Understanding the Powder Coating Manufacturing Process
The powder coating manufacturing process is a complex, controlled process used to manufacture powder coating materials. The powder coating production process is designed to create high-quality, consistent, sprayable particles with predictable curing behavior.
Powder coating material production refers to the creation of the powder coating materials used in spray applications. This manufacturing process should not be confused with the application of powder coating on a surface, which is a dry finishing process that involves electrostatically spraying a plastic or polymer powder onto a grounded part or component.
Powder coating material manufacturing is a complex four-step process that includes raw material weighing and blending, extrusion melting and mixing, cooling and flaking, and grinding with post-extrusion processing to produce fine powder particles of specific sizes.
The final success of the actual powder in coating a surface heavily depends on the materials and quality assurance processes used in how the powder coating is made in the industrial manufacturing process of the powder. If not manufactured correctly, the powder coating may fail to adhere to the surface of the part or component, and its finish, quality, and durability may suffer.
Raw Material Composition in Powder Coating Manufacturing
The raw materials used in powder coating manufacturing are of the utmost importance. Using quality, superior materials will result in a high-performance end product. Using inferior materials in the blending process will almost guarantee downstream problems before components are powder coated.
The raw materials can be divided into three parts: the polymer resins or binders; the curing agents and accelerators; and the pigments and extenders.
Polymer Resins or Binders
The polymer resins or binders are the core material used in powder coating and help determine the success of the chemical and mechanical properties of the final powder. The polymer resin systems or binders can be further broken down into thermosetting resins and thermoplastic resins.
Thermosetting Resins
Thermosetting resins include epoxies; polyesters; hybrids, which are mixtures of epoxies and polyesters; polyurethanes; and acrylics.
Thermoplastic Resins
Thermoplastics are polyvinyl chloride (PVC); nylon; polyolefins, such as polyethylene and polypropylene; and fluoropolymers. These resin systems or binders determine the durability, flexibility, and chemical-resistant properties of the final product.
Curing Agents or Accelerators
Next are the curing agents or accelerators, which are used in thermosetting powders. The curing agents are known as thermal hardeners or crosslinkers, as they enable thermal hardening. They are dicyandiamide (DICY) for epoxies and triglycidyl isocyanurate (TGIC) and hydroxyalkyl amide (HAA) for polyesters.
Pigments and Extenders
Pigments provide color, opacity, ultraviolet protection, and corrosion resistance. The fillers or extenders are additive minerals, such as barytes, calcite, mica, and talc, that improve the strength of the final powder coating, while reducing cost and improving texture and flow of the powder.
Extenders or additives are also used to fine-tune the performance of the powder. Properly mixing resins, curing agents, pigments, and additives is critical because it affects durability, corrosion resistance, gloss consistency, and surface uniformity.
There are trade-offs in the creation and development of powder coatings. The best solution is finding the perfect mixture of resins, curing agents, and pigments paired with additives for a specific powder coating application. Each project will require a different powder coating, as not all projects are the same.
This made-to-order development of powder coatings requires careful assessment of the properties and performance requirements of the customer’s desired end product.
Blending and Homogenization of Powder Coating Ingredients
Raw Material Weighing and Blending
The blending and homogenization of the dry powder coating ingredients is critical and is designed to transform the raw materials into a uniform, high-quality blend. This complex process starts with raw material weighing.
The raw materials are accurately weighed to ensure consistency before blending. The proper amount of each raw material is measured and added slowly to a hopper. This is done to ensure all the raw materials are evenly mixed and dispersed throughout. This process creates a dry powder. Proper blending ensures pigment dispersion throughout the mixture, resulting in a powder coating with more uniform color, better consistency, higher gloss, and a smoother appearance.
This powder coating formulation ensures a homogeneous blend by uniformly distributing all the raw materials. The dry powder mixture or blend is then fed into a high-intensity shear mixer. This process uses speed and creates an intense mixing action to reduce clumps and irregularities.
Incomplete homogenization at this point can result in color variation across batches, inconsistent curing behavior, and uneven gloss or texture in the finished coatings when applied.
Thermal Processing and Extrusion in Powder Production
Extrusion Process Melting and Mixing
Once the raw materials are thoroughly blended, they are fed into the hopper of an extruder where melting begins. This extrusion process is performed to ensure the raw materials are mixed further at a molecular level and dispersed uniformly. The blend is heated to 158°F to 250°F until it liquefies. The blend then passes through several different controlled heating zones to ensure a careful uniform heating throughout the mixture without burning the blended materials.
Precise temperature control is needed during the extrusion process to avoid premature curing or degradation. The heat during thermal processing causes the resins to soften and blend together with the pigments and additives. The resulting blend is uniform and forced out forming a continuous sheet. At this point the blend is said to be “locked-in,” and very little can be done to alter it later on. That is why precise and continuous monitoring of the process is essential.
Heat can significantly alter the effectiveness of the final powder coating. Careful application of heat ensures the correct viscosity, curing, adhesion, and structural integrity of the final product. Too much heat at this stage causes component breakdown, color fading, and reduced viscosity. This can lead to defects in the final powder-coated part, such as peeling, cracking, poor corrosion resistance, and reduced durability.
Cooling, Solidification, and Material Conditioning
Cooling and Flaking
After the blend is extruded, it must be uniformly cooled, as the temperatures of the extruded material range from 200°F to 250°F. The cooling process involves moving the blend onto chilled rolls, which move the blend further down another cooling surface, such as a rolling belt or rotating drum, to cool some more. The cooling must be uniform throughout this process to ensure the durability and integrity of the final product.
The blend is cooled to a brittle solid to allow for efficient grinding without smearing or melting. This cooling is essential as it adds durability and helps to prevent premature chemical reactions, known as “B-staging” in the blend. The cooling process also helps ensure optimal powder coating adhesion to surfaces.
If contamination or uneven cooling occurs, the final powder will exhibit poor adhesion, flaking, color discoloration, blisters, and peeling. Corrosion resistance and durability will also be reduced. The product at this stage is broken down from long sheets or ribbons into flakes and chips. This will help aid the grinding process.
Particle Size Control and Powder Finishing
Grinding and Post-Extrusion Processing
The cooled chips or flakes are then ground by a grinding machine and processed into a fine, uniform powder.
Grinding is the stage when chips or flakes are converted into powder that can be sprayed onto a component.
Ideal powders are ground to a consistent size and range, which helps to ensure consistent coating during the application process. Particle size distribution during a powder coating application is affected by the size and shape of the particles. Smaller, well-distributed particles will result in smoother, more uniform application finishes providing for higher performance, durability, and corrosion resistance.
Particle control is essential for predictable application performance across different coating lines. Particles that are too fine or too coarse may not apply or adhere properly to a surface, leading to inconsistencies in the coating.
Particles may pass through several fine filters to remove any oversized particles. The final size of the particles depends on the final use of the powder coating application. The particles may be sieved numerous times to achieve the desired size.
Quality Assurance in Powder Coating Manufacturing
Quality assurance is accomplished by testing the powder coating to ensure it meets performance, durability, and corrosion standards for the specific application. Quality assurance is a holistic operation that starts at the beginning of the powder coating manufacturing process through the selection of the highest quality raw materials to ensuring accurate blending and mixing.
Precise control of heating and cooling temperatures ensures quality and durability in the final product, as does precise grinding to a uniform particle size. Any deviation at any stage of the process will cause problems in the treated component, such as uneven color, poor gloss finish, rusting, and dimple marks.
At every stage, the product must be screened, sampled, and verified to ensure the highest levels of quality are met. This process also focuses on repeatability in production to ensure the customer’s desired powder coating is reproducible. After the powder is ready for shipment, additional evaluations are conducted, including visual and microscopic inspection, review of customer specifications, and real-world testing of the coating.
Why Powder Manufacturing Quality Matters to Finished Coatings
Powder coating manufacturing quality is key, as it dictates the powder coating’s durability, appearance, consistency, and resistance to corrosion. Using superior, high-quality raw materials and precise, well-distributed particles ensures better adhesion, uniform coverage, and resistance to chipping, corrosion, and fading.
Poor quality powder leads to defects such as orange peeling or uneven adhesion. High-quality powder provides a smoother finish, reliable color matching, and longer-lasting, professional results. The ultimate success of the powder coating depends on consistent attention to detail at every phase of the process.
Rhinehart Finishing
For superior results in powder coating and wet spray operations, Rhinehart Finishing is an industry leader with more than 125 years of combined experience in the finishing industry.
Our state-of-the-art facility allows us to provide customers with world-class products that meet or exceed their requirements. Rhinehart’s industrial powder coating services are the best-in-class in the industry. Our powder coating process and powder coating testing methods are superior and the benefits of powder coating from Rhinehart are realized in our attention to detail in surface preparation and pretreatment of all surfaces.
The result is a made-to-order, professional, high-quality, corrosion-resistant finish.
We also offer numerous value-added services, such as chemical conversion coatings, assembly, custom masking, and vibratory finishing. We are ISO 9001:2015 Certified, ensuring our customers receive the highest-quality product every time. Please contact us to get a quote on your next project.