4 Types of Coating Techniques

14th December 2023
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Spray Coating

Spray coating is applied utilizing compressed air with a pressure between 0.2 to 0.5 MPa to propel a flow of air through the central orifice of the spray gun. This creates a negative pressure zone at the nozzle's front end, drawing the coating material from the container into the negative pressure zone.

The coating material is then ejected from the nozzle, rapidly entering the compressed air flow. This causes the atomization of the liquid, forming a mist of paint particles that fly towards and adhere to the surface of the object being coated, creating a continuous coating film.

Pros

  1. Versatility: Air spray coating is highly adaptable and is not significantly limited by the type of coating material or the shape of the object being coated. It can be used in various coating operations and only requires a compressed air source, making it one of the widely adopted coating methods.
  2. High-quality Finish: The coating film obtained through spray coating is smooth and even, achieving excellent decorative quality.
  3. Thorough Atomization: Air spray coating results in good atomization, minimizing issues such as pinholes and bubbles.
  4. Higher Coating Efficiency: Air spray coating is efficient, offering a faster application compared to brush coating, with the ability to coat 150-200 square meters per hour.

Cons

  1. Pollution: Air spray coating requires a considerable amount of solvents to achieve a better finish effect. The released solvents during operation contribute to environmental pollution and also pose risks to human health.
  2. Paint Loss: Air spray coating, however, has a significant paint loss as the sprayed mist easily disperses, potentially causing environmental pollution. The paint utilization rate is typically around 50%.

Spray Coating

 

Roll Coating

Paint rollers are used to apply coating on large flat surface. The rollers are rotated in a coating trough, picking up a certain amount of coating material. This process results in the formation of a wet film with a designated thickness on the roller's surface. As the roller rotates and comes into contact with the substrate, the coating material is seamlessly applied to the substrate's surface, creating uniform coating finishes.

Roll coating is exceptionally well-suited for baking and UV coatings, demanding coatings with excellent leveling, wetting properties, and adhesion. Ideally, the coating should exhibit rapid curing and form a film within a short timeframe. Roll coating streamlines continuous production operations and hugely enhance the efficiency. However, roll coating is only suitable for large flat surface, and can not ensure a high-quality coating finish on objects of different shapes.

 

Brush Coating

Brush coating is a method of applying paint by directly contacting the surface of the substrate with a paintbrush, ensuring even wetting and uniform coating to form a paint film. It is one of the simplest painting technique, suitable for coating objects of any shape. The advantages of brush coating include easy operation, paint savings, minimal tool requirements, wide applicability.

It can be used on various materials and shapes. Brush coating is highly adaptable, suitable for almost all types of paints except those that dry too quickly. The mechanical action of the brush facilitates effective wetting of the substrate's surface, penetrating into fine pores, enhancing the adhesion of the paint film. However, brush coating is so slow in efficiency compared to other coating techniques.

 Varnishing a wooden shelf using paintbrush

Varnishing a wooden shelf using paintbrush

Dip Coating

Dipping is a traditional coating method characterized by simple equipment, flexible operation, and suitability for streamlined workpieces with simple shapes, no recesses, and no paint pockets. However, it is not suitable for substrates with deep grooves, blind holes, or areas where excess paint is difficult to remove.

Dip coatings are done by immersing the entire part into a tanks filled with liquid paint. After a short soaking period, the workpiece is removed from the paint, causing the paint to adhere to the surface and form a coating. Excess paint is then allowed to drip off, returning to the paint tank.

Features:

  1. Easy-to-use equipment for manual or automated dipping in small or large batches, making it suitable for efficient, high-volume production.
  2. Minimal paint loss, high utilization, and low environmental impact.
  3.  Decorative quality is generally lower than spray or brush methods, with a tendency for uneven thickness and potential for sagging on the coating surface.
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