing standpoint, which is particularly important when custom racks are required for a job. Additionally, the APT engineers have a well-established relationship with local rack fabricators to facilitate sound rack design, rapid rack prototyping and scaling into production.

The post Plating Methods & Tooling Design Considerations for Rack Plating appeared first on Advanced Plating Technologies.

By R. Savija
All specifications for electroplating, whether military, federal, ISO, ASTM or SAE-AMS specifications, have an initial section that contains essential information to be supplied by the purchaser to the electroplater. More times than not, much of this information is omitted from part prints and purchasing documents which opens the door to potential miscommunication and finishing shortfalls. This blog details some of the more common omissions that are discovered by Advanced Plating Technologies’ engineering staff during quoting or contract review of specifying a plating process.

Specification of the plating thickness and tolerance requirements:

Often a minimum/maximum thickness tolerance without a defined checkpoint cannot be realistically obtained with a traditional electroplating process. For example, a plating specification that lists a minimum plating thickness of 0.0003” and a maximum plating thickness of 0.0005” for all surfaces of an electroplated part would not be achievable on most part geometries due to the inherent variations in electrolytic plating distribution.

Plating thickness varies due to the inconsistent distribution of plating current on an electroplated part. Ionic plating current, like electrical current, takes a preferential path of least resistance with the corners and ends of a part receiving a higher current density and therefore higher plating thickness. If the design of a component requires a very tight plating tolerance, it is important to designate a functional surface where a plating thickness check point can be established. If the plating is specified as 0.0003” minimum and 0.0005” maximum with a specific checkpoint, a plating protocol can generally be developed to consistently meet this requirement. Any specific part dimensional tolerances should be addressed in combination with a plating thickness checkpoint to allow for a combined plating thickness and part dimensional inspection protocol.

Hardness or Strength Requirements

Most electroplating specifications require hydrogen embrittlement relief baking for high strength or hardened steels having a strength greater than 180ksi or Rockwell hardness of 40 HRC or more. In addition, pre-plate stress relief bakes are often required within plating specifications for hardened or cold-worked ferrous materials. Often the hardness of a steel component is not listed on the drawing or purchase order which requires follow up during quoting or contract review. In some cases the hardness of a steel material is not so obvious, such as with music wire used in springs and wire-forms. The purchaser rarely specifies the tensile strength of music wire on the drawing. A closer examination, however of the music wire specifications such as ASTM A228 indicate that all music wire has a tensile strength well above180 ksi which is the strength equivalent of 40 HRc.

Condition of the As-received Material

It is not uncommon for a metal finishing facility to receive parts with a heavy oil or heavy heat treat scale. This type of a condition is generally not discussed during the quoting stage nor are there advisories on part prints, specifications or purchasing documents. Excessive oil and heat treatment scale require additional operations to prepare the parts for successful finishing. The additional processes are often “off-line” in that they are a separate process independent from the plating line. Such processes include aggressive chemical descales, vapor degreasing and sand/vapor blasting processes. These steps add additional time/cost that are generally not included in a standard quote. In such cases, further discussion is required to determine the most cost effective way to prepare future orders of parts for plating. Often proper cleaning of parts prior to heat treatment, alternative heat treatment methods such as vacuum heat treating or cleaning prior to heat treatment can ensure parts are received ready-to-plate thereby eliminating additional preparatory steps.

Surface Roughness

It is a common misconception that electroplating can actually cover-up up surface imperfections on the part and that electroplating can significantly improve surface roughness. In most plating applications, this is not the case and it is generally recommended that the pre-plate surface roughness be slightly better than the desired post-plate surface finish. For example, if a post-plate Ra of 16uin is required, it is generally recommended that a pre-plate Ra of 10-12uin be provided. This is especially true of electroless processes such as electroless nickel that have virtually no “leveling” properties.

Plating Buildup on Threads

It is not uncommon for improper allowance to be made for plating buildup on threads. Since plating builds on two sides of the part and both sides of the thread land, a total of four times the nominal plating thickness should be used as a guide for the increase (male) or decrease (female) in thread pitch. The formula below details the calculation for change in pitch diameter as a function of the plating thickness and included angle (Note: the included angle for most common thread forms is 60-degrees):

As an example, a 0.0002” plating thickness will cause the pitch diameter of a male thread to increase by a factor of four or 0.0008” for standard 60° UNC or UNF threads. This plating buildup is even further exacerbated on the lead threads of long fasteners or shafts where a localized plating thickness at the lead thread may be as high as four to five times the nominal thickness depending on where the plating thickness checkpoint is established. In such a case, the target plating thickness of 0.0002” may be as high as 0.0008” as measured at the lead thread resulting in as high as 0.0032” increase in thread pitch. In such applications, it is very important to discuss allowances for thread pitch build and define a plating thickness checkpoint to ensure that parts can be successfully plated and meet post-plate gauging requirements.

Racking Locations

For parts that are rack plated, allowance must be made for contact locations of the rack tips. The rack tips are what physically contact the part to fixture it throughout the plating process. At the rack tip contact points there will nearly always be rack marks and lack of full plating coverage. This is due to the fact that current passes through the rack tips and into the part at the contact points. In addition, plating chemistry/solutions cannot fully wet the surface of the part beneath the rack contact points. Due to the fact that the plating coverage will be incomplete with visible marks at the contact points, it is important that the purchaser convey non-functional or non-critical locations on the drawing where racking is permissible. This is usually a location where the purchaser deems that rack marks are not detrimental to the function or appearance of the part.

The above points detail just a few commonly overlooked areas that are critical to a successful outcome in a metal finishing process. By carefully reviewing the ordering information listed within most plating specifications, the purchaser can be assured that details critical to a successful plating outcome are detailed at time of quote or purchase. Advanced Plating Technologies is happy to provide guidance along these lines by talking with any of our estimating or process engineers. Visit the contact us section of our website to submit a plating inquiry or general question regarding specifying a plating process. Our Technical Library contains common plating topics, specifications and white papers specific to the plating process.

The post Critical Details Often Overlooked When Specifying a Plating Process appeared first on Advanced Plating Technologies.

Are you new to the metal finishing industry? Perhaps you’ve recently been promoted to a buyer of electroplated material/services within your organization’s supply chain department…a new supplier quality engineer overseeing metal finishing applications…a design engineer who has to address surface engineering as a key component of product design…or a student contemplating a career in metal surface finishing.

No matter what your informational needs are, the following online resources are a great starting point, each providing a wealth of technical and training information and links related to metal surface finishing technology, environmental impact and regulatory compliance.

Surface Finishing Resources

• The National Association for Surface Finishing (NASF) headquartered in Washington D.C. serves many missions; advocacy for businesses, technologists and professionals in the surface coatings industry; legislative and regulatory advisory; technical conferences; and online courses and certifications for all levels of information needs. In-person, webinar and home study course work options provide flexible training opportunities. NASF’s two volume Advanced Surface Technology practical reference provides state-of-the-art coatings reference information useful to finishers, suppliers and the OEM Community.
• In-depth environmental compliance information, regulations, and best practice solutions can be found at the National Metal Finishing Resource Center (NMFRC) online website. Online training and related technical reference books provide environmental compliance professionals with a strong foundation of knowledge for compliant operation of plating facilities.
• PF Products Finishing is an online information portal of Products Finishing magazine. Its editorial coverage centers on products and technology exclusive to anodizing, electroplating, powder coating, painting, and other finishing operations. Technical articles, case studies and white papers provide actionable information for more efficient and profitable finishing operations.

• Advanced Plating Technologies Metal Finishing Specification Database.  Our database  provides metal surface finishing professionals with industry’s largest single-source collection of plating specifications. Here you will find a condensed summary of key AMS, Military, ASTM specifications as well as manufacturer specific plating standards.  Our specification database is an extension of our capabilities and will serves as an excellent technical resource for anyone involved in the surface finishing industry.

No matter what your need may be, from stainless steel passivation, gold plating services to select powder coating and all surface finishes in-between, Advance Plating Technologies delivers engineered metal finishing solutions satisfying the most demanding of applications.

Have questions? Email us at sales@advancedplatingtech.com for more information.

The post Educational Resources for Metal Surface Finishing Professionals appeared first on Advanced Plating Technologies.