Powder coatings are ideal for ferrous and non-ferrous metal requiring a protective and decorative finish. Thermo setting powder coatings are now generally recognized as having a significant role in the metal finishing industries worldwide. Powder coatings have been a commercial reality now for close to forty years.
Powder coating is the most exciting finishing method to be introduced in the past hundred years. Rarely does a new technique offer significant performance advantages and at the same time offer reduced costs. Powder coating not only meets those criteria, but also at the same time offers the best solution to meeting environmental regulations both now and in the future.
Worldwide government controls on solvent emissions and other pollutants released in to the atmosphere are rightly becoming more stringent. These will continue to restrict the uses of liquid paints containing volatile, toxic, flammable solvents, which pollute the air we breathe cause financial loss and are an ever-present health hazard.
Powder coating is one of the lease expensive finishing methods available today. While material and equipment costs are similar t liquid finishing systems, the savings achieved in energy, labor, production, waste disposal, and meeting PCB standards makes the real cost of powder coatings less than liquid finishing. In liquid finishing, the over-sprayed paint cannot be reclaimed; the clean up time and waste disposal is costly and difficult.
Powder coatings are used for the same key reasons as any surface finishing process:
- To protect the substrate as they have been applied to
- To enhance the appearance of the item they have been applied to
Powder coating systems save energy because they are solvent-free. The fact that powder coatings contain no solvents also means that air and water pollution problems are virtually eliminated. This reduces the high cost of anti-pollution equipment and the time and money spent dealing with federal and state regulatory agencies. With powder coating systems, there is no liquid paint sludge to be sent to a hazardous waste site. This represents a major reduction in an increasingly difficult and expensive disposal problem. Because powder coatings do not require any flash-off time, and the process allows closed spacing of racks on a conveyor / trolley, more parts are coated per hour resulting in lower unit costs. Reject rates are usually much lower for a powder coating system compared to a wet system, in spite of the increased production rate.
Labor costs are often substantially lower in plants using powder coating because automatic system\s require less manpower and the worker environment is more favorable.
The key benefits of powder coatings can be summarized as follows:
- Ease of application
- Environmentally friendly
- Excellence of finish
- Excellence of performance
The other benefits can be summarized as below:
- The elimination to a large extent of solid waste disposal problems
- Solvent emissions are virtually eliminated, resulting in much easier compliance with PCB regulations
- Energy costs are greatly reduced and volatile organic component easily controlled
- No solvents required in mixing, cleaning or maintenance
- Up to 96% of powder over spray can be recovered and reused. The remaining percentage residual can be easily be disposed off as a solid
- Powder coatings are single coat finishes, with no primer required
- High film thickness can be achieved with a single coat.
- As the process is simple, quick drying / curing can be automated, enabling high volume industrial applications plants to operate economically with minimum of rejects.
These benefits have enabled powder coatings to take a significant share of the industrial finishing market.
The powder coating booth plays an important role in saving the powder. The Powder booth as such may not do that but the powder recovery system makes it happen. Hence it is very much important to understand the concept before choosing the recovery system.
The following are the major reason for having different version of powder recovery system.
- Number of colors being sprayed per shift or day.
- Production out put in terms of area covered (sqm) per shift / day.
- Acceptable limit of Dust level.
- Environmental aspects.
- Customer budget.
Before starting any thing about powder coating booth, let us understand, what is powder coating booth? And what does it do? Why we require booth?
The powder coating booth is a simple enclosure with a cutouts provided for component entry/exit, operator accessibility and slot for conveyor. When you start powder coating in this enclosure / booth, the powder which is coming out of powder spray gun shall produce a mist of powder inside the booth. This becomes a hinders for an operator to see the object for further coating. Hence enclosure will have a negative suction created by a suction blower. The suction volume should be arrived in such a way that the average suction velocity at each and every cutout (cross-sectional area) should be 0.6 to 0.7m/sec. This suction takes away the powder from the enclosure.
But after taking out from the enclosure system, we need to collect it back as a recovery powder. To do this we have the following methods;
- Mono – Cyclone recovery system
- Multi cyclone recovery system
- Cartridge recovery system
Even after recovering the powder, very small sized particles will come out from the recovery system. This finest powder, even if you collect, it is difficult to charge the powder for further coating. Hence it is advisable to collect it in a bag for disposal.
After the recovery, we suggest to have after filter recovery system. This means that the finer powder particle needs to be collected by means of filtering system. So, the following are the after filter recovery system.
- Cartridge after filter with reverse pulse cleaning system
- Bag filter with manual cleaning system
- None of the above, letting it out side.
More commonly we find that customer will not be having any of the after filter recovery system. They simply let out the finer powder to the atmosphere.
At this juncture, let us recall our selves the following points.
- Booth is an simple metal enclosure
- It is having cut out openings for component entry/exit and operator accessibility
- This enclosure is having suction blower and sucks the powder spray while spraying.
- This suction takes place through recovery unit (cyclone/ multi-cyclone / cartridge)
- While passing through the recovery unit, 95 -98% of the powder gets collected at bottom and the remaining finer powder gets transferred to after filter system / let out to atmosphere.
- In the after filter system (cartridge / bag filter), the powder gets collected in the bottom and the air gets out from the system as a pure air.
- The dimension of the enclosure depends on product dimension, conveyor speed, production out put, geometry of the product, No. of guns fitted and No. of operators coating.
- The suction capacity (blower capacity) depends on cut out openings and system resistance.
A typical sketch of powder booth with multi-cyclone and cartridge after filter system is as explained below.