Category Archive: Industry News

What are the Different Types of Powder Coating Paint?

Powder coating paint can be divided into two main categories; thermoplastic powder and thermoset polymer. Both types of powder coating paint require heat in order to flow and form a uniform film. Each type of paint has its own unique chemical properties and method of application.

Thermoplastic powder is generally applied with a fluidized bed process. No electrostatic charge is required. This type of paint is usually applied to a part that is heated to a temperature well above the powder’s melting point. The heat causes the powder to melt, adhere to the part and form a scratch-resistant, uniform film of paint. Unlike thermoset polymers, thermoplastic powders remain chemically unchanged throughout the process, which means that they can be re-melted and reused.

Polyester-based thermoset polymers are often used on items that are continuously exposed to the elements.
Thermoset powder coating paint differs from thermoplastic powder in that it undergoes a chemical change, called crosslinking, as it cures. After it has been heat cured, this type of finish cannot be re-melted or reused. Thermosetting polymers tend to be more durable than thermoplastics and offer a wider variety of finishes.

There are four categories of thermoset powders that are based on the type of resin used as their base. The four basic resins used for thermoset powders are epoxy, acrylic, polyester and fluoropolymer. In manufacturing thermoset polymers, the resins typically are first ground into a fine powder to make them suitable for spray gun application.

Epoxy-based powder coating is resistant to both impact and scratching. Its inability to stand up to bad weather and ultraviolet rays generally limits its use to indoor applications. Epoxy powder coating paint is generally used for coating home appliances, automotive underbody parts and industrial equipment. It also is a popular choice for painting metal furniture, such as bed frames and futons.

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Which Alloys Are Prone to Corrosion, and How Can We Prevent This?

Some exposed metallic alloys, such as those used in electromagnets, are prone to corrosion and may disintegrate into a powder even in clean, temperature-stable interior conditions if not adequately treated to prevent corrosion.

Do All Alloys Corrode?
Almost all alloys corrode or rust to an extent. Corrosion is a type of oxidation, and rusting is a component of corrosion. Rusting occurs when the alloy is in contact with air and humidity, resulting in the formation of an iron oxide coating. Corrosion happens when alloys are exposed to oxygen and chemicals, resulting in the development of metal oxides or salts.

Corrosion Occurrence in Steel

As standard steel is made up of a variety of metals, including iron, it can corrode. Stainless steel, which is 18 percent or more chromium, creates a protective coating (chromium oxide) on the surface of the alloy, while a vanadium concentration also plays a substantial role in preventing corrosion.

Corrosion in Aluminum and Magnesium

Aluminum alloys do corrode, but when water comes into contact with the metallic surface, it develops a protective coating called ‘aluminum alloy oxide’ which makes it more corrosion resistant. Magnesium is prone to corrosion (especially galvanic corrosion), which appears as a grey layer on the surface. Out of all metallic alloys, magnesium alloys have the worst corrosion resistance properties.

Do Zinc and Nickel Corrode?

When zinc is exposed to air, it interacts with carbon dioxide to generate a zinc hydroxide film. This shields the metal from external air reactions, which is why zinc is used to galvanize other alloys and prevent corrosion. Pure nickel is extremely corrosion-resistant, particularly when exposed to a range of reducing agents. It is resistant to oxidation when it is alloyed with chromium, resulting in a wide range of alloys with excellent corrosion resistance in both reduction and oxidation conditions.

Types of Corrosion in Alloys
Corrosion is the result of a series of often complex chemical reactions that may be induced by a variety of factors, that depend on the setting. Uniform corrosion is the most typical form of corrosion, described as an even attack over a material’s surface. It is the most innocuous since the attack is mild in intensity, making the impact on material performance simpler to measure and analyze due to the ability to consistently repeat and test the phenomenon.

Read more: Which Alloys Are Prone to Corrosion, and How Can We Prevent This?

5 Most Common Types of Metal Coatings that Everyone Should Know About

For centuries, metals have been the go-to choice for multiples applications due to their durability, versatility and strength. However, among the challenges that people face when using metals, corrosion is arguably the most common and widely recognized.

Multiple solutions have been proposed to increase the longevity of metallic structures and enhance their corrosion resistance. Among them, metal coatings stand out as one of the most effective and convenient protection methods.

There are numerous methods for coating metallic surfaces, each with its own set of limitations and benefits. In the following sections we will take a detailed look at some of the most common types of metal coatings, and discuss their suitability for various applications.

How Metal Coatings Protect Surfaces and Structures
Metal corrosion is a deteriorative process that occurs under specific conditions. The most common type of corrosion occurs when metals react with moisture and oxygen to create various corrosion products. Iron, for example, reacts with water and oxygen in the atmosphere to form iron (III) oxide, or rust.

The logic behind metal coatings, therefore, is to create an inert (non-reactive) barrier around the metallic object being protected to prevent it from reacting with air and moisture.

Common Types of Metal Coatings and Their Benefits
Below, we have compiled a list of the most common types of metal coatings used across various industries, and the advantages and disadvantages of each.

Anodizing
Anodizing is a process used to promote the formation of a protective oxide layer on the surface of a metal. The resulting oxide layer forms more rapidly and is usually thicker than if it was produced naturally. While several non-ferrous metals can be anodized, aluminum responds most effectively to this process. (Background reading: Understanding Ferrous and Non-Ferrous Metals: Why You Should Understand These Key Differences.)

Read more: 5 Most Common Types of Metal Coatings that Everyone Should Know About

Using Protective Coatings in Heat Treatment

This article introduces a practical technique pioneered by a metallurgist at the Indian Institute of Technology. The technique enables any kind of steel to be heated without the problems associated with oxidation and decarburization.

Heat treatment is an important operation in the manufacture of engineered metallic components, machine parts and tools. The oxidation and decarburization of steel take place when steel components are heated in the presence of air or products of combustion. Undesired and excessive oxidation can lead to problems such as scale pit marks, dimensional changes, poor surface finish, rejections and quench cracking. Additionally, these problems may lead to the need for expensive operations like shot blasting, machining and acid pickling. Protection against scaling and decarburization is achieved by heating in molten salts, fluidized-bed furnaces, protective gaseous media or vacuum. These measures demand heavy capital investment, highly skilled personnel and special safety precautions. Many companies cannot afford them, yet they are under mounting pressure to prevent oxidation and decarburization.

Understanding Oxidation and Decarburization
When steel is heated in an open furnace in the presence of air or products of combustion, two surface phenomena take place: oxidation and decarburization. The oxidation of steel is caused by the presence of oxygen, carbon dioxide and/or water vapor. The oxidation may manifest itself in a range from a tight, adherent straw-colored film that forms at a temperature of about 180°C (lower temperatures) to a loose, blue-black oxide scale (higher temperatures) with a resultant loss of metal.

Decarburization, or the depletion of surface carbon content, takes place when steel is heated to temperatures above 650°C. It progresses as a function of time, temperature and furnace atmosphere. The equilibrium relationship depends on the ratio of carbon dioxide to carbon monoxide.

Harmful Effects
Oxidation and decarburization may lead to a number of unwanted effects on the dimensions, surface quality or metallurgical properties of the component. These include dimensional and material loss, which must be accounted for in the manufacturing process. Often, surface quality is deteriorated due to pitting. Metallurgical transformation during austenitizing and subsequent quenching may be non-uniform. Surface hardness and strength are also lowered due to a layer of scaling. The fatigue strength of heat-treated products is reduced, which is especially true in the case of automobile leaf springs.

Read more: Using Protective Coatings in Heat Treatment

What is Powder Coating?

Powder coating is a dry finishing process that has become extremely popular since its introduction in North America over in the 1960s. Representing over 15% of the total industrial finishing market, powder is used on a wide array of products. More and more companies specify powder coatings for a high-quality, durable finish, allowing for maximized production, improved efficiencies, and simplified environmental compliance. Used as functional (protective) and decorative finishes, powder coatings are available in an almost limitless range of colors and textures, and technological advancements have resulted in excellent performance properties.

How Powder Coating Works
Powder coatings are based on polymer resin systems, combined with curatives, pigments, leveling agents, flow modifiers, and other additives. These ingredients are melt mixed, cooled, and ground into a uniform powder similar to baking flour. A process called electrostatic spray deposition (ESD) is typically used to achieve the application of the powder coating to a metal substrate. This application method uses a spray gun, which applies an electrostatic charge to the powder particles, which are then attracted to the grounded part. After application of the powder coating, the parts enter a curing oven where, with the addition of heat, the coating chemically reacts to produce long molecular chains, resulting in high cross-link density. These molecular chains are very resistant to breakdown. This type of application is the most common method of applying powders. Powder coatings can also be applied to non-metallic substrates such as plastics and medium density fiberboard (MDF).

Sometimes a powder coating is applied during a fluidized bed application. Preheated parts are dipped in a hopper of fluidizing powder and the coating melts, and flows out on the part. Post cure may be needed depending on the mass and temperature of the part and the type of powder used. No matter which application process is utilized, powder coatings are easy to use, environmentally friendly, cost effective, and tough!

Durability of Powder Coating
Powder coating is a high-quality finish found on thousands of products you come in contact with each day. Powder coating protects the roughest, toughest machinery as well as the household items you depend on daily. It provides a more durable finish than liquid paints can offer, while still providing an attractive finish. Powder coated products are more resistant to diminished coating quality as a result of impact, moisture, chemicals, ultraviolet light, and other extreme weather conditions. In turn, this reduces the risk of scratches, chipping, abrasions, corrosion, fading, and other wear issues.

Read more: What is Powder Coating?

Coating Procedures for Plastisol Coatings

Plastisol coatings are applied to many different products in order to supply them with aesthetic qualities, tactile softness and gripping power. For instance, tools like pliers and screwdrivers are often fitted with plastisol coatings on their handles in order to provide the user with a solid grip instead of sheer metal. Plastisol coatings involve a plasticized resin combined with many PVC particles, which provide the plastisol with increased durability, toughness and thickness. In order to stay affixed to substrates, plastisol must be combined with a primer, which connects the plastisol particles to the substrate. Different kinds of primers are used depending on the adhesion coating method and the intended result. The plastisol itself has many desirable features, including chemical resistance to acids, alkalines, detergents, oils and certain solvents. Plastisol coatings also maintain structural integrity to – 65 degrees Fahrenheit and provide extraction resistance to different oils and detergents. A plastisol coating can perform well for approximately ten years. Plastisol mixtures can be varied to allow differences in gloss, thickness, toughness and other physical properties.

There are many types of coating procedures that work well with plastisols, most all of which involve heating (curing) the substrate and plastisol resin and a cooling period. These different plastisol coating procedures yield a variety of results and differences in the thickness, texture and geometry of the coating. Some coatings are directly applied to a substrate while others are made in molds.

Dip Molding
Dip molding is accomplished in either a hot or cold dip process. In hot dip molding, the substrate is heated and the plastisol resin is heated until bubbles appear, as if it were boiling. The substrate is then slowly dipped straight into the liquid plastisol and then removed slightly faster so the entire piece is coated in plastisol. Cold dip molding is used when the substrate cannot undergo heating, such as in the case of a wooden or fabric substrate, and it is simply dipped into the heated plastisol resin as is. After the dipping procedure, both hot and cold dip molding require the substrate be briefly “cured,” or heated until the plastisol achieves a solid state.

Slush Molding
Slush molding is similar to dip molding but involves an extra step to ensure complete coating of a substrate. The process is generally used in cases where the substrate has a complex geometry and includes nooks and crannies that may be difficult to coat by simply dipping the piece into the plastisol resin. Following the dipping procedure, a substrate undergoes slush molding by being affixed into a centrifuge that spins very quickly. This spinning process ensures that the resin fills in all the parts of the substrate. The substrate is then cured and the resin solidifies as in dip molding.

Rotational Molding
Rotational molding is used to make products that are hollow, such as buoys and balls. A mold of the product is filled with heated resin, and then the mold rotates at slow speed, allowing the liquid within to slowly coat the entirety of the mold. The plastisol eventually solidifies in the shape of the mold.

Casting
Casting is similar to rotational molding but does not involve the movement. When a product with a complex geometry needs to be coating in plastisol, a mold can be made of the shape of plastisol needed. The heated plastisol liquid is then poured into the mold and heated until it solidifies. Once it solidifies, the plastisol mold acts as a sleeve for the product, and can be affixed to the substrate with a small amount of adhesive.

Spray Coating
Spray coating is used to apply a very thin film coating of plastisol to a substrate. The substrate is sprayed with heated liquid plastisol by a gun, and then heated to allow the plastisol to solidify.

Read more: Coating Procedures for Plastisol Coatings

Pretreatment for Painting

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.

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Providing Superior, Extended Corrosion Protection

The hybridized matrix membrane developed in the study presents a unique design strategy for highly hydrophobic coatings showing great long-term corrosion resistance.

Addressing the Corrosion Problem of Magnesium Alloy
Thanks to their low weight, high specific strength, and recyclability, magnesium (Mg) alloys are employed across many industries, including the automotive and aeronautical sectors and electronic equipment.

Despite this, magnesium alloys can easily suffer from corrosion in aqueous conditions because of their strong chemical activity, restricting their widespread applicability.

Multifarious techniques, including electrodeposition, ionic implants, and surface coatings, have been used to improve the corrosion resistance of magnesium alloys.

Surface coatings, particularly organic surface coatings, offer great corrosion resistance with the advantages of being facile and inexpensive.

PDMS Coatings for Better Corrosion Resistance
Compared to traditional organic coatings, PDMS is a unique polymeric material having low surface energy, high chain flexibility, superior thermal oxidation resistance, and chemical corrosion resistance thanks to the robust silicon-oxygen-silicon backbones.

PDMS is extensively used in flexible electronic devices and microfluidics. Moreover, due to its strong water-repellent nature, PDMS is a preferred material for corrosion resistant coatings.

While PDMS polymer coatings exhibit strong corrosion resistance and barrier function, their protective powers become weaker when they absorb water after extended contact with a corrosive medium.

Meanwhile, doping or hybridization can lead to the formation of microcracks and microspores in organic coatings, which ultimately causes poor corrosion resistance durability.

Read more: Providing Superior, Extended Corrosion Protection

The Powder Coating Process

Powder coating is a dry finishing process used to apply a dry coating material. The coating material is made up of finely ground particles of resin and pigment for color, along with other additives for specific functions such as gloss or hardness. The dry powder coating is delivered to a spray gun tip that is fitted with an electrode to provide an electrostatic charge to the powder as it passes through a charged area at the gun tip. The charged powder particles are attracted to a grounded part and are held there by electrostatic attraction until melted and fused into a uniform coating in a curing oven.

Since its introduction more than 40 years ago, powder coating has grown in popularity and is now used by many manufacturers of common household and industrial products. In North America, it is estimated that more than 5,000 finishers apply powder to produce high-quality, durable finishes on a wide variety of products. Powder-coated finishes resist scratches, corrosion, abrasion, chemicals and detergents, and the process can cut costs, improve efficiency and facilitate compliance with environmental regulations.

Because powder coating materials contain no solvents, the process emits negligible, if any, volatile organic compounds (VOCs) into the atmosphere. It requires no venting, filtering or solvent recovery systems in the application area such as those needed for liquid finishing operations. Exhaust air from the powder booth can be safely returned to the coating room, and less oven air is exhausted to the outside, making powder coating a safe, clean finishing alternative and saving considerable energy and cost.

Theoretically, 100 percent of the powder overspray can be recovered and reused. Even with some loss in the collection filtering systems and on part hangers, powder utilization can be very high. Oversprayed powder can be reclaimed by a recovery unit and returned to a feed hopper for recirculation through the system. The waste that results can typically be disposed of easily and economically.

Powder coating requires no air-drying or flash-off time. Parts can be racked closer together than with some liquid coating systems, and more parts can be coated automatically. It is very difficult to make powder coating run, drip or sag, resulting in significantly lower reject rates for appearance issues.

Powder coating operations require minimal operator training and supervision when compared with some other coating technologies. Employees typically prefer to work with dry powder rather than liquid paints, and housekeeping problems and clothing contamination are kept to a minimum. Also, compliance with federal and state regulations is easier, saving both time and money. In short, powder coating can provide the five “Es:” economy, efficiency, energy savings, environmental compliance and an excellent finish.

Read more: The Powder Coating Process

What is CARC Paint?

CARC (Chemical Agent Resistant Coating) is a paint used on military vehicles to make metal surfaces highly resistant to corrosion and penetration of chemical agents. It provides surfaces that are easily and effectively decontaminated after exposure to liquid chemical agents.

There are three types of coatings in the CARC system: anepoxy polyamide primer, an aliphatic polyurethane paint (PUP), and epoxy polyamide enamel. Each of the coatings is supplied as a two-component system. When the two components are combined, a terminal reaction begins which makes an impermeable coating.

During application of CARC, the surfaces to be coated with CARC must sometimes be stripped. After stripping, the surface must be cleaned of all oils, grease, and water. When the item is ready for coating, the two components are mixed and allowed to stand for a prescribed period. The mixture must then be applied within a given time period known as its “pot life” in order to be effective.

Trans-Acc is fully certified to meet the military’s most strict CARC paint requirements and is an experienced CARC supplier to the defense industry, for use in various military applications. For more information about outsourcing CARC Coating solutions, see Military CARC Coating Services.

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