This article will take an in-depth look at industrial coatings. It will bring more understanding on topics such as:
This chapter will discuss the principle behind industrial coatings, as well as their various uses.
An industrial coating is a layer of a substance added to a surface to provide protection and to enhance the appearance of the surface. The main function of an industrial coating is to protect a surface from the elements and other forms of damage. They are applied to a wide variety of surfaces, including concrete, timber, metal, plastic, glass, rubber, leather, mortar, and asbestos.
There is an endless variety of industrial coatings, each of which offers different characteristics and provides unique and beneficial properties. The type of environment and the nature of the surface to be coated determines the specific coating that should be used. Coating manufacturers provide consultation and guidance regarding how coatings should be used and applied.
Industrial coatings are applied in a way designed to be both aesthetic and protective. There are several types of industrial coatings, including Xylan-dry film lubricants, resins, xylene, and others.
The purposes and uses of industrial coatings are broad, with the main purpose being the protection of equipment from different types of corrosion. Aesthetics are also an important factor for certain types of equipment and conditions. Industrial coatings are commonly used to prevent concrete or steel from damage.
A secondary use of industrial coatings is to improve the resistance of materials to fire or other potential hazards. They are applied to the linings of water tanks and reservoirs to create a safe environment for potable water that protects against corrosion.
The most frequently used industrial coatings are polymers. Some examples of polymers that are used as industrial coatings are epoxy, moisture cure urethane, polyurethane, and fluoropolymer.
There are various considerations in industrial coating applications. These include:
In order for the industrial coating to take hold, the substrate, or base material to receive the protective layer, must be clean. Most industrial coatings depend on a mechanical or physical bond to stick tightly to the surface of a substrate. Chemical bonding with the substrate surface creates an impenetrable layer of protection. If the surface is not completely clean (i.e. if the surface contains dust particles, chemicals, or other contaminants), the industrial coating is likely to fail prematurely.
The key to the success of the application of an industrial coating is preparing the surface before coating. Before starting the process, the surface of the substrate must be cleared of moisture, dry contaminants, and salts using the correct techniques, like heating processes, blasting procedures, and chemical cleaners. Proper cleaning of surfaces before coating prevents fisheyes, blistering, adhesion failure, alligatoring, bubbling, and cissing.
Priming must be included in every industrial coating procedure. Priming helps the coating and sealant adhere to the surface of the substrate for long-lasting performance. When there are incompatible substrates and coating materials, primers help them to work together. It also aids the part’s final aesthetic by removing imperfections at the surface level.
Once the application of the primer is complete, the substrate is ready for the coating process. There are different types of coating processes. Each coating method is designed to totally coat the substrate in the protective coating material. The substrate’s size and complexity affect the coating application method. The most common industrial coating processes are dip coating, brush coating, roll coating, spray coating, spin coating, and flow coating.
The performance of industrial coatings is affected by the curing and drying procedures. If the curing and drying procedures are inadequately completed, then the industrial coatings are likely to underperform. Every industrial coating must have a product data sheet that provides the specifications on the right drying and cure-through procedures for optimal coating results.
Industrial coatings require the curing process to be done at the correct temperature for the appropriate duration. The temperature specifications apply to the substrate’s temperature but not the oven’s temperature. For this reason, bake times vary for parts of varying thicknesses.
After the coating process is complete, parts must be inspected to ensure that the coating is in line with the acceptable parameters. Most industrial coatings have certain degrees of thickness that they must fall within to ensure that they cover the part and don’t fail to express the small details or complexities. Paint lines that are well run have quality inspection standards in position to ensure the compliance of every coating project with the acceptable thickness averages.
When opting for the right industrial coating method, both the equipment and the coating material are important. An optimal industrial coating line will need strong pump seals, clean filters and spray tips, and regularly flushed air lines. If equipment is not maintained regularly, the results can be substandard or flawed.
Suppliers of industrial coatings should work with their customers to ensure the auditing of processes with the feedback that they get from applicators, the cleaning of the working areas, and the regular maintenance of equipment.
Considerations in selecting a custom industrial coating formulation include:
The ideal industrial coating formulation depends on the substrate. The formulation may require the following materials: urethane, acrylic, or epoxy. Manufacturers must consider whether parts are made from a variety of materials and when the industrial coating will be needed during the manufacturing process.
Certain substrate and coating pairs can also be bridged by the application of the correct primer or the incorporation of additives to aid in the binding or other properties. Substrates require unique protections such as corrosion protection, food safety regulation compliance, and many more. This must be considered by the manufacturers.
Different methods of application and materials may offer results that are superior to others, depending on the conditions of the surface of the substrate. Some substrates are vulnerable to the changes that occur in composition through different methods of application and curing procedures. For instance, if a manufacturer is working with a substrate made of plastic and paired with a coating, they need a heat cure to ensure the endurance of the prescribed bake temperature without warping.
When selecting a type of coating, the application’s environmental factors must be considered. Industrial coatings need an environment that is stable and clean within specific temperature and humidity conditions. If there are inconsistent conditions in the environment, there are more likely to be inconsistent finish results. For instance, uncontrolled humidity and temperature conditions with industrially active, warmer days and cooler nights will result in thermal shock.
During the application or drying period, the coating can be chemically altered by exposure to splashes, chemical fumes and contaminants. Any contamination before curing the coating will reduce its effectiveness. Manufacturers must ensure the protection of their treated parts from abrasion, UV radiation, and physical impact before the completion of the curing process.
The final result is affected by the details of the application process. The precise method of application (such as spraying, brushing, dipping, etc.) must be carefully planned by the manufacturers, and they must also ensure whether the planned process ensures accurate thickness control. Other processes to consider include substrate preparation, post-cure cleaning and treatments, baking and curing equipment, space availability, and drying conditions in controlled environments.
Different coatings exhibit different industrial coating properties. For example, epoxy and urethane coatings can withstand a great diversity of chemicals and physical impact, though epoxies also struggle with outdoor exposure. Meanwhile, both coatings can be damaged by nitric acid. During the application process, water-based coatings are safer for technicians, but in vulnerable substrates, they may increase the risk of corrosion. Ultimately, many of the aesthetic and functional properties are largely dependent on the material of the coating and the application process. Other properties are coating flexibility and elongation; smooth texture, gloss, and film; color quality, retention, and specificity; moisture permeability; solderability and conductivity for further processing. During every stage of a custom industrial coating formulation, it’s important to consider the part’s application use. Application use is one of the key factors in determining the coating properties needed to perform its end function.
The various coating techniques include:
A cost-effective process provides high quality coating that is uniform on substrates of different shapes or sizes including large surface areas. Dip coating can be carried out manually or automatically for application productions of high volume.
Parts are sunk deep in a tank full of liquid polymer and then withdrawn at a constant rate at temperature or atmospheric conditions that are controlled. The viscosity of the coating, rate of withdrawal from the tank, number of dipping cycles, and length of immersion determine the thickness of the coating. Solidification often occurs at high temperatures inside an oven.
In order for surfaces to be free of contaminants, it is essential prior to dipping them. For process control and to meet standards of consistent quality control, flow and run off properties are important. The internal and external surfaces are coated at the same time with deep coating.
For long lasting protection against abrasion, water, corrosion, humidity, heat or cold, wind, and UV light, master bond eco-friendly liquid polymeric formulations must be selected. These formulations are available in a wide range of colors and they also enhance appearance. Special coating grades are optically clear, tough, guard against solvents or acids, have low friction, vibration/ impact resistance and exhibit exceptional electrical insulation characteristics.
E Coat is a cross between plating and painting and involves submerging a part in a water-based solution that contains a paint emulsion. The solution and part are subjected to an electric current that condenses the solution and forms it over the part. The process allows a part to be coated on the inside and outside. Any metal surface that can be reached by the solution or is exposed is coated.
The E Coat process provides excellent protection against corrosion and rust as well as enhances the appearance of a part. Additionally, E Coat is exceptionally durable with protection against salt spray and offers dielectric and acid resistance. When compared to powdered coatings and solvent based spraying, E Coat provides complete coverage, consistent thickness, and parts may be processed wet or dry.
Since E Coat is so durable, it is widely used by the oil and gas industry, HVAC systems, water and wastewater management, and aerospace. It can be applied to any type of substrate including castings, stampings, structural iron, pipe, springs, and aluminum castings, to name a few.
For outstanding leveling and liquid polymer distribution, experienced personnel and proper brush or bristles are required. To achieve the desired film thickness, multiple coats may be needed.
The synthetic or natural bristles of the brush must be compatible with the product being applied. For covering substrate surfaces that are irregular such as corners, edges, bolt heads, piping, welds, the shape, size, and brush angle must be considered. Brushes must be clean before use. Brushing is slow compared to other techniques used for coating though it has a short set up time. Benefits of brushing include low capital cost, low wastage, and economic suitability for runs of production.
Roll coating is used to apply a base, intermediate, and topcoat to flat substrate using rollers. One method of roll coating uses three rollers, which are soft application roll, polished steel roll, and metering or doctor roll. The material to be coated travels through the three rolls, with each roll performing a specific application. Roll coating can be performed manually or using an automatic conveying system.
For high volume productions, automated roll coating equipment like gravure coating, direct roller coaters can effectively apply liquid polymeric coatings in uniform thicknesses to flat surfaces. In selecting the proper machine, there are some key parameters that include the thickness or width of substrate, the type of substrate, speed of operation, and the full or partial cost.
Roll coaters are found in a wide range of configurations. They offer reliability, cost effectiveness, and high quality finishes comply with a diverse set of requirements. This technique is a popular and continuous energy efficient process that requires less labor. It also offers reduced waste, excellent weight control, efficient coating transfer, and design flexibility.
A special form of roll coating is gravure roll coating, which is a process where adhesives are coated on the substrate. Gravure roll coating uses a roll or applicator ball that is etched to control the amount of coating being applied. The size of the gravure determines the dimensions of the finished coating.
There are several methods used for gravure coating with direct and offset being the most common. With direct, the steel roll has the pattern that is to be engraved or coated and has a blade that eliminates access adhesive. Offset roll coating is a variation of direct and uses an offset roll placed between the gravure and coating material to apply the coating that is placed between the applicator and the gravure roll.
This is an economical, versatile, fast coating process for parts of different types, sizes and shapes including large surface areas. Spraying can be done manually or automatically for viscous or non-viscous liquid coatings with high transfer efficiency for uniform quality finishes.
The desired film thickness is achieved by using different types of spray guns and other equipment, such as air atomized conventional sprays, airless sprays, and air assisted airless sprays. This equipment provides optimal use of material and addresses individual requirements such as quality of finish, desired film thickness, edge build-ups, reduction of overspray, reliable performance, and wasted product concerns.
A key factor in the use of spraying as an application method is the quality of the compressed air, which is measured by size and concentration of solid particles; water vapor content measured by pressure dew point temperature; and concentration of oil with the contamination level influenced by the compressor, dryer, and filtration.
When using a compressed air system, it is necessary to determine the type of air needed for the spraying application. Since all air has water in it, the concentration of water increases as the air is compressed. If dry air is preferred, drying equipment should be used to remove the water. With oil lubricated air compressors, filters are used to reduce the amount of oil with different grades of filters available to produce different qualities of air.
Spraying has a key advantage: it can be achieved from a vertical angle and helps provide a safe work environment. Common drawbacks include uneven spraying, sagging, orange peel, pinholes, overspray, and spluttering. For good optimization and flow, careful features for control must be followed.
Defect-free coatings set high standards for spray application techniques and facilitate transfer efficiency methods. For smooth finishes, it’s necessary to find the best spray distance, angle and pattern.
In this technique, a coating is applied in the center of the substrate and then spun by centrifugal force at high speed. The spin coater revolves until the desired film thickness is achieved. The key parameters that help to meet the specific application requirements are the spinning rate, resin materials, substrates, surface tension, acceleration, and viscosity.
Spin coating is the most effective technique in providing thin coatings, thickness uniformity and consistency, and a quality finish that is repeatable without variation. The spin coating process is simple, can be carried out rapidly, and is utilized in the coating across substrates of small or large size. The problems that can be encountered during processing include uncoated areas, streaks, comets, swirl patterns, and too thin or too thick films.
This technique is an easy, fast, reliable manual, or automatic process for the application of liquid coatings. It is mostly recommended to be used on large, flat horizontal sheets and panels that can’t be dip coated easily. In flow coating, high coating thicknesses can be achieved with only a single coat.
Flow coating requires little space, minimizes waste, is economical, and has high transfer efficiency. In the design, coatings are to be dispensed on the upper part of the workpiece and flow down to completely cover the flat surface areas. This controlled flow of gravity is a function of the compound’s viscosity. The finish or uniformity is affected by curing conditions such as temperature or humidity. Flow coating is not suitable for parts containing holes or pultrusions.
Slot die coating is a pre-metered coating method where the thickness of the final coating is dependent on the rate at which the coating is applied. The material in slot die coating is delivered through a narrow slot positioned over the surface to be coated. The process places a thin film onto the substrate and can be integrated into several types of operations.
The mechanism for slot die coating includes metering, distribution, head positioning, and substrate movement systems. The metering system controls the flow while the distribution system ensures that the coating is spread evenly. The head positioning system keeps the head correctly oriented relative to the substrate. The movement system keeps the substrate moving past the slotted head.
PVD coating, also known as thin film coating, vaporizes solid materials in a vacuum and applies them to the substrate. The material is applied atom by atom to form a thin bond of metal or metal ceramic layer that enhances the appearance, durability, and function of a component. The result of the process is an extremely thin pure coating that is environmentally friendly.
The four steps of PVD coating are ablation, transport, reaction, and deposition. The main types of PVD coating are sputtering and thermal deposition where thermal deposition uses high temperature and vacuum pressure for vaporization while sputtering uses a vacuum chamber with a high energy source.
Sputtering is a slow process and complex but produces a pure uniform coating. Thermal deposition has high throughput and efficiency but requires extra tooling.
PVD requires precision timing for the vaporized atoms to bond with the target material. Reactive or inert gasses, such as oxygen or nitrogen, assist in forming a strong bond between the coating and substrate. The final step in the process involves rotating the substrate while monitoring the rate of deposition using various tools. The process can be automated using conveyor belts placed before the vaporized arc for a specified length of time.
The process for PVD coating is used by a wide assortment of industries, including food packaging, medicine, optics, cooking tools, and plumbing fixtures. It is suitable for use with inorganic solid materials that have a high melting point.
The various types of industrial coatings include:
These types of coatings offer properties that are balanced and unbeatable by any other material. Teflon coatings exhibit excellent dielectric stability, low coefficient of friction, almost total chemical inertness, and heat resistance.
Teflon coatings are the original non-stick finishes. Industrial products made out of Teflon coatings or fluoropolymer resins exhibit exceptional high temperature resistance and are also resistant to chemical reactions, stress cracking, and corrosion. These industrial coatings can be used on aluminum, carbon steel, stainless steel, brass, steel alloys and magnesium as well as on non-metallic like glass, plastics, and fiberglass.
Characteristics of Teflon coatings include:
There are only a few solid substances that can adhere to a Teflon finish. Almost all substances release easily on Teflon finishes, even though tacky materials may show some adhesion.
The range of the coefficient of friction of Teflon is 0.05 – 0.20 and it depends on the sliding speed, load, and particular Teflon coating used.
Teflon surfaces are not easily wet since they are both oleophilic and hydrophobic. Cleaning up is easy and more thorough – surfaces are self-cleaning in many cases.
Teflon industrial coatings can continuously operate at temperatures of up to 500 °F (260 °C) or 1112 °F( 600 °C) with adequate ventilation.
Most Teflon industrial coatings can withstand severe temperature extremes without losing their physical properties. Teflon industrial coatings can be utilized at low temperatures like -454 °F (-270 °C).
Teflon industrial coatings are unaffected by chemical environments.
Teflon has a low dissipation factor, high dielectric strength, and very high surface resistivity over a broad range of frequencies.
As beneficial as Teflon coatings are, there are aspects of it that have to be considered when working with Teflon, especially during the curing process. When it is being cured, Teflon coatings produce a toxic out gas, Phosgene, which is very dangerous. Manufacturers of coatings have data and information regarding the use of Teflon coatings and should be consulted for how to deal with the dangers involved with its use.
This type of coating is considered by many to be the toughest, most durable, and longest-lasting non-stick coating. The difference between Excalibur and other coatings is that Excalibur is a full coating system, rather than simply an applied coating over an existing substrate.
When stainless steel is arc-sprayed onto a component, becoming one with it, the Excalibur’s system begins. Next, the stainless steel matrix is impregnated with non-stick coatings that are premium. The result is a coating system with the toughness of stainless steel together with the release properties of the non-stick.
The application of Excalibur Coating includes steps such as:
When the surface properties of an ideal material in engineering construction are wrong, these types of coatings come into play. Xylan is capable of binding strongly to surfaces that do not readily accept other PTFE coatings and it is applied as a thin film. These coatings offer controlled friction, wear resistance, non-stick and release properties, and lubrication and at the same time can also prevent corrosion.
These types of coatings were developed to deliver a broad range of performance attributes that are valuable. These single coat thin films offer excellent corrosion and resistance to chemicals. Other benefits of fluoropolymer include resistance to galling, electrical resistance, abrasion resistance, non-stick, non-wetting, and reduced friction. OEM components that are coated with fluoropolymer have a longer life before replacement.
These types of coatings provide a unique combination of properties that are surface enhancing, unlike any in the industry. They are resistant to extreme temperatures, exhibit superior surface hardness, are anti-galling, and exhibit anti-friction properties. In the high-performance field, Nitro coat is the coating of choice.
Nitro coat barrier coatings are applied to the surface chemically, utilizing some of the most advanced application technology present in industries. To most metallic substrates, very thin, extremely uniform, and dense coatings are applied easily. High performance components that are coated using the nitro coat process demonstrate significant performance consistently under severe extreme conditions in the field and in the laboratory.
These types of coatings are mostly used to improve the performance of a material to increase its operating temperature, load carrying capacity and coefficient of friction. This coating offers effective lubrication in a broad range of loads, in most cases exceeding 250,000 psi. By transferring lubricant between the two surfaces that are to be mated, moly coatings lubricate sacrificially. This helps in the reduction of both the coefficient of friction and wear.
Molybdenum coatings are a combination of high-performance resins and molybdenum disulphide lubricant. The curing of the coating is done thermally for the thorough bonding of the base metal of the part coated.
These are high molecular weight coatings that are specially blended to offer remarkable corrosion resistance across a diversity of environments. These types of coatings effectively perform as abrasion-resistant coatings while offering outstanding barrier protection from alkaline compounds, harsh chemicals and solvents, and caustic solutions.
These types of coatings are developed to protect against oxidation produced by high heats naturally, while simultaneously protecting metal surfaces against acid, water and other corrosive agents. They are applied in the offshore, military, and chemical processes. They offer significant performance benefits. These heat/corrosion coatings can extend the life span of steel engine components.
These types of coatings are two-coat non-stick systems in which there is a primer and a topcoat. They exhibit the highest operating temperature of any fluoropolymer, good abrasion resistance, good chemical resistance, and extremely low coefficient of friction. They are able to withstand a maximum temperature of use which is 600 degrees Fahrenheit. The thickness of application of this coating is 1-3 mm.
These types of coatings are resin bonded polymer coatings with remarkable resistance to chemical reactions and thermal degradation. This coating is virtually unaffected by any solvent up to 500 °F (260 °C), making it a famous alternative for chemical processing industry use. For outstanding corrosion and chemical resistance, PPS coatings may be used by themselves. PPS also serves as an effective primer with the use of a topcoat. On top of its thermal and chemical advantages, PPS also provides outstanding abrasion and wear resistance.
PVDF is a pure fluoropolymer that is highly reactive and utilized in applications that require the highest strength, purity, resistance to acids, solvents, heat and bases, and low smoke generation during a fire event. At high temperatures, PVDF can be dissolved in polar solvents that include amines and organic esters, making them practical for use in coatings that are resistant to corrosion and architectural finishes that are durable on building panels.
PVDF can be readily melted for use in extrusion or injection molding equipment. Components that are coated with PVDF are extensively used in high purity semiconductor markets, in the paper and pulp industry, nuclear waste processing, water treatment, and chemical processing. PVDF is able to meet the food and pharmaceutical processing industries’ specifications.
These types of coatings provide outstanding chemical resistance and good electrical use properties. ECTFE coatings suit applications that must exceed the capabilities of PVDF for thermal resistance and chemical resistance.
These are coatings that are applied as free-flowing dry powders. These types of coatings are dry, and they don’t need a solvent to keep the components together. Powder coatings are applied using a fluidized bed or an electrostatic spray. To fuse the particles together and make them adhere to the surface, parts are heated before and after application. These types of coatings are mainly used to coat metals and sometimes thermoplastics or thermosets.
Metallized Coatings
Metallized coatings, known as thermal spray coatings, are applied to surfaces in a molten or semi-molten form as a method of corrosion protection that includes spraying metals onto steel or concrete surfaces. Metals commonly used for metallized coatings are aluminum, zinc, and their alloys.
Metallized coatings are used due to their long service life, instantaneous curing, and absence of volatile organic compounds (VOCs). They can be applied under any conditions, with the metal being heated before application. Metallized coatings are used outdoors due to their greater resistance to impact and UV rays.
Hard coat refers to a fast setting urethane or polyurea elastomer. It works well on wood or other materials, with some forms having UL-tested fire ratings. Hard coat forms a solid finish on surfaces such as styrofoam and urethane foam. They contain no solvents and are volatile organic compounds that can serve as vapor barriers.
The formulations of hard coat have varying properties, including soft and rubbery or hard and rigid. Hard coat can be tinted to a base color, which is not UV stable unless it has an aliphatic formulation. In most cases, hard coat is applied without color and painted. Primer is necessary to achieve stable adhesion, especially in extreme and harsh conditions. As with many other types of industrial coatings, surface preparation is required for best results when applying hard coat.
Low Friction Coatings
Low friction coatings have a friction coefficient from 0.2 down to 0.05, with the lowest coefficient being offered by polytetrafluoroethylene. There are several types of low friction coatings with the application determining the type of coating being used. Each of the types has different values with varying degrees of wear resistance and hardness.
High static friction coefficients can be generated between mating parts the forces of which can be reduced with the application of a low friction coating. A further benefit of low friction is the minimal chance of foreign substances sticking to treated surfaces. Aside from their use with metals, low friction coatings can be used on elastomers and rubber to reduce their friction values.
This chapter will discuss the applications and benefits of industrial coatings. When working with any coating or coating material, it is essential that workers strictly follow manufacturer’s guidelines for the success of the process and the safety of workers. Every manufacturer publishes specific and concise directions regarding the safe handling of coating materials. Additionally, they provide contact information when questions arise regarding application.
There are many diverse types of industrial coatings with many different characteristics. For instance, the PVDF coating is highly reactive and is used in applications where highest strength is required. Each coating provides many benefits to the equipment on which it is applied; for instance, by improving the equipment’s wear resistance or strength. Therefore, when selecting a coating for equipment, one must be cautious of the properties of the coating material and the environment in which the equipment is going to be used. The bottom line is that industrial coatings are there to protect equipment from harsh weather or environmental conditions that end up damaging the equipment, ultimately prolonging its lifespan.
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