Powder Coating
Powder coating is a process of coating metal with a plastic finish applied for a decorative and protective finish in powder form and baked to a fluid state to bond it to the metal surface. Powder coating has many advantages over traditional liquid coating: It’s better for the environment, applies thicker without running, and is easy to style with. Although certain aspects of powder coating can be tricky, it’s certainly not difficult, especially for an enterprising soul. Proper cleaning and tools can be the difference between an amateur and a good powder coating job. The result is uniform, durable, high-quality and attractive finish.
PRETREATMENT Methods
Mechanical cleaning includes methods like,
- Scratch Brushing
- Blasting
This by abrasive action not only removes the surface impurities but also eliminates scratches and Surface irregularities. Cleaning is very good, however, coating must be done immediately because the cleaned surface is in a highly reactive state and corrosion occurs very soon. Chemical cleaning includes removal of dirt, oil and grease, and the oxidation products present on the surface by means of chemicals. The chemicals may be applied by wiping, spraying or dipping. The nature of chemicals used depends upon the base metal.
SEQUENTIAL PROCESS FOR PRETREATMENT
Seven (or eight) stage treatment for zinc/iron phosphate include following stages:
1. Degreasing
2. Water rinse
3. Derusting
4. Water rinse
5. Activation: This gives more compact and uniform coating of zinc phosphate. This step can be omitted for iron phosphate process.
6. Phosphating: This forms coating of zinc phosphate (4 to 6 microns) OR iron phosphate (1 to 1.5 microns) on the clean surface of M.S.
7. Water rinse
8. Passivation: This will seal the pores of phosphating.
9. Drying.
CLEANER-COATER SYSTEM-3 IN 1 CHEMICAL
Cleaner-coater system for mild steel is a much simplified treatment than 8 tank process. This is done in a single tank with 3 in 1 che1mical. In this system, all three processes of degreasing, derusting and iron phosphating are done with single chemical, thus making the process time effective. However, its corrosion resistance and bonding properties are not as good as that of 8 tank process.)
Apply the powder to the object to be powder coated
This is done using a “gun” or compressed air sprayer which electrostatically charges the powder material so that it sticks to the grounded base metal object receiving the coating. Every time have to Make sure that, the electrostatic charge has been hooked up to whatever part we are coating. The powder we use won’t properly adhere unless it’s given a charge to hold onto.
After applying the coat but before curing, should be careful not to brush or blow on the powder coat, as this will cause some of the powder to fall off, leaving you with a less precise coat.
Cure the metal at a temperature appropriate for the powder material
A conventional oven is suitable for this purpose if the metal is small enough to fit, otherwise, an infrared heat lamp or other flame less heat source needs to be used. Normally, the object is heated to 350° to 375° F (175° to 190° C) for about 10 to 15 minutes, and allowed to cool.
Coating Types
- Thermoset
- Thermoplastic
Use thermoplastic coatings for items you might eventually remould, and thermoset coatings for items that will remain essentially permanent. The main difference between thermoplastic and thermoset is the reversibility of the coat. Like their name implies, thermoset coatings cannot re-melt after undergoing an irreversible chemical bonding process. Conversely, thermoplastic coatings can remelt because no chemical process takes place.
Thermoset:
Thermoset coatings are ideal for things like electronics and appliances because they need to withstand higher amounts of heat, which might cause thermoplastic coatings to melt. Thermosets are said to reinforce the structural integrity of an item, making them particularly suitable for heavy wear-and-tear. They also supply the item with superior chemical and heat resistance, as mentioned above.
Advantages: Beautiful aesthetic look; added strength and stability; resistant to extreme temperatures.
Disadvantages: Irreversible process means thermoset can’t be recycled; more difficult to finish; can’t be reshaped.
Thermoplastics:
Thermoplastics offer a mixture of strength and flexibility. They are commonly used for items such as plastic bags and even mechanical parts. Thermoplastics are used for many items, such as park benches, that require both plasticity and durability.
Advantages: High Lubricity or tack[3]; Recyclable; Able to remolded and/or reshaped; Increased impact resistance.
Disadvantages: Will melt off if overheated.