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Sealers

Sealers for thermal spray are substances applied to thermal – sprayed coatings to enhance their performance and protect the underlying substrate.

1.What is the Functions of Sealers for thermal spray?

  • Porosity Reduction

Thermal – sprayed coatings often have some degree of porosity due to the way the molten or semi – molten particles are deposited. Sealers penetrate these pores, filling them up. This is crucial as pores can act as pathways for corrosive substances, moisture, or gases to reach the substrate. By reducing porosity, sealers improve the coating’s corrosion resistance. For example, in a marine environment, a thermal – sprayed zinc coating on a steel structure can be sealed to prevent seawater from seeping through the pores and corroding the steel.

  • Enhanced Adhesion and Coating Integrity

Sealers can improve the adhesion between the thermal – sprayed coating and the substrate. They can also strengthen the overall integrity of the coating by binding the individual sprayed particles more tightly together. This helps to prevent delamination of the coating over time, especially in applications where the coated component is subjected to mechanical stress, vibration, or thermal cycling.

  • Surface Smoothness and Aesthetics

Applying a sealer can give the thermal – sprayed coating a smoother and more uniform appearance. This is beneficial for applications where aesthetics are important, such as in the automotive or consumer goods industries. Additionally, a smooth surface can reduce friction in components where movement is involved, like in mechanical parts with thermal – sprayed coatings.

2.What is the Types of Sealers for thermal spray?

  • Organic Sealers

Epoxy – based Sealers:

Epoxy sealers are widely used due to their excellent adhesion, chemical resistance, and mechanical properties. They can form a hard, durable film over the thermal – sprayed coating. Epoxy sealers are suitable for protecting coatings in industrial environments where resistance to chemicals, abrasion, and moisture is required. For example, in a chemical processing plant, an epoxy – sealed thermal – sprayed ceramic coating on a storage tank can prevent chemical attack on the underlying metal.

Polyurethane – based Sealers:

Polyurethane sealers offer good abrasion resistance, UV resistance, and a high – gloss finish. They are often used in applications where the thermal – sprayed coating needs to be protected from environmental factors such as sunlight and weathering, as well as from minor abrasion. In outdoor equipment or architectural applications, polyurethane – sealed thermal – sprayed metal coatings can maintain their appearance and performance over long periods.

Acrylic – based Sealers:

Acrylic sealers are known for their quick – drying properties and relatively good UV resistance. They are commonly used in applications where a fast – drying sealer is required, and where the coating does not need to withstand extremely harsh chemical or mechanical conditions. For example, in some consumer product manufacturing, acrylic – sealed thermal – sprayed coatings can provide a basic level of protection and a pleasing appearance.

  • Inorganic Sealers


Glass – based Sealers:

Glass – based sealers, also known as glass frits, are applied as a powder or slurry and then heat – treated to form a glassy layer on the thermal – sprayed coating. They offer high – temperature resistance, excellent chemical resistance, and good abrasion resistance. Glass – based sealers are often used in high – temperature applications, such as in the aerospace industry on thermal – sprayed coatings for turbine components.

Silicate – based Sealers:

Silicate – based sealers can react with the surface of the thermal – sprayed coating to form a hard, inorganic layer. They are relatively inexpensive and can provide good protection against moisture and some chemicals. Silicate – based sealers are sometimes used in large – scale construction or infrastructure projects to seal thermal – sprayed coatings on concrete or metal structures.

3.What is the Application Methods of sealers for Thermal Spray?

  • Spraying:

Organic sealers, especially epoxy, polyurethane, and acrylic – based ones, are often applied by spraying. This method allows for a uniform application over large surfaces. Air – spray guns or electrostatic spray guns can be used depending on the specific requirements of the application, such as the viscosity of the sealer and the desired thickness of the sealer film.

  • Dipping:

Smaller components with thermal – sprayed coatings can be dipped into a bath of the sealer. This ensures that all surfaces, including hard – to – reach areas, are coated with the sealer. However, it may require careful control of the dipping time and the removal process to avoid excessive sealer build – up.

  • Brushing or Roller – coating:

For some applications where a more manual approach is feasible, such as in on – site repairs or small – scale projects, sealers can be applied using brushes or rollers. This method is suitable for applying sealers to irregularly shaped surfaces or in areas where spraying may not be practical.

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