Category Archive: Industry News

The basics of liquid and powder coatings

New to liquid and powder coating? Consider this.

According to the Fabricator:

“Almost all metal fabricators consider on-time part delivery a key metric. In today’s just-in-time manufacturing environment, the parts need to be there so the customers don’t miss a beat in their own manufacturing facilities.

“To maintain their ability to get parts where they need to be and when they need to be there, more fabricators are investigating in-house finishing capabilities. They know that once metal parts leave the shop to receive a liquid or a powder coating, they have lost their ability to guarantee a delivery date. It is quite literally out of their hands.

“Now, a finishing contractor may be a good supply chain partner, but a metal fabricator is one of its many customers—perhaps one of the smaller ones. If the custom coater needs to clear the production schedule for one of its largest customers, guess where that leaves the small batch from the metal fabricator?

“Metal fabricators looking to take on finishing should know about two of the most common finishing alternatives—liquid and powder coating—and the requirements involved for a company hoping to apply one or both.

What Makes up the Coating?

“Liquid. The basic raw materials comprising a liquid coating are additives, carriers, pigments, and resins. Additives make up the smallest portion of any liquid coating composition, but they impart special characteristics on the overall finish; for example, they might assist with rust prevention or UV protection. The carrier is the main liquid used to formulate the paint. The carrier can be water, solvent, or a combination of the two. Liquid coatings heavy in solvents traditionally have been the dominant form of liquid finish applied to metal parts over the years, but more interest has been directed to waterborne and high-solids coatings, which release a minimal amount of volatile organic compounds (VOCs) during application when compared to traditional solventborne coatings.

“Pigments play a role in final appearance and performance to some extent. As a rule, the volume of pigments influences the gloss of the film. The more pigment present, the lower the coating’s gloss. Resins act as the base of the liquid coating. They primarily govern the overall performance of the coating, helping the paint to excel for particular applications.

“Powder. Powder coatings don’t require a carrier. The additives, pigments, and resins are formulated in a powder form. To apply the material to parts, the powder is electrostatically charged and conveyed via compressed air. The charged powder is attracted to a grounded part. The part is then taken through an oven, where the heat changes the powder from a solid to a liquid and then to a solid coating. Generally, powders do not have any or extremely low VOCs.

How Does the Coating Affect the Environment?

“Liquid. Solventborne coatings are often specified for a finish because of their dependable performance and ability to air-dry in a matter of minutes. Unfortunately, most of the traditional liquid paint formulations from yesteryear no longer are around because of the need to reduce VOCs emitted during application.

“That has led to the development of more environmentally friendly coatings, such as new waterborne formulations and high-solids coatings, that emit low VOCs. The waterbornes, which have come a long way from the early versions used 15 years ago, are slowly growing in acceptance. However, some manufacturers still have reservations about applying a water-based product directly to metal. High-solids are liquid coatings that have a solids content of at least 65 percent, which means minimal solvents are present. But fewer solvents also means that the coating is more viscous. That has led to the development of multipart application systems (referred to as 2K systems if two parts are mixed, 3K if three parts are mixed, etc.) that are formulated to be mixed only seconds before application.

“All finishers that apply liquid coatings spray to waste. The overspray can’t be reclaimed. If filters are used to capture the overspray, the finisher has to dispose of the filters according to regulations established by local authorities.

“Powder. The powder booth does not require an exhaust. As stated previously, if any VOCs are emitted during the powder coating process, they are typically very low.

“Powder coatings can be recycled with the right reclamation equipment. Companies looking for Class A finishes have reclamation systems that depend on thorough cleaning and maintenance because any cross-contamination of reclaimed material ruins the original material’s ability to deliver a specific color.

“Again, disposal of unreclaimed powder coating material is governed by local regulations. In some instances, local law may require disposal in sealed containers or require that the powder coating material be baked into the form of a brick for disposal in a local landfill.

What Are the Characteristics of the Final Coating?

“Liquid. When someone talks about a Class A finish, typically used to define the coating quality on a new automobile, most people think of liquid coatings. Specialty finishes, such as those incorporating metallic flakes, also are possible in liquid coatings.

“Durability has improved over the years as well, especially with the emergence of 2K coatings. These are typically used on large metal parts that can’t be powder-coated because they can’t fit into a typical booth and oven setup.

“Liquid coating finishes can be applied in various thicknesses. Obviously, the more mils applied, the better the protection. In many instances, a manufacturer, such as an automaker, will seek to balance maximum protection with the minimum amount of paint mil thickness.

“Powder. Powder coatings offer the same characteristics that come with liquid coatings.

“Properly cured powder coatings can offer superior protection against chipping, scratching, UV rays, and corrosive elements. This is why powder coatings are often specified to coat metal products destined for outdoor use.

“Material development has progressed to the point where powder coatings can deliver a Class A finish. In fact, a major European automaker and a U.S. motorcycle manufacturer are using powder coatings for their clear coating. However, many manufacturers, including automakers, still prefer liquid coatings for that topnotch finish.

“Standard powder coating finishes are applied in the thickness range of 2 to 4 mils. Specialty finishes like a hammertone or a texture are usually 3 to 5 mils thick. Functional coatings can be 10 to 40 mils thick.

What Type of Cleaning Is Necessary Before Parts Are Coated?

“Liquid. A lot of fabricators simply wipe the part clean with a rag soaked in solvent. Others rely on a wash of some kind with pretreatment chemicals.

“Solvent helps to prepare the metal surface because it has aggressive cleaning action and actually prepares the surface for adhering to the paint. New coatings that have less solvent content may require much more formalized pretreatment processes to achieve a quality finish.

“Powder. Pretreatment is critical when it comes to powder coating. If a powder coating is going to last, the part needs to be thoroughly cleaned.

“Pretreatment can range from a simple abrasive media blasting chamber to a multistage pretreatment system with several chemical application and rinse stations and an oven. (Parts have to be dried and cooled before any application of powder takes place.) Some of the pretreatment chemicals, such as zinc phosphate, have to be treated before disposal, but newer, environmentally friendly pretreatment chemicals have emerged in recent years to ease the disposal hassles. The Environmental Protection Agency, however, likely will seek changes in the near future that will call for treatment of all wastewater prior to discharge.

What Are the Basic Booth Requirements?

“Liquid. Booths or stations used in liquid coating are typically made of metal. Whether in a manual or an automated setup, the paint is often sprayed to waste.

“Fumes are exhausted outside during the painting process to keep the work environment in and around the paint booth free from the strong odors.

“Powder. In some instances, particularly if batch finishing is occurring, a shop might use the same booth for both liquid and powder coating. But fabricators need to keep in mind that if they choose to powder coat in a liquid application booth and exhaust overspray outside the building, employees could be walking out to cars with all new finishes at the end of the shift on a very hot day—depending on where that powder overspray landed. For the most part, however, filters and correct powder coating technique should prevent most powder overspray from going outside.

“If a company is doing any kind of high-volume powder coating, it should consider a reclamation system. Single-color reclamation systems are cartridge-based and typically made of stainless steel. Multicolor systems, which are designed for fast color changeout, are plastic, making them easier to clean. Sophisticated fan setups keep the overspray in the booth, and the polymer-based interior walls prevent the powder from adhering to them. The overspray is collected and recycled for another application.

How Do the Application Guns Work?

“Liquid. Conventional spray guns for liquid coatings rely on highly pressurized compressed air (2 to 3.5 bar) to propel atomized coating material to the surface. These guns have a low transfer efficiency when compared to more modern paint application guns and may not be approved for use in some areas. However, they are relatively inexpensive and easy to maintain.

“High-volume, low-pressure (HVLP) spray guns also atomize the paint like a conventional spray gun, but use low-pressure air, usually less than 0.7 bar, to propel the paint onto the object. The lower velocity of the air results in less paint jetting through the spray gun’s air nozzle and allows for a more controlled application. Higher application rates are then possible.

“Other spray gun technologies are airless spray guns that force the paint through a smaller nozzle and electrostatic-based guns that rely on paint being “attracted” to the object to be coated. (In electrostatic application, a charge is applied to the liquid coating while it is being atomized. In turn, the coating is attracted to any surface that is grounded, which happens to be the workpiece. Obviously, this approach works very well with metal workpieces.) For new users of paint technology, conventional or HVLP spray guns are typically the choice for paint application.

“Powder. Powder coatings rely on the charging of material for application as well. Today’s market primarily uses corona guns to do this.

“These guns impart a strong electrostatic charge on the powder material as it leaves the spray gun via compressed air. As the powder coating is discharged, it is attracted to the grounded metal part hanging from a metal rack. It is necessary for the rack to have some area of exposed metal to ensure a solid grounding for good electrostatic powder application.

“Tribo guns also are used for powder application. With this method, the powder material picks up a positive charge while rubbing against the gun’s interior Teflon® walls.

“An operator needs less experience to apply powder coatings in an efficient and effective manner than someone applying liquid coatings.

What Are the General Oven Requirements?

“Liquid. Because most liquid coatings can air-day, ovens aren’t necessarily needed. However, if a manufacturer wants to speed up drying times, it needs an oven that is capable of heating between 130 and 170 degrees F.

“Powder. Powder coatings need a much hotter oven to melt the particles so that they can flow and react chemically to form a smooth finish on the workpiece. Most powder coatings reach this stage in an oven heated to 350 to 400 degrees F. For a proper curing, the substrate must be at this temperature for at least 10 minutes.

“On some occasions a manufacturer can use the same oven for drying liquid coatings and curing powder coatings (as long as both coating chemistries are compatible with each other). The key is scheduling parts headed through the oven so that the temperature can be adjusted accordingly for specific coating jobs.

Why Use a Liquid Coating?

“This coating technology is prevalent for many reasons:

“It can be cured quickly, resulting in faster production cycles.

“It is cost-effective in the sense that the initial investment for the equipment is much less than for powder coating equipment (although liquid material is more expensive than powder and can’t be reclaimed).

“The coating can be used to finish parts containing sensitive materials, such as a metal cylinder with a rubber seal, because it does not require dramatically high temperatures to dry.

“It can be used to finish very large parts that are not able to fit into an oven or can’t be moved easily.

“A thin coating is achievable. It can routinely be applied as thin as 0.5 mil.

“It provides an automotive-quality finish (although this performance advantage over powder coatings has been narrowed greatly over the years).

Why Use a Powder Coating?

“Users of powder coatings turn to this technology for a few specific reasons:

“As soon as the workpiece has cooled after curing, the part doesn’t require overly protective handling and immediately can be sent to downstream processes such as assembly or packaging.

“It is very durable. It is commonly used for outdoor applications ranging from outdoor furniture to agricultural.

“The process does not emit VOCs, which means local air quality regulations aren’t likely to be an issue for the manufacturer undertaking powder coating. Additionally, the material can be reclaimed, if the right equipment is installed, which limits the amount of waste material that has to be placed into the waste stream.

“Although it requires a large upfront investment, the long-term costs of applying powder are less than those for a liquid system. In some instances, the price of liquid material may be four times more.”

Original Source

“CARC” (Chemical Agent Resistant Coating)

New to CARC? Consider this.

According to Military Trader:

“Chemical Agent Resistant Coating or CARC is, in simple terms, a low gloss military version of the polyurethane paints that were developed for use in commercial industry. CARC has a low porosity that prevents chemical warfare agents from “soaking in” to the finish and makes decontamination easy to perform. TB 43-0242 states, “[Chemical agents] just bead up on the surface like water on a newly waxed car.” More importantly, the CARC finish is not affected by the solvents used in the decontamination process.

“The finish is also much more durable and resistant to fading, lasting up to four times longer than the alkyd paint previously used by the Army. This durability promised to keep fielded vehicles looking better for a longer period of time and to reduce the number of times a vehicle would need to be repainted in its life cycle, thus reducing maintenance costs. The resistance to solvents allows regular washing of vehicles without fear of damaging the finish.

“To provide some idea about the durability of the CARC finish, TB 43-0242 gives the following as a test to determine if a vehicle is painted with CARC, “wet a cloth with acetone and rub hard on the painted surface for 10 seconds. Wet a clean corner of the cloth with acetone and rub another 10 seconds if no paint comes off the second time, it’s CARC.”

BACKGROUND OF CARC
“The first chemical agent resistant coatings were developed as early as 1974, and by 1983 the Army was ready to make CARC the required coating for all combat, combat support, tactical wheeled vehicles, aircraft and tactical ground support equipment. The US Army officially adopted CARC in May of 1983.

“Besides its chemical resistance and durability, CARC has some other unique properties. For example, the base green color, “Green 383.” uses pigments that mimic the reflective properties of chlorophyll which is found in living plants, making the vehicle harder to detect using infrared detectors. During the Gulf War, “Tan 686” was reformulated to reduce the amount of solar heat absorption and keep vehicles cooler in the desert environment. The new color became “Tan 686A” and was standardized in the latter stages of the conflict.

“To create these special pigments, CARC is a two-part coating that is mixed before application. The components are not interchangeable, it is not possible to mix component A of one color with component B of another color, and intermixing components from different manufacturers is also not feasible. Once mixed, unused CARC will not keep and must be disposed of as a hazardous material. CARC is also highly flammable and it is recommended that the cans and mixing equipment be grounded when mixing the paint. A one part CARC was also made available for brush or roller touchup at the unit level.

CARC HEALTH CONCERNS
“One problem of CARC is the toxicity of its components. Polyurethane paints were in use in the commercial and automotive industries for some years before the Army adopted CARC, so the health risks associated with them were well documented. All polyurethane paints contain isocyanates, and this alone poses a significant health risk. Add to this the array of volatile solvents and cleaners needed and you have a recipe for serious health risks.

“Hexamethylene diisocyanate (HDI) is the isocyanate found in CARC. It can be released when CARC is being sprayed, and it is also released when CARC burns making the smoke from welding and vehicle fires a greater potential health hazard. HDI is also a known sensitizer for asthmatics; soldiers with asthma were not to be involved with the application of CARC as “a severe life threatening allergic reaction may occur.”

“CARC poses no known health risks once dry unless disturbed by sanding or grinding. As a result of the hazards involved with applying CARC, individual units and crews were no longer responsible for the painting of vehicles. Complete repaints had to be done at the direct support, general support or depot level, provided the facility had an OSHA approved paint booth.

“This rule also applied to complete repaints of non-CARC painted equipment as the Army strove to become compliant with ever more stringent environmental regulations. Moving the responsibility for major painting tasks to the maintenance level also served to improve the quality of the paint finish and help maintain greater uniformity in camouflage patterns.

“The October 1990 version of TB 43-209 is the source for CARC patterns for several military vehicles.

“Soldiers at the unit level were limited to touching up their vehicles using a brush or roller; they were not supposed to spray CARC for any reason. Touch ups for cosmetic reasons were also officially prohibited; only blemishes in the paint that went to bare metal were to be retouched, to inhibit corrosion. Unit level touch up was only supposed to be performed using the one part CARC. Rules governing CARC application were spelled out in AR 750-1, paragraph 4-41.

“It was determined that brush or roller application of CARC could be done outdoors without needing a respirator, as long as the individual was exposed to no more than one quart each day. It was, however, required that the individual wear chemical goggles, NBC gloves, a hat, and long sleeves. Use of the M40 NBC mask was permitted at the commander’s discretion.

“As with any army, rules are not always followed. The U.S. Army provides a good barometer in its PS Magazine. According to PS Magazines online article index, from 1990-2000, there were 22 articles on CARC, 8 of which were about CARC touch up and what painting was allowed at the unit level. It would appear that many soldiers were unfamiliar with AR 750-1!

THE CHANGEOVER TO CARC

“When the Army adopted CARC in 1983, it issued a set of guidelines on how the transition from alkyd to CARC was to transpire. The transition began in October 1985 (start of Fiscal Year 1986) for systems already in the field. The guidelines were as follows:

1. At the unit level, crews were to continue touching up the existing paint jobs until such a time as the whole vehicle was in need of a repaint, complete repaints were to be done only as needed.
2. Any vehicle in a depot level repair program would be repainted using CARC and the 3-color scheme.
3. If an approved 3-color CARC pattern was not available for the vehicle, the Green 383 base color was to be applied.
4. Vehicles painted in CARC were to be marked near the data plate with “CARC mo/yr.”

“It was spelled out that any new systems in procurement as of the May 1983 message would be procured with CARC in the 3-color patterns. Systems already in production would convert to CARC as soon as possible, but no later than October 1985.

“Some fielded systems that were near the end of their life cycles were left in the old 4-color alkyd patterns until they left service. By the onset of the Gulf War in 1991, most everything was CARC painted, but the occasional piece of support equipment could be found in the old pattern into the 1990’s. Once a piece of equipment was painted in CARC, all markings were to be applied using CARC or lusterless black pressure sensitive decals.

CARC OR NO CARC
“Certain items were not to be coated with CARC, they were spelled out in AR750-1, paragraph 4-41, line 10:

a.) Painted items that attain surface temperatures of 400 degrees Fahrenheit serve a heat-conducting function or serve a function of expanding and contracting during operation. Examples are manifolds, turbo chargers, cooling fins, and rubber hoses.
b.) Displacement watercraft that will be subject to prolonged salt-water immersion. Examples are the logistical support vessel and the landing craft utility.
c.) Non-deployable equipment and fixed installation systems. Examples are railroad rolling stock and fixed power generation systems.
d.) Installation / TDA equipment such as military police cars, non-tactical fire trucks and buses.
e.) Aluminum transmissions that are enclosed in combat vehicle powerpack compartments. However any ferrous components of the transmission must be protected with CARC or other rust-preventative agents.

“AR 750-1, paragraph 14-4, also spelled out, “If items do not require painting, do not paint them. For example, items made of fabric or which have anodized or parkerized surfaces are not painted.”

“The old practice of continuing camouflage pattern painting onto vehicle soft-tops was also ended, as there was no flex agent available to mix with CARC paints.

CARC ON WOOD
“It was found that CARC did not last well on wood. Wood expands and contracts with weather changes and CARC lacked the flexibility needed move with the wood, so cracks would form and the finish would begin to peel. It was recommended in TM 43-0139, “Properly seasoned wood shall be sealed prior to application of CARC with a polyurethane sealer …wood shall be treated…dried to a moisture content no greater than 20% and pressure treated in accordance with [the] American Wood Preservers Bureau…” At some point in the 1990s, it was decided that CARC was not to be used on wood at all because it simply did not last.

THE FUTURE OF CARC
“Given the volatile and toxic nature of the CARC coatings, research to develop more environmentally friendly coatings with the same properties as CARC were underway even before CARC became standardized. CARC has a Volatile Organic Compound (VOC) content of 420 g/L. This was pushing the limits of federal and local regulations stemming from the Clean Air Act of 1990.

“The Army, as well as the private sector, began experimenting with waterborne coatings in an effort to meet the requirements of new clean air regulations. By the close the century the US Army Research Laboratory had developed a coating that had a VOC content of 220g/L while exhibiting many of the same characteristics of CARC. Development and testing continued as the century drew to a close.”

Original Source

Top 5 Myths about Powder Coating

When it comes to powder coating, be wary of these myths.

According to ICI Online:

“Many people have their preconceived notions about powder coating which are not all very accurate. Before discussing the top 5 myths about powder coating, let’s go over the process and how it works.

What is powder coat?

“Powder coating is a type of coating that is applied as a free-flowing, dry powder. The main difference between conventional paint and powder coating is that powder coating does not require a solvent to keep the binder and filler parts in a liquid suspension form. The result is a paint-like finish.

“Once a metal is prepared for powder coat, depending on the application process, a powder is applied to the metal with an electrostatic gun, this creates a positive electric charge and when sprayed on the metal part, adheres to the metal. Once applied, the metal part goes into a sizeable hi-temp oven where it melts down and creates a film.

Myth #1. Powder coat doesn’t crack or chip.

“Although powder coat creates a film over the part, it, unfortunately, is not damage proof. Like many materials, under certain conditions powder coat can crack or chip and then peel away like an eggshell. Even when the powder coating is applied correctly, the environment can play a role in the effectiveness of the coating. Extreme heat, cold, or rough grainy substances, such as dirt, or salt may corrode the coating faster than you intended.

Myth #2. Powder coat can be applied to the same materials as wet paint.

“Although used as an alternative to wet paint, this is not the case for all materials. Earlier, when I talked about the powder coat process, you can see why it would not work on materials such as plaster, wood, rubber and other non-compatible electrostatic materials. The primary utilization for powder coat is on metals.

Myth #3. Powder Coat is great for covering imperfections.

“This one is a little tricky because the powder coat applies to the top of a surface, it seems logical that it would hide flaws. If there is discoloration on the surface, the powder coat can usually cover that depending on the color of the blemish. However, if the surface is scratched, dented, or has other imperfections the powder coat will not hide these. Powder Coat can end up drawing attention to such flaws.

Myth #4. Powder coat has a quicker dry and cure time than wet paint.

“Powder coat does not have a dry time, only a cure time. The powder remains dry during the entire application process, so there is no “dry-time” as opposed to liquid paint. For the curing process, the object is placed in a large “oven” to bake the powder into a “skin.” For example, at ICI for a standard bumper, we first prime the bumper with powder coating, cure it for 15-30 min and then use the black powder coat and cure it at 420 degrees Fahrenheit for 45 min.

Myth #5. Powder coat prevents rust and corrosion.

“This one is one of the most common misconceptions amid powder coating. Although the powder coat creates a skin, it does not prevent rust or corrosion, especially for exterior parts. Primer and proper application are essential to the longevity of your powder coated components.”

Original Source

Pretreatment for Painting

Have you ever wondered why you need to pretreat before you paint? Consider this.

According to Products Finishing:

A high-quality conversion coating is essential for the durability of painted metal goods. The process of applying an inorganic conversion coating to a metallic surface involves removing any surface contaminants, then chemically converting the clean surface into a non-conductive, inorganic conversion coating. Conversion coatings increase the overall surface area and promote adhesion of the subsequently applied organic film. In addition, conversion coatings change the chemical nature of the surface, which increases corrosion resistance. It is these two functions, increasing surface area and changing the surface chemistry, that serve as a base for preparing the substrate material for paint finishes.

There are a number of driving forces in the pretreatment industry today with quality, cost and the environment being the most predominant. While these aren’t new issues, the pretreatment industry has responded to the needs of finishers by creating technology to address each of these requirements. In understanding the complete manufacturing process, including paint formulations, application equipment and regulatory impacts, it’s possible to address each driver simultaneously.

The conversion coating chemistries predominately used today are either zinc or iron phosphate. There is movement to replace these technologies with new types of phosphate-free or very-low-phosphate metal pretreatments. The new-generation technologies have been commercialized by many vendors over the past several years and are rapidly becoming industry standards. Regardless of the chemistry, conversion coatings are used to promote adhesion and improve corrosion resistance. Depending on the conversion coating and the desired performance, the conversion coating can be applied at a number of points in the process.

Cleaning

To increase the effectiveness of the finish, parts must be clean prior to coating. Aqueous cleaning, vapor degreasing or ultrasonic cleaning are typical cleaning processes, and of the three, aqueous cleaning makes up the majority. For parts that will subsequently be finished with organic coatings, surface pretreatment is required.

Depending on the chemistry, iron phosphate systems can either be a cleaner coater, where the cleaning and coating take place in the same stage, or have a separate cleaning stage. Separate cleaning steps are essential for zinc phosphate systems and the new phosphate-free and low-phosphate conversion coatings. If the cleaner does not fulfill its purpose of removing unwanted soils from the substrate, subsequent processing steps will not produce a uniform conversion coating and therefore adequately protect the metal surface from corrosion.

Typical soils are either organic or inorganic. Rust preventative oils and lubricants, metal forming blends and rolling oils are examples of organic soils. Inorganic soils include mill or heat scale, metallic fines and laser scale.

Three types of cleaners are used in metal finishing: solvent cleaners, acid cleaners and alkaline cleaners. Using the proper cleaner for the application is critical, since the method of cleaning can affect coating characteristics such as coating weight and crystal structure as well as subsequent coating performance.

Solvent cleaners are usually used on small surface areas and offer limited ability to remove difficult oils. Solvents usage is diminishing in favor of more environmentally friendly options. Acid cleaners are chosen for removing inorganic soils such as surface oxides.

Alkaline cleaners deliver optimum results on organic soils. These cleaners are versatile enough to effectively clean the surface by lifting the soil up and dispersing it into the main cleaner bath, where it is held until it is removed mechanically using thermal oil separation, ultrafiltration or by overflowing the cleaner tank to drain off surface oils.

Rinsing

Proper rinsing is a critical, yet often-overlooked step in the pretreatment process. The water rinse process stops chemical reactions from taking place and removes unreacted chemicals from a part’s surface. Effective water rinsing also minimizes the migration of chemicals from one processing stage to the next. For effective rinsing, keeping the rinse water fresh reduces the amount of contamination present on the surface of the parts.

Since the key is controlling the amount of surface contamination on the part, if there is only a single rinse stage, a fresh water halo can be installed in between the chemical and water rinse stage rather than adding fresh water to the main tank. This allows the rinse tank to run at higher levels of contamination while the halo adds fresh water to the tank, but more importantly it floods the part and reduces the surface contamination. In the case of multiple rinse stages, they are counter-flowed and can effectively minimize water used in the rinse stages, requiring only a fraction of the water volume and reducing the amount of effluent produced. You can also reduce water consumption by optimizing your equipment design with proper racking of parts.

The Choices

Traditionally, the choices for a pretreatment process have been either an iron or zinc phosphate which provided the degree of performance necessary for the operation. Recently, there have been developments to replace this traditional technology with products that address ever-growing concerns with energy and water usage, environmental impact and the general operation of the process.

1) Iron Phosphate Pretreatment Systems. Iron phosphate systems, also known as alkali metal phosphates, are used for parts that require a durable finish but are not exposed to severely corrosive environments. These systems can involve two to six stages, with the shortest sequence being a cleaner-coater stage followed by a tap-water rinse. Short sequence systems are employed if performance requirements are low.

Parts that are more difficult to clean or have higher quality requirements call for a separate cleaning stage, appropriate rinse tanks, iron phosphate, post-treatment rinse and a DI rinse. A post-treatment rinse (chrome or non-chrome) results in improved corrosion performance over the phosphate alone.

Iron phosphates produce an amorphous conversion coating on steel that ranges in color from iridescent blue to gray, depending on operating conditions and product formulation. Mixed metals may be treated with modified formulas that typically contain fluoride.

Iron phosphate processes are much easier to operate and require fewer process stages than zinc phosphating. However, iron phosphates do not provide the degree of corrosion protection imparted by zinc phosphates.

2) Zinc Phosphate Pretreatment Systems. A zinc phosphate system varies from an iron system in two critical areas. First, it requires the use of a surface conditioner stage. Second, a zinc phosphate bath has additional metal ions in the solution which are incorporated into the coating along with the metal ions from the substrate being processed.

Surface Conditioning

Surface conditioning rinses are used in zinc phosphating to refine crystal morphology and control coating weight. State-of-the-art conditioners are liquid products that can be consistently applied using metering pumps.

The surface conditioning rinse takes place just before the zinc phosphate stage and is the only step in the process that is followed by another chemical stage, the zinc phosphate bath. The traditional surface conditioning chemistry is a colloidal suspension of a titanium salt. As these traditional baths age, they become less effective and must be dumped frequently or overflowed to maintain effectiveness.

Recently, zinc phosphate has been used to replace the titanium salt chemistry. This technology improves the refinement of the zinc phosphate coating, yet is not affected by the chemical make-up of the water or bath age.

Zinc Phosphate

Zinc phosphating coatings provide exceptional painted part durability in corrosive environments and have the ability to coat mixed metals (steel, zinc-coated steel and aluminum). Several small developments have taken place over the past few years, such as decreasing the environmental impact, improved performance and ease of operation. New zinc phosphate systems operate at lower temperatures, in some cases are free of nitrites and nickel, and offer a reduction in sludge, and some products are internally accelerated. The objectives of the products were to increase quality, operate easily and, in the case of internally accelerated systems, eliminate the need for additional accelerators.

Depending on the metal mix in the system, additives are used to assist in the formation of the conversion coating on the substrate. For example, free fluoride added to the bath optimizes the conversion coating on aluminum and/or zinc. Adding calcium ions to the zinc phosphate bath produces a microcrystalline phosphate coating needed for rubber bonding. Depending on the final application and performance requirements, various other metal ions, organic acids, chelating agents and other chemicals can modify the overall characteristics of the zinc phosphate conversion coating.

Over the years, zinc phosphating systems have evolved from conventional systems containing high levels of zinc and nickel accelerated by sodium nitrite. An additional metal ion, manganese, was incorporated into the base chemistry to create the polycrystalline systems used today. Current polycrystalline systems can be either internally or externally accelerated, and in some processes, nickel was removed to create a nickel-free process.

New-Generation Conversion Coatings

New conversion coating technologies are being introduced that have four significant processing benefits. These coating processes are shorter, simpler and operate at lower temperatures than current zinc or iron phosphate processes. They perform well on all standard substrates of steel, zinc and aluminum. They significantly reduce the environmental impact, while their corrosion performance meets metal finishing specifications for painted metal substrates. All of these benefits provide significant cost savings to manufacturers willing to convert their existing processes.

The new-generation conversion coating process is based on zirconium and additional propriety chemicals. When applied to a metal substrate, these chemicals react to form an amorphous zirconium oxide coating 20-80 nm thick that is significantly different from the iron phosphate and zinc phosphate coatings in use today. The new coating is thinner than traditional iron or zinc phosphate conversion coatings.

The new conversion coating process contains no zinc, nickel, manganese or phosphates; rather, it is based on zirconium containing chemicals. Zirconium is not regulated as a hazardous metal in North America or Europe. The new coating can be applied in fewer total stages than a zinc phosphate process and fewer chemical stages than both zinc and iron phosphate. In its simplest form, the process consists of five stages—two chemical stages and three water-rinse stages. The reduced number of stages will result in a 10- to 30-percent reduction in the overall plant footprint when converting from a standard zinc phosphate to the new-generation conversion coating process. A reduction in water usage also can be realized that is directly related to the reduction in process steps.

Post-Treatment

After a metal surface receives a conversion coating, the surface is water rinsed to remove unreacted chemicals, and a post-treatment may be applied. The post-treatment can increase corrosion and humidity resistance as compared with conversion coatings without final rinses. In the case of electrocoat applications, final deionized (DI) or reverse osmosis (RO) water rinse is required to minimize drag-in of high-conductivity water on the substrate surface from the post rinse. In these cases, it is imperative to have a reactive final rinse that maintains its properties after the DI or RO rinsing rather than a dry-in-place rinse.

Post-treatments historically have been based on chromic acid. With more stringent effluent guidelines, most finishers have converted to either trivalent-chrome or non-chrome post-treatments. The automotive industry has set standards to virtually eliminate the use of hexavalent chrome in vehicles produced after 2007. Recent advances in dry-in-place (DIP) polymeric post-treatments have shown excellent results when compared with standard non-chrome/DI rinsed systems.

Phosphate Coating Evaluation

There are three characteristics that define a conversion coating: the coating weight, the crystal size or morphology, and the chemical composition. When within the designed specifications for the application and material, all three characteristics contribute to ensuring the proper and expected adhesion and corrosion performance.

Coating Weight

Coating weight is defined as the amount of coating deposited within a specific surface area. Typically, coating weight is expressed in either grams per square meter (g/sq m) or milligrams per square foot (mg/sq ft). Each conversion coating technology is designed to deposit a specific coating weight on a substrate. Coating weight is an excellent indicator of whether the conversion coating bath is in proper chemical balance. If the coating weight is low and outside the specified range, something may be wrong within the process, and immediate attention is required.

Crystal Structure

The crystal structure of the conversion coating is measured through the use of a microscope, either an optical or, most commonly, a scanning electron microscope (SEM) at magnifications ranging from 100 to 1,000 times. In the case of new-generation coatings, this magnification is not sufficient, and other instruments such as an Atomic Force Microscope (AFM) or Field Emission SEM (FE-SEM) are necessary to achieve visible images of the coatings at 30,000 times and greater.

Regardless of the instrument required, the conversion coating is a combination of crystalline and microstructures chemically deposited on the metal surface. Instrumentation is used to determine the size, shape and uniformity of the coating. These instruments are excellent tools to examine any metal or coating imperfections that would go unnoticed with the naked eye. This visual examination of any non-uniform treated surface helps in the troubleshooting the pretreatment process. Through the use of the microscopes, the uniformity of the conversion coating can be monitored to ensure proper coverage and structure size. It is well-documented that structure size plays a very important role on paint adhesion.

Coating Composition

In addition to coating weight and crystal structure, the chemical composition of the coating plays a significant role in corrosion performance. Basically, corrosion is alkaline in nature, so the more alkaline resistance a coating delivers, the better the corrosion performance.

Chemical composition can be determined through a simple analysis in the laboratory using more advanced equipment, such as scanning electron microscopes with energy dispersive x-ray or x-ray diffraction. Use of this type of equipment is impractical on site, but can effectively evaluate performance in a laboratory setting. The chemical composition of the coating can help troubleshoot the process in applications where corrosion performance is below expectations.

Visual Inspection

Because the three coating characteristics take some time for evaluation, a simple visual inspection of the coating at the manufacturing site can look for problems. Phosphate coatings should be uniform in appearance whenever possible. Variations in color are normal on mixed metal sub-assemblies such as automobiles using various zinc-galvanized steel alloys.

Although color may vary, there should not be any visible shiny spots in the coating. Shiny areas indicate a condition known as inhibition. Inhibition is where the phosphate coating has not formed due to surface contamination.

Mapping is a widely used term today that describes various types of patterns that are visible on the conversion coating. These patterns are often most visible after the application of the paint film, making them extremely costly to repair. Mapping is normally caused by an uneven chemical reaction with the metal due to contamination such as oils, compounds, sealers or other materials left on the surface. The contaminants either react with the metal forming a permanent stain, or they are not removed by a chemical stage in process, i.e. poor cleaning, where the contamination is not removed in the cleaning stage and the next chemical stage must remove the surface contaminate. If this is the conversion chemical stage then the time needed to deposit the coating is compromised.

Patterns such as streaking may be a result of drying in drain vestibules, misaligned spray nozzles, or other air and solution flow imbalances within the phosphate system. In most cases, skilled operators can rapidly correct these patterns by realigning nozzles or adjusting pressures. In some instances, additional wetting harnesses are added to systems to address these problems. Some systems are incapable of correcting certain patterns due to original design flaws. Slight patterns are not normally detrimental to ultimate coating quality. The technologies that are available offer the metal finisher several options to choose from to meet a customer’s performance requirements. Currently, iron and zinc phosphate predominate as the products of choice when it comes to applying a conversion coating to a metal surface prior to painting. However, with the ever-changing business climate and the need to reduce costs, systems must become more environmentally friendly while reducing energy and water demands. With the development of the new-generation coatings, the landscape is changing, and the metal finishing industry has an opportunity to meet the cost and environmental constraints while meeting the performance expectations of its customers.

Original Source

All About Industrial Lubricants and Grease

New to industrial lubricants and grease? Consider this.

According to Thomas Net:

“Lubricants are substances applied to reduce friction and wear on surfaces that have relative motion between them. Although this is a lubricant’s primary function, it can also serve as a heat-transfer agent, a corrosion preventative, a sealing agent, and as a means of trapping and expelling contaminants in mechanical systems. While oils and greases are common forms of liquid and semisolid lubricants, they can be found in other forms as well: dry lubricants, gas lubricants (such as air), etc. Specifying lubricants for mechanical systems must take into consideration not only the need to reduce friction and wear but also the need for them to perform some or all of these secondary functions. Equipment manufacturers endeavor to find optimum formulations for their designs and equipment operators are advised to follow manufacturers’ recommendations for their selection and use.

“This article will discuss liquid lubricants, solid lubricants, and grease.

Types of Industrial Lubricants and Grease

Liquid Lubricants

“Liquid lubricants are largely produced from petroleum and synthetic fluids. The abundance of petroleum makes its use in petroleum-based oils ubiquitous and economical. Synthetic oils are generally more costly but are used in applications where their improved performance characteristics make the cost tradeoffs worthwhile.

“Among the many characteristics of liquid lubricants, viscosity is a dominant factor. Viscosity is defined as dynamic, or absolute, viscosity, in units of lb-sec/ft2. It is described as the measure of the velocity gradient between stationary and moving parts of a fluid. Kinematic viscosity, v, is defined as dynamic viscosity, or µ, divided by density, ρ, with units of ft2/sec. Kinematic viscosity is also expressed as SSU (or SUS), for Saybolt Seconds Universal, which assigns a number to a lubricant after running it through a capillary-type viscometer under Newtonian flow conditions. A common unit of dynamic velocity in the cgs system is the centipoise. Viscosity can be affected by temperature, shear, and high pressure.

“The Society of Automotive Engineers (SAE) classifies oils by viscosity, with SAE 5W, 10W, and 20W measured at 0°F and SAE 20, 30, 40, and 50 measured at 212°F. Any multigrade oil, SAE 10W-40, for example, will meet the viscosity requirements at both temperatures. Industrial liquid lubricants are classified by ASTM D2422 and ISO 3448. ISO VG (for viscosity grade) 2 through 1500 (in eighteen steps) represents the kinematic viscosity of 2 and 1500 mm2/sec (or, centistoke) measured at 40°C.

“The viscosity index, or VI, assigns a number from 0 to 100 based on an oil’s change in viscosity with change in temperature. A higher number indicates less change in viscosity with change in temperature. The scale was based on comparisons of Pennsylvania and Gulf crudes as the defining limits, but advances in refining have since achieved VIs that exceed both scale endpoints.

“An oil’s pour point defines the temperature at which an oil will flow and is an important consideration for cold starting engines and for gravity lubricators. Pour-point depressants can lower the pour point. A related attribute is the cloud point—the temperature at which any wax in the formulation begins to visibly separate, usually just slightly above the solidification temperature. This is important because wax can clog filters.

“Other attributes of lubricating oils include their flash and fire points, their propensity to foam when used in high-speed rotating applications such as turbines and crankcases, and their ability to withstand high-pressure when used in hypoid gearing and other extreme-pressure situations. A special group of lubricants, dubbed EP lubricants, (for extended pressure), are specifically formulated to inhibit the wear that might result when highly-loaded gears make metal-to-metal contact.

“As noted above, high pressure has an effect on viscosity, tending to increase it as pressures reach higher regions. Designers of highly-loaded machines use this fact and are able to specify relatively low-viscosity fluids that might be unsuitable for use in lower-pressure applications.

“Synthetic oils are formulated generally to increase one characteristic—high VI or thermal stability, for instance—albeit often at the expense of another characteristic such as pour point. Synthetic oils tend to be costlier than mineral-based lubricants and hence are employed in industrial settings only when the performance gains warrant the added expense, as in instruments and heat-transfer systems such as industrial ovens. Synthetics are made from a variety of fluids such as polyglycol for brake fluid, phosphate esters for fire-resistant hydraulic fluid, silicones for use with rubber and plastic, etc.

“The oil used in engines performs many functions besides lubrication: corrosion prevention, cooling, sealing, etc. Engine oil manufactures compound these products with a host of additives, including detergents, VI improvers, EP enhancers, pour-point depressors, and so forth to meet the many functions that engine oils serve.

“You can you the Thomas’ Supplier Discover Platform to find Suppliers of Liquid Lubricants.

Solid Lubricants

“Solid lubricants, sometimes called dry-film lubricants, are chiefly forms of synthetic or natural graphite or molybdenum disulfide, applied loosely to sliding surfaces or mixed with binders. They are used mainly where temperature or pressure extremes or environmental conditions make liquid lubricants impractical. High-vacuum environments are one such setting, where molybdenum disulfide is preferred. Graphite needs the presence of water vapor to act as a lubricant, making it unsuitable for use under vacuum conditions.

“Both graphite and molybdenum disulfide achieve their low coefficients of friction due to the laminar, plate-like structure of their molecules and the relatively weak structure between plates. Some liken their effect as similar to trying to cross a room on which playing cards have been spread over the floor: the individual cards slide easily past each other, minimizing friction between foot and floor.

“Polytetrafluoroethylene (PTFE), another anti-friction material, does not share the same layered structure of graphite and molybdenum disulfide. It is used as an additive in oils and grease and some lubricating sprays. It can be applied as an anti-friction coating or film to a variety of machine parts including compressor pistons, slides, O-rings, etc. It is sometimes combined with aluminum for hard- coat anodizing.

“Solid lubricants can be applied as unbonded powders or granules or mixed with organic or inorganic binders to create curable coatings on friction surfaces. Molybdenum disulfide is sometimes vapor deposited onto compression fittings where it serves as an anti-seize agent.

Industrial Grease

“Grease is composed of liquid lubricant and a thickener, usually soap, in addition to additives which impart desirable properties to the formulation such as corrosion resistance and tackiness. Normally a semisolid, grease liquifies at a temperature referred to as the dropping point, which can range from 200 to 500°F and higher depending on the thickening agent. Greases thickened with calcium- or lime-soaps tend to have dropping points in the lower ranges while those thickened with clays liquify at temperatures quite a bit higher.

“The NLGI (National Lubricating Grease Institute) rates the consistency of greases from a semifluid (000) to very hard (5) and block type (6) based on penetration tests of the material in a worked state, whereby a standardized object is dropped into the product at a known temperature and time and the depth to which the object sinks is noted. As a point of reference, most grease-lubricated rolling-element bearings use an NLGI 2 grade.

“The consistency rating is not the equivalent of oil viscosity, however. This rating is determined by the viscosity of the base lubricant. Most grease manufactures will publish this data. Greases with identical NLGI ratings can have different performance characteristics. Again, as a point of reference, many grease-lubricated rolling-element bearings will use grease with viscosities similar to SAE 20 or 30 oil. As with oils, grease may be modified with EP agents to protect against damage to precision surfaces from shock loading, severe loads, static loading, or frequent starts/stops. Use of EP agents is recommended only when needed as they can be detrimental to bearing surfaces and the like, especially at elevated temperatures.

Types of Industrial Grease used in Industrial Applications

“Aluminum complex grease is used where high temperatures are expected. With a dropping point of 500°F and a maximum useable temperature of 250-325°F, this smooth grease is often used in food machinery.

“Modified Bentonite clay is used when exposure to very high temperatures is expected. This smooth grease, with a dropping point of 600°F, a maximum useable temperature of 250-325°F, and excellent water resistance, is popular for use in ovens as it has the ability to create its own seal, a plus where bearing seals are exposed to those high temperatures.

“Calcium12 hydroxy stearate is a smooth grease with very good water resistance, albeit lower maximum useable temperature than other greases (250°F) and a dropping point of 290°F.

“Lithium 12 hydroxy stearate is a popular grease for many bearing applications, with good water resistance, smooth texture, a dropping point of 380°F, a maximum useable temperature of 250-325°F, and a capability for long life. It is a very pumpable grease.

“Lithium complex is used in high temperature, high-speed bearings. With a smooth texture and decent water resistance, a dropping point of 550°F, and maximum useable temperature of 250-325°F, it is considered an improvement on Lithium 12, though this still makes up the majority of grease used for general purposes.
Polyurea is good for long life applications. This smooth grease has excellent water resistance, a dropping point of 460°F, and a maximum useable temperature of 250-325°F. It is often used on food machinery.
Sodium tallowate, once the primary grease for wheel bearings, is usually employed only in older, slower bearings and exhibits poor water resistance, a fibrous texture, a dropping point of 390°F, and a maximum useable temperature of 250°F. It is a low-cost grease with good rust preventative properties.

Lubrication Theory

“Hydrodynamic lubrication relies on pressure developed in the lubricating fluid to support the bearing load. For hydrodynamic conditions to exist, there is necessarily a balance that must be achieved between speed, load, and viscosity. These conditions can be met over a fairly broad range. However, high loads, starting and stopping, etc., can all act to disrupt this balance, causing irregularities in the surfaces to come into contact. This so-called boundary-lubrication condition is the reason that soft metals are used in babbitted journal bearings so that the babbitt becomes a sacrificial surface rather than the harder shaft journal. It is the same reason that EP lubricants are used in certain gear applications as additives in the lubricant provide a cushion of sorts during these boundary-lubrication events. So-called µn/P, or Stribeck curves, plot coefficient of friction, f, against the nondimensional group µn/P (viscosity x speed/pressure) for shafts in lubricated journal bearings. As the shaft comes up to speed, the plot moves through zones of boundary lubrication to mixed lubrication to hydrodynamic lubrication.

“When selecting anti-friction metals such as tin- and lead-base babbitts, bronze, copper-lead, and even cast iron, as well as the various forms of sintered bearings, considering the running material (shaft, way, etc.) is equally important. For instance, soft steel will run well in babbitt, cast iron, or soft brass, but not in soft steel or bronze. Hardened steel will run well in soft bronze and many other metals, but not in hardened heat-treated bronze.
Hardened nickel-steel runs poorly in hardened nickel-steel.

“Rolling element bearings have high loads in the contact zones which tends to deform the elements. There is, theoretically, a thin film of lubricant that exists between the rolling elements and the races, known as elastohydrodynamic, or EHD, film.

Considerations

Handling and Storage
“Oil is commonly shipped in 55-gallon drums and 5-gallon pails, and grease is often supplied in 35 lb. kegs. Oil is also supplied in bulk and stored in tanks. Most lubricants have shelf lives which are often determined by the additives in them. A good practice is to use the oldest stock first. In general, a room that is clean, dry, and free from temperature swings provides the best storage conditions for maximizing shelf life. Drums that are stored outdoors should be positioned on their sides and protected by tarps or shelters.

“During handling, drums may be rolled on their sides but should never be dropped. Drum-handling jaws for forklifts are available that surround the drum perimeters; forklift blades alone should not be used to grasp drum sides.

“It has been shown that oil cleanliness can have an impact on equipment life. The International Standards Organization (ISO) rates oil cleanliness by particles per milliliter based on the number of particles and their sizes. Even new oil can have particle counts higher than would be recommended for some machines, and filtering oil before use can be beneficial for equipment life. Likewise, careful handling of lubricants to avoid mixing different formulations and introducing contaminants is an important part of any lubrication program. Grease should also be carefully controlled to avoid mixing formulations.

“Used lubricants should be recovered or disposed of in accordance with sound environmental practices.”

Original Source

Special Coatings Support Mars Rover

Ever wondered how rovers can survive the harsh environments of space? Liquid coating.

According to Products Finishing Online:

“NASA’s Mars 2020 mission successfully launched on July 30 and is currently on its way to the red planet. Known as Perseverance, the Mars rover’s mission is to search for signs of ancient life and cache rock and soil samples for possible return to Earth.

“To protect Perseverance, a special paint job is needed. Chris Salvo of NASA’s Jet Propulstion Laboratory (JPL) who manages the team who puts together the rover’s mechanical subsystem, explains the role the paint job plays in standing up to the extreme temperatures of space travel and the harsh environment of the red planet. A special reflective white paint is used to reflect sunlight and prior to painting, the aluminum surfaces of the rover chassis are scuffed and carefully cleaned to ensure the paint adheres correctly. Detailed masking is required to make sure areas requiring paint are coated precisely and operational surfaces are left unimpeded.

“’This very special formulation of paint has to live through all the difficulties of getting to Mars, shaking on the launch vehicle, as well as existing on the surface of Mars in the hot and cold cycles,’ Salvo says in a video released by JPL.

“Once painted, the rover’s chassis is then baked in a thermal vacuum chamber to remove any volatile materials such as water particles that might be drawn out of the paint by the vacuum of space and cause problems.

“Various components within the rover also require special coatings. A proprietary impingement lubricant coating process known as Microseal developed by Curtiss-Wright’s Surface Technologies Division (Parsippany, N.J.) has been used on numerous components for NASA’s Mars 2020 Mission, many within Perseverance’s sample caching system.

“Curtiss-Wright Surface Technologies has a long standing relationship with NASA. Microseal was selected for the Perseverance mission because of its friction reduction properties under a wide range of temperatures from cryogenic temperatures to over 1,000° F, and its ability to perform in hard vacuum conditions.

“’High performance in harsh conditions typical to space applications demands a reliable solution like Microseal,’ says David Rivellini, senior vice president and general manager, Curtiss-Wright Surface Technologies. ‘The Microseal process outperforms conventional lubricants as it remains stable under extreme conditions and is resilient to shock, radiation, vibration, acceleration and electrical discharge.’

“The Microseal process creates an ultra-thin adherent film that fills voids on the surface of components. The film is designed to perform within a vacuum and in extreme temperatures ranging from -423°F to 2000°F (-253°C to 1093°C). The company says the process creates a continuous lubricating surface that reduces friction and prevents galling and seizing. It also dissipates heat, remains stable under extreme environmental conditions, and does not attract contaminant particles.

“According to Pierce Cleary, director of business development, Curtiss-Wright Surface Technologies applies the Microseal process to surfaces using a specially designed, patented air tool that mixes micro-size particles. Particles leave the tool at speeds of nearly 600 feet per second, depositing a firmly adherent thin film that fills the surface voids.

“’Regardless of the surface geometry of the treated part, once the coating reaches a thickness of fifty to eighty millionths of an inch, no further coating will be accepted,’ explains Cleary, ‘Coverage is uniform on all surfaces the air tool can reach, and the process is burnishable to original dimensions, eliminating the need for special machining or tolerance allowance.’

“Due to the complex and proprietary nature of the equipment, Microseal application takes place at one of Curtiss-Wright Surface Technologies’ worldwide facilities. The company inspects incoming parts for cleanliness and freedom from surface defects and closely monitors the entire application process.

“The latest Mars rover mission includes numerous new technologies including a robotic helicopter that will mark humanity’s first attempt at flight in an alien atmosphere. Perseverance is scheduled to arrive on the red planet on February 18, 2021.”

Original Source

Thermoset Powder Coating

New to thermoset powder coating? Here is a breakdown.

According to Thomas Net:

“Thermoset materials are used for the majority of powder coating processes because they can provide a surface layer that is both durable and decorative. Most thermoset powders have a molecular weight lower than that of thermoplastic materials and higher than that of liquid coatings. Thermosets are solid resins that, when heated, melt, flow, and—unlike thermoplastics—can crosslink with one another or other reactive substances to form compounds with higher molecular weights. After curing, a thermoset coating remains thermally stable, meaning it cannot be melted back into a liquid from further heating.

“In a powder coating system, the more brittle thermoset resins can be broken up into a very fine powder that can then be fabricated into an exceptionally thin, paint-like film. This film exhibits chemical and physical properties comparable to those of liquid-based coatings. In addition, advancements in thermoset technology have continuously increased the versatility of this material group, allowing for more customization options. Many standard thermoset materials can now be chemically altered to provide the specific characteristics required for a given application.

Thermoset Powder Coating Properties

“The most commonly used thermoset powder coating resins derive from the epoxy, hydroxyl or carboxyl, acrylic, and silicone groups. They generally require lower curing temperatures than thermoplastics, and manufacturers often introduce additives to accelerate or delay the curing reaction. It is important to subject a powder-coated product to thorough heating and allow the thermoset to flow evenly over the targeted surface because once the thermoset powder has completed crosslinking, it cannot be reflowed to correct any flaws in the coating. To achieve successful coating results, it also necessary to match the thermoset formulation with the product’s intended corrosion resistance, curing cycle, texture, and aesthetic properties.

“One of the most significant developments in thermoset powder coating involves the capacity to engineer resin types with variable properties designed to complement metal finishing treatments. This broader range of characteristics has led to an increase in specialized roles for thermoset powders, with polyesters and acrylics finding greater use in the automotive and appliance industries despite the traditional reliance on epoxy-based coatings. Most thermoset powders can provide a high level of corrosion, temperature, and impact resistance. They can also be designed with a wide range of colors, glosses, and surface finishes. Coating texture can be wrinkled, smooth, or matte, while film thickness is highly adjustable.

Epoxy-Based Powder Coatings

“Epoxies are the most common thermoset resins used in industrial powder coating, and they have a wide range of formulation options. Different types of epoxy can be fabricated into functional thick film or more decorative thin film, while their crosslinking properties are similar to those of epoxy adhesives and paints. Most epoxy-based materials are crafted to be thermally stable at room temperature. Some standard epoxy powder coatings include:

“Functional Film: Thick, functional film epoxies are often employed for electrical insulation and corrosion resistance applications. As insulation, epoxy powder bonds to a surface and follows its contours with relatively few voids or other defects. This is useful for devices such as electrical motors, switch gears, and automotive alternators. Anti-corrosion epoxy provides low cost and long-lasting protection for products in chemically hazardous environments, such as underground gas and oil pipes.
Thin Film: Thin film coatings are typically designed to provide specific decorative results while preserving the durability and resistance characteristics of other epoxy groups. They are generally restricted to interior coatings, as de-glossing and chalking are frequent risks for thin exterior layers. Thin epoxy film coatings are commonly found in fire extinguishers, furniture, hospital equipment, and a wide number of household appliances.
Epoxy-Polyester Blends: An epoxy resin crosslinked with a reactive acid polyester will form a blend, or hybrid, material that has flexibility and impact resistance qualities similar to those of other epoxies, but provides a higher level of ultraviolet light protection. These blends are effective when applied as an electrostatic spray and have a range of applications similar to those of thin film epoxies.

Acrylic Powder Coatings
“Acrylic powder coatings are beneficial for their high level of exterior durability and relative ease of application. Acrylics require curing temperatures close to those of hydroxyl polyesters, and they combine high quality surface aesthetics with flexibility and impact resistance. They also exhibit excellent alkali resistance, making them well-suited for use on appliances, such as ovens and washing machines. Acrylic powder coatings can be effectively applied through electrostatic spraying and have adjustable thin film characteristics. However, acrylics are more responsive to substrate attributes than most other powder coatings, making them incompatible with certain chemical compounds. Aside from their use in appliances, acrylic powder coatings can also be found on aluminum extrusions, automotive trim components, and tractors.

Hydroxyl and Carboxyl Polyester Powder Coatings
“Hydroxyl polyester powder, also known as urethane, provides both a high quality surface finish and resistance to wear. It is usually fabricated as thin film because its thick film form exhibits lower impact resistance and flexibility. A hydroxyl polyester coating has aesthetic qualities comparable to those of liquid paint, and it is commonly used for coating light fixtures, furniture, automotive components, wheels, and appliances. During curing, some hydroxyl polyesters release an emission that needs to be vented away from the cure oven to prevent defects or contamination.

“Carboxyl polyesters have durability characteristics similar to those of epoxy-polyester blends and weathering resistance comparable to urethane. They have consistent mechanical properties across a range of standard coating thicknesses and provide a high level of flow, glossiness, and material strength. However, their resistance to chemical solvents can be lower than that of hydroxyl coatings. Carboxyl polyester powder coating is commonly used on irrigation pipes, outdoor furniture, fences, aluminum extrusions, and steel wheels.”

Original Source

“CARC” (Chemical Agent Resistant Coating): A Cold War Camouflage

What is CARC and how is it used?

According to MilitaryTrader.com:

“Chemical Agent Resistant Coating or CARC is, in simple terms, a low gloss military version of the polyurethane paints that were developed for use in commercial industry. CARC has a low porosity that prevents chemical warfare agents from “soaking in” to the finish and makes decontamination easy to perform. TB 43-0242 states, ‘[Chemical agents] just bead up on the surface like water on a newly waxed car.’ More importantly, the CARC finish is not affected by the solvents used in the decontamination process.

“The finish is also much more durable and resistant to fading, lasting up to four times longer than the alkyd paint previously used by the Army. This durability promised to keep fielded vehicles looking better for a longer period of time and to reduce the number of times a vehicle would need to be repainted in its life cycle, thus reducing maintenance costs. The resistance to solvents allows regular washing of vehicles without fear of damaging the finish.

“To provide some idea about the durability of the CARC finish, TB 43-0242 gives the following as a test to determine if a vehicle is painted with CARC, ‘wet a cloth with acetone and rub hard on the painted surface for 10 seconds. Wet a clean corner of the cloth with acetone and rub another 10 seconds if no paint comes off the second time, it’s CARC.’

BACKGROUND

“The first chemical agent resistant coatings were developed as early as 1974, and by 1983 the Army was ready to make CARC the required coating for all combat, combat support, tactical wheeled vehicles, aircraft and tactical ground support equipment. The US Army officially adopted CARC in May of 1983.

“Besides its chemical resistance and durability, CARC has some other unique properties. For example, the base green color, “Green 383.” uses pigments that mimic the reflective properties of chlorophyll which is found in living plants, making the vehicle harder to detect using infrared detectors. During the Gulf War, “Tan 686” was reformulated to reduce the amount of solar heat absorption and keep vehicles cooler in the desert environment. The new color became “Tan 686A” and was standardized in the latter stages of the conflict.

“To create these special pigments, CARC is a two-part coating that is mixed before application. The components are not interchangeable, it is not possible to mix component A of one color with component B of another color, and intermixing components from different manufacturers is also not feasible. Once mixed, unused CARC will not keep and must be disposed of as a hazardous material. CARC is also highly flammable and it is recommended that the cans and mixing equipment be grounded when mixing the paint. A one part CARC was also made available for brush or roller touchup at the unit level.

HEALTH CONCERNS

“One problem of CARC is the toxicity of its components. Polyurethane paints were in use in the commercial and automotive industries for some years before the Army adopted CARC, so the health risks associated with them were well documented. All polyurethane paints contain isocyanates, and this alone poses a significant health risk. Add to this the array of volatile solvents and cleaners needed and you have a recipe for serious health risks.

“Hexamethylene diisocyanate (HDI) is the isocyanate found in CARC. It can be released when CARC is being sprayed, and it is also released when CARC burns making the smoke from welding and vehicle fires a greater potential health hazard. HDI is also a known sensitizer for asthmatics; soldiers with asthma were not to be involved with the application of CARC as ‘a severe life threatening allergic reaction may occur.’

“CARC poses no known health risks once dry unless disturbed by sanding or grinding. As a result of the hazards involved with applying CARC, individual units and crews were no longer responsible for the painting of vehicles. Complete repaints had to be done at the direct support, general support or depot level, provided the facility had an OSHA approved paint booth.

“This rule also applied to complete repaints of non-CARC painted equipment as the Army strove to become compliant with ever more stringent environmental regulations. Moving the responsibility for major painting tasks to the maintenance level also served to improve the quality of the paint finish and help maintain greater uniformity in camouflage patterns.

“The October 1990 version of TB 43-209 is the source for CARC patterns for several military vehicles.

“Soldiers at the unit level were limited to touching up their vehicles using a brush or roller; they were not supposed to spray CARC for any reason. Touch ups for cosmetic reasons were also officially prohibited; only blemishes in the paint that went to bare metal were to be retouched, to inhibit corrosion. Unit level touch up was only supposed to be performed using the one part CARC. Rules governing CARC application were spelled out in AR 750-1, paragraph 4-41.

“It was determined that brush or roller application of CARC could be done outdoors without needing a respirator, as long as the individual was exposed to no more than one quart each day. It was, however, required that the individual wear chemical goggles, NBC gloves, a hat, and long sleeves. Use of the M40 NBC mask was permitted at the commander’s discretion.

“As with any army, rules are not always followed. The U.S. Army provides a good barometer in its PS Magazine. According to PS Magazines online article index, from 1990-2000, there were 22 articles on CARC, 8 of which were about CARC touch up and what painting was allowed at the unit level. It would appear that many soldiers were unfamiliar with AR 750-1!

THE CHANGEOVER

“When the Army adopted CARC in 1983, it issued a set of guidelines on how the transition from alkyd to CARC was to transpire. The transition began in October 1985 (start of Fiscal Year 1986) for systems already in the field. The guidelines were as follows:

1. At the unit level, crews were to continue touching up the existing paint jobs until such a time as the whole vehicle was in need of a repaint, complete repaints were to be done only as needed.
2. Any vehicle in a depot level repair program would be repainted using CARC and the 3-color scheme.
3. If an approved 3-color CARC pattern was not available for the vehicle, the Green 383 base color was to be applied.
4. Vehicles painted in CARC were to be marked near the data plate with “CARC mo/yr.”

“It was spelled out that any new systems in procurement as of the May 1983 message would be procured with CARC in the 3-color patterns. Systems already in production would convert to CARC as soon as possible, but no later than October 1985.

“Some fielded systems that were near the end of their life cycles were left in the old 4-color alkyd patterns until they left service. By the onset of the Gulf War in 1991, most everything was CARC painted, but the occasional piece of support equipment could be found in the old pattern into the 1990’s. Once a piece of equipment was painted in CARC, all markings were to be applied using CARC or lusterless black pressure sensitive decals.

CARC OR NO CARC

“Certain items were not to be coated with CARC, they were spelled out in AR750-1, paragraph 4-41, line 10:

a.) Painted items that attain surface temperatures of 400 degrees Fahrenheit serve a heat-conducting function or serve a function of expanding and contracting during operation. Examples are manifolds, turbo chargers, cooling fins, and rubber hoses.
b.) Displacement watercraft that will be subject to prolonged salt-water immersion. Examples are the logistical support vessel and the landing craft utility.
c.) Non-deployable equipment and fixed installation systems. Examples are railroad rolling stock and fixed power generation systems.
d.) Installation / TDA equipment such as military police cars, non-tactical fire trucks and buses.
e.) Aluminum transmissions that are enclosed in combat vehicle powerpack compartments. However any ferrous components of the transmission must be protected with CARC or other rust-preventative agents.

“AR 750-1, paragraph 14-4, also spelled out, ‘If items do not require painting, do not paint them. For example, items made of fabric or which have anodized or parkerized surfaces are not painted.’ The old practice of continuing camouflage pattern painting onto vehicle soft-tops was also ended, as there was no flex agent available to mix with CARC paints.

CARC ON WOOD

“It was found that CARC did not last well on wood. Wood expands and contracts with weather changes and CARC lacked the flexibility needed move with the wood, so cracks would form and the finish would begin to peel. It was recommended in TM 43-0139, ‘Properly seasoned wood shall be sealed prior to application of CARC with a polyurethane sealer …wood shall be treated…dried to a moisture content no greater than 20% and pressure treated in accordance with [the] American Wood Preservers Bureau…’ At some point in the 1990s, it was decided that CARC was not to be used on wood at all because it simply did not last.

THE FUTURE OF CARC

“Given the volatile and toxic nature of the CARC coatings, research to develop more environmentally friendly coatings with the same properties as CARC were underway even before CARC became standardized. CARC has a Volatile Organic Compound (VOC) content of 420 g/L. This was pushing the limits of federal and local regulations stemming from the Clean Air Act of 1990. The Army, as well as the private sector, began experimenting with waterborne coatings in an effort to meet the requirements of new clean air regulations. By the close the century the US Army Research Laboratory had developed a coating that had a VOC content of 220g/L while exhibiting many of the same characteristics of CARC. Development and testing continued as the century drew to a close.”

Original Source

Descaling – Metallurgical Processes

What is descaling? Here’s a breakdown of the process.

According to AZO Materials:

“Descaling is the process of removing oxide deposits from a heated stock, either before or during forging operations.

“Scales are formed on a metal surface during heat treatment processes. Oxide scales discolor the metal surface and hinder subsequent finishing operations.

“Descaling is a metal cleaning process that removes unwanted surface deposits on metals to provide a smooth surface finish and is a part of the pre-finishing processes which include cleaning, stripping and pickling. Of these processes cleaning and pickling are used for scale removal.

“Pre-finishing is vital for subsequent finishing operations like electroplating. Some finishing processes require a high degree of cleanliness, while others require minimum cleanliness.

“Physical methods for descaling include use of wire brushes, extra blows, scraping devices, polishing or blasting. Chemical methods that are used for scale removal are acid descaling and alkali descaling.

Types of Descaling

“The various methods of descaling metals are listed below:

Mechanical Cleaning

“For metals that react with chemical, the metal is descaled by physical means. Oxide scale deposits can be removed by using wire brushes and scraping devices like wool pads. Abrasive blasting methods and waterjet spraying can also be used for descaling.

Aqueous Alkaline Cleaning

“Mild alkaline solutions such as sodium hydroxide, sodium phosphate, sodium metasilicate and sodium carbonate can be used for cleaning the metal surface and removing the oxide scales.

“The stronger the concentration of alkali, the faster the cleaning process. This cleaning method is often followed by mechanical cleaning methods.

Acid Cleaning (Pickling)

“Acid cleaning, also known as pickling, is yet another process used for removing oxide scale deposits from a metal surface. It is also used to neutralize any remaining alkalis from the previous cleaning process.

“This method of cleaning is suitable for ferrous, aluminum and copper alloys. An acid solution, called the pickle liquor, is used for descaling the metal surface. The waste product formed from the pickling of metals is known as pickling sludge.

Industrial Applications

“Some of the main application areas of descaling are listed below:
“Descaling of carbon steels
“Cleaning of ferrous alloys
“Oxide layer removal in jewelry.”

Original Source

Powder Coating: A Better Kind Of Paint

New to powder coating? Consider this.

According to PowderCoating.org:

“Powder coating is a high-quality durable finish found on thousands of products you come in contact with each day. Compared to liquid paint, powder coatings are more environmentally sound, durable, and safe for the whole family. When shopping at your favorite retailers, don’t forget to ask for Powder Coated TOUGH products!

Stronger

“Rough and Tough – Powder coating protects the roughest, toughest machinery as well as the household items you depend on daily such as appliances, bathroom fixtures and even furniture. It provides a more durable finish than liquid paints can offer, while still providing an attractive finish.

“Long Lasting – Powder coated products are more resistant to diminished coating quality as a result of impact, moisture, chemicals, ultraviolet light, heat and other extreme weather conditions. That’s why powder coating is used on products exposed to extreme conditions such as vehicle rims, outdoor furniture and grills.

“Try and Scratch Me – Powder coated finishes provide a durability that reduces the risk of scratches, chipping, abrasions, corrosion, fading, and other wear issues.

Greener

“Breathe Easier – Unlike liquid paints, powder coatings contain no solvents and release little or no amount of Volatile Organic Compounds (VOC) into the atmosphere. Thus, there is no longer a need for finishers to buy costly pollution control equipment. Companies can comply more easily and economically with the regulations of the U.S. Environmental Protection Agency.

“Preserve the Planet – Unlike many liquid paints, powder coatings offer a smaller carbon footprint which reduces the adverse effects on the environment.

“Waste Not, Want Not – Companies using liquid paints generate unwanted hazardous waste that must be disposed of properly. Powder coatings are able to be recycled and reused and generate zero hazardous waste.

Better

“Looking Good! – It’s tough. It looks great. And it lasts a long, long time. In addition to being durable, powder coating is an attractive choice due to environmental advantages.

“Did You Know, Rain, Sleet, or Snow? – Powder coated products are more resistant to damage from impact, moisture, chemicals, ultraviolet light, heat and other extreme weather conditions.

“The Best Finish in Town – A better kind of paint.”

Original Source