Industrial coatings and finishes come in a variety of different types. Each has its own properties, which makes each one ideal for varying situations. Some are perfect for outdoor settings, while others do not work well in severe weather or sunlight. Some can be used in contact with food while others emit harmful chemicals.
There are endless environments in which machine parts, surfaces, and home objects need protection, which means there are a number of industrial coatings available to choose from. Understanding the properties of each coating and its uses will help with selecting the best industrial coating for any project.
Above all, knowing which finish best suits a given situation will prevent future problems and avoid the need for redoing a project or fixing mishaps during the process. It will also make the coating and the object it is protecting last longer. This can mean the difference between a coating lasting months versus decades.
The proper industrial coating saves time and money, both immediately and for years ahead. It can prevent disaster, too, as some coatings and finishes are not designed to protect against severe weather or heavy impact. For instance, no one would use paint when the project calls for galvanization, as paint cannot withstand the same types of environments as a zinc coating. Researching and knowing the basic applications of different coatings will always improve the project’s efficiency.
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Paint is one of the most commonly used industrial finishes. It offers some protection for a surface, but it is by no means the strongest coating available. That said, it does come in many types and colors, depending on the intended use. Paint is easy to apply in comparison to other coatings and is most often done using a spray gun and spray booth. Paint works well both indoors and outdoors and certain paints are better suited to specific areas.
Paint is a solvent-based industrial coating, which means it requires a liquid solvent for application. It protects against corrosion, moisture, and even chemicals that could cause damage to a surface. It retains color well and is used in countless applications in many industries. The level of protection it provides depends on what kind of paint is used, though paint, in general, is not one of the most durable options for industrial finishes.
Powder coatings are a popular alternative to paint—and one of the least expensive—when a stronger finish is needed. They are applied using electrostatic and are then cured with heat up to 204℃ (400℉). They are more durable than paint and provide a coating anywhere from 6 mils thick to over 15 mils.
Powder coating produces minimal waste and no volatile organic compounds (VOCs), which makes them one of the more environmentally friendly industrial finishes. Because they are applied as a powder, they also do not require solvents in the same way paints do. Powder coating is corrosion-resistant and withstands impact, chemicals, and moisture.
Powder coating has few disadvantages, though getting a thinner coating can be difficult. It is also important to know what kind of powder coating to use, as thermoset and thermoplastic powder coatings are used in different settings. Confusing the two can result in a lack of protection for a surface or equipment.
Urethane coatings are used in countless applications, from structural steel to masonry surfaces. They are usually applied either by spraying, brushing, or rolling on, and they can be formulated differently depending on their intended purpose. The thickness of these coats is easy to adjust, as multiple coats can be applied.
Urethane is great for an outdoor industrial finish. They are excellent in low temperatures and in water, which is why they are often used on barges and in other submerged environments. They also provide a beautiful glossy finish and retain their color well. Urethane finishes are not always the best for the environment, but their configuration can be adjusted to reduce VOC emissions.
Ceramic Epoxy Coatings
Ceramic epoxy is exactly what it sounds like—a combination of ceramic particles and epoxy resin. The finished product is a coating stronger than epoxy alone, and it protects the surface beneath it like a ceramic shell. While other industrial coatings require specialized equipment like ovens for curing, ceramic epoxy is cured at room temperature.
Ceramic epoxy coatings are ideal protection against corrosion, erosion, and abrasion. They work well on pipes and valves, and bond easily with most metals, including steel and aluminum. They are not ideal for softer surfaces like wood. Ceramic epoxy is chemical-resistant, and it lasts a long time. It can even come in contact with food, which only adds to its advantages.
Fluoropolymer coatings are most often used as non-stick finishes in the cooking industry. The fluorine in the carbon-fluoride bonds that make up this coating have a negative charge, which means they do not bond well with other sources. This is why non-stick cookware is so easy to clean.
Fluoropolymers have other uses, too. They are used in the auto industry on ball bearings and other areas that experience a lot of friction and wear. They are corrosion- and heat-resistant, and they act as insulators. This makes them unique from some other industrial finishes in that they can be used in the electrical industry on wiring, as they do not conduct electricity.
Galvanization is a more specialized kind of industrial coating. It can only be used on steel or iron due to the materials and high heat involved. Galvanization, most commonly performed using hot-dip galvanizing, is the process of coating metal with another metal—in this case, zinc. Hot-dip galvanizing is when a piece is dipped directly into molten zinc to coat it. Electro galvanizing can provide a thinner coating when needed.
This process can be dangerous and requires special equipment and personal protective equipment (PPE). It is not a DIY option the way painting can be. The most common use for galvanization is to protect steel from corrosion. The zinc absorbs corrosive materials—unlike other coatings that repel them—and corrodes first before the materials can damage the surface below. A chromate layer over the zinc can help galvanization last longer.
Inorganic Zinc Coatings
Inorganic zinc coatings are not the same as galvanization, though they have a similar use. Inorganic zinc coatings differ from galvanization because in this case, the coating is not pure zinc. Therefore, it reacts less with the outer environment. For example, inorganic zinc coatings are often more resistant to acid.
While organic zinc coatings use resins like epoxy or urethane to bind them to a surface, inorganic zinc coatings use a zinc silicate binder. The binder attaches the zinc to the steel to give it galvanic protection. This type of finish is excellent protection against corrosion and weather and works well with a topcoat like epoxy. However, when inorganic zinc is applied as a topcoat, it can create problems like a porous surface.
Phenolic coatings, more commonly called epoxy-phenolic coatings, are a type of finish that combines epoxy resin with thermosetting phenolic resin. This type of coating is often used in transport containers for alkaline liquids, whether they be detergent or ingestible liquids.
Phenolic coatings have great resistance to many acids including sulfuric acid and hydrochloric acid, as well as other chemicals. They are often used on fasteners, and they are very flexible. This means that if the container is damaged, the phenolic coating inside is less likely to be damaged as well and will often bend with the material with which it is bonded.
Phosphate coatings typically come in two types: manganese phosphate and zinc phosphate. These types are used in distinctly separate situations and are applied using different methods. Regardless of which is used, this finish gives a unique dark gray or black coloring when applied to a piece.
Manganese phosphate coatings are the hardest of all phosphate coatings. They are used in places that would otherwise wear down easily, like bearings and fasteners, and are intended to protect against corrosion. They are often used in engines, as they are also excellent lubricants. The application process for manganese phosphate coatings involves first preparing the surface with cleaning, rinsing, washing with mineral acid before rinsing again. The manganese phosphate is then applied by way of dipping for up to 20 minutes before another rinsing and then dipping in oil.
Zinc phosphate coatings are used more for rust protection. They can be applied either by immersion, like manganese phosphate or by spraying onto a surface. They are used in a wide range of industries, including electrical, automotive, and hydraulics. They are also often used on military equipment.
Plastic Dip Coatings
Plastic dip coating is another hot-dip coating process, but instead of coating with zinc, the piece is dipped in a fluidized bed of polymer powder or vinyl Plastisol. Polymer powder can also be sprayed onto a heated metal object, similar to the powder coating spray method.
When dipping in polymer powder, the metal piece is heated up to 400℃ (752℉). This melts the polymer powder so it will adhere to the piece once it is dipped in the fluidized bed. This is done until the metal cools and no more polymer powder sticks to the object. Afterward, the piece is heated again to fully melt the polymer and even out the coating.
The process of coating with vinyl Plastisol is similar, but in this case, the metal is only heated to 200℃ (392℉) and placed in the fluidized bed until it cools. The metal is then reheated to cure the coating.
No matter what type of method is used, plastic dip coating is used for preventing corrosion of metals. It prevents air and water from reaching the surface of the metal and can be used on a wider variety of metals than galvanizing.
Xylan coatings are a particular type of fluoropolymer coating. They are often used in the automotive and offshore industries and perform well in extreme conditions. For example, they can function in temperatures ranging from -251℃ to 287℃ (-420℉ to 550℉). They are often used on pipe plugs and fasteners.
Xylan coatings function as protection against corrosion, chemicals, and weather. They are thinner than most coatings available at 1 mil—though multiple coats can increase thickness—and can adhere to almost anything. They are often used in high-pressure environments and function well as lubricants.
Xylan coatings are easily one of the most versatile industrial finishes available. As a fluoropolymer, they are also used on cookware, though their applications exceed those of other fluoropolymers.
Thermal Spray Coatings
Thermal spraying is a broad term for spraying different materials onto a surface for protection. Some of the materials used in this process include plastics and ceramics, but metals and composites are also options, depending on the project. Thermal spraying is a good choice if a very thick coat is needed, and it can produce a coat well over 20 microns thick. These coatings are usually applied using either electricity or combustion.
Because of the range of materials used in thermal spraying, there are also many variations of the process and its applications. While it can be used as corrosion protection, as with many other industrial coatings, this is another option for protection against electrical conductivity. It is also used for medical implants, damage repair, and temperature resistance.
Thermal spraying can be hazardous, so it is essential to know which materials are applied using which methods, as well as the proper PPE to wear during this process. Noise, UV light, and heat protection are necessary, and one should be wary of airborne particles, as they can pose health issues.
In the end, choosing an industrial coating or finish comes down to more than just personal preference. Many factors must be considered, from safety to environmental use to equipment. Some are more dangerous and require more protection for the person applying the coating while others, like paint, are more suitable for DIY projects. The different types of industrial coatings and finishes extend far beyond this list, as do their applications.
Related: Everything Engineers and Product Manufacturers Need to Know About Industrial Metal Finishing
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