Powder Coating – Frequently Asked Questions

 

Here are some frequently asked questions about power coating and its usage.

 

What is powder coating?

Powder Coating is a type of coating that is applied as a free-flowing, dry powder. The main difference between a conventional liquid paint and a powder coating is that the powder coating does not require a solvent to keep the binder and filler parts in a liquid suspension form. The coating is typically applied electrostatically and is then cured under heat to allow it to flow and form a “hard film layer “. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as household appliances, aluminium extrusions, drum hardware, and automobile and bicycle parts. Newer technologies allow other materials, such as MDF (medium-density fibreboard), to be powder coated using different methods

• What are the advantages of power coating technology?

1. Powder coatings contain no solvents and release little or no amount of Volatile Organic Compounds (VOC) into the atmosphere. Thus, there is no longer a need for finishers to buy costly pollution control equipment. Companies can comply more easily and economically with the regulations of the U.S. Environmental Protection Agency.
2. Powder coatings can produce much thicker coatings than conventional liquid coatings without running or sagging.
3. Powder coated items generally have fewer appearance differences between horizontally coated surfaces and vertically coated surfaces than liquid coated items.
4. The wide range of specialty effects are easily accomplished using powder coatings that would be impossible to achieve with other coating processes.
5. Curing time is significantly faster with powder coating as compared to liquid coating.

• Ready for immediate use whereas some liquid paints have to be mixed with solvents or catalysts
• Minimal pollution
• Powder coatings are compliant with environmental legislation
• Faster process times
• No flash off time is required
• Reduced energy requirements
• No solvent to evaporate and evacuate from the oven (after burners)
• Higher utilisation
• Losses as low as 5% when using recovered powder whereas liquid paints contain up to 70% solvent
• Minimal operator training
• Operators require much less training to apply powders than solvent-based systems
• Reduced packaging costs
• Tougher powder coating films require less packaging to protect work during transportation
• Heavier coating weights
• Corrosion protection

 

What are the industries where powder coating is useful?

1. Electrical control panels, 2.Automobile ,3. Furnitures , 4. Aluminium extrusion , 5.Domestic Appliances, Refrigerators , Washing machine , Water heater , Microwaves etc  6. Facades .7. Railways 8. Transformers 9. Doors and  Windows 10. Electronics 

What are the steps involved in power coating?

The powder coating process involves three basic steps:

1. Part preparation or the pre-treatment
2. The powder application
3. Curing

1. Part preparation processes and equipment.

Removal of oil, dirt, lubrication greases, metal oxides, welding scale etc. is essential prior to the powder coating process. It can be done by a variety of chemical and mechanical methods. The selection of the method depends on the size and the material of the part to be powder coated, the type of impurities to be removed and the performance requirement of the finished product.

Chemical pre-treatments involve the use of phosphates or chromates in submersion or spray application. These often occur in multiple stages and consist of degreasing, etching, de-smutting, various rinses and the final phosphating or chromating of the substrate. The pre-treatment process both cleans and improves bonding of the powder to the metal. Recent additional processes have been developed that avoid the use of chromates, as these can be toxic to the environment. Titanium zirconium and silanes offer similar performance against corrosion and adhesion of the powder.

In many high end applications, the part is electrocoated following the pretreatment process, and subsequent to the powder coating application. This has been particularly useful in automotive and other applications requiring high end performance characteristics.

Another method of preparing the surface prior to coating is known as abrasive blasting or sandblasting and shot blasting. Blast media and blasting abrasives are used to provide surface texturing and preparation, etching, finishing, and degreasing for products made of wood, plastic, or glass. The most important properties to consider are chemical composition and density; particle shape and size; and impact resistance.

Silicon carbide grit blast medium is brittle, sharp, and suitable for grinding metals and low-tensile strength, non-metallic materials. Plastic media blast equipment uses plastic abrasives that are sensitive to substrates such as aluminum, but still suitable for de-coating and surface finishing. Sand blast medium uses high-purity crystals that have low-metal content. Glass bead blast medium contains glass beads of various sizes.

Cast steel shot or steel grit is used to clean and prepare the surface before coating. Shot blasting recycles the media and is environmentally friendly. This method of preparation is highly efficient on steel parts such as I-beams, angles, pipes, tubes and large fabricated pieces.

Different powder coating applications can require alternative methods of preparation such as abrasive blasting prior to coating. The online consumer market typically offers media blasting services coupled with their coating services at additional costs.

2. Powder application processes

The most common way of applying the powder coating to metal objects is to spray the powder using an electrostatic gun, or corona gun. The gun imparts a positive electric charge to the powder, which is then sprayed towards the grounded object by mechanical or compressed air spraying and then accelerated toward the workpiece by the powerful electrostatic charge. There are a wide variety of spray nozzles available for use in electrostatic coating. The type of nozzle used will depend on the shape of the workpiece to be painted and the consistency of the paint. The object is then heated, and the powder melts into a uniform film, and is then cooled to form a hard coating. It is also common to heat the metal first and then spray the powder onto the hot substrate. Preheating can help to achieve a more uniform finish but can also create other problems, such as runs caused by excess powder.

Another type of gun is called a tribo gun, which charges the powder by (triboelectric) friction. In this case, the powder picks up a positive charge while rubbing along the wall of a Teflon tube inside the barrel of the gun. These charged powder particles then adhere to the grounded substrate. Using a tribo gun requires a different formulation of powder than the more common corona guns. Tribo guns are not subject to some of the problems associated with corona guns, however, such as back ionization and the Faraday cage effect.

Powder can also be applied using specifically adapted electrostatic discs.

Another method of applying powder coating, called the fluidized bed method, is by heating the substrate and then dipping it into an aerated, powder-filled bed. The powder sticks and melts to the hot object. Further heating is usually required to finish curing the coating. This method is generally used when the desired thickness of coating is to exceed 300 microns. This is how most dishwasher racks are coated.

Electrostatic fluidized bed coating

Electrostatic fluidized bed application uses the same fluidizing technique as the conventional fluidized bed dip process but with much less powder depth in the bed. An electrostatic charging medium is placed inside the bed so that the powder material becomes charged as the fluidizing air lifts it up. Charged particles of powder move upward and form a cloud of charged powder above the fluid bed. When a grounded part is passed through the charged cloud the particles will be attracted to its surface. The parts are not preheated as they are for the conventional fluidized bed dip process.

Electrostatic magnetic brush (EMB) coating

A coating method for flat materials that applies powder with a roller, enabling relatively high speeds and accurate layer thickness between 5 and 100 microns. The base for this process is conventional copier technology. It is currently in use in some coating applications and looks promising for commercial powder coating on flat substrates (steel, aluminium, MDF, paper, board) as well as in sheet to sheet and/or roll to roll processes. This process can potentially be integrated in an existing coating line.

3. Curing

When a thermoset powder is exposed to elevated temperature, it begins to melt, flows out, and then chemically reacts to form a higher molecular weight polymer in a network-like structure. This cure process, called cross-linking, requires a certain temperature for a certain length of time in order to reach full cure and establish the full film properties for which the material was designed. Normally the powders cure at 200 °C (390 °F) for 10 minutes. The curing schedule could vary according to the manufacturer’s specifications. The application of energy to the product to be cured can be accomplished by convection cure ovens, infrared cure ovens, or by laser curing process. The latter demonstrates significant reduction of curing time.

What are the companies that supply quality powder for coating?

Akzo Nobel , Jotun , Asian Paints PPG  , Kansai Nerolac , Berger Paints.We have just listed a few big player of the market however there are smaller companies that also supply quality material.

What are the best machines for powder coating?

Waganor Systems , Nordsen Equipment , Gema, Mitsuba System , Statefield Equipments 

Who are the best powder coating companies in my area?

We would be glad to provide you with the list of reliable and affordable power coating companies in your area. Please get in touch with us, we would be happy to help. Marc Industries, MJ Coaters , Arunoday Industries , Unique Powder Coats , Laxmi Coatings , JK Coating Centre  are some of the players in the powder coating industry in and around western India .

 

What training do we provide for power coating?

1. Consultancy for setting up of  new powder coating setup . 
2. Surface preparation process
3. Training of  applicators and  supervisor for  best  quality coating . 
4. Training for  quality parameters for good quality finish.
5. Maintaining of various records for quality monitoring.
6. Six sigma and lean manufacturing.

This page is an attempt to provide answers to powder Coating Frequently asked questions. You can comment below to ask any Powder Coating related queries / questions you may have. We aim to provide a timely response to help the Powder Coating community. We believe in sharing knowledge and keeping this website interactive for the visitors. You / your company may hire us for your powder coating projects, simply get in touch !