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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.
Consumers today demand better quality and more durable product. They are not only requesting the product’s primary function, but they also want to have the product have a longer lifetime.
In this article, we discuss the iron parts processing and surface preparation for the powder coating.
1. Different types of powder coating
There are two primary classifications of powder coating materials: “thermoplastic” and “thermoset.”
Thermoplastic: the metal surface is preheated to a temperature higher than the thermoplastic material’s melting temperature. When the weather cooled down, it forms a firm 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 the molecular structure, forming a strong bond between the metal surface and the 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: treat stainless steel material and directly do powder coating, while 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 minor defects from casting and metal forming.
For a thermoplastic powder coating, the coating is even thicker.
Therefore, the surface roughness for powder coating is not very high in 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 article, we mainly discuss the first parts: preparation of the body.
Preparation of the surface starts with a process to ensure that the body is adequately 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 specific properties, but the associated priming material must 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
As we can see from the above photo, there is four parts sample. The left 1st parts are parts without the plastic membrane cover stripped. The left 2nd parts are parts with the plastic membrane cover denied. 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 proper 2nd parts condition is enough.
The parts’ condition before surface finishing has a sharp edge and burr at the drilling hole. The edge should be round for easy assembly, especially for commercial products.
5. Conclusion
In these articles, we introduce two powerful powder coating techniques and how to do the powder coating. Also, we focus on the topic of surface preparation before powder coating. Then we show an example of iron stamping parts.
Vibratory finishing surface preparation is a cost-effective solution to prepare the surface before powder coating. This process removes the dirt and soil as well as grease from the punching and stamping process. Other approaches like shot blasting and vibratory finishing are proven to be an effective and efficient way of processing metal parts.
