Surface preparation of before powder coating

Consumers today demand better quality and more durable product. They are not only requesting the basic function of the product, but they also want to have the product have a longer lifetime.

Powder coating is one of the processes that protect the product base material from corrosion and scratches. Therefore, powder coating is widely applied in industry and commercial use.

This article, we discuss the iron parts processing and surface preparation for the powder coating.

 

1. Different types of powder coating

There are two basic classifications of powder coating materials: “thermoplastic” and “thermoset.”

Thermoplastic: the metal surface is preheated to the temperature which higher than the melting temperature of the thermoplastic material. When the temperature cooled down, it forms a strong layer at the surface of the parts.

Usually the most popular thermoplastic powder coating is epoxy powder coating and nylon powder coating.

Thermoset: the thermoset powder coating is hardened with increase temperature (usually 120-135 °C) because of a chemical reaction. This chemical reaction results in a change in molecular structure which forms a strong bond between metal surface and thermoset.

 

2. The most frequent materials that we do powder coating:

  • Aluminum materials: can do vibratory finishing or shot blasting to clean the surface before powder coating
  • Steel materials: stainless steel material can be treated and directly do powder coating, while for iron material need to make corrosion protection (soak in the rust inhibitor) then do powder coating

Because the thickness of the powder coating is between 25 to 200 microns, so it can cover the most minor defects from casting and metal forming. For thermoplastic powder coating, coating is even thicker. Therefore, the surface roughness for powder coating is not very high demand.

3. The process of powder coating

The process of powder coating is different according to the substrate materials and the coating materials. Generally, we divide the powder coating process into four steps:

  • Preparation of the surface
  • Application of the powder
  • Heating of the part
  • Curing of the coating

In this articles, we mainly discuss the first parts: preparation of the surface.

Preparation of the surface starts with a process to ensure that the surface is properly cleaned and free of “soils” such as manufacturing oils. Subsequent surface treatments might include blasting if required,

Thermoplastic powders usually need a primer to promote adhesion. However, Thermoset powders do not need a primer because they have a built-in adhesion promoter. Primers may be used with thermoset powders to enhance certain properties, but the associated priming material must be able to withstand the curing temperatures required for powder coatings.

 

4. Case Study

4.1 Parts condition before finishing:

Material: iron material

Appearance: before processing, parts have punched burr at the edge and also around the hole

Shape: The iron parts is a punched sheet with one small hole of 6mm

Size: 57mmX160mm, thickness 2mm

Process before finishing: Stamping process

The process after finishing: epoxy powder coating

 

4.2 Parts surface requirement

  • No need to strip the plastic cover before processing
  • Edge radiusing and deburring
  • Deburring at the drilling hole
  • Improve the entire surface smoothness for the powder coating process

 

4.3 How we process the parts

Step (1) Grinding (2) Drying
Grinding Vibratory finishing machine with separation
Tumbling Speed 50/60HZ (full speed)
Chip Type Ceramic media ACT 20X20
Media to Parts Ratio 3:1
Compound Type LC-13, PH 8 (mild grinding compound) MC-8 diluted compound
Water Level Just cover the mass Soak in the solvent
Tumble Time 2 hours 15 min
Note Automatic separation Manually take the parts out

 

4.4 Parts before and after processing

 

parts surface finishing before and after
parts surface finishing before and after

 

As we can see from the above photo, there are 4 parts sample. The left 1st parts is parts without the plastic membrane cover stripped. The left 2nd parts is parts with the plastic membrane cover stripped. The right 2nd part is the parts deburred with ceramic media. The right 1st part is ceramic parts deburred then polished with zirconia ball.

For powder coating, the right 2nd parts condition is enough for powder coating.

 

parts surface condition before finishing
parts surface condition before finishing

 

The parts condition before surface finishing have the sharp edge and burr at drilling hole. The edge should rounded for easy assembly especially for commercial products.

 

5. Conclusion

In this articles, we introduce two major types of powder coating technique and the process how to do the powder coating. Also we focus on the topic of surface preparing before powder coating. Then we show an example of a iron stamping parts.

Vibratory finishing surface preparation is the cost effective solution to prepare the surface before powder coating. This process remove the dirt and soil as well as grease from the punching and stamping process. There are also other approaches like shot blasting, vibratory finishing process approved to be the effective and efficient way of processing metal parts.