A Complete Guide to Powder Coating
Powder coating was introduced in the 1950s, but it started gaining popularity in the last two decades. Powder coating offers the most economical, durable, quality and eco-friendly finishes in the market. Some of the industries benefiting from this technology include the architectural, automotive, appliance, and agriculture.
Powder coating is similar to painting, only that the paint, in this case, is dry. It is an environmentally friendly way of painting, which involves the electrostatic application of a finely ground dry paint to specially prepared aluminum surfaces.
Powder, on the other hand, is a dry finish with no VOCs. Thus it less affected by the environmental regulations. Also, the nature of the powder coating makes it safer and more economical to use than its liquid counterpart.
Powder Coating Process
The powder coating process is broken down into three main steps:-
1. Pre-treatment (Chemical processing)
The first step involves the removal of metal oxides, lubrication greases, soil, oil, and welding scales. This step is essential and can be achieved using various mechanical and chemical methods. The method to use depends on the type of debris as well as the size and material of the surface to be powder coated. Also, the type of soil to be removed and the use of the final product dictates the method to be used. Chemical processing is meant to clean the surface and improve the bonding of the fine powder to the metal surface.
If the surface to be coated has a lot of laser scale, lust, or pre-existing paint, a blast room is used. This is a room where the painter uses compressed air to propel a rough material against the surface you want to paint. Typically, appropriate blast materials (grit) or steel shots are used to blast off the debris off the surface.
If the surface is covered with oil, chemical or solvent residue, the painter should consider passing the surface through a wash station. Here, the surface is sprayed with detergents or chemicals such as iron phosphate. Afterwards, the surface is cleaned using steam or hot water. A surface that has been passed through a wash station will produce a quality powder coat. Some surfaces require manual removal of debris using spray wands.
In some cases, the pre-treatment process will require the application of a dry-off oven. It resembles a curing oven, but it involves drying the washed parts to eliminate any water or chemicals on the surface. Also, a dry-off oven can be used to heat the surface to an optimum temperature for the powder application.
2. Electrostatic Application of Powder
After the object has been cleaned and dried, the section is loaded onto the overhead conveyor system. It is then moved to the painting booth. Powder spray guns such as corona guns are used to apply the paint powder to the aluminium surface.
The gun electrostatically charges the dry powder as it is ejected by compressed air from the hopper towards the grounded section. Compressed air blows the powder out of the powder spray gun as a tiny cloud. Due to the charges, it is attracted to the earthed aluminum surface. The attraction very strong and it ensures the powder adheres to the surface during the curing process. The conveyor system moves the aluminum section out of the paint booth and into a long oven which is the final phase.
Each time you spray the powder, some of it will fall on the floor, and some will remain in the air. Thus you will require a powder spray booth to get rid of the overspray. In case you do not have sufficient space to set up a powder spray booth, then you should go for a powder spray wall.
Once the surface is powder coated, you need to place it in a powder curing oven. The oven heats the coated product to 200 degrees Celsius. First, the high temperature melts the powder paint which flows together forming a film. Secondly, it cures the resin system in the film, forming a smooth surface. The other components in the powder paint cause the surface to be anchored or attracted to the conversion coating. The coating reacts chemically producing long molecular chains which are closely knit. The molecular chains are very strong and resistant to breakdown.
After the curing process, the sections are taken to a cooling station. Afterwards, they are examined, packed, and dispatched to the clients.
Powder coatings can be applied to non-metallic surfaces such as plastics. Though spray painting is the most common technique of application, powder coating can also be achieved in a fluidized bed application. Here, the preheated surfaces are dipped into a hopper containing a mixture of the coating melts and the fluidizing powder. Post-cure can be required depending on the size and temperature of the surface and the type of fluidizing powder used.
Powder Coating Equipment
In the recent years, the powder coating technology has obtained a mushrooming acceptance in the industrial finishing market of America. The rampant growth can be attributed to the environmental regulation of water, air, as well as waste disposal. These regulations impacted negatively on the liquid finishes which demand filtering, venting, and solvent recovery systems for controlling the VOCs (Volatile Organic Compounds).
- Powder Coating Guns
- Powder Coating Ovens
- Powder Coating Booths
- Powder Coating Lamps
- Blast Rooms
- Parts Washers
- Powder Spray Walls
- Pre-treatment Enclosures
- Spray Wands
- Powder Coating Feed Systems
Powder Coating Guns
Powder coating guns are one of most efficient and helpful tools used in the powder coating process. From imparting an electrostatic charge to the paint, to controlling the deposition of the powder spray on the surface, these guns can do it all. And though they have a notorious name, these guns do not pose any health hazard to the painters.
Powder coating guns include two broad categories – automatic guns and manual guns. While the automatic powder coating guns are great for high production especially that which requires application on many products together, manual powder coating guns offer great help when working on complex, difficult to reach and stand-alone units.
Power coating guns can further be of three types namely corona spray guns, corona bells and tribo guns.
Powder Coating Ovens
Powder coating ovens are a great tool for providing the heat required to change powder particles from their initial state to a solid thermosetting product. This makes powder coating ovens a must-have in order to obtain high quality end products. There are various types of powder coating ovens available today. The most popular ones among these include electric heat powder coating ovens, infrared ovens and natural gas convection heat ovens. As in case of any machine, it is important to consider a few factors when using powder coating ovens. For example, arranging a proper air flow, even heat distribution, constant cleaning of the oven intake, tidiness of the workplace and keeping clean records of maintenance tasks are a few key factors to be kept in mind. Taking care of these factors ensures a hassle-free functioning of the powder coating oven and gives great end results.
Powder Coating Booths
A powder coating booth is a great saviour when it comes to protecting your work-station from overspray. In simple words, overspray is the stray powder that ends up in the air or on the ground whenever you spray powder paint on a surface. Having a powder spray booth thus ensures that your workshop area outside the booth is absolutely tidy with clean and clear air.
Different workshops can have different requirements. Therefore, powder coating booths are available in various types and sizes. Every powder coating booth comes with its own exhaust fan that keeps the air outside clean and enables the painter inside to see what he is doing clearly. Undoubtedly, powder coating ovens help in providing a very clean and safe working environment to the people and also protect the final product from any possible contamination in the air.
Powder Coating Lamps
Powder coating lamps are a wonderful tool for curing objects like thin gauge metals and tiny pieces. In order to cure an object successfully, it is important to keep a close check on the temperature and the distance of the powder coating lamp from the object because close proximity or high temperature can sometimes burn or discolour the powder coat. Due to such nuances of the curing process, powder coating lamps are also available as hand-held equipment. Whichever powder coating lamp you select, you must take into consideration the temperature requirements, distance specifications and testing the completion of the cure in order to achieve best results.
Blast rooms help in avoiding the troubles and costs associated with reworks. Workshops that operate with impure raw materials such as tube stock or plate steel get rust or welding residue on the surface of their objects. A surface that is layered with old paint, scaling or rust will not hold the paint for long even after curing because its powder will fall off after a short while and require expensive reworks. Blast rooms come to the rescue in all such cases because they enable the removal of all the debris from the surface and provide a clean surface that facilitates powder coating adhesion.
There are two types of blasting systems namely wet (slurry) blasting system and dry blasting system.
The dry blasting system requires a few points to be taken into consideration for its proper installation and functioning. These points include checking the design of the blasting enclosure, size of the room and the capacity and portability of the blast pot.
Parts washers play a very important role in the powder coating process. They help in cleaning a workpiece by removing dirt, corrosion, grease, oil, ink and paint from the product’s surface. This cleaning process is essential for the second stage of powder coating process in order to strengthen the adhesions on the product’s surface and obtain high quality results. The material used for washing can either be a chemical or a detergent. Sometimes it is useful to have more than one parts washer so that you can have different cleaning solutions in each washer. Just like other machinery, parts washers also come in various styles and sizes. You can choose one or more for yourself depending upon your requirements like the size of your unit, types of parts to be washed, type of grunge to be removed, your budget, etc. Parts washers are available in plastic and metal bodies. Your choice of washer would depend upon the type of chemicals you plan to use for cleaning. The size that you buy will also depend upon your personal requirements. Parts washers are available as benchtop units as well as full-size stand-alone equipment.
Powder Spray Walls
Powder spray walls are a phenomenal invention for workshops that have limited space and cannot accommodate a spray booth. The functions of a powder spray wall include dust infiltration and maintaining the required air flow while consuming less space. Basically, a spray wall is a filtration system without walls and a roof. It helps the painter in delivering quality finish on small parts, frames and wheels while saving floor space and getting results as good as those achieved using a spray booth. Some powder spray walls come with a reclamation system that draws in the impure air circulating in the workshop, filters it and then releases it back in order to maintain clean and safe air in the workshop. To select a useful powder spray wall, it is important to carefully consider its construction, lighting, exhaust unit and control.
Pre-treatment enclosures are necessitated to be used in most powder coating workshops in order to abide by environmental regulations. A pre-treatment enclosure is basically an enclosed area where the pre-treatment process takes place. For example, a blast room can be called a pre-treatment enclosure. Pre-treatment enclosures help in preventing contaminants in the surrounding areas from entering the equipment. They also help in maintaining appropriate temperature and pressure. A good pre-treatment enclosure should be easy to set-up. It should also have proper enclosure design, lighting and doors. Blast enclosures, chemical enclosures and manual wash enclosures are the main types of pre-treatment enclosures.
Spray wands are used to manually clean surfaces of products to be coated. This means that they are a useful tool for the pre-treatment stage of powder coating process. Since most spray wands are operated manually, they are often used in small workshops that have a few surfaces to coat. Surfaces cleaned using spray wands have very good powder adhesion which makes them highly durable. Similar to all wash stations, spray wand stations help in cleaning, pre-treating and rinsing surfaces of various sizes, shapes, complexities and configurations. Spray wands make use of chemicals such as iron phosphate, detergents, steam or hot water. When used properly, these wands give us wonderfully clean surfaces that are not layered with any oil residues, solvents or chemicals. This makes the final application process very smooth and successful. Two main types of spray wands include hand-held wands and high-pressure wands.
Powder Coating Feed Systems
A powder coating feed system is a very crucial part of the delivery system that exists inside every professional powder coating gun. The powder coating feed system provides powder to the gun’s pump and the delivery system stores, prepares and maintains a steady flow of the powder to the gun. The most common feed systems include the hopper and box-fed feed systems.
Guns with a hopper-fed system have reduced chances of powder contamination. This type of feed system is best suited for operation in areas with humidity issues, systems with a reclamation unit, operators who need limited colour application and in applications that demand special effects. Guns with box-fed systems enable quick colour change, are flexible, require low initial investment and are quick to set up and start operations. This type of powder coating feed system is best suited for single colour powder, coaters who use different powders for different instances and operators who coat a few parts.
It goes without saying that selecting a gun with the right feed system is very important if you want to create high quality products.