Powder coating is a kind of layer that is applied as a free-streaming, dry powder. It is manufactured through a series of steps involving premixing, extrusion, grinding, and blending.
Unlike liquid coating where there is a need to thin the material to achieve the application viscosity; powder coating works on a very different principle of application through an electrostatic gun. This means the substrate and the powder are given opposite charges, which then allow them to adhere to each other.
This is followed by curing through a specific baking schedule (different for different products) in an oven. There are two major types of powder coating: Thermoplastic & Thermosetting powders:
- Thermoplastic Powders maintain their chemical composition as they cool & solidify and they can re-melt after curing when exposed to sufficiently high heat.
- Thermosetting powders are used much more frequently in the world of powder coating; they cannot re-melt after undergoing an irreversible chemical bonding process.
Thermosetting powders are derived from three major subtypes i.e. Pure Epoxy,
Epoxy Polyester & Pure Polyester powders:
- Pure Epoxy powders are superior in terms of chemical resistance & corrosion protection & normally recommended for interior applications like industrial equipment, metal furniture, dielectric application, etc.
- Epoxy Polyester powders are superior in terms of mechanical properties, provide excellent flow & corrosion protection & are strongly recommended for interior applications like household appliances, light fittings, etc.
- Pure Polyester powders are superior in terms of outdoor durability & hence recommended for Exterior application Like aluminum extrusions, door frames, automotive components, etc.
Thermoplastic powders are derived from four major subtypes i.e. Polyethylene, Polypropylene, Nylon, Polyvinyl powders:
- Polyethylene powders were the first thermoplastic powder coating offered to the industry. Polyethylene powders provide coatings of excellent chemical resistance & toughness with outstanding electrical insulation properties.
- Polypropylene powders offer many of the useful properties it has as a plastic material. Because natural polypropylene is so inert it shows little tendency to adhere to metal or other substrates. This characteristic makes it necessary to chemically modify the natural polypropylene when it is used as a surface coating powder, so that adhesion of the coating to the substrate can be obtained.
- Nylon powders are superior in performance with excellent abrasion resistance & Impact resistance. The most interesting use of nylon powder coating is in the field of mechanical design.
- Polyvinyl powders are powders with superior exterior durability. They bond well to most metal substrates when applied over a suitable primer. They are also FDA approved for food contact & can be used for a number of similar applications. This powder is also a great electrical insulator.
Major advantages of powder coating over liquid coating:
- Powder coating production lines produce less hazardous waste than conventional liquid paints.
- Zero VOC – there is no discharge of any volatile organic compound into the atmosphere means environmentally ecofriendly.
- Powder coating- A wide range of specialty effects is easily accomplished which would be impossible to achieve with other coating processes.
- Powder coatings can produce much thicker coatings than conventional liquid coating without run down or sagging.
Major disadvantages of powder coatings:
- The startup cost is very high – since heating is through an oven, the cost of running the oven tends to be very high. Hence Grand Polycoats is the best powder coating manufacturer in India that offers low bake powder technology for reduced energy consumption during application.
- Restriction on the size of objects/components being coated – only items that can fit inside an oven can be coated.
- Contamination problem – Due to the size of the particles, there are chances of contamination through external dust or powder of different origin.
- Thin layer coating system – In powder coating, it is difficult to achieve a thin layer of powder coating. The minimum DFT is 25-35 micron.
- Change over time – changing from one color to another or one product to another, the change over time is very high because cleaning is very tedious.
Frequently Asked Questions:
What are the industries where powder coating is useful?
Powder coating is widely used in the following industries:
- Home appliances
What are the steps involved in powder coating? (Part preparation or the pre-treatment, The powder application, Curing)
Powder coating involves three basic steps:
- Part preparation or the pre-treatment: This involves removing dirt, oils, greases, metal oxides, etc and is done using various chemicals.
- The powder application: The common method is to spray the powder using an electrostatic or corona gun. The gun gives off a negative charge, which is sprayed towards a grounded object by compressed air spraying, which is then accelerated towards the surface by a strong electric charge.
- Curing: When the thermosetting powder is exposed to a high temperature, it melts, flows, and then reacts to make a higher weight polymer in a network-like structure.
Does powder coating prevent rust?
Yes, powder coating is corrosion and rust-resistant. The coating provides a protective line of defense that helps prevent corrosion and rust.
How do you maintain powder coating?
You can maintain powder coating by avoiding harsh cleansers and pressure cleaning; protect exposed surfaces with wax and proper cleaning and maintenance.
Can aluminum be powder coated?
Yes, aluminum can be powder coated however the thin layer of aluminum oxide must be removed from the surface of aluminum before applying powder coating.