Wet coating is a surface refinement process in which liquid coating materials are applied to a component. Typically, the coating is sprayed on, allowing even complex geometries to be evenly covered. After application, the coating hardens, forming a protective and functional surface. 

This process offers numerous benefits: it effectively protects components against corrosion, chemical attacks, and mechanical wear, while also enabling aesthetic enhancement with diverse color options and smooth finishes. Wet coatings are suitable for a variety of materials such as steel, aluminum, and stainless steel, and can meet specific requirements like chemical resistance, non-stick properties, or electrical insulation. 

Major applications include the automotive, chemical, and mechanical engineering industries, as well as food technology. In particular, specialized wet coatings like PTFE excel in the food sector due to their non-stick properties and compliance with FDA and EU regulations. Additionally, they ensure the durability and optimal functionality of machinery and equipment in the packaging industry and laboratory technology. 

PTFE Coatings: Properties of Teflon

PTFE coatings, commonly known as Teflon, are distinguished by a range of outstanding properties. They provide excellent non-stick and sliding characteristics that virtually eliminate material adhesion, along with exceptional chemical, thermal, and electrical resistance. PTFE is resistant to oxygen, ozone, and UV light, making it ideal for demanding environments. Its low coefficient of friction minimizes resistance between moving parts, increasing the longevity and efficiency of coated components. 

PTFE Melting Point and Temperature Resistance 

Another advantage of PTFE is its high-temperature resistance: it remains stable and functional at temperatures of up to 260°C, with a melting point of 326.8°C. These thermal properties enable its use in environments with extreme temperature fluctuations, such as in the chemical, food, and laboratory industries, as well as in mechanical engineering. Even under prolonged heat exposure, PTFE maintains its non-stick and insulating properties, making it indispensable for a wide range of industrial applications.

Limitations and Common Applications

Despite its many advantages, PTFE has some limitations. Its low mechanical strength can lead to “cold flow,” where the material deforms under load, limiting its use in high-stress areas.

PTFE is preferred in applications that leverage its specific properties. Guides, bearings, and seals benefit from its low friction and high wear resistance. It is also valued in the automotive and packaging industries, where its sliding properties enhance the efficiency and durability of components.

Variants of Wet Coating Technologies

Wet coatings offer a broad spectrum of properties tailored to specific applications through the use of various materials. Each coating technology brings unique advantages, making it particularly suitable for certain fields. Below are the key technologies.

PFA Coating: Chemical Resistance and Flexibility

PFA coatings (perfluoroalkoxy) combine excellent chemical resistance with flexibility and high-temperature tolerance. They are similar to PTFE coatings but can be applied in thicker layers, expanding their range of applications. With a melting point of around 260°C, PFA coatings are ideal for environments subjected to high thermal and chemical stress. 

Typical applications for PFA coatings include the chemical industry, where components are regularly exposed to aggressive substances. Their chemical resistance and ability to form thicker layers make PFA a popular choice for reactors, containers, and pipelines. 

FEP Coating: Superior Sliding Properties

FEP coatings (fluorinated ethylene propylene) are characterized by their thermoplastic nature, which allows for a nearly pore-free surface. When heated, the coating melts and forms a smooth, uniform layer, providing excellent sliding properties and reliable chemical resistance. 

FEP coatings excel in applications requiring precise, thin layers, such as in the automotive and packaging industries, where low friction and even surfaces are critical. 

Silicone Coating: High-Temperature Resistance

Silicone coatings are renowned for their exceptional resistance to high temperatures. They are ideal for applications exposed to thermal stress without losing their non-stick or sliding properties. These characteristics make them a preferred choice in the food industry, particularly for baking molds and cooking utensils.

Additionally, silicone coatings offer durability and easy cleaning, making them perfect for applications with stringent hygiene requirements.

Sol-Gel Coating: Abrasion Resistance and Hardness

Sol-gel coatings are based on inorganic materials like silicon dioxide and are known for their high hardness and abrasion resistance. These properties make them ideal for applications that endure intense mechanical stress. 

Typical uses for this technology include the baking industry, where sol-gel coatings are applied to baking trays and molds for their temperature resistance and durability. They are also utilized in mechanical engineering, providing a resilient and long-lasting surface that withstands high loads. 

The Teflon Coating Process

The Teflon coating process is a multi-stage procedure requiring precision and care to achieve the desired properties. Each phase ensures the creation of a durable, functional, and high-quality surface. The steps of the process are outlined below.

Component Preparation: Inspection and Cleaning

• Inspection: The process begins with a thorough inspection of each component to assess its condition and suitability for coating. Any contamination or damage is identified.

• Cleaning: Comprehensive cleaning is essential to ensure optimal adhesion. Techniques like sandblasting remove dirt, oils, rust, and old coatings, creating a clean and textured surface ideal for the coating process.

Teflon Application: Thin and Thick Layer Techniques

• Selection of Method: Depending on requirements, the component is coated using either the thin-layer or thick-layer method: 
  • Thin-Layer Method: Coatings are applied using the wet coating process, with typical thicknesses between 15 and 80 µm. This method is ideal for achieving even, thin coatings with non-stick and sliding properties.
  • Thick-Layer Method: For robust layers, the material is applied electrostatically as a powder. After melting, thicker, protective layers are formed.
• Coating Application: The coating material is precisely applied to the component to ensure even distribution, which is critical for achieving the desired functional properties. 

Sintering and Post-Processing

• Sintering: After application, the coating is cured at high temperatures, developing its final properties such as chemical resistance and non-stick effects. 
• Mechanical Post-Processing: For thick layers, additional steps like turning, grinding, or milling may be necessary to meet specific requirements. Glass bead blasting or electropolishing may also be performed if needed. 
• Quality Assurance: Finally, a comprehensive quality check is conducted. Coating thickness is measured, and components are tested for pore-free surfaces. Only those meeting all criteria are approved. 

Applications of Wet Coatings

Wet coatings are used in a wide range of industries due to their versatile properties. From technical to hygienic requirements, they offer tailored solutions that enhance both functionality and durability.

Industrial Applications: Automotive, Engineering, and Packaging

• Automotive Industry: Wet coatings are prized in the automotive sector for their low friction and chemical resistance. They are used in guides, seals, and bearings to reduce wear and improve efficiency, while also protecting against corrosion and mechanical stress, significantly extending component lifespans. 

• Engineering: In mechanical engineering, wet coatings protect against chemical and thermal stresses while improving the sliding properties of machine parts. Coated components remain operational even under intense use, ensuring high reliability in demanding environments. 

• Packaging Industry: In packaging, non-stick and sliding properties play a crucial role. Coated machine parts ensure smooth material flow and prevent packaging materials from sticking, enhancing production efficiency. 

Food Industry: Benefits of FDA- and EU-Approved Coatings

• Hygiene Standards: In the food industry, wet coatings are highly sought after for their non-stick and cleaning properties. Many, like PTFE, meet the stringent FDA and EU regulations, allowing safe use in direct contact with food. 

• Non-Stick Coatings for Cooking and Baking Equipment: From coated baking molds to cooking utensils, the non-stick properties prevent food adhesion, simplifying cleaning and improving manufacturing and processing efficiency. 

• Durability and Protection: Coatings used in food technology not only protect against corrosion and chemical influences but also help maintain the functionality of production equipment, reducing maintenance intervals and boosting operational efficiency.