Powder Coating Thickness

Powder coating has gained popularity in many industries because of its durability, the appearance of the finished product, and its eco-friendly benefits. Thickness is one of the most critical parameters of powder coating since it affects the functional properties of the coated item as well as its appearance. Understanding powder coating thickness, how to measure it, and the best practices is crucial in any coating project.

What Is Powder Coating Thickness?

Powder coating thickness refers to the depth of powder applied to the substrate. This thickness is expressed in microns (μm), with one micron being one thousandth of a millimeter. The thickness of the powder coating varies based on the application method, the type of powder being used, and the project being undertaken. Standard thicknesses for most uses range between 50 and 150 microns, though this can change depending on specific project requirements and environmental factors.

Why Proper Powder Coating Thickness Matters

The thickness of a powder coating is not just a technical specification; it plays a pivotal role in determining the coating’s effectiveness in several key areas:

• Corrosion Resistance: Insufficient thickness can lead to poor protection against factors such as moisture, chemicals, and salts, resulting in the corrosion of the substrate[1]. Thus, its thickness should be proper so the coating would create a substantial barrier against these factors.
• Durability: A well-applied and the right thickness of the powder will be more durable and able to bear physical wear and tear, impacts, and abrasion as compared to the thinner or uneven layers [2]. This is particularly significant in industrial and automotive sectors, for instance, on surfaces that come into contact with abrasive substances.
• Aesthetic Appeal: The appearance of the coated surface depends on the consistency of the coating thickness [3]. Uneven thickness may cause defects like drips or an orange peel texture.
• Adhesion: Proper coating thickness is important because it ensures that the powder coating properly sticks to the substrate. If the coating is too thin, it may not stick properly, which will eventually lead to peeling or flaking. However, if the coating is applied too thick, it can also lead to poor adhesion because of the stress inherent to the coating’s layer.

Measuring Powder Coating Thickness

Measuring the thickness of a powder coating is a crucial factor in quality control. The following are the commonly used methods, each of which has its own advantages and disadvantages based on the applications and the substrate in use.

• Magnetic Induction is an ideal method for determining the thickness of coatings on ferrous metals. The thickness of the coating is measured using a magnetic probe and the strength of the magnetic field between the probe and the metal substrate [4]. This method does not harm the sample and gives a precise determination of coating thickness on steel and iron substrates.
• Eddy Current Testing: Eddy current testing is frequently employed among non-ferrous metals, such as aluminum. This technique involves passing an alternating current through the substrate to create a magnetic field. The thickness of the coating is then determined by the impedance caused by the coating’s presence. Eddy current inspection has the advantage of not causing damage and can be used for many different purposes, as with magnetic induction.
• Ultrasonic Testing: Ultrasonic testing is powerful, as it can determine the thickness of coatings on both metal and non-metal objects. This type employs ultrasonic frequencies directed through the coating. It is done by calculating the time it takes for the sound waves to bounce off the substrate being measured. Ultrasonic testing can be very effective for measuring the thickness of thick coatings or multi-layered coating systems.
• Microscopy: This technique precisely measures coating thickness by analyzing the cross-section of the coated substrate through a microscope [4]. This destructive method cuts the coated material to obtain a sample for the measurement of coating thickness; however, it is accurate, particularly for coatings that have to meet certain thickness standards.

Factors Affecting the Thickness of Powder Coating

Several factors can influence the thickness of a powder coating, making it essential to control these variables during the application process:

• Type of Coating: Different powders (e.g., epoxy, polyester, or polyurethane) may require varying thicknesses to provide the right characteristics [5]. For instance, epoxy coatings may be applied at a higher thickness to enhance chemical resistance, while polyester coatings may be applied at a moderate thickness to enhance UV resistance.
• Application Method: The way through which the powder coating is applied greatly affects the final thickness. Techniques like electrostatic spray deposition (ESD) ensure that the flow and deposition of the powder are well controlled, thus giving a uniform thickness of the coating [5]. Fluidized bed coating, however, is known to give thicker coating and is commonly used for the durable products.
• Curing Process: The method of curing in which the powder is exposed to heat to form a rigid and long-lasting coating also plays a role in determining the final thickness [5]. Different oven temperatures or curing times may cause changes in the coating thickness, with under-cured being thin and weak and over-cured being thick and brittle.
• Substrate Material: Different materials require different coating thicknesses. To provide the best adhesion and protection, the coating thickness of metal substrates is not the same as that of plastic or wooden substrates [6]. Furthermore, the surface texture of the substrate also plays a role in the amount of powder that can be applied to a particular surface; a surface with a rough texture will need more powder to cover the surface area fully.

Industry Standards for Powder Coating Thickness

Powder coatings are used in various applications, each requiring specific thicknesses to ensure optimal performance. Well-defined guidelines exist to meet the quality standards of both manufacturers and consumers.

• Architectural Coatings: In architectural applications, powder coatings have to conform to certain standards, such as those set by the American Architectural Manufacturers Association (AAMA). AAMA have different standards for the thickness depending on the type of coatings and its intended use.
• Automotive Coatings: In the automotive application, powder coatings can be applied for decorative and protective coatings. The thickness of the coating depends on the part to be coated, but a standard range is between 50 and 120 microns. It is possible to apply thicker layers of coating to parts of the vehicle that are subjected to more wear and tear, such as the wheels and suspension system.
• Industrial Coatings: In the industrial sector, where machinery and equipment are exposed to harsh conditions, heavy-duty coatings are essential for surface protection [5]. These coatings typically range from 100 to 200 microns in thickness, though they may be thicker depending on specific application requirements.

Consequences of Improper Powder Coating Thickness

The proper thickness of the powder coating is critical in as much as it determines the performance and the service life of the coated part. Deviating from the specified thickness can lead to several issues:

• Inadequate Thickness: If the coating is oversimplified, it will not be able to provide the much-required protection against corrosion, abrasion, and other environmental conditions [7]. This results in early failure of the coating, which means that the surface must be repaired or recoated.
• Excessive Thickness: It may seem that applying more powder to the surface will provide better protection, but, in fact, it’s not true. Very thick coatings can result in problems, such as a lack of adhesion, cracks, or an uneven surface [7]. Also, the thicker coatings are likely to have defects like orange peel texture or bubbles that can affect both the appearance and functionality of the coating.
• Increased Costs: It is also vital to apply the right thickness in order to save on the costs [7]. Excessive thickness is not only wasteful of material and money, but it also requires more energy for curing, and more man hours for touching up errors.

Best Practices for Achieving Optimal Thickness

To achieve the optimal powder coating thickness, it is essential to follow best practices throughout the coating process:

• Calibration of Equipment: It is also important to service the application equipment, which may include spray guns or curing ovens, to achieve uniform coating thickness [8]. This assists in the prevention of variation that may cause inadequacy or inconsistency in the coverage provided.
• Surface Preparation: The surface to be coated should be cleaned, degreased, and sandblasted to ensure that it is clean and ready to receive the powder and that the coating has the correct thickness [8].
• Monitoring and Testing: The coating thickness can be controlled during the application process and after the application, which will lead to the right level of coating thickness being achieved. Magnetic induction or eddy current testing can be done without damaging the part, and real-time adjustments and quality control can be done.

Powder coating thickness is a vital factor influencing the performance, appearance, and service life of the powder coated product. By understanding the right thickness, the techniques for measuring it, and the factors that affect it, manufacturers can ensure that the powder coated products are of the right quality and can be trusted to last for a long time.

References

[1] Gots, V., Lastivka, O., Berdnyk, O., Tomin, O., & Shilyuk, P. (2020). Corrosion resistance of polyester powder coatings using fillers of various chemical nature. Key Engineering Materials, 864, 115-121.

[2] Swain, B., Bhuyan, S., Behera, R., Mohapatra, S. S., & Behera, A. (2020). Wear: a serious problem in industry. Tribology In Materials And Manufacturing-Wear, Friction And LubricationIntechOpen.

[3] Rossi, S., Russo, F., & Bouchakour Rahmani, L. (2020). Study of the durability and aesthetical properties of powder coatings admixed with pearlescent pigments. Coatings, 10(3), 229.

[4] Giurlani, W., Berretti, E., Innocenti, M., & Lavacchi, A. (2020). Measuring the thickness of metal coatings: A review of the methods. Coatings, 10(12), 1211.

[5] Pélissier, K., & Thierry, D. (2020). Powder and high-solid coatings as anticorrosive solutions for marine and offshore applications? A review. Coatings, 10(10), 916.

[6] Gulling, D. (2024). Custom Components in Architecture: Strategies for Customizing Repetitive Manufacturing. Taylor & Francis.

[7] Dabees, S., Mirzaei, S., Kaspar, P., Holcman, V., & Sobola, D. (2022). Characterization and evaluation of engineered coating techniques for different cutting tools. Materials, 15(16), 5633.

[8] Wu, H., Xie, X., Liu, M., Chen, C., Liao, H., Zhang, Y., & Deng, S. (2020). A new approach to simulate coating thickness in cold spray. Surface and Coatings Technology, 382, 125151.